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rfc:rfc3126

Table of Contents

Network Working Group D. Pinkas Request for Comments: 3126 Integris Category: Informational J. Ross

                                                               N. Pope
                                                  Security & Standards
                                                        September 2001
                    Electronic Signature Formats
                for long term electronic signatures

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

 This document defines the format of an electronic signature that can
 remain valid over long periods.  This includes evidence as to its
 validity even if the signer or verifying party later attempts to deny
 (i.e., repudiates the validity of the signature).
 The format can be considered as an extension to RFC 2630 and RFC
 2634, where, when appropriate additional signed and unsigned
 attributes have been defined.
 The contents of this Informational RFC is technically equivalent to
 ETSI TS 101 733 V.1.2.2. The ETSI TS is under the ETSI Copyright (C).
 Individual copies of this ETSI deliverable can be downloaded from
 http://www.etsi.org

Pinkas, et al. Informational [Page 1] RFC 3126 Electronic Signature Formats September 2001

Table of Contents

 1.  Introduction                                                    4
 2  Overview                                                         5
 2.1  Aim                                                            5
 2.2  Basis of Present Document                                      5
 2.3  Major Parties                                                  6
 2.4  Electronic Signatures and Validation Data                      7
 2.5  Forms of Validation Data                                       8
 2.6  Extended Forms of Validation Data                             11
 2.7  Archive Validation Data                                       13
 2.8  Arbitration                                                   15
 2.9  Validation Process                                            15
 2.10  Example Validation Sequence                                  16
 2.11  Additional optional features                                 21
 3. Data structure of an Electronic Signature                       22
 3.1  General Syntax                                                22
 3.2  Data Content Type                                             22
 3.3  Signed-data Content Type                                      22
 3.4  SignedData Type                                               22
 3.5  EncapsulatedContentInfo Type                                  23
 3.6  SignerInfo Type                                               23
 3.6.1  Message Digest Calculation Process                          23
 3.6.2  Message Signature Generation Process                        24
 3.6.3  Message Signature Verification Process                      24
 3.7  CMS Imported Mandatory Present Attributes                     24
 3.7.1  Content Type                                                24
 3.7.2  Message Digest                                              24
 3.7.3  Signing Time                                                24
 3.8  Alternative Signing Certificate Attributes                    24
 3.8.1  ESS Signing Certificate Attribute Definition                25
 3.8.2  Other Signing Certificate Attribute Definition              25
 3.9  Additional Mandatory Attributes                               26
 3.9.1  Signature policy Identifier                                 26
 3.10  CMS Imported Optional Attributes                             28
 3.10.1  Countersignature                                           29
 3.11  ESS Imported Optional Attributes                             29
 3.11.1  Content Reference Attribute                                29
 3.11.2  Content Identifier Attribute                               29
 3.11.3  Content Hints Attribute                                    29
 3.12   Additional Optional Attributes                              30
 3.12.1  Commitment Type Indication Attribute                       30
 3.12.2  Signer Location attribute                                  32
 3.12.3  Signer Attributes attribute                                33
 3.12.4  Content Time-Stamp attribute                               34
 3.13  Support for Multiple Signatures                              34
 3.13.1  Independent Signatures                                     34
 3.13.2  Embedded Signatures                                        34

Pinkas, et al. Informational [Page 2] RFC 3126 Electronic Signature Formats September 2001

 4.  Validation Data                                                35
 4.1  Electronic Signature Time-Stamp                               36
 4.1.1  Signature Time-Stamp Attribute Definition                   36
 4.2  Complete Validation Data                                      37
 4.2.1  Complete Certificate Refs Attribute Definition              38
 4.2.2  Complete Revocation Refs Attribute Definition               38
 4.3  Extended Validation Data                                      40
 4.3.1  Certificate Values Attribute Definition                     40
 4.3.2  Revocation Values Attribute Definition                      41
 4.3.3  ES-C Time-Stamp Attribute Definition                        42
 4.3.4  Time-Stamped Certificates and CRLs Attribute Definition     42
 4.4  Archive Validation Data                                       43
 4.4.1  Archive Time-Stamp Attribute Definition                     43
 5.  Security Considerations                                        44
 5.1  Protection of Private Key                                     44
 5.2  Choice of Algorithms                                          44
 6.  Conformance Requirements                                       45
 6.1  Signer                                                        45
 6.2  Verifier using time-stamping                                  46
 6.3  Verifier using secure records                                 46
 7. References                                                      47
 8. Authors' Addresses                                              48
 Annex A (normative): ASN.1 Definitions                             49
 A.1  Definitions Using X.208 (1988) ASN.1 Syntax                   49
 A.2  Definitions Using X.680 1997 ASN.1 Syntax                     57
 Annex B (informative): General Description                         66
 B.1  The Signature Policy                                          66
 B.2  Signed Information                                            67
 B.3  Components of an Electronic Signature                         68
 B.3.1  Reference to the Signature Policy                           68
 B.3.2  Commitment Type Indication                                  69
 B.3.3  Certificate Identifier from the Signer                      69
 B.3.4.  Role Attributes                                            70
 B.3.4.1  Claimed Role                                              71
 B.3.4.2  Certified Role                                            71
 B.3.5  Signer Location                                             72
 B.3.6  Signing Time                                                72
 B.3.7  Content Format                                              73
 B.4  Components of Validation Data                                 73
 B.4.1  Revocation Status Information                               73
 B.4.2  CRL Information                                             74
 B.4.3  OCSP Information                                            74
 B.4.4  Certification Path                                          75
 B.4.5  Time-Stamping for Long Life of Signature                    76
 B.4.6  Time-Stamping before CA Key Compromises                     77
 B.4.6.1  Time-Stamping the ES with Complete validation data        77
 B.4.6.2  Time-Stamping Certificates and Revocation Information     78
 B.4.7  Time-Stamping for Long Life of Signature                    79

Pinkas, et al. Informational [Page 3] RFC 3126 Electronic Signature Formats September 2001

 B.4.8  Reference to Additional Data                                80
 B.4.9  Time-Stamping for Mutual Recognition                        80
 B.4.10  TSA Key Compromise                                         81
 B.5  Multiple Signatures                                           81
 Annex C (informative):  Identifiers and roles                      82
 C.1  Signer Name Forms                                             82
 C.2  TSP Name Forms                                                82
 C.3  Roles and Signer Attributes                                   83
 Full Copyright Statement                                           84

1. Introduction

 This document is intended to cover electronic signatures for various
 types of transactions, including business transactions (e.g.,
 purchase requisition, contract, and invoice applications) where long
 term validity of such signatures is important.  This includes
 evidence as to its validity even if the signer or verifying party
 later attempts to deny (i.e., repudiates, see [ISONR]) the validity
 of the signature).
 Electronic signatures can be used for any transaction between an
 individual and a company, between two companies, between an
 individual and a governmental body, etc.  This document is
 independent of any environment.  It can be applied to any environment
 e.g., smart cards, GSM SIM cards, special programs for electronic
 signatures etc.
 An electronic signature produced in accordance with this document
 provides evidence that can be processed to get confidence that some
 commitment has been explicitly endorsed under a signature policy, at
 a given time, by a signer under an identifier, e.g., a name or a
 pseudonym, and optionally a role.
 The European Directive on a community framework for Electronic
 Signatures defines an electronic signature as: "data in electronic
 form which is attached to or logically associated with other
 electronic data and which serves as a method of authentication".  An
 electronic signature as used in the current document is a form of
 advanced electronic signature as defined in the Directive.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
 "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
 as shown) are to be interpreted as described in [RFC2119].

Pinkas, et al. Informational [Page 4] RFC 3126 Electronic Signature Formats September 2001

2 Overview

2.1 Aim

 The aim of this document is to define an Electronic Signature (ES)
 that remains valid over long periods.  This includes evidence as to
 its validity even if the signer or verifying party later attempts to
 deny (repudiates) the validity of the signature.
 This document specifies the use of trusted service providers (e.g.,
 Time-Stamping Authorities (TSA)), and the data that needs to be
 archived (e.g., cross certificates and revocation lists) to meet the
 requirements of long term electronic signatures.  An electronic
 signature defined by this document can be used for arbitration in
 case of a dispute between the signer and verifier, which may occur at
 some later time, even years later.  This document uses a signature
 policy, referenced by the signer, as the basis for establishing the
 validity of an electronic signature.

2.2 Basis of Present Document

 This document is based on the use of public key cryptography to
 produce digital signatures, supported by public key certificates.
 A Public key certificate is a public keys of a user, together with
 some other information, rendered unforgeable by encipherment with the
 private key of the Certification Authority (CA) which issued it
 (ITU-T Recommendation X.509 [1]).
 This document also specifies the uses of time-stamping services to
 prove the validity of a signature long after the normal lifetime of
 critical elements of an electronic signature and to support non-
 repudiation.  It also, as an option, defines the use of additional
 time-stamps to provide very long-term protection against key
 compromise or weakened algorithms.
 This document builds on existing standards that are widely adopted.
 This includes:
  • RFC 2459 [RFC2459] Internet X.509 Public Key Infrastructure

Certificate and CRL Profile (PKIX);

  • RFC 2630 [CMS] Crytographic Message Syntax (CMS);
  • RFC 2634 [ESS] Enhanced Security Services (ESS);
  • RFC 2439 [OCSP] One-line Certificate Status Protocol (OCSP);
  • ITU-T Recommendation X.509 [1] Authentication framework;
  • RFC (to be published) [TSP] PKIX Time Stamping protocol (TSP).
 NOTE:  See clause 8 for a full set of references.

Pinkas, et al. Informational [Page 5] RFC 3126 Electronic Signature Formats September 2001

2.3 Major Parties

 The following are the major parties involved in a business
 transaction supported by electronic signatures as defined in this
 document:
  • the Signer;
  • the Verifier;
  • the Arbitrator;
  • Trusted Service Providers (TSP).
 A Signer is an entity that initially creates the electronic
 signature. When the signer digitally signs over data using the
 prescribed format, this represents a commitment on behalf of the
 signing entity to the data being signed.
 A verifier is an entity that verifies an evidence.  (ISO/IEC 13888-1
 [13]).  Within the context of this document this is an entity that
 validates an electronic signature.
 An arbitrator, is an entity which arbitrates disputes between a
 signer and a verifier when there is a disagreement on the validity of
 a digital signature.
 Trusted Service Providers (TSPs) are one or more entities that help
 to build trust relationships between the signer and verifier.  Use of
 some specific TSP services MAY be mandated by signature policy.  TSP
 supporting services may provide the following information: user
 certificates, cross-certificates, time-stamping tokens, CRLs, ARLs,
 OCSP responses.
 The following TSPs are used to support the validation or the
 verification of electronic signatures:
  • Certification Authorities;
  • Registration Authorities;
  • Repository Authorities (e.g., a Directory);
  • Time-Stamping Authorities;
  • One-line Certificate Status Protocol responders;
  • Attribute Authorities;
  • Signature Policy Issuers.
 Certification Authorities provide users with public key certificates.
 Registration Authorities allows the registration of entities before a
 CA generates certificates.

Pinkas, et al. Informational [Page 6] RFC 3126 Electronic Signature Formats September 2001

 Repository Authorities publish CRLs issued by CAs, cross-certificates
 (i.e., CA certificates) issued by CAs, signature policies issued by
 Signature Policy Issuers and optionally public key certificates
 (i.e., leaf certificates) issued by CAs.
 Time-Stamping Authorities attest that some data was formed before a
 given trusted time.
 One-line Certificate Status Protocol responders (OSCP responders)
 provide information about the status (i.e., revoked, not revoked,
 unknown) of a particular certificate.
 A Signature Policy Issuer issues signatures policies that define the
 technical and procedural requirements for electronic signature
 creation, validation and verification, in order to meet a particular
 business need.
 Attributes Authorities provide users with attributes linked to public
 key certificates

2.4 Electronic Signatures and Validation Data

 Validation of an electronic signature in accordance with this
 document requires:
  • The electronic signature; this includes:
  1. the signature policy;
  2. the signed user data;
  3. the digital signature;
  4. other signed attributes provided by the signer;
  5. other unsigned attributes provided by the signer.
 Validation data which is the additional data needed to validate the
 electronic signature; this includes:
  1. certificates references;
  2. certificates;
  3. revocation status information references;
  4. revocation status information;
  5. time-stamps from Time Stamping Authorities (TSAs).
  • The signature policy specifies the technical requirements on

signature creation and validation in order to meet a particular

       business need.  A given legal/contractual context may recognize
       a particular signature policy as meeting its requirements.

Pinkas, et al. Informational [Page 7] RFC 3126 Electronic Signature Formats September 2001

 For example: a specific signature policy may be recognized by court
 of law as meeting the requirements of the European Directive for
 electronic commerce.  A signature policy may be written using a
 formal notation like ASN.1 or in an informal free text form provided
 the rules of the policy are clearly identified.  However, for a given
 signature policy there shall be one definitive form which has a
 unique binary encoded value.
 Signed user data is the user's data that is signed.
 The Digital Signature is the digital signature applied over the
 following attributes provided by the signer:
  • hash of the user data (message digest);
  • signature Policy Identifier;
  • other signed attributes
 The other signed attributes include any additional information which
 must be signed to conform to the signature policy or this document
 (e.g., signing time).
 According to the requirements of a specific signature policy in use,
 various Validation Data shall be collected and attached to or
 associated with the signature structure by the signer and/or the
 verifier.  The validation data includes CA certificates as well as
 revocation status information in the form of certificate revocation
 lists (CRLs) or certificate status information provided by an on-line
 service.  Additional data also includes time-stamps and other time
 related data used to provide evidence of the timing of given events.
 It is required, as a minimum, that either the signer or verifier
 obtains a time-stamp over the signer's signature or a secure time
 record of the electronic signature must be maintained.  Such secure
 records must not be undetectably modified and must record the time
 close to when the signature was first validated.

2.5 Forms of Validation Data

 An electronic signature may exist in many forms including:
  • the Electronic Signature (ES), which includes the digital

signature and other basic information provided by the signer;

  • the ES with Time-Stamp (ES-T), which adds a time-stamp to the

Electronic Signature, to take initial steps towards providing

       long term validity;

Pinkas, et al. Informational [Page 8] RFC 3126 Electronic Signature Formats September 2001

  • the ES with Complete validation data (ES-C), which adds to the

ES-T references to the complete set of data supporting the

       validity of the electronic signature (i.e., revocation status
       information).
 The signer must provide at least the ES form, but in some cases may
 decide to provide the ES-T form and in the extreme case could provide
 the ES-C form.  If the signer does not provide ES-T, the verifier
 must either create the ES-T on first receipt of an electronic
 signature or shall keep a secure time record of the ES.  Either of
 these two approaches provide independent evidence of the existence of
 the signature at the time it was first verified which should be near
 the time it was created, and so protects against later repudiation of
 the existence of the signature.  If the signer does not provide ES-C
 the verifier must create the ES-C when the complete set of revocation
 and other validation data is available.
 The ES satisfies the legal requirements for electronic signatures as
 defined in the European Directive on electronic signatures, see Annex
 C for further discussion on relationship of this document to the
 Directive.  It provides basic authentication and integrity protection
 and can be created without accessing on-line (time-stamping)
 services. However, without the addition of a time-stamp or a secure
 time record the electronic signature does not protect against the
 threat that the signer later denies having created the electronic
 signature (i.e., does not provide non-repudiation of its existence).
 The ES-T time-stamp or time record should be created close to the
 time that ES was created to provide protection against repudiation.
 At this time all the data needed to complete the validation may not
 be available but what information is readily available may be used to
 carry out some of the initial checks.  For example, only part of the
 revocation information may be available for verification at that
 point in time.  Generally, the ES-C form cannot be created at the
 same time as the ES, as it is necessary to allow time for any
 revocation information to be captured.  Also, if a certificate is
 found to be temporarily suspended, it will be necessary to wait until
 the end of the suspension period.
 The signer should only create the ES-C in situations where it was
 prepared to wait for a sufficient length of time after creating the
 ES form before dispatching the ES-C.  This, however, has the
 advantage that the verifier can be presented with the complete set of
 data supporting the validity of the ES.
 Support for ES-C by the verifier is mandated (see clause 6 for
 specific conformance requirements).

Pinkas, et al. Informational [Page 9] RFC 3126 Electronic Signature Formats September 2001

 An Electronic Signature (ES), with the additional validation data
 forming the ES-T and ES-C is illustrated in Figure 1:

+————————————————————ES-C—–+

+——————————————–ES-T—–+
+——Elect.Signature (ES)———-+ +————+ +———–+
+———+ +———-+ +———+ Time-Stamp Complete
Signature Other Digital over digital certificate
Policy ID Signed Signature signature and
Attributes +————+ revocation
+———+ +———-+ +———+ references
+————————————+ +———–+
+—————————————————–+

+———————————————————————+

       Figure 1: Illustration of an ES, ES-T and ES-C
 The verifiers conformance requirements of an ES with a time-stamp of
 the digital signature is defined in subclause 6.2.
 The ES on its own satisfies the legal requirements for electronic
 signatures as defined in the European Directive on electronic
 signatures.  The signers conformance requirements of an ES are
 defined in subclause 6.1, and are met using a structure as indicated
 in figure 2:
             +------Elect.Signature (ES)-----------|
             |+---------+ +----------+ +---------+ |
             ||Signature| |  Other   | | Digital | |
             ||Policy ID| |  Signed  | |Signature| |
             ||         | |Attributes| |         | |
             |+---------+ +----------+ +---------+ |
             |+-----------------------------------+|
                Figure 2: Illustration of an ES

Pinkas, et al. Informational [Page 10] RFC 3126 Electronic Signature Formats September 2001

 Where there are requirements for long term signatures without time-
 stamping the digital signature, then a secure record is needed of the
 time of verification in association with the electronic signature
 (i.e., both must be securely recorded).  In addition the certificates
 and revocation information used at the time of verification should to
 be recorded as indicated in figure 3 as an ES-C(bis).
 +-------------------------------------------------------ES-C-----+
 |                                                                |
 | +------Elect.Signature (ES)----------+|           +-----------+|
 | |+---------+ +----------+ +---------+||           |Complete   ||
 | ||Signature| |  Other   | | Digital |||           |certificate||
 | ||Policy ID| |  Signed  | |Signature|||           |and        ||
 | ||         | |Attributes| |         |||           |revocation ||
 | |+---------+ +----------+ +---------+||           |references ||
 | +------------------------------------+|           +-----------+|
 |                                                                |
 +----------------------------------------------------------------+
              Figure 3: Illustration of an ES-C(bis)
 The verifiers conformance requirements of an ES-C(bis) is defined in
 subclause 6.3.
 Note: A time-stamp attached to the electronic signature or a secure
 time record helps to protect the validity of the signature even if
 some of the verification data associated with the signature become
 compromised AFTER the signature was generated.  The time-stamp or a
 secure time record provides evidence that the signature was generated
 BEFORE the event of compromise; hence the signature will maintain its
 validity status.

2.6 Extended Forms of Validation Data

 The complete validation data (ES-C) described above may be extended
 to form an ES with eXtended validation data (ES-X) to meet following
 additional requirements.
 Firstly, when the verifier does not has access to,
  • the signer's certificate,
  • all the CA certificates that make up the full certification

path,

  • all the associated revocation status information, as referenced

in the ES-C.

Pinkas, et al. Informational [Page 11] RFC 3126 Electronic Signature Formats September 2001

 then the values of these certificates and revocation information may
 be added to the ES-C.  This form of extended validation data is
 called a X-Long.
 Secondly, if there is a risk that any CA keys used in the certificate
 chain may be compromised, then it is necessary to additionally time-
 stamp the validation data by either:
  • time-stamping all the validation data as held with the ES(ES-

C), this eXtended validation data is called a Type 1 X-Time-

       Stamp; or
    *  time-stamping individual reference data as used for complete
       validation.
 This form of eXtended validation data is called a Type 2 X-Time-
 Stamp.
 NOTE:  The advantages/drawbacks for Type 1 and Type 2 X-Time-Stamp
 are discussed in this document (see clause B.4.6.)
 If all the above conditions occur then a combination of the two
 formats above may be used.  This form of eXtended validation data is
 called a X-Long-Time-Stamped.
 Support for the extended forms of validation data is optional.
 An Electronic Signature (ES) , with the additional validation data
 forming the ES-X long is illustrated in Figure 4:
+-------------------------------------------------------- ES-X Long--+
|+---------------------------------------- EC-C --------+            |
||+---- Elect.Signature (ES)----+             +--------+| +--------+ |
|||+-------+-+-------+-+-------+| +----------+|Complete|| |Complete| |
||||Signa- | |Other  | |Digital|| |Time-Stamp||certi-  || |certi-  | |
||||ture   | |Signed | |Signa- || |over      ||ficate  || |ficate  | |
||||Policy | |Attri- | |ture   || |digital   ||and     || |and     | |
||||ID     | |butes  | |       || |signature ||revoc.  || |revoc.  | |
|||+-------+ +-------+ +-------+| +----------+|refs    || |data    | |
||+-----------------------------+             +--------+| +--------+ |
|+------------------------------------------------------+            |
+--------------------------------------------------------------------+
        Figure 4: Illustration of an ES and ES-X long.

Pinkas, et al. Informational [Page 12] RFC 3126 Electronic Signature Formats September 2001

 An Electronic Signature (ES) , with the additional validation data
 forming the eXtended Validation Data - Type 1 is illustrated in
 Figure 5:
+----------------------------------------------------------- ES-X 1 -+
|+----------------------------------------- EC-C --------+           |
|| +---- Elect.Signature (ES)----+             +--------+| +-------+ |
|| |+-------+ +-------+ +-------+| +----------+|Complete|| |       | |
|| ||Signa- | |Other  | |Digital|| |Time-Stamp||certifi-|| | Time- | |
|| ||ture   | |Signed | |Signa- || |over      ||cate and|| | stamp | |
|| ||Policy | |Attri- | |ture   || |digital   ||revoc.  || | over  | |
|| ||ID     | |butes  | |       || |signature ||refs    || | CES   | |
|| |+-------+ +-------+ +-------+| +----------+|        || |       | |
|| +-----------------------------+             +--------+| +-------+ |
|+-------------------------------------------------------+           |
+--------------------------------------------------------------------+
        Figure 5: Illustration of ES with ES-X Type 1
 An Electronic Signature (ES) , with the additional validation data
 forming the eXtended Validation Data - Type 2 is illustrated in
 Figure 6:
+--------------------------------------------------------- ES-X 2 ---+
|+---------------------------------------- EC-C --------+            |
||+---- Elect.Signature (ES)----+             +--------+| +--------+ |
|||+-------+ +-------+ +-------+| +----------+|Complete|| |Times   | |
||||Signa- | |Other  | |Digital|| |Time-Stamp||certs   || |Stamp   | |
||||ture   | |Signed | |Signa- || |over      ||and     || |over    | |
||||Policy | |Attri- | |ture   || |digital   ||revoc.  || |Complete| |
||||ID     | |butes  | |       || |signature ||refs    || |certs   | |
|||+-------+ +-------+ +-------+| +----------+|        || |and     | |
||+-----------------------------+             +--------+| |revoc.  | |
||                                                      | |refs    | |
|+------------------------------------------------------+ +--------+ |
+--------------------------------------------------------------------+
        Figure 6: Illustration of ES with ES-X Type 2

2.7 Archive Validation Data

 Before the algorithms, keys and other cryptographic data used at the
 time the ES-C was built become weak and the cryptographic functions
 become vulnerable, or the certificates supporting previous time-
 stamps expires, the signed data, the ES-C and any additional
 information (ES-X) should be time-stamped.  If possible this should
 use stronger algorithms (or longer key lengths) than in the original
 time-stamp.

Pinkas, et al. Informational [Page 13] RFC 3126 Electronic Signature Formats September 2001

 This additional data and time-stamp is called Archive Validation Data
 (ES-A).  The Time-Stamping process may be repeated every time the
 protection used to time-stamp a previous ES-A become weak.  An ES-A
 may thus bear multiple embedded time stamps.
 An example of an Electronic Signature (ES), with the additional
 validation data for the ES-C and ES-X forming the ES-A is illustrated
 in Figure 7.
       +-------------------------------- ES-A --------- ----------+
       |  +-------------------- ES-A -----------------+           |
       |  |  +--------- ES-X -------------- +         |           |
       |  |  |..............................| +-----+ |  +-----+  |
       |  |  |..............................| |Time | |  |Time |  |
       |  |  |..............................| |Stamp| |  |Stamp|  |
       |  |  |                              | +-----+ |  +-----+  |
       |  |  +----------------------------- +         |           |
       |  +-------------------------------------------+           |
       +----------------------------------------------------------+
                    Figure 7: Illustration of ES -A
 Support for ES-A is optional.

Pinkas, et al. Informational [Page 14] RFC 3126 Electronic Signature Formats September 2001

2.8 Arbitration

 The ES-C may be used for arbitration should there be a dispute
 between the signer and verifier, provided that:
  • a copy of the signature policy referenced by the signer is

available;

  • the arbitrator knows where to retrieve the signer's certificate

(if not already present), all the cross-certificates and the

       required CRLs and/or OCSPs responses referenced in the ES-C;
  • none of the issuing key from the certificate chain have ever

been compromised;

  • the cryptography used at the time the ES-C was built has not

been broken at the time the arbitration is performed.

 When the second condition is not met, then the plaintiff must provide
 an ES-X Long.
 When it is known by some external means that the third condition is
 not met, then the plaintiff must provide an ES-X Time-Stamped.
 When the two previous conditions are not met, the plaintiff must
 provide the two above information (i.e., an ES-X Time-Stamped and
 Long).
 When the last condition is not met, the plaintiff must provide an
 ES-A.
 It should be noticed that a verifier may need to get two time stamps
 at two different instants of time: one soon after the generation of
 the ES and one soon after some grace period allowing any entity from
 the certification chain to declare a key compromise.

2.9 Validation Process

 The Validation Process validates an electronic signature in
 accordance with the requirements of the signature policy.  The output
 status of the validation process can be:
  • valid;
  • invalid;
  • incomplete verification.
 A Valid response indicates that the signature has passed verification
 and it complies with the signature validation policy.

Pinkas, et al. Informational [Page 15] RFC 3126 Electronic Signature Formats September 2001

 A signature validation policy is a part of the signature policy which
 specifies the technical requirements on the signer in creating a
 signature and verifier when validating a signature.
 An Invalid response indicates that either the signature format is
 incorrect or that the digital signature value fails verification
 (e.g., the integrity checks on the digital signature value fails or
 any of the certificates on which the digital signature verification
 depends is known to be invalid or revoked).
 An Incomplete Validation response indicates that the format and
 digital signature verifications have not failed but there is
 insufficient information to determine if the electronic signature is
 valid under the signature policy.  This can include situations where
 additional information, which does not effect the validity of the
 digital signature value, may be available but is invalid.
 In the case of Incomplete Validation, it may be possible to request
 that the electronic signature be checked again at a later date when
 additional validation information might become available.  Also, in
 the case of incomplete validation, additional information may be made
 available to the application or user, thus allowing the application
 or user to decide what to do with partially correct electronic
 signatures.
 The validation process may also output validation data:
  • a signature time-stamp;
  • the complete validation data;
  • the archive validation data.

2.10 Example Validation Sequence

 Figure 8, and subsequent description, describes how the validation
 process may build up a complete electronic signature over time.
 Soon after receiving the electronic signature (ES) from the signer
 (1), the digital signature value may be checked,  the validation
 process must at least add a time-stamp (2), unless the signer has
 provided one which is trusted by the verifier.  The validation
 process may also validate the electronic signature, as required under
 the identified signature policy, using additional data (e.g.,
 certificates, CRL, etc.) provided by trusted service providers.  If
 the validation process is not complete then the output from this
 stage is the ES-T.

Pinkas, et al. Informational [Page 16] RFC 3126 Electronic Signature Formats September 2001

 When all the additional data (e.g., the complete certificate and
 revocation information) necessary to validate the electronic
 signature first becomes available, then the validation process:
  • obtains all the necessary additional certificate and revocation

status information;

  • completes all the validation checks on the ES, using the

complete certificate and revocation information (if a time-

       stamp is not already present, this may be added at the same
       stage combining ES-T and ES-C process);
  • records the complete certificate and revocation references (3);
  • indicates the validity status to the user (4).
       +----------------------------------------- ES-C ----------+
       |+----------------------------- ES-T --------+            |
       ||+--- Elect.Signature (ES) ----+            | +--------+ |
       |||+-------+ +-------+ +-------+|+----------+| |Complete| |
       ||||Signa- | |Other  | |Digital|||Time-Stamp|| |certifi-| |
       ||||ture   | |Signed | |Signa- |||over      || |cate and| |
       ||||Policy | |Attri- | |ture   |||digital   || |revoca- | |
       ||||ID     | |butes  | |       |||signature || |tion    | |
       |||+-------+ +-------+ +-------+|+----------+| |referen-| |
       ||+------------\----------------+    ^       | |ces     | |
       ||              \                    |       | +--------+ |
       ||               \ 1                /        |      ^     |
       |+----------------\----------------/---------+      |     |
       +------------------\--------------/--------------- /------+
                           \            /2    ----3------/
        +----------+        |          /     /
        | Signed   |\       v         /     |
        |User data | \     +--------------------+     +------------+
        +----------+  \--->| Validation Process |---> |- Valid     |
                           +---|--^-------|--^--+ 4   |- Invalid   |
                               |  |       |  |        |- Validation|
                               v  |       v  |        |  Incomplete|
                           +---------+ +--------+     +------------+
                           |Signature| |Trusted |
                           | Policy  | |Service |
                           | Issuer  | |Provider|
                           +---------+ +--------+
 Figure 8: Illustration of an ES with Complete validation data (ES-C)

Pinkas, et al. Informational [Page 17] RFC 3126 Electronic Signature Formats September 2001

 At the same time as the validation process creates the ES-C, the
 validation process may provide and/or record the values of
 certificates and revocation status information used in ES-C, called
 the ES-X Long (5).  This is illustrated in figure 9:
+----------------------------------------------------- ES-X ---------+
|+---------------------------------------- ES-C --------+ +--------+ |
||+--- Elect.Signature (ES) ----+            +--------+ | |Complete| |
|||+-------+ +-------+ +-------+|+----------+|Complete| | |certifi-| |
||||Signa- | |Other  | |Digital|||Time-Stamp||certifi-| | |cate    | |
||||ture   | |Signed | |Signa- |||over      ||cate and| | |and     | |
||||Policy | |Attri- | |ture   |||digital   ||revoca- | | |revoca- | |
||||ID     | |butes  | |       |||signature ||tion    | | |tion    | |
|||+-------+ +---|---+ +-------+|+----------+|referen-| | |Data    | |
||+--------------\--------------+    ^       |ces     | | +--------+ |
||                \                  |       +--------+ |      ^     |
||                 \ 1             2/           ^       |      |     |
|+------------------\--------------/------------|-------+     /      |
+--------------------\------------/------------/-------------/-------+
                      \          /    ---3----/             /
 +----------+          |        /    /   ------------5-----/
 | Signed   |\         v       |     |  /
 |User data | \     +--------------------+     +-----------+
 +----------+  \--->| Validation Process |---> | - Valid   |
                    +---|--^-------|--^--+ 4   | - Invalid |
                        |  |       |  |        +-----------+
                        v  |       v  |
                    +---------+ +--------+
                    |Signature| |Trusted |
                    | Policy  | |Service |
                    | Issuer  | |Provider|
                    +---------+ +--------+
  Figure 9: Illustration ES with eXtended validation data (Long)
 When the validation process creates the ES-C it may also create
 extended forms of validation data.  A first alternative is to time-
 stamp all data forming the Type 1 X-Time-Stamp (6).  This is
 illustrated in figure 10:

Pinkas, et al. Informational [Page 18] RFC 3126 Electronic Signature Formats September 2001

 +----------------------------------------------------- ES-X -------+
 |+---------------------------------------- ES-C --------+ +------+ |
 ||+--- Elect.Signature (ES) ----+            +--------+ | |Time- | |
 |||+-------+ +-------+ +-------+|+----------+|Complete| | |Stamp | |
 ||||Signa- | |Other  | |Digital|||Time-Stamp||certifi-| | |over  | |
 ||||ture   | |Signed | |Signa- |||over      ||cate and| | |CES   | |
 ||||Policy | |Attri- | |ture   |||digital   ||revoca- | | +------+ |
 ||||ID     | |butes  | |       |||signature ||tion    | |     ^    |
 |||+-------+ +--|----+ +-------+|+----------+|referen-| |     |    |
 ||+-------------|---------------+     ^      |ces     | |     |    |
 ||              |                     |      +--------+ |     |    |
 ||               \ 1                 2/         ^       |     |    |
 |+----------------\------------------/----------|-------+     |    |
 +------------------\----------------/-----------/-------------/----+
                     \              /   ----3---/             /
  +----------+        |            /   /  ---------------6---/
  | Signed   |\       v           |   |  /
  |User data | \     +--------------------+     +-----------+
  +----------+  \--->| Validation Process |---> | - Valid   |
                     +---|--^-------|--^--+ 4   | - Invalid |
                         |  |       |  |        +-----------+
                         v  |       v  |
                     +---------+ +--------+
                     |Signature| |Trusted |
                     | Policy  | |Service |
                     | Issuer  | |Provider|
                     +---------+ +--------+
    Figure 10: Illustration of ES with eXtended validation data -
               Type 1 X-Time-Stamp

Pinkas, et al. Informational [Page 19] RFC 3126 Electronic Signature Formats September 2001

 Another alternative is to time-stamp the certificate and revocation
 information references used to validate the electronic signature (but
 not the signature) (6'); this is called Type 2 X-Time-Stamped.  This
 is illustrated in figure 11:
+----------------------------------------------------- ES-X -----------+
|+---------------------------------------- ES-C --------+ +----------+ |
||+--- Elect.Signature (ES) ----+            +--------+ | |Time-Stamp| |
|||+-------+ +-------+ +-------+|+----------+|Complete| | |over      | |
||||Signa- | |Other  | |Digital|||Time-Stamp||certifi-| | |Complete  | |
||||ture   | |Signed | |Signa- |||over      ||cate and| | |Certifi-  | |
||||Policy | |Attri- | |ture   |||digital   ||revoc.  | | |cate and  | |
||||ID     | |butes  | |       |||signature ||refs    | | |revoc.    | |
|||+-------+ +---^---+ +-------+|+----^-----++---^----+ | |refs      | |
||+--------------\--------------+     |          |      | +----------+ |
|+----------------\------------------/-----------|------+      ^       |
+----------------1-\----------------/-----------/--------------|-------+
                    \              /  -----3---/               |
 +----------+        |           2/  /   ---------------6'-----/
 | Signed   |\       v           |  |   /
 |User data | \     +--------------------+     +-----------+
 +----------+  \--->| Validation Process |---> | - Valid   |
                    +---|--^-------|--^--+ 4   | - Invalid |
                        |  |       |  |        +-----------+
                        v  |       v  |
                    +---------+ +--------+
                    |Signature| |Trusted |
                    | Policy  | |Service |
                    | Issuer  | |Provider|
                    +---------+ +--------+
  Figure 11: Illustration of ES with eXtended validation data -
             Type 2 X-Time-Stamp
 Before the algorithms used in any of electronic signatures become or
 are likely, to be compromised or rendered vulnerable in the future,
 it is necessary to time-stamp the entire electronic signature,
 including all the values of the validation and user data as an ES
 with Archive validation data (ES-A)

Pinkas, et al. Informational [Page 20] RFC 3126 Electronic Signature Formats September 2001

 An ES-A is illustrated in figure 12:

——————————————– ES-A ——————–+ —————————————————————-+ | +——————————- EC-C ——–++—–+ | |

Time-
+– Elect.Signature (ES) -+ +——–+Stamp +——-+
+——++——-++——-+——+Completeover Complete
Signa-Other DigitalTime- certifi-CES certi- +—-
ture Signed Signa- Stamp cate and+—–+ ficate Arch-
PolicyAttri- ture over revoca- +——+ and ive
ID butes digit.tion Time- revoca-Time
+——++——++——-signa-referen-Stamp- tion stamp
+————————+ture ces over data +—-
+——++——–+Complete\+——-+
cert.

+————-|—————-|———|—-+|and rev| | | |

             \               |         /     |refs.  |        |  |  |
              \              |        /      +-------+        |  |  |

—————–\————-|——-/————————+ | | +———-+ \ | / / |

Signed \2 3 / /————–7——-/
User data \ /

+——-\–+ \ | | / | ———\————|——–|—-|—/—————————–+

        \           v        |    |   |
        1\        +--------------------+     +-----------+
          \------>| Validation Process |---> | - Valid   |
                  +---|--^-------|--^--+ 4   | - Invalid |
                      |  |       |  |        +-----------+
                      v  |       v  |
                  +---------+ +--------+
                  |Signature| |Trusted |
                  | Policy  | |Service |
                  | Issuer  | |Provider|
                  +---------+ +--------+
 Figure 12: Illustration of an ES with Archive validation data (ES-A)

2.11 Additional optional features of an ES

 This document also defines additional optional features of an
 electronic signature to:
  • indicate a commitment type being made by the signer;
  • indicate the role under which a signature was created;
  • support multiple signatures.

Pinkas, et al. Informational [Page 21] RFC 3126 Electronic Signature Formats September 2001

3. Data structure of an Electronic Signature

 This clause uses and builds upon the Cryptographic Message Syntax
 (CMS), as defined in RFC 2630 [CMS], and Enhanced Security Services
 (ESS), as defined in RFC 2634 [ESS].  The overall structure of
 Electronic Signature is as defined in [CMS].  The Electronic
 Signature (ES) uses attributes defined in [CMS], [ESS] and this
 document.  This document defines in full the ES attributes which it
 uses and are not defined elsewhere.
 The mandated set of attributes and the digital signature value is
 defined as the minimum Electronic Signature (ES) required by this
 document.  A signature policy MAY mandate other signed attributes to
 be present.

3.1 General Syntax

 The general syntax of the ES is as defined in [CMS].

3.2 Data Content Type

 The data content type of the ES is as defined in [CMS].
 The data content type is intended to refer to arbitrary octet
 strings, such as ASCII text files; the interpretation is left to the
 application.  Such strings need not have any internal structure
 (although they could have their own ASN.1 definition or other
 structure).

3.3 Signed-data Content Type

 The Signed-data content type of the ES is as defined in [CMS].
 The signed-data content type consists of a content of any type and
 zero or more signature values.  Any number of signers in parallel can
 sign any type of content.  The typical application of the signed-data
 content type represents one signer's digital signature on content of
 the data content type.
 To make sure that the verifier uses the right certificate, this
 document mandates that the hash of the signers certificate is always
 included in the Signing Certificate signed attribute.

3.4 SignedData Type

 The syntax of the SignedData type of the ES is as defined in [CMS].

Pinkas, et al. Informational [Page 22] RFC 3126 Electronic Signature Formats September 2001

 The fields of type SignedData have the meanings defined [CMS] except
 that:
  • version is the syntax version number. The value of version

must be 3.

  • The identification of signer's certificate used to create the

signature is always present as a signed attribute.

  • The degenerate case where there are no signers is not valid in

this document.

3.5 EncapsulatedContentInfo Type

 The syntax of the EncapsulatedContentInfo a type of the ES is as
 defined in [CMS].
 For the purpose of long term validation as defined by this document,
 it is advisable that either the eContent is present, or the data
 which is signed is archived in such as way as to preserve the any
 data encoding. It is important that the OCTET STRING used to generate
 the signature remains the same every time either the verifier or an
 arbitrator validates the signature.
 The degenerate case where there are no signers is not valid in this
 document.

3.6 SignerInfo Type

 The syntax of the SignerInfo a type of the ES is as defined in [CMS].
 Per-signer information is represented in the type SignerInfo.  In the
 case of multiple independent signatures, there is an instance of this
 field for each signer.
 The fields of type SignerInfo have the meanings defined in [CMS]
 except that signedAttributes must, as a minimum, contain the
 following attributes:
  • ContentType as defined in clause 3.7.1.
  • MessageDigest as defined in clause 3.7.2.
  • SigningTime as defined in clause 3.7.3.
  • SigningCertificate as defined in clause 3.8.1.
  • SignaturePolicyId as defined in clause 3.9.1.

3.6.1 Message Digest Calculation Process

 The message digest calculation process is as defined in [CMS].

Pinkas, et al. Informational [Page 23] RFC 3126 Electronic Signature Formats September 2001

3.6.2 Message Signature Generation Process

 The input to the digital signature generation process is as defined
 in [CMS].

3.6.3 Message Signature Verification Process

 The procedures for CMS signed data validation are as defined in [CMS]
 and enhanced in this document.
 The input to the signature verification process includes the signer's
 public key verified as correct using either the ESS Signing
 Certificate attribute or the Other Signing Certificate attribute.

3.7 CMS Imported Mandatory Present Attributes

 The following attributes MUST be present with the signed-data defined
 by this document.  The attributes are defined in [CMS].

3.7.1 Content Type

 The syntax of the content-type attribute type of the ES is as defined
 in [CMS].

3.7.2 Message Digest

 The syntax of the message-digest attribute type of the ES is as
 defined in [CMS].

3.7.3 Signing Time

 The syntax of the message-digest attribute type of the ES is as
 defined in [CMS] and further qualified by this document.
 The signing-time attribute type specifies the time at which the
 signer claims to have performed the signing process.
 This present document recommends the use of GeneralizedTime.

3.8 Alternative Signing Certificate Attributes

 One, and only one, of the following two alternative attributes MUST
 be present with the signed-data defined by this document to identify
 the signing certificate.  Both attributes include an identifier and a
 hash of the signing certificate.  The first, which is adopted in
 existing standards, may be only used with the SHA-1 hashing
 algorithm.  The other shall be used when other hashing algorithms are
 to be supported.

Pinkas, et al. Informational [Page 24] RFC 3126 Electronic Signature Formats September 2001

 The signing certificate attribute is designed to prevent the simple
 substitution and re-issue attacks, and to allow for a restricted set
 of authorization certificates to be used in verifying a signature.

3.8.1 ESS Signing Certificate Attribute Definition

 The syntax of the signing certificate attribute type of the ES is as
 defined in [ESS], and further qualified and profile in this document.
 The ESS signing certificate attribute must be a signed attribute.
 This document mandates the presence of this attribute as a signed CMS
 attribute, and the sequence must not be empty.  The certificate used
 to verify the signature must be identified in the sequence, the
 Signature Validation Policy may mandate other certificate references
 to be present, that may include all the certificates up to the point
 of trust.  The encoding of the ESSCertID for this certificate must
 include the issuerSerial field.
 The issuerAndSerialNumber present in the SignerInfo must be
 consistent with issuerSerial field.  The certificate identified must
 be used during the signature verification process.  If the hash of
 the certificate does not match the certificate used to verify the
 signature, the signature must be considered invalid.
 The sequence of policy information field is not used in this
 document.
 NOTE: Where an attribute certificate is used by the signer to
 associate a role, or other attributes of the signer, with the
 electronic signature this is placed in the Signer Attribute attribute
 as defined in clause 3.12.3.

3.8.2 Other Signing Certificate Attribute Definition

 The following attribute is identical to the ESS SigningCertificate
 defined above except that this attribute can be used with hashing
 algorithms other than SHA-1.
 This attribute must be used in the same manner as defined above for
 the ESS SigningCertificate attribute.
 The following object identifier identifies the signing certificate
 attribute:
 id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
     member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
     smime(16) id-aa(2) 19 }

Pinkas, et al. Informational [Page 25] RFC 3126 Electronic Signature Formats September 2001

 The signing certificate attribute value has the ASN.1 syntax
 OtherSigningCertificate
 OtherSigningCertificate ::=  SEQUENCE {
     certs        SEQUENCE OF OtherCertID,
     policies     SEQUENCE OF PolicyInformation OPTIONAL
                  -- NOT USED IN THIS DOCUMENT
 }
 OtherCertID ::= SEQUENCE {
      otherCertHash            OtherHash,
      issuerSerial             IssuerSerial OPTIONAL
 }
 OtherHash ::= CHOICE {
     sha1Hash OtherHashValue,  -- This contains a SHA-1 hash
     otherHash OtherHashAlgAndValue
 }
 OtherHashValue ::= OCTET STRING
 OtherHashAlgAndValue ::= SEQUENCE {
   hashAlgorithm  AlgorithmIdentifier,
   hashValue      OtherHashValue
 }

3.9 Additional Mandatory Attributes

3.9.1 Signature policy Identifier

 This document mandates that a reference to the signature policy, is
 included in the signedData, this reference is either explicitly
 identified or implied by the semantics of the signed content and
 other external data.  A signature policy defines the rules for
 creation and validation of an electronic signature, is included as a
 signed attribute with every signature.  The signature policy
 identifier must be a signed attribute.
 The following object identifier identifies the signature policy
 identifier attribute:
 id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
     member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
     smime(16) id-aa(2) 15 }
 Signature-policy-identifier attribute values have ASN.1 type
 SignaturePolicyIdentifier.

Pinkas, et al. Informational [Page 26] RFC 3126 Electronic Signature Formats September 2001

 SignaturePolicyIdentifier ::= CHOICE{
          SignaturePolicyId          SignaturePolicyId,
          SignaturePolicyImplied     SignaturePolicyImplied }
 SignaturePolicyId ::= SEQUENCE {
         sigPolicyIdentifier   SigPolicyId,
         sigPolicyHash         SigPolicyHash,
         sigPolicyQualifiers   SEQUENCE SIZE (1..MAX) OF
                               SigPolicyQualifierInfo      OPTIONAL
                                                                  }
 SignaturePolicyImplied ::= NULL
 The presence of the NULL type indicates that the signature policy is
 implied by the semantics of the signed data and other external data.
 The sigPolicyId field contains an object-identifier which uniquely
 identifies a specific version of the signature policy.  The syntax of
 this field is as follows:
    SigPolicyId ::= OBJECT IDENTIFIER
 The sigPolicyHash field contains the identifier of the hash algorithm
 and the hash of the value of the signature policy.
 If the signature policy is defined using a computer processable
 notation like ASN.1, then the hash is calculated on the value without
 the outer type and length fields and the hashing algorithm must be as
 specified in the field signPolicyHshAlg.
 If the signature policy is defined using another structure, the type
 of structure and the hashing algorithm must be either specified as
 part of the signature policy, or indicated using a signature policy
 qualifier.
    SigPolicyHash ::= OtherHashAlgAndValue
 A signature policy identifier may be qualified with other information
 about the qualifier.  The semantics and syntax of the qualifier is as
 associated with the object-identifier in the sigPolicyQualifierId
 field.  The general syntax of this qualifier is as follows:
    SigPolicyQualifierInfo ::= SEQUENCE {
         sigPolicyQualifierId  SigPolicyQualifierId,
         sigQualifier          ANY DEFINED BY sigPolicyQualifierId
 }

Pinkas, et al. Informational [Page 27] RFC 3126 Electronic Signature Formats September 2001

 This document specifies the following qualifiers:
  • spuri: This contains the web URI or URL reference to the

signature policy

  • spUserNotice: This contains a user notice which should be

displayed whenever the signature is validated.

  1. - sigpolicyQualifierIds defined in this document
 SigPolicyQualifierId ::=  OBJECT IDENTIFIER
     id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
     member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
     smime(16) id-spq(5) 1 }
    SPuri ::= IA5String
     id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
     member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
     smime(16) id-spq(5) 2 }
    SPUserNotice ::= SEQUENCE {
         noticeRef        NoticeReference OPTIONAL,
         explicitText     DisplayText OPTIONAL
 }
    NoticeReference ::= SEQUENCE {
         organization     DisplayText,
         noticeNumbers    SEQUENCE OF INTEGER
 }
    DisplayText ::= CHOICE {
         visibleString    VisibleString  (SIZE (1..200)),
         bmpString        BMPString      (SIZE (1..200)),
         utf8String       UTF8String     (SIZE (1..200))
 }

3.10 CMS Imported Optional Attributes

 The following attributes MAY be present with the signed-data defined
 by this document.  The attributes are defined in ref [CMS] and are
 imported into this specification and were appropriate qualified and
 profiling by this document.

Pinkas, et al. Informational [Page 28] RFC 3126 Electronic Signature Formats September 2001

3.10.1 Countersignature

 The syntax of the countersignature attribute type of the ES is as
 defined in [CMS].  The countersignature attribute must be an unsigned
 attribute.

3.11 ESS Imported Optional Attributes

 The following attributes MAY be present with the signed-data defined
 by this document.  The attributes are defined in ref [ESS] and are
 imported into this specification and were appropriate qualified and
 profiling by this document.

3.11.1 Content Reference Attribute

 The content reference attribute is a link from one SignedData to
 another.  It may be used to link a reply to the original message to
 which it refers, or to incorporate by reference one SignedData into
 another.
 The content reference attribute MUST be used as defined in [ESS].
 The content reference MUST be a signed attribute.
 The syntax of the content reference attribute type of the ES is as
 defined in [ESS].

3.11.2 Content Identifier Attribute

 The content identifier attribute provides an identifier for the
 signed content for use when reference may be later required to that
 content, for example in the content reference attribute in other
 signed data sent later.
 The content identifier must be a signed attribute.
 The syntax of the content identifier attribute type of the ES is as
 defined in [ESS].
 The minimal signedContentIdentifier should contain a concatenation of
 user-specific identification information (such as a user name or
 public keying material identification information), a GeneralizedTime
 string, and a random number.

3.11.3 Content Hints Attribute

 The content hints attribute provides information that describes the
 format of the signed content.  It may be used by the signer to
 indicate to a verifier the precise format that MUST be used to

Pinkas, et al. Informational [Page 29] RFC 3126 Electronic Signature Formats September 2001

 present the data (e.g., text, voice, video) to a verifier.  This
 attribute MUST be present when it is mandatory to present the signed
 data to human users on verification.
 The syntax of the content hints attribute type of the ES is as
 defined in ESS (RFC 2634, section 2.9 [9]).
 When used to indicate the precise format of the data to be presented
 to the user the following rules apply:
 The contentType (defined in RFC 2630 [8]) indicates the type of the
 associated content.  It is an object identifier (i.e., a unique
 string of integers) assigned by an authority that defines the content
 type.
 The UTF8String shall define the presentation format.  The format may
 be defined by MIME types as indicated below.
 Note 1: The contentType can be id-data defined in CMS (RFC 2630 [8]).
 The UTF8String can be used to indicate the encoding of the data, like
 MIME type.  RFC 2045 [25] provides a common structure for encoding a
 range of electronic documents and other multi-media types, see annex
 B for further information, a system supporting verification of
 electronic signature may present information to users in the form
 identified by the MIME type.
 id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
 rsadsi(113549) pkcs(1) pkcs7(7) 1 }

3.12 Additional Optional Attributes

3.12.1 Commitment Type Indication Attribute

 There may be situation were a signer wants to explicitly indicate to
 a verifier that by signing the data, it illustrates a type of
 commitment on behalf of the signer.  The commitmentTypeIndication
 attribute conveys such information.
 The commitmentTypeIndication attribute must be a signed attribute.
 The commitment type may be:
  • defined as part of the signature policy, in which case the

commitment type has precise semantics that is defined as part

       of the signature policy.

Pinkas, et al. Informational [Page 30] RFC 3126 Electronic Signature Formats September 2001

  • be a registered type, in which case the commitment type has

precise semantics defined by registration, under the rules of

       the registration authority.  Such a registration authority may
       be a trading association or a legislative authority.
 The signature policy specifies a set of attributes that it
 "recognizes".  This "recognized" set includes all those commitment
 types defined as part of the signature policy as well as any
 externally defined commitment types that the policy may choose to
 recognize.  Only recognized commitment types are allowed in this
 field.
 The following object identifier identifies the commitment type
 indication attribute:

id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}

Commitment-Type-Indication attribute values have ASN.1 type CommitmentTypeIndication.

CommitmentTypeIndication ::= SEQUENCE {

 commitmentTypeId            CommitmentTypeIdentifier,
 commitmentTypeQualifier     SEQUENCE SIZE (1..MAX) OF
                             CommitmentTypeQualifier      OPTIONAL

}

CommitmentTypeIdentifier ::= OBJECT IDENTIFIER

CommitmentTypeQualifier ::= SEQUENCE {

  commitmentTypeIdentifier   CommitmentTypeIdentifier,
  qualifier                  ANY DEFINED BY
                             commitmentTypeIdentifier

}

 The use of any qualifiers to the commitment type is outside the scope
 of this document.
 The following generic commitment types are defined in this document:
    id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    cti(6) 1}
    id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    cti(6) 2}

Pinkas, et al. Informational [Page 31] RFC 3126 Electronic Signature Formats September 2001

    id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 3}
    id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    cti(6) 4}
    id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 5}
    id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 6}
 These generic commitment types have the following meaning:
 Proof of origin indicates that the signer recognizes to have created,
 approved and sent the message.
 Proof of receipt indicates that signer recognizes to have received
 the content of the message.
 Proof of delivery indicates that the TSP providing that indication
 has delivered a message in a local store accessible to the recipient
 of the message.
 Proof of sender indicates that the entity providing that indication
 has sent the message (but not necessarily created it).
 Proof of approval indicates that the signer has approved the content
 of the message.
 Proof of creation indicates that the signer has created the message
 (but not necessarily approved, nor sent it).

3.12.2 Signer Location attribute

 The signer-location attribute is an attribute which specifies a
 mnemonic for an address associated with the signer at a particular
 geographical (e.g., city) location.  The mnemonic is registered in
 the country in which the signer is located and is used in the
 provision of the Public Telegram Service (according to ITU-T
 Recommendation F.1 [PTS]).
 The signer-location attribute must be a signed attribute.

Pinkas, et al. Informational [Page 32] RFC 3126 Electronic Signature Formats September 2001

 The following object identifier identifies the signer-location
 attribute:

id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}

Signer-location attribute values have ASN.1 type SignerLocation.

 SignerLocation ::= SEQUENCE {
      -- at least one of the following must be present
    countryName          [0] DirectoryString      OPTIONAL,
      -- as used to name a Country in X.500
    localityName         [1] DirectoryString      OPTIONAL,
       -- as used to name a locality in X.500
    postalAdddress       [2] PostalAddress        OPTIONAL

}

 PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString

3.12.3 Signer Attributes attribute

 The signer-attributes attribute is an attribute which specifies
 additional attributes of the signer (e.g., role).
 It may be either:
  • claimed attributes of the signer; or
  • certified attributes of the signer;
 The signer-attributes attribute must be a signed attribute.
 The following object identifier identifies the signer-attribute
 attribute:
 id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
     us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
 signer-attribute attribute values have ASN.1 type SignerAttribute.
    SignerAttribute ::= SEQUENCE OF CHOICE {
       claimedAttributes      [0]  ClaimedAttributes,
       certifiedAttributes    [1]  CertifiedAttributes
 }
 ClaimedAttributes ::= SEQUENCE OF Attribute
 CertifiedAttributes ::= AttributeCertificate
          -- as defined in X.509 : see section 10.3

Pinkas, et al. Informational [Page 33] RFC 3126 Electronic Signature Formats September 2001

 NOTE:  The claimed and certified attribute are imported from ITU-T
 Recommendations X.501 [16] and ITU-T Recommendation X.509:Draft
 Amendment on Certificate Extensions, October 1999.

3.12.4 Content Time-Stamp attribute

 The content time-stamp attribute is an attribute which is the time-
 stamp of the signed data content before it is signed.
 The content time-stamp attribute must be a signed attribute.
 The following object identifier identifies the signer-attribute
 attribute:
    id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) id-aa(2) 20}
 Content time-stamp attribute values have ASN.1 type ContentTimestamp:
 ContentTimestamp::= TimeStampToken
 The value of messageImprint field within TimeStampToken must be a
 hash of the value of eContent field within encapContentInfo within
 the signedData.
 For further information and definition of TimeStampToken see [TSP].

3.13 Support for Multiple Signatures

3.13.1 Independent Signatures

 Multiple independent signatures are supported by independent
 SignerInfo from each signer.
 Each SignerInfo must include all the attributes required under this
 document and must be processed independently by the verifier.

3.13.2 Embedded Signatures

 Multiple embedded signatures are supported using the counter-
 signature unsigned attribute (see clause 3.10.1).  Each counter
 signature is carried in Countersignature held as an unsigned
 attribute to the SignerInfo to which the counter-signature is
 applied.

Pinkas, et al. Informational [Page 34] RFC 3126 Electronic Signature Formats September 2001

4. Validation Data

 This clause specifies the validation data structures which builds on
 the electronic signature specified in clause 3.  This includes:
  • Time-Stamp applied to the electronic signature value.
  • Complete validation data which comprises the time-stamp of the

signature value, plus references to all the certificates and

       revocation information used for full validation of the
       electronic signature.
 The following optional eXtended forms of validation data are also
 defined:
  • X-timestamp: There are two types of time-stamp used in extended

validation data defined by this document.

  1. Type 1 -Time-Stamp which comprises a time-stamp over the ES

with Complete validation data (ES-C).

  1. Type 2 X-Time-Stamp which comprises of a time-stamp over the

certification path references and the revocation information

          references used to support the ES-C.
  • X-Long: This comprises a Complete validation data plus

the actual values of all the certificates and revocation

             information used in the ES-C.
  • X-Long-Time-Stamp: This comprises a Type 1 or Type 2 X-

Timestamp plus the actual values of all the certificates

             and revocation information used in the ES-C.
 This clause also specifies the data structures used in Archive
 validation data:
  • Archive validation data comprises a Complete validation data,

the certificate and revocation values (as in a X-Long

       validation data), any other existing X-timestamps, plus the
       Signed User data and an additional archive time-stamp over all
       that data.  An archive time-stamp may be repeatedly applied
       after long periods to maintain validity when electronic
       signature and timestamping algorithms weaken.
 The additional data required to create the forms of electronic
 signature identified above is carried as unsigned attributes
 associated with an individual signature by being placed in the

Pinkas, et al. Informational [Page 35] RFC 3126 Electronic Signature Formats September 2001

 unsignedAttrs field of SignerInfo.  Thus all the attributes defined
 in clause 4 are unsigned attributes.
 NOTE:  Where multiple signatures are to be supported, as described in
 clause 3.13, each signature has a separate SignerInfo.  Thus, each
 signature requires its own unsigned attribute values to create ES-T,
 ES-C etc.

4.1 Electronic Signature Timestamp

 An Electronic Signature with Timestamp is an Electronic Signature for
 which part, but not all, of the additional data required for
 validation is available (e.g., some certificates and revocation
 information is available but not all).
 The minimum structure Timestamp validation data is the Signature
 Timestamp Attribute as defined in clause 4.1.1 over the ES signature
 value.

4.1.1 Signature Timestamp Attribute Definition

 The Signature Timestamp attribute is timestamp of the signature
 value. It is an unsigned attribute.  Several instances of this
 attribute from different TSAs may occur with an electronic signature.
 The Signature Validation Policy specifies, in the
 signatureTimestampDelay field of TimestampTrustConditions, a maximum
 acceptable time difference which is allowed between the time
 indicated in the signing time attribute and the time indicated by the
 Signature Timestamp attribute.  If this delay is exceeded then the
 electronic signature must be considered as invalid.
 The following object identifier identifies the Signature Timestamp
 attribute:
    id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 14}
 The Signature timestamp attribute value has ASN.1 type
 SignatureTimeStampToken.
 SignatureTimeStampToken ::= TimeStampToken
 The value of messageImprint field within TimeStampToken must be a
 hash of the value of signature field within SignerInfo for the
 signedData being timestamped.

Pinkas, et al. Informational [Page 36] RFC 3126 Electronic Signature Formats September 2001

 For further information and definition of TimeStampToken see [TSP].

4.2 Complete Validation Data

 An electronic signature with complete validation data is an
 Electronic Signature for which all the additional data required for
 validation (i.e., all certificates and revocation information) is
 available. Complete validation data (ES-C) build on the electronic
 signature Time-Stamp as defined above.
 The minimum structure of a Complete validation data is:
  • the Signature Time-Stamp Attribute, as defined in clause 4.1.1;
  • Complete Certificate Refs, as defined in clause 4.2.1;
  • Complete Revocation Refs, as defined in clause 4.2.2.
 The Complete validation data MAY also include the following
 additional information, forming a X-Long validation data, for use if
 later validation processes may not have access to this information:
  • Complete Certificate Values, as defined in clause 4.2.3;
  • Complete Revocation Values, as defined in clause 4.2.4.
 The  Complete validation data MAY also include one of the following
 additional attributes, forming a X-Time-Stamp validation data, to
 provide additional protection against later CA compromise and provide
 integrity of the validation data used:
  • ES-C Time-Stamp, as defined in clause 4.2.5; or
  • Time-Stamped Certificates and CRLs references, as defined in

clause 4.2.6.

 NOTE 1: As long as the CA's are trusted such that these keys cannot
 be compromised or the cryptography used broken, the ES-C provides
 long term proof of a valid electronic signature.
 A valid electronic signature is an electronic signature which passes
 validation according to a signature validation policy.
 NOTE 2: The ES-C provides the following important property for long
 standing signatures; that is having been found once to be valid, must
 continue to be so months or years later.  Long after the validity
 period of the certificates have expired, or after the user key has
 been compromised.

Pinkas, et al. Informational [Page 37] RFC 3126 Electronic Signature Formats September 2001

4.2.1 Complete Certificate Refs Attribute Definition

 The Complete Certificate Refs attribute is an unsigned attribute.  It
 references the full set of CA certificates that have been used to
 validate a ES with Complete validation data (ES-C) up to (but not
 including) the signer's certificate.  Only a single instance of this
 attribute must occur with an electronic signature.
 Note: The signer's certified is referenced in the signing certificate
 attribute (see clause 3.1).

id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
 The complete certificate refs attribute value has the ASN.1 syntax
 CompleteCertificateRefs.
 CompleteCertificateRefs ::=  SEQUENCE OF OTHERCertID
 OTHERCertID is defined in clause 3.8.2.
 The IssuerSerial that must be present in OTHERCertID.  The certHash
 must match the hash of the certificate referenced.
 NOTE:  Copies of the certificate values may be held using the
 Certificate Values attribute defined in clause 4.3.1.

4.2.2 Complete Revocation Refs Attribute Definition

 The Complete Revocation Refs attribute is an unsigned attribute.
 Only a single instance of this attribute must occur with an
 electronic signature.  It references the full set of the CRL or OCSP
 responses that have been used in the validation of the signer and CA
 certificates used in ES with Complete validation data.
 The following object identifier identifies the CompleteRevocationRefs
 attribute:

id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
 The complete revocation refs attribute value has the ASN.1 syntax
 CompleteRevocationRefs.
 CompleteRevocationRefs ::=  SEQUENCE OF CrlOcspRef

Pinkas, et al. Informational [Page 38] RFC 3126 Electronic Signature Formats September 2001

 CrlOcspRef ::= SEQUENCE {
     crlids           [0] CRLListID        OPTIONAL,
     ocspids          [1] OcspListID       OPTIONAL,
     otherRev         [2] OtherRevRefs     OPTIONAL
 }
 CompleteRevocationRefs must contain one CrlOcspRef for the signing
 certificate, followed by one for each OTHERCertID in the
 CompleteCertificateRefs attribute.  The second and subsequent
 CrlOcspRef fields must be in the same order as the OTHERCertID to
 which they relate.  At least one of CRLListID or OcspListID or
 OtherRevRefs should be present for all but the "trusted" CA of the
 certificate path.
 CRLListID ::=  SEQUENCE {
     crls        SEQUENCE OF CrlValidatedID}
 CrlValidatedID ::=  SEQUENCE {
      crlHash                   OtherHash,
      crlIdentifier             CrlIdentifier OPTIONAL}
 CrlIdentifier ::= SEQUENCE {
     crlissuer                 Name,
     crlIssuedTime             UTCTime,
     crlNumber                 INTEGER OPTIONAL
                                             }
 OcspListID ::=  SEQUENCE {
     ocspResponses        SEQUENCE OF OcspResponsesID}
 OcspResponsesID ::=  SEQUENCE {
     ocspIdentifier              OcspIdentifier,
     ocspRepHash                 OtherHash    OPTIONAL
                                             }
 OcspIdentifier ::= SEQUENCE {
      ocspResponderID    ResponderID,
                        -- As in OCSP response data
      producedAt      GeneralizedTime
                        -- As in OCSP response data
                                              }
 When creating an crlValidatedID, the crlHash is computed over the
 entire DER encoded CRL including the signature.  The crlIdentifier
 would normally be present unless the CRL can be inferred from other
 information.

Pinkas, et al. Informational [Page 39] RFC 3126 Electronic Signature Formats September 2001

 The crlIdentifier is to identify the CRL using the issuer name and
 the CRL issued time which must correspond to the time "thisUpdate"
 contained in the issued CRL.  The crlListID attribute is an unsigned
 attribute.  In the case that the identified CRL is a Delta CRL then
 references to the set of CRLs to provide a complete revocation list
 must be included.
 The OcspIdentifier is to identify the OSCP response using the issuer
 name and the time of issue of the OCSP response which must correspond
 to the time "producedAt" contained in the issued OCSP response.
 Since it may be needed to make the difference between two OCSP
 responses received within the same second, then the hash of the
 response contained in the OcspResponsesID may be needed to solve the
 ambiguity.
 NOTE: Copies of the CRL and OCSP responses values may be held using
 the Revocation Values attribute defined in clause 4.3.2.
 OtherRevRefs ::= SEQUENCE {
    otherRevRefType      OtherRevRefType,
    otherRevRefs         ANY DEFINED BY otherRevRefType
 }
 OtherRevRefType ::= OBJECT IDENTIFIER
 The syntax and semantics of other revocation references is outside
 the scope of this document.  The definition of the syntax of the
 other form of revocation information is as identified by
 OtherRevRefType.

4.3 Extended Validation Data

4.3.1 Certificate Values Attribute Definition

 The Certificate Values attribute is an unsigned attribute.  Only a
 single instance of this attribute must occur with an electronic
 signature.  It holds the values of certificates referenced in the
 CompleteCertificateRefs attribute.
 Note: If an Attribute Certificate is used, it is not provided in this
 structure but must be provided by the signer as a signer-attributes
 attribute (see clause 12.3).
 The following object identifier identifies the CertificateValues
 attribute:
 id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
     us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}

Pinkas, et al. Informational [Page 40] RFC 3126 Electronic Signature Formats September 2001

 The certificate values attribute value has the ASN.1 syntax
 CertificateValues.
 CertificateValues ::=  SEQUENCE OF Certificate
 Certificate is defined in RFC2459 and ITU-T Recommendation X.509 [1])

4.3.2 Revocation Values Attribute Definition

 The Revocation Values attribute is an unsigned attribute.  Only a
 single instance of this attribute must occur with an electronic
 signature.  It holds the values of CRLs and OCSP referenced in the
 CompleteRevocationRefs attribute.
 The following object identifier identifies the Revocation Values
 attribute:
    id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 24}
 The revocation values attribute value has the ASN.1 syntax
 RevocationValues.
 RevocationValues ::=  SEQUENCE {
    crlVals           [0] SEQUENCE OF CertificateList     OPTIONAL,
    ocspVals          [1] SEQUENCE OF BasicOCSPResponse   OPTIONAL,
    otherRevVals      [2] OtherRevVals
 }
 OtherRevVals ::= SEQUENCE {
    otherRevValType       OtherRevValType,
    otherRevVals          ANY DEFINED BY otherRevValType
 }
 OtherRevValType ::= OBJECT IDENTIFIER
 The syntax and semantics of the other revocation values is outside
 the scope of this document.  The definition of the syntax of the
 other form of revocation information is as identified by
 OtherRevRefType.
 CertificateList is defined in RFC 2459 [RFC2459] and in ITU-T
 Recommendation X.509 [X509]).
 BasicOCSPResponse is defined in RFC 2560 [OCSP].

Pinkas, et al. Informational [Page 41] RFC 3126 Electronic Signature Formats September 2001

4.3.3 ES-C Time-Stamp Attribute Definition

 This attribute is used for the Type 1 X-Time-Stamped validation data.
 The ES-C Time-Stamp attribute is an unsigned attribute.  It is time-
 stamp of a hash of the electronic signature and the complete
 validation data (ES-C).  It is a special purpose TimeStampToken
 Attribute which time-stamps the ES-C.  Several instances instance of
 this attribute may occur with an electronic signature from different
 TSAs.
 The following object identifier identifies the ES-C Time-Stamp
 attribute:
    id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 25}
 The ES-C time-stamp attribute value has the ASN.1 syntax
 ESCTimeStampToken.
 ESCTimeStampToken ::= TimeStampToken
 The value of messageImprint field within TimeStampToken must be a
 hash of the concatenated values (without the type or length encoding
 for that value) of the following data objects as present in the ES
 with Complete validation data (ES-C):
  • signature field within SignerInfo;
  • SignatureTimeStampToken attribute;
  • CompleteCertificateRefs attribute;
  • CompleteRevocationRefs attribute.
 For further information and definition of the Time Stamp Token see
 [TSP].

4.3.4 Time-Stamped Certificates and CRLs Attribute Definition

 This attribute is used for the Type 2 X-Time-Stamp validation data.
 A TimestampedCertsCRLsRef attribute is an unsigned attribute.  It is
 a list of referenced certificates and OCSP responses/CRLs which are
 been time-stamped to protect against certain CA compromises.  Its
 syntax is as follows:
 The following object identifier identifies the
 TimestampedCertsCRLsRef attribute:

Pinkas, et al. Informational [Page 42] RFC 3126 Electronic Signature Formats September 2001

    id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 26}
 The attribute value has the ASN.1 syntax TimestampedCertsCRLs.
 TimestampedCertsCRLs ::= TimeStampToken
 The value of messageImprint field within TimeStampToken must be a
 hash of the concatenated values (without the type or length encoding
 for that value) of the following data objects as present in the ES
 with Complete validation data (ES-C):
  • CompleteCertificateRefs attribute;
  • CompleteRevocationRefs attribute.

4.4 Archive Validation Data

 Where an electronic signature is required to last for a very long
 time, and a the time-stamp on an electronic signature is in danger of
 being invalidated due to algorithm weakness or limits in the validity
 period of the TSA certificate, then it may be required to time-stamp
 the electronic signature several times.  When this is required an
 archive time-stamp attribute may be required.  This time-stamp may be
 repeatedly applied over a period of time.

4.4.1 Archive Time-Stamp Attribute Definition

 The Archive Time-Stamp attribute is time-stamp of the user data and
 the entire electronic signature.  If the Certificate values and
 Revocation Values attributes are not present these attributes must be
 added to the electronic signature prior to the time-stamp.  The
 Archive Time-Stamp attribute is an unsigned attribute.  Several
 instances of this attribute may occur with on electronic signature
 both over time and from different TSAs.
 The following object identifier identifies the Nested Archive Time-
 Stamp attribute:
    id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
    body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
    id-aa(2) 27}
 Archive time-stamp attribute values have the ASN.1 syntax
 ArchiveTimeStampToken
 ArchiveTimeStampToken ::= TimeStampToken

Pinkas, et al. Informational [Page 43] RFC 3126 Electronic Signature Formats September 2001

 The value of messageImprint field within Time-StampToken must be a
 hash of the concatenated values (without the type or length encoding
 for that value) of the following data objects as present in the
 electronic signature:
  • encapContentInfo eContent OCTET STRING;
  • signedAttributes;
  • signature field within SignerInfo;
  • SignatureTimeStampToken attribute;
  • CompleteCertificateRefs attribute;
  • CompleteRevocationData attribute;
  • CertificateValues attribute

(If not already present this information must be included in

       the ES-A);
    *  RevocationValues attribute
       (If not already present this information must be included in
       the ES-A);
    *  ESCTimeStampToken attribute if present;
    *  TimestampedCertsCRLs attribute if present;
    *  any previous ArchiveTimeStampToken attributes.
 For further information and definition of TimeStampToken see [TSP]
 The time-stamp should be created using stronger algorithms (or longer
 key lengths) than in the original electronic signatures.

5. Security Considerations

5.1 Protection of Private Key

 The security of the electronic signature mechanism defined in this
 document depends on the privacy of the signer's private key.
 Implementations must take steps to ensure that private keys cannot be
 compromised.

5.2 Choice of Algorithms

 Implementers should be aware that cryptographic algorithms become
 weaker with time.  As new cryptoanalysis techniques are developed and
 computing performance improves, the work factor to break a particular
 cryptographic algorithm will reduce.  Therefore, cryptographic
 algorithm implementations should be modular allowing new algorithms
 to be readily inserted.  That is, implementers should be prepared for
 the set of mandatory to implement algorithms to change over time.

Pinkas, et al. Informational [Page 44] RFC 3126 Electronic Signature Formats September 2001

6. Conformance Requirements

 This document only defines conformance requirements up to a ES with
 Complete validation data (ES-C).  This means that none of the
 extended and archive forms of Electronic Signature (ES-X, ES-A) need
 to be implemented to get conformance to this standard.
 This document mandates support for elements of the signature policy.

6.1 Signer

 A system supporting signers according to this document must, at a
 minimum, support generation of an electronic signature consisting of
 the following components:
  • The general CMS syntax and content type as defined in RFC 2630

(see clauses 4.1 and 4.2).

  • CMS SignedData as defined in RFC 2630 with version set to 3 and

at least one SignerInfo must be present (see clauses 4.3, 4.4,

       4.5, 4.6).
  • The following CMS Attributes as defined in RFC 2630:
  1. ContentType; This must always be present

(see clause 3.7.1);

  1. MessageDigest; This must always be present

(see clause 3.7.2);

  1. SigningTime; This must always be present

(see clause 3.7.3).

  • The following ESS Attributes as defined in RFC 2634:
  1. SigningCertificate: This must be set as defined in clauses

3.8.1 and 3.8.2.

  • The following Attributes as defined in clause 3.9:
  1. SignaturePolicyIdentifier; This must always be present.
  • Public Key Certificates as defined in ITU-T Recommendation

X.509 [1] and profiled in RFC 2459 [7] (see clause 9.1).

Pinkas, et al. Informational [Page 45] RFC 3126 Electronic Signature Formats September 2001

6.2 Verifier using time-stamping

 A system supporting verifiers according to this document with time-
 stamping facilities must, at a minimum, support:
  • Verification of the mandated components of an electronic

signature, as defined in clause 5.1.

  • Signature Time-Stamp attribute, as defined in clause 4.1.1.
  • Complete Certificate Refs attribute, as defined in clause

4.2.1.

  • Complete Revocation Refs Attribute, as defined in clause

4.2.2.

  • Public Key Certificates, as defined in ITU-T Recommendation

X.509 and profiled in RFC 2459.

  • Either of:
  1. Certificate Revocation Lists, as defined in ITU-T

Recommendation X.509 [1] and profiled in RFC 2459 [7]; or

  1. On-line Certificate Status Protocol responses, as defined in

RFC 2560.

6.3 Verifier using secure records

 A system supporting verifiers according to the present document
 shall, at a minimum, support:
  • Verification of the mandated components of an electronic

signature, as defined in subclause 5.1.

  • Complete Certificate Refs attribute, as defined in subclause

4.2.1.

  • Complete Revocation Refs Attribute, as defined in subclause

9.2.2.

  • A record shall be maintained, which cannot be undetectably

modified, of the electronic signature and the time when the

       signature was first validated using the referenced certificates
       and revocation information.
  • Public Key Certificates, as defined in ITU-T Recommendation

X.509 [1] and profiled in RFC 2459 [7] (see subclause 10.1).

Pinkas, et al. Informational [Page 46] RFC 3126 Electronic Signature Formats September 2001

  • Either of:
  1. Certificate Revocation Lists, as defined in ITU-T

Recommendation X.509 [1] and profiled in RFC 2459 [7] Or

  1. On-line Certificate Status Protocol, as defined in RFC 2560

[8] (see subclause 10.3).

7. References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [ESS]      Hoffman, P., "Enhanced Security Services for S/MIME", RFC
            2634, June 1999.
 [CMS]      Housley, R., "Cryptographic Message Syntax", RFC 2630,
            June 1999.
 [OCSP]     Myers, M., Ankney, R., Malpani, A., Galperin, S. and C.
            Adams, "On-line Status Certificate Protocol", RFC 2560,
            June 1999.
 [TSP]      Adams, C., Cain, P., Pinkas, D. and R. Zuccherato,
            "Internet X.509 Public Key Infrastructure Time-Stamp
            Protocol (TSP)", RFC 3161, August 2001.
 [PTS]      Public Telegram Service. ITU-T Recommendation F1.
 [RFC2459]  Housley, R., Ford, W., Polk, W. and D. Solo, "Internet
            X.509 Public Key Infrastructure, Certificate and CRL
            Profile", RFC 2459, January 1999.
 [PKCS9]    RSA Laboratories, "The Public-Key Cryptography Standards
            (PKCS)", RSA Data Security Inc., Redwood City, California,
            November 1993 Release.
 [ISONR]    ISO/IEC 10181-5:  Security Frameworks in Open Systems.
            Non-Repudiation Framework. April 1997.
 [TS101733] ETSI Standard TS 101 733 V.1.2.2 (2000-12) Electronic
            Signature Formats.  Note: copies of ETSI TS 101 733 can be
            freely downloaded from the ETSI web site www.etsi.org.

Pinkas, et al. Informational [Page 47] RFC 3126 Electronic Signature Formats September 2001

8. Authors' Addresses

 This Informational RFC has been produced in ETSI TC-SEC.
    ETSI
    F-06921 Sophia Antipolis, Cedex - FRANCE
    650 Route des Lucioles - Sophia Antipolis
    Valbonne - France
    Tel: +33 4 92 94 42 00  Fax: +33 4 93 65 47 16
    secretariat@etsi.fr
    http://www.etsi.org
 Contact Point
    Harri Rasilainen
    ETSI
    650 Route des Lucioles
    F-06921 Sophia Antipolis, Cedex
    FRANCE
    EMail: harri.rasilainen@etsi.fr
    Denis Pinkas
    Integris
    68, Route de Versailles
    78434 Louveciennes CEDEX
    FRANCE
    EMail: Denis.Pinkas@bull.net
    John Ross
    Security & Standards
    192 Moulsham Street
    Chelmsford, Essex
    CM2 0LG
    United Kingdom
    EMail: ross@secstan.com
    Nick Pope
    Security & Standards
    192 Moulsham Street
    Chelmsford, Essex
    CM2 0LG
    United Kingdom
    EMail: pope@secstan.com

Pinkas, et al. Informational [Page 48] RFC 3126 Electronic Signature Formats September 2001

Annex A (normative): ASN.1 Definitions

 This annex provides a summary of all the ASN.1 syntax definitions for
 new syntax defined in this document.

A.1 Definitions Using X.208 (1988) ASN.1 Syntax

 NOTE:  The ASN.1 module defined in clause A.1 has precedence over
 that defined in Annex A-2 in the case of any conflict.
    ETS-ElectronicSignatureFormats-88syntax { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 5}

DEFINITIONS EXPLICIT TAGS ::=

BEGIN

– EXPORTS All -

IMPORTS

– Crypographic Message Syntax (CMS): RFC 2630

ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo, id-contentType,
id-messageDigest, MessageDigest, id-signingTime, SigningTime,
id-countersignature, Countersignature
FROM CryptographicMessageSyntax
  { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) modules(0) cms(1) }

– ESS Defined attributes: RFC 2634 – (Enhanced Security Services for S/MIME)

id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference,
id-aa-contentIdentifier, ContentIdentifier
FROM ExtendedSecurityServices
   { iso(1) member-body(2) us(840) rsadsi(113549)
     pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }

– Internet X.509 Public Key Infrastructure – Certificate and CRL Profile: RFC 2459

Certificate, AlgorithmIdentifier, CertificateList, Name,
GeneralNames, GeneralName, DirectoryString,Attribute,

Pinkas, et al. Informational [Page 49] RFC 3126 Electronic Signature Formats September 2001

AttributeTypeAndValue, AttributeType, AttributeValue,
PolicyInformation, BMPString, UTF8String
FROM PKIX1Explicit88
{iso(1) identified-organization(3) dod(6) internet(1)
 security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit-
 88(1)}

– X.509 '97 Authentication Framework

AttributeCertificate

FROM AuthenticationFramework
{joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3}

– The imported AttributeCertificate is defined using the X.680 1997 – ASN.1 Syntax, – an equivalent using the 88 ASN.1 syntax may be used.

– OCSP 2560

BasicOCSPResponse, ResponderID

FROM OCSP {-- OID not assigned -- }

– Time Stamp Protocol Work in Progress

TimeStampToken

FROM PKIXTSP
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}

– S/MIME Object Identifier arcs used in this document –

– S/MIME OID arc used in this document – id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2) – us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }

– S/MIME Arcs – id-mod OBJECT IDENTIFIER ::= { id-smime 0 } – modules – id-ct OBJECT IDENTIFIER ::= { id-smime 1 } – content types – id-aa OBJECT IDENTIFIER ::= { id-smime 2 } – attributes

Pinkas, et al. Informational [Page 50] RFC 3126 Electronic Signature Formats September 2001

– id-spq OBJECT IDENTIFIER ::= { id-smime 5 } – signature policy qualifier – id-cti OBJECT IDENTIFIER ::= { id-smime 6 } – commitment type identifier

– Definitions of Object Identifier arcs used in this document –

– The allocation of OIDs to specific objects are given below with the – associated ASN.1 syntax definition

– OID used referencing electronic signature mechanisms based on this – standard for use with the IDUP API (see annex D)

id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=

{ itu-t(0) identified-organization(4) etsi(0)
   electronic-signature-standard (1733) part1 (1)
       idupMechanism (4)etsiESv1(1) }

CMS Attributes Defined in this document –

– Mandatory Electronic Signature Attributes

– OtherSigningCertificate

  id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
  smime(16) id-aa(2) 19 }

OtherSigningCertificate ::= SEQUENCE {

  certs        SEQUENCE OF OtherCertID,
  policies     SEQUENCE OF PolicyInformation OPTIONAL
               -- NOT USED IN THIS DOCUMENT

}

OtherCertID ::= SEQUENCE {

   otherCertHash            OtherHash,
   issuerSerial             IssuerSerial OPTIONAL

}

OtherHash ::= CHOICE {

  sha1Hash     OtherHashValue,  -- This contains a SHA-1 hash
  otherHash    OtherHashAlgAndValue

}

OtherHashValue ::= OCTET STRING

Pinkas, et al. Informational [Page 51] RFC 3126 Electronic Signature Formats September 2001

OtherHashAlgAndValue ::= SEQUENCE {

hashAlgorithm    AlgorithmIdentifier,
hashValue        OtherHashValue

}

– Signature Policy Identifier

  id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
  smime(16) id-aa(2) 15 }

"SignaturePolicy CHOICE {

       SignaturePolicyId          SignaturePolicyId,
       SignaturePolicyImplied     SignaturePolicyImplied

}

SignaturePolicyId ::= SEQUENCE {

      sigPolicyIdentifier   SigPolicyId,
      sigPolicyHash         SigPolicyHash,
      sigPolicyQualifiers   SEQUENCE SIZE (1..MAX) OF
                            SigPolicyQualifierInfo OPTIONAL

}

SignaturePolicyImplied ::= NULL

SigPolicyId ::= OBJECT IDENTIFIER

SigPolicyHash ::= OtherHashAlgAndValue

SigPolicyQualifierInfo ::= SEQUENCE {

      sigPolicyQualifierId  SigPolicyQualifierId,
      sigQualifier          ANY DEFINED BY sigPolicyQualifierId

}

SigPolicyQualifierId ::=

      OBJECT IDENTIFIER
  id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
  smime(16) id-spq(5) 1 }
 SPuri ::= IA5String
  id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
  smime(16) id-spq(5) 2 }
 SPUserNotice ::= SEQUENCE {

Pinkas, et al. Informational [Page 52] RFC 3126 Electronic Signature Formats September 2001

      noticeRef        NoticeReference   OPTIONAL,
      explicitText     DisplayText       OPTIONAL

}

 NoticeReference ::= SEQUENCE {
      organization     DisplayText,
      noticeNumbers    SEQUENCE OF INTEGER

}

 DisplayText ::= CHOICE {
      visibleString    VisibleString  (SIZE (1..200)),
      bmpString        BMPString      (SIZE (1..200)),
      utf8String       UTF8String     (SIZE (1..200))

}

– Optional Electronic Signature Attributes

– Commitment Type

id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}

CommitmentTypeIndication ::= SEQUENCE {

commitmentTypeId                 CommitmentTypeIdentifier,
commitmentTypeQualifier          SEQUENCE SIZE (1..MAX) OF
                                 CommitmentTypeQualifier   OPTIONAL

}

CommitmentTypeIdentifier ::= OBJECT IDENTIFIER

CommitmentTypeQualifier ::= SEQUENCE {

  commitmentTypeIdentifier   CommitmentTypeIdentifier,
  qualifier                  ANY DEFINED BY commitmentTypeIdentifier

}

  id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-
  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  cti(6) 1}
  id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-
  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  cti(6) 2}
  id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-
  body(2)  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  cti(6) 3}
  id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-

Pinkas, et al. Informational [Page 53] RFC 3126 Electronic Signature Formats September 2001

  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
 cti(6) 4}
  id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-
  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  cti(6) 5}
  id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-
  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  cti(6) 6}

– Signer Location

 id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-
 body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
 id-aa(2) 17}

SignerLocation ::= SEQUENCE {

  1. - at least one of the following must be present

countryName [0] DirectoryString OPTIONAL,

  1. - as used to name a Country in X.500

localityName [1] DirectoryString OPTIONAL,

  1. - as used to name a locality in X.500

postalAdddress [2] PostalAddress OPTIONAL }

PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString

– Signer Attributes

  id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}

SignerAttribute ::= SEQUENCE OF CHOICE {

    claimedAttributes     [0] ClaimedAttributes,
    certifiedAttributes   [1] CertifiedAttributes

}

ClaimedAttributes ::= SEQUENCE OF Attribute

CertifiedAttributes ::= AttributeCertificate – as defined in X.509 : see section 10.3

– Content Time-Stamp

  id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  id-aa(2) 20}

Pinkas, et al. Informational [Page 54] RFC 3126 Electronic Signature Formats September 2001

ContentTimestamp::= TimeStampToken

– Validation Data

– Signature Time-Stamp

  id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  id-aa(2) 14}

SignatureTimeStampToken ::= TimeStampToken

– Complete Certificate Refs.

id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}

CompleteCertificateRefs ::= SEQUENCE OF OTHERCertID

– Complete Revocation Refs

 id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-
 body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
 id-aa(2) 22}

CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef

CrlOcspRef ::= SEQUENCE {

  crlids           [0] CRLListID      OPTIONAL,
  ocspids          [1] OcspListID     OPTIONAL,
  otherRev         [2] OtherRevRefs   OPTIONAL

}

CRLListID ::= SEQUENCE {

  crls        SEQUENCE OF CrlValidatedID}

CrlValidatedID ::= SEQUENCE {

   crlHash                   OtherHash,
   crlIdentifier             CrlIdentifier OPTIONAL

}

CrlIdentifier ::= SEQUENCE {

  crlissuer                 Name,
  crlIssuedTime             UTCTime,
  crlNumber                 INTEGER OPTIONAL

}

OcspListID ::= SEQUENCE {

Pinkas, et al. Informational [Page 55] RFC 3126 Electronic Signature Formats September 2001

  ocspResponses        SEQUENCE OF OcspResponsesID}

OcspResponsesID ::= SEQUENCE {

  ocspIdentifier              OcspIdentifier,
  ocspRepHash                 OtherHash    OPTIONAL

}

OcspIdentifier ::= SEQUENCE {

ocspResponderID    ResponderID,
                  -- as in OCSP response data
producedAt      GeneralizedTime
                  -- as in OCSP response data

}

OtherRevRefs ::= SEQUENCE {

 otherRevRefType         OtherRevRefType,
 otherRevRefs            ANY DEFINED BY otherRevRefType

}

OtherRevRefType ::= OBJECT IDENTIFIER

– Certificate Values

id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}

CertificateValues ::= SEQUENCE OF Certificate

– Certificate Revocation Values

id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-

  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  id-aa(2) 24}

RevocationValues ::= SEQUENCE {

 crlVals          [0] SEQUENCE OF CertificateList     OPTIONAL,
 ocspVals         [1] SEQUENCE OF BasicOCSPResponse   OPTIONAL,
 otherRevVals     [2] OtherRevVals

}

OtherRevVals ::= SEQUENCE {

 otherRevValType  OtherRevValType,
otherRevVals      ANY DEFINED BY otherRevValType

}

OtherRevValType ::= OBJECT IDENTIFIER

– ES-C Time-Stamp

Pinkas, et al. Informational [Page 56] RFC 3126 Electronic Signature Formats September 2001

id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}

ESCTimeStampToken ::= TimeStampToken

– Time-Stamped Certificates and CRLs

id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-

  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  id-aa(2) 26}

TimestampedCertsCRLs ::= TimeStampToken

– Archive Time-Stamp

id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-

  body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
  id-aa(2) 27}

ArchiveTimeStampToken ::= TimeStampToken

END – ETS-ElectronicSignatureFormats-88syntax –

A.2 Definitions Using X.680 1997 ASN.1 Syntax

NOTE: The ASN.1 module defined in clause A.1 has precedence over that defined in clause A.2 in the case of any conflict.

    ETS-ElectronicSignatureFormats-97Syntax { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 6}

DEFINITIONS EXPLICIT TAGS ::=

BEGIN

– EXPORTS All -

IMPORTS

– Cryptographic Message Syntax (CMS): RFC 2630

ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo, id-contentType,
id-messageDigest, MessageDigest, id-signingTime,
SigningTime, id-countersignature, Countersignature
 FROM CryptographicMessageSyntax
  { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)

Pinkas, et al. Informational [Page 57] RFC 3126 Electronic Signature Formats September 2001

  smime(16) modules(0) cms(1) }

– ESS Defined attributes: RFC 2634 (Enhanced Security Services – for S/MIME)

 id-aa-signingCertificate, SigningCertificate, IssuerSerial,
 id-aa-contentReference, ContentReference,
 id-aa-contentIdentifier, ContentIdentifier
FROM ExtendedSecurityServices
  { iso(1) member-body(2) us(840) rsadsi(113549)
     pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }

– Internet X.509 Public Key Infrastructure - - Certificate and CRL Profile:RFC 2459

 Certificate, AlgorithmIdentifier, CertificateList, Name,
 GeneralNames, GeneralName, DirectoryString, Attribute,
 AttributeTypeAndValue, AttributeType, AttributeValue,
 PolicyInformation.
FROM PKIX1Explicit93
  {iso(1) identified-organization(3) dod(6) internet(1)
   security(5) mechanisms(5) pkix(7) id-mod(0)
   id-pkix1-explicit-88(1)}

– X.509 '97 Authentication Framework

      AttributeCertificate
      FROM AuthenticationFramework
      {joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3}

– OCSP 2560

    BasicOCSPResponse, ResponderID
FROM OCSP

– { OID not assigned }

– Time Stamp Protocol Work in Progress TimeStampToken

FROM PKIXTSP
{iso(1) identified-organization(3) dod(6) internet(1)
 security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}

Pinkas, et al. Informational [Page 58] RFC 3126 Electronic Signature Formats September 2001

– S/MIME Object Identifier arcs used in this document –

– S/MIME OID arc used in this document – id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2) – us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }

– S/MIME Arcs – id-mod OBJECT IDENTIFIER ::= { id-smime 0 } – modules – id-ct OBJECT IDENTIFIER ::= { id-smime 1 } – content types – id-aa OBJECT IDENTIFIER ::= { id-smime 2 } – attributes – id-spq OBJECT IDENTIFIER ::= { id-smime 5 } – signature policy qualifier – id-cti OBJECT IDENTIFIER ::= { id-smime 6 } – commitment type identifier

– Definitions of Object Identifier arcs used in this document –

– The allocation of OIDs to specific objects are given below with the – associated ASN.1 syntax definition

– OID used referencing electronic signature mechanisms based on this – standard for use with the IDUP API (see annex D)

id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=

{ itu-t(0) identified-organization(4) etsi(0)
 electronic-signature-standard (1733) part1 (1)
 idupMechanism (4)etsiESv1(1) }

CMS Attributes Defined in this document –

– Mandatory Electronic Signature Attributes – OtherSigningCertificate

id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)

  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
  smime(16) id-aa(2) 19 }

OtherSigningCertificate ::= SEQUENCE {

  certs        SEQUENCE OF OtherCertID,
  policies     SEQUENCE OF PolicyInformation OPTIONAL
               -- NOT USED IN THIS DOCUMENT

}

Pinkas, et al. Informational [Page 59] RFC 3126 Electronic Signature Formats September 2001

OtherCertID ::= SEQUENCE {

   otherCertHash            OtherHash,
   issuerSerial             IssuerSerial OPTIONAL

}

OtherHash ::= CHOICE {

  sha1Hash OtherHashValue,  -- This contains a SHA-1 hash
  otherHash OtherHashAlgAndValue

}

OtherHashValue ::= OCTET STRING

OtherHashAlgAndValue ::= SEQUENCE {

hashAlgorithm  AlgorithmIdentifier,
hashValue    OtherHashValue

}

– Signature Policy Identifier

id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)

  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
  smime(16) id-aa(2) 15 }

"SignaturePolicy CHOICE {

       SignaturePolicyId          SignaturePolicyId,
       SignaturePolicyImplied     SignaturePolicyImplied

}

SignaturePolicyId ::= SEQUENCE {

      sigPolicyIdentifier   SigPolicyId,
      sigPolicyHash         SigPolicyHash,
      sigPolicyQualifiers   SEQUENCE SIZE (1..MAX) OF
                              SigPolicyQualifierInfo OPTIONAL

}

SignaturePolicyImplied ::= NULL

SigPolicyId ::= OBJECT IDENTIFIER

SigPolicyHash ::= OtherHashAlgAndValue

SigPolicyQualifierInfo ::= SEQUENCE {

      sigPolicyQualifierId    SIG-POLICY-QUALIFIER.&id
                               ({SupportedSigPolicyQualifiers}),
      qualifier               SIG-POLICY-QUALIFIER.&Qualifier
                              ({SupportedSigPolicyQualifiers}
                               {@sigPolicyQualifierId})OPTIONAL }

Pinkas, et al. Informational [Page 60] RFC 3126 Electronic Signature Formats September 2001

SupportedSigPolicyQualifiers SIG-POLICY-QUALIFIER ::=

                         { noticeToUser | pointerToSigPolSpec }

SIG-POLICY-QUALIFIER ::= CLASS {

      &id             OBJECT IDENTIFIER UNIQUE,
      &Qualifier      OPTIONAL }

WITH SYNTAX {

      SIG-POLICY-QUALIFIER-ID     &id
      [SIG-QUALIFIER-TYPE &Qualifier] }

noticeToUser SIG-POLICY-QUALIFIER ::= {

    SIG-POLICY-QUALIFIER-ID id-sqt-unotice SIG-QUALIFIER-TYPE
                                          SPUserNotice
                                                      }

pointerToSigPolSpec SIG-POLICY-QUALIFIER ::= {

    SIG-POLICY-QUALIFIER-ID id-sqt-uri SIG-QUALIFIER-TYPE SPuri }
  id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
  smime(16) id-spq(5) 1 }
 SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
  smime(16) id-spq(5) 2 }
 SPUserNotice ::= SEQUENCE {
      noticeRef        NoticeReference OPTIONAL,
      explicitText     DisplayText OPTIONAL

}

 NoticeReference ::= SEQUENCE {
      organization     DisplayText,
      noticeNumbers    SEQUENCE OF INTEGER

}

 DisplayText ::= CHOICE {
      visibleString    VisibleString  (SIZE (1..200)),
      bmpString        BMPString      (SIZE (1..200)),
      utf8String       UTF8String     (SIZE (1..200))

}

– Optional Electronic Signature Attributes

– Commitment Type

Pinkas, et al. Informational [Page 61] RFC 3126 Electronic Signature Formats September 2001

id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}

CommitmentTypeIndication ::= SEQUENCE {

commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
                                         CommitmentTypeQualifier
                                         OPTIONAL}

CommitmentTypeIdentifier ::= OBJECT IDENTIFIER

CommitmentTypeQualifier ::= SEQUENCE {

      commitmentQualifierId       COMMITMENT-QUALIFIER.&id,
      qualifier                   COMMITMENT-QUALIFIER.&Qualifier
                                                OPTIONAL }

COMMITMENT-QUALIFIER ::= CLASS {

                  &id             OBJECT IDENTIFIER UNIQUE,
                  &Qualifier      OPTIONAL }

WITH SYNTAX {

       COMMITMENT-QUALIFIER-ID     &id
                      [COMMITMENT-TYPE &Qualifier] }
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) cti(6) 6}

– Signer Location

Pinkas, et al. Informational [Page 62] RFC 3126 Electronic Signature Formats September 2001

id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}

SignerLocation ::= SEQUENCE {

  1. - at least one of the following must be present

countryName [0] DirectoryString OPTIONAL,

  1. - As used to name a Country in X.500

localityName [1] DirectoryString OPTIONAL,

  1. - As used to name a locality in X.500

postalAdddress [2] PostalAddress OPTIONAL }

PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString

– Signer Attributes

id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}

SignerAttribute ::= SEQUENCE OF CHOICE {

    claimedAttributes  [0] ClaimedAttributes,
    certifiedAttributes [1] CertifiedAttributes }

ClaimedAttributes ::= SEQUENCE OF Attribute

CertifiedAttributes ::= AttributeCertificate – As defined in X.509 : see section 10.3

– Content Time-Stamp

id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1)

    member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
    smime(16) id-aa(2) 20}

ContentTimestamp::= TimeStampToken

– Validation Data

– Signature Time-Stamp

id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)

   member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
   smime(16) id-aa(2) 14}

SignatureTimeStampToken ::= TimeStampToken

– Complete Certificate Refs.

id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)

Pinkas, et al. Informational [Page 63] RFC 3126 Electronic Signature Formats September 2001

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}

CompleteCertificateRefs ::= SEQUENCE OF OTHERCertID

– Complete Revocation Refs

id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}

CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef

CrlOcspRef ::= SEQUENCE {

  crlids           [0] CRLListID   OPTIONAL,
  ocspids          [1] OcspListID  OPTIONAL,
otherRev     [2] OtherRevRefs OPTIONAL
                                        }

CRLListID ::= SEQUENCE {

  crls        SEQUENCE OF CrlValidatedID}

CrlValidatedID ::= SEQUENCE {

   crlHash                   OtherHash,
   crlIdentifier             CrlIdentifier OPTIONAL}

CrlIdentifier ::= SEQUENCE {

  crlissuer                 Name,
  crlIssuedTime             UTCTime,
  crlNumber                 INTEGER OPTIONAL
                                          }

OcspListID ::= SEQUENCE {

  ocspResponses        SEQUENCE OF OcspResponsesID}

OcspResponsesID ::= SEQUENCE {

  ocspIdentifier              OcspIdentifier,
  ocspRepHash                 OtherHash    OPTIONAL
                                          }

OcspIdentifier ::= SEQUENCE {

ocspResponderID    ResponderID,
                      -- As in OCSP response data
producedAt      GeneralizedTime
                      -- As in OCSP response data
                                           }

OtherRevRefs ::= SEQUENCE {

 otherRevRefType  OTHER-REVOCATION-REF.&id,
otherRevRefs  OTHER-REVOCATION-REF.&Type

Pinkas, et al. Informational [Page 64] RFC 3126 Electronic Signature Formats September 2001

                                            }

OTHER-REVOCATION-REF ::= CLASS {

  &Type,
  &id  OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
  &Type ID &id }

– Certificate Values

id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)

  us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}

CertificateValues ::= SEQUENCE OF Certificate

– Certificate Revocation Values

id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1)

   member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
   smime(16) id-aa(2) 24}

RevocationValues ::= SEQUENCE {

 crlVals          [0] SEQUENCE OF CertificateList OPTIONAL,
 ocspVals         [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
 otherRevVals      [2] OtherRevVals }

OtherRevVals ::= SEQUENCE {

 otherRevValType  OTHER-REVOCATION-VAL.&id,
otherRevVals  OTHER-REVOCATION-VAL.&Type
                                             }

OTHER-REVOCATION-VAL ::= CLASS {

  &Type,
  &id  OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
  &Type ID &id }

– ES-C Time-Stamp

id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1)

   member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
   smime(16) id-aa(2) 25}

ESCTimeStampToken ::= TimeStampToken

– Time-Stamped Certificates and CRLs

id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1)

Pinkas, et al. Informational [Page 65] RFC 3126 Electronic Signature Formats September 2001

  member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
  smime(16) id-aa(2) 26}

TimestampedCertsCRLs ::= TimeStampToken

– Archive Time-Stamp

id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1)

 member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
 smime(16) id-aa(2) 27}

ArchiveTimeStampToken ::= TimeStampToken

END – ETS-ElectronicSignatureFormats-97Syntax

Annex B (informative): General Description

 This annex captures the concepts that apply to this document and the
 rational for the elements of the specification defined using ASN.1 in
 the main text of this document.
 The specification below includes a description why the component is
 needed, with a brief description of the vulnerabilities and threats
 and the manner by which they are countered.

B.1 The Signature Policy

 The signature policy is a set of rules for the creation and
 validation of an electronic signature, under which the signature can
 be determined to be valid.  A given legal/contractual context may
 recognize a particular signature policy as meeting its requirements.
 A signature policy may be issued, for example, by a party relying on
 the electronic signatures and selected by the signer for use with
 that relying party.  Alternatively, a signature policy may be
 established through an electronic trading association for use amongst
 its members. Both the signer and verifier use the same signature
 policy.
 The signature policy may be explicitly identified or may be implied
 by the semantics of the data being signed and other external data
 like a contract being referenced which itself refers to a signature
 policy.
 An explicit signature policy has a globally unique reference, which
 is bound to an electronic signature by the signer as part of the
 signature calculation.

Pinkas, et al. Informational [Page 66] RFC 3126 Electronic Signature Formats September 2001

 The signature policy needs to be available in human readable form so
 that it can be assessed to meet the requirements of the legal and
 contractual context in which it is being applied.  To facilitate the
 automatic processing of an electronic signature the parts of the
 signature policy which specify the electronic rules for the creation
 and validation of the electronic signature also needs to be in a
 computer processable form.
 The signature policy thus includes the following:
  • Information about the signature policy that can be displayed to

the signer or the verifiers.

  • Rules, which apply to functionality, covered by this document

(referred to as the Signature Validation Policy).

  • Rules which may be implied through adoption of Certificate

Policies that apply to the electronic signature (e.g., rules

       for ensuring the secrecy of the private signing key).
    *  Rules, which relate to the environment used by the signer,
       e.g., the use of an agreed CAD (Card Accepting Device) used in
       conjunction with a smart card.
 An explicit Signature Validation Policy may be structured so that it
 can be computer processable.  Any format of the signature validation
 policy is allowed by this document.  However, for a given explicit
 signature policy there must be one definitive form that has a unique
 binary encoded value.
 The Signature Validation Policy includes rules regarding use of TSPs
 (CA, Attribute Authorities, Time Stamping Authorities) as well as
 rules defining the components of the electronic signature that must
 be provided by the signer with data required by the verifier to
 provide long term proof.

B.2 Signed Information

 The information being signed may be defined as a MIME-encapsulated
 message which can be used to signal the format of the content in
 order to select the right display or application.  It can be composed
 of formatted text (e.g., EDIFACT), free text or of fields from an
 electronic form (e-form).  For example, the Adobe(tm) format "pdf"
 may be used or the eXtensible Mark up Language (XML).

Pinkas, et al. Informational [Page 67] RFC 3126 Electronic Signature Formats September 2001

B.3 Components of an Electronic Signature

B.3.1 Reference to the Signature Policy

 The definition of electronic signature includes: "a commitment has
 been explicitly endorsed under a "Signature policy", at a given time,
 by a signer under an identifier, e.g., a name or a pseudonym, and
 optionally a role".
 When two independent parties want to evaluate an electronic
 signature, it is fundamental that they get the same result.  To meet
 this requirement same signature policy must be used by the signer and
 verifier.
 The signature policy may be explicitly identified or may be implied
 by the semantics of the data being signed and other external data
 which designate the signature policy to be used.
 By signing over the signature policy identifier the signer explicitly
 indicates that he or she has applied the signature policy in creating
 the signature.  Thus, undertakes any explicit or implied commitments.
 In order to unambiguously identify an explicit signature policy that
 is to be used to verify the signature an identifier and hash of the
 "Signature policy" shall be part of the signed data.  Additional
 information about the explicit policy (e.g., web reference to the
 document) may be carried as "qualifiers" to the signature policy
 identifier.
 When the signature policy not explicitly identified, but is implied
 by the semantics of the data being signed, then the signature will
 include a signature policy identifier that indicates that the
 signature policy is implied.  In this case the verification rules
 must be determined by using other external data which will designate
 the signature policy to be used.  If it may be determined from the
 context that all the documents to be verified refer to the same
 signature policy, then that policy may be predetermined or fixed
 within the application.
 In order to identify unambiguously the "Signature Validation Policy"
 to be used to verify the signature an identifier and hash of the
 "Signature policy" must be part of the signed data.  Additional
 information about the policy (e.g., web reference to the document)
 may be carried as "qualifiers" to the signature policy identifier.

Pinkas, et al. Informational [Page 68] RFC 3126 Electronic Signature Formats September 2001

B.3.2 Commitment Type Indication

 The definition of electronic signature includes: "a commitment has
 been explicitly endorsed under a signature policy, at a given time,
 by a signer under an identifier, e.g., a name or a pseudonym, and
 optionally a role".
 The commitment type can be indicated in the electronic signature
 either:
  • explicitly using a "commitment type indication" in the

electronic signature;

  • implicitly or explicitly from the semantics of the signed data.
 If the indicated commitment type is explicit using a "commitment type
 indication" in the electronic signature, acceptance of a verified
 signature implies acceptance of the semantics of that commitment
 type. The semantics of explicit commitment types indications must be
 specified either as part of the signature policy or may be registered
 for generic use across multiple policies.
 If a signature includes a commitment type indication other than one
 of those recognized under the signature policy the signature must be
 treated as invalid.
 How commitment is indicated using the semantics of the data being
 signed is outside the scope of this document.
 NOTE:  Examples of commitment indicated through the semantics of the
 data being signed, are:
  • An explicit commitment made by the signer indicated by the type

of data being signed over. Thus, the data structure being

       signed can have an explicit commitment within the context of
       the application (e.g., EDIFACT purchase order).
  • An implicit commitment which is a commitment made by the signer

because the data being signed over has specific semantics

       (meaning) which is only interpretable by humans, (i.e., free
       text).

B.3.3 Certificate Identifier from the Signer

 The definition of the ETSI electronic signature includes: "a
 commitment has been explicitly endorsed under a signature policy, at
 a given time, by a signer under an identifier, e.g., a name or a
 pseudonym, and optionally a role."

Pinkas, et al. Informational [Page 69] RFC 3126 Electronic Signature Formats September 2001

 In many real life environments users will be able to get from
 different CAs or even from the same CA, different certificates
 containing the same public key for different names.  The prime
 advantage is that a user can use the same private key for different
 purposes.  Multiple use of the private key is an advantage when a
 smart card is used to protect the private key, since the storage of a
 smart card is always limited.  When several CAs are involved, each
 different certificate may contain a different identity, e.g., as a
 national or as an employee from a company.  Thus when a private key
 is used for various purposes, the certificate is needed to clarify
 the context in which the private key was used when generating the
 signature.  Where there is the possibility of multiple use of private
 keys it is necessary for the signer to indicate to the verifier the
 precise certificate to be used.
 Many current schemes simply add the certificate after the signed data
 and thus are subject to various substitution attacks.  An example of
 a substitution attack is a "bad" CA that would issue a certificate to
 someone with the public key of someone else.  If the certificate from
 the signer was simply appended to the signature and thus not
 protected by the signature, any one could substitute one certificate
 by another and the message would appear to be signed by some one
 else.
 In order to counter this kind of attack, the identifier of the signer
 has to be protected by the digital signature from the signer.
 Although it does not provide the same advantages as the previous
 technique, another technique to counter that threat has been
 identified.  It requires all CAs to perform a Proof Of Possession of
 the private key at the time of registration.  The problem with that
 technique is that it does not provide any guarantee at the time of
 verification and only some proof "after the event" may be obtained,
 if and only if the CA keeps the Proof Of Possession in audit trail.
 In order to identify unambiguously the certificate to be used for the
 verification of the signature an identifier of the certificate from
 the signer must be part of the signed data.

B.3.4 Role Attributes

 The definition of electronic signature includes: "a commitment has
 been explicitly endorsed under a non repudiation security policy, at
 a given time, by a signer under an identifier, e.g., a name or a
 pseudonym, and optionally a role."

Pinkas, et al. Informational [Page 70] RFC 3126 Electronic Signature Formats September 2001

 While the name of the signer is important, the position of the signer
 within a company or an organization can be even more important.  Some
 contracts may only be valid if signed by a user in a particular role,
 e.g., a Sales Director.  In many cases whom the sales Director really
 is, is not that important but being sure that the signer is empowered
 by his company to be the Sales Director is fundamental.
 This document defines two different ways for providing this feature:
  • by placing a claimed role name in the CMS signed attributes

field;

  • by placing a attribute certificate containing a certified role

name in the CMS signed attributes field.

 NOTE:  Another possible approach would have been to use additional
 attributes containing the roles name(s) in the signer's certificate.
 However, it was decided not to follow this approach as it breaks the
 basic philosophy of the certificate being issued for one primary
 purpose.  Also, by using separate certificates for management of the
 signer's identity certificate and management of additional roles can
 simplify the management, as new identity keys need not be issued if a
 use of role is to be changed.

B.3.4.1 Claimed Role

 The signer may be trusted to state his own role without any
 certificate to corroborate this claim.  In which case the claimed
 role can be added to the signature as a signed attribute.

B.3.4.2 Certified Role

 Unlike public key certificates that bind an identifier to a public
 key, Attribute Certificates bind the identifier of a certificate to
 some attributes, like a role.  An Attribute Certificate is NOT issued
 by a CA but by an Attribute Authority (AA).  The Attribute Authority
 will be most of the time under the control of an organization or a
 company that is best placed to know which attributes are relevant for
 which individual.
 The Attribute Authority may use or point to public key certificates
 issued by any CA, provided that the appropriate trust may be placed
 in that CA.  Attribute Certificates may have various periods of
 validity.  That period may be quite short, e.g., one day.  While this
 requires that a new Attribute Certificate is obtained every day,
 valid for that day, this can be advantageous since revocation of such
 certificates may not be needed.  When signing, the signer will have
 to specify which Attribute Certificate it selects.  In order to do

Pinkas, et al. Informational [Page 71] RFC 3126 Electronic Signature Formats September 2001

 so, a reference to the Attribute Certificate will have to be included
 in the signed data in order to be protected by the digital signature
 from the signer.
 In order to identify unambiguously the attribute certificate(s) to be
 used for the verification of the signature an identifier of the
 attribute certificate(s) from the signer must be part of the signed
 data.

B.3.5 Signer Location

 In some transactions the purported location of the signer at the time
 he or she applies his signature may need to be indicated.  For this
 reason an optional location indicator must be able to be included.
 In order to provide indication of the location of the signer at the
 time he or she applied his signature a  location attribute may be
 included in the signature.

B.3.6 Signing Time

 The definition of electronic signature includes: "a commitment has
 been explicitly endorsed under a signature policy, at a given time,
 by a signer under an identifier, e.g., a name or a pseudonym, and
 optionally a role."
 There are several ways to address this problem.  The solution adopted
 in this document is to sign over a time which the signer claims is
 the signing time (i.e., claimed signing time) and to require a
 trusted time stamp to be obtained when building a ES with Time-Stamp.
 When a verifier accepts a signature, the two times must be within
 acceptable limits.
 The solution that is adopted in this document offers the major
 advantage that electronic signatures can be generated without any
 on-line connection to a trusted time source (i.e., they may be
 generated off-line).
 Thus two dates and two signatures are required:
  • a signing time indicated by the signer and which is part of the

data signed by the signer (i.e., part of the basic electronic

       signature);
  • a time indicated by a Time-Stamping Authority (TSA) which is

signed over the digital signature value of the basic electronic

       signature.  The signer, verifier or both may obtain the TSA
       time-stamp.

Pinkas, et al. Informational [Page 72] RFC 3126 Electronic Signature Formats September 2001

 In order for an electronic signature to be valid under a signature
 policy, it must be time-stamped by a TSA where the signing time as
 indicated by the signer and the time of time stamping as indicated by
 a TSA must be "close enough" to meet the requirements of the
 signature validation policy.
 "Close enough" means a few minutes, hours or even days according to
 the "Signature Validation Policy".
 NOTE:  The need for Time-Stamping is further explained in clause
 B.4.5.  A further optional attribute is defined in this document to
 time-stamp the content, to provide proof of the existence of the
 content, at the time indicated by the time-stamp.
 Using this optional attribute a trusted secure time may be obtained
 before the document is signed and included under the digital
 signature.  This solution requires an on-line connection to a trusted
 time-stamping service before generating the signature and may not
 represent the precise signing time, since it can be obtained in
 advance.  However, this optional attribute may be used by the signer
 to prove that the signed object existed before the date included in
 the time-stamp (see 3.12.3, Content Time-Stamp).
 Also, the signing time should be between the time indicated by this
 time-stamp and time indicated by the ES-T time-stamp.

B.3.7 Content Format

 When presenting signed data to a human user it may be important that
 there is no ambiguity as to the presentation of the signed
 information to the relying party.  In order for the appropriate
 representation (text, sound or video) to be selected by the relying
 party a content hint may be indicated by the signer.  If a relying
 party system does not use the format specified in the content hints
 to present the data to the relying party, the electronic signature
 may not be valid.

B.4 Components of Validation Data

B.4.1 Revocation Status Information

 A verifier will have to prove that the certificate of the signer was
 valid at the time of the signature.  This can be done by either:
  • using Certificate Revocation Lists (CRLs);
  • using responses from an on-line certificate status server (for

example; obtained through the OCSP protocol).

Pinkas, et al. Informational [Page 73] RFC 3126 Electronic Signature Formats September 2001

B.4.2 CRL Information

 When using CRLs to get revocation information, a verifier will have
 to make sure that he or she gets at the time of the first
 verification the appropriate certificate revocation information from
 the signer's CA. This should be done as soon as possible to minimize
 the time delay between the generation and verification of the
 signature.  This involves checking that the signer certificate serial
 number is not included in the CRL.  The signer, the verifier or any
 other third party may obtain either this CRL.  If obtained by the
 signer, then it must be conveyed to the verifier.  It may be
 convenient to archive the CRL for ease of subsequent verification or
 arbitration.
 Alternatively, provided the CRL is archived elsewhere which is
 accessible for the purpose of arbitration, then the serial number of
 the CRL used may be archived together with the verified electronic
 signature.
 It may happen that the certificate serial number appears in the CRL
 but with the status "suspended" (i.e., on hold).  In such a case, the
 electronic signature is not yet valid, since it is not possible to
 know whether the certificate will or will not be revoked at the end
 of the suspension period.  If a decision has to be taken immediately
 then the signature has to be considered as invalid.  If a decision
 can wait until the end of the suspension period, then two cases are
 possible:
  • the certificate serial number has disappeared from the list and

thus the certificate can be considered as valid and that CRL

       must be captured and archived either by the verifier or
       elsewhere and be kept accessible for the purpose of
       arbitration.
  • the certificate serial number has been maintained on the list

with the status definitively revoked and thus the electronic

       signature must be considered as invalid and discarded.
 At this point the verifier may be convinced that he or she got a
 valid signature, but is not yet in a position to prove at a later
 time that the signature was verified as valid.  Before addressing
 this point, an alternative to CRL is to use OCSP responses.

B.4.3 OCSP Information

 When using OCSP to get revocation information , a verifier will have
 to make sure that he or she gets at the time of the first
 verification an OCSP response that contains the status "valid".  This

Pinkas, et al. Informational [Page 74] RFC 3126 Electronic Signature Formats September 2001

 should be done as soon as possible after the generation of the
 signature.  The signer, the verifier or any other third party may
 fetch this OCSP response. Since OSCP responses are transient and thus
 are not archived by any TSP including CA, it is the responsibility of
 every verifier to make sure that it is stored in a safe place.  The
 simplest way is to store them associated with the electronic
 signature.  An alternative would be to store them in some storage so
 that they can then be easily retrieved.
 In the same way as for the case of the CRL, it may happen that the
 certificate is declared as invalid but with the secondary status
 "suspended".
 In such a case, the electronic signature is not yet valid, since it
 is not possible to know whether the certificate will or will not be
 revoked at the end of the suspension period.  If a decision has to be
 taken immediately then the electronic signature has to be considered
 as invalid.  If a decision can wait until the end of the suspension
 period, then two cases are possible:
  • An OCSP response with a valid status is obtained at a later

date and thus the certificate can be considered as valid and

       that OCSP response must be captured.
  • An OCSP response with an invalid status is obtained with a

secondary status indicating that the certificate is

       definitively revoked and thus the electronic signature must be
       considered as invalid and discarded.
 As in the CRL case, at this point, the verifier may be convinced that
 he or she got a valid signature, but is not yet in a position to
 prove at a later time that the signature was verified as valid.

B.4.4 Certification Path

 A verifier will have to prove that the certification path was valid,
 at the time of the signature, up to a trust point according to the
 naming constraints and the certificate policy constraints from the
 "Signature Validation Policy".  It will be necessary to capture all
 the certificates from the certification path, starting with those
 from the signer and ending up with those of the self-signed
 certificate from one trusted root of the "Signature Validation
 Policy".  In addition, it will be necessary to capture the Authority
 Revocation Lists (ARLs) to prove than none of the CAs from the chain
 was revoked at the time of the signature.

Pinkas, et al. Informational [Page 75] RFC 3126 Electronic Signature Formats September 2001

 As in the OCSP case, at this point, the verifier may be convinced
 that he or she got a valid signature, but is not yet in a position to
 prove at a later time that the signature was verified as valid.

B.4.5 Time-Stamping for Long Life of Signature

 An important property for long standing signatures is that a
 signature, having been found once to be valid, must continue to be so
 months or years later.
 A signer, verifier or both may be required to provide on request,
 proof that a digital signature was created or verified during the
 validity period of the all the certificates that make up the
 certificate path.  In this case, the signer, verifier or both will
 also be required to provide proof that all the user and CA
 certificates used were not revoked when the signature was created or
 verified.
 It would be quite unacceptable, to consider a signature as invalid
 even if the keys or certificates were later compromised.  Thus there
 is a need to be able to demonstrate that the signature keys was valid
 around the time that the signature was created to provide long term
 evidence of the validity of a signature.
 It could be the case that a certificate was valid at the time of the
 signature but revoked some time later.  In this event, evidence must
 be provided that the document was signed before the signing key was
 revoked.
 Time-Stamping by a Time Stamping Authority (TSA) can provide such
 evidence.  A time stamp is obtained by sending the hash value of the
 given data to the TSA.  The returned "time-stamp" is a signed
 document that contains the hash value, the identity of the TSA, and
 the time of stamping.  This proves that the given data existed before
 the time of stamping.  Time-Stamping a digital signature (by sending
 a hash of the signature to the TSA) before the revocation of the
 signer's private key, provides evidence that the signature has been
 created before the key was revoked.
 If a recipient wants to hold a valid electronic signature he will
 have to ensure that he has obtained a valid time stamp for it, before
 that key (and any key involved in the validation) is revoked.  The
 sooner the time-stamp is obtained after the signing time, the better.
 It is important to note that signatures may be generated "off-line"
 and time-stamped at a later time by anyone, for example by the signer
 or any recipient interested in the value of the signature.  The time
 stamp can thus be provided by the signer together with the signed

Pinkas, et al. Informational [Page 76] RFC 3126 Electronic Signature Formats September 2001

 document, or obtained by the recipient following receipt of the
 signed document.
 The time stamp is NOT a component of the Electronic Signature, but
 the essential component of the ES with Time-Stamp.
 It is required in this document that signer's digital signature value
 is time-stamped by a trusted source, known as a Time-Stamping
 Authority.
 This document requires that the signer's digital signature value is
 time-stamped by a trusted source before the electronic signature can
 become a ES with Complete validation data (ES-C).  The acceptable
 TSAs are specified in the Signature Validation Policy.
 Should both the signer and verifier be required to time-stamp the
 signature value to meet the requirements of the signature policy, the
 signature policy MAY specify a permitted time delay between the two
 time stamps.

B.4.6 Time-Stamping before CA Key Compromises

 Time-Stamped extended electronic signatures are needed when there is
 a requirement to safeguard against the possibility of a CA key in the
 certificate chain ever being compromised.  A verifier may be required
 to provide on request, proof that the certification path and the
 revocation information used a the time of the signature were valid,
 even in the case where one of the issuing keys or OCSP responder keys
 is later compromised.
 The current document defines two ways of using time-stamps to protect
 against this compromise:
  • Time-Stamp the ES with Complete validation data, when an OCSP

response is used to get the status of the certificate from the

       signer.
  • Time-Stamp only the certification path and revocation

information references when a CRL is used to get the status of

       the certificate from the signer.
 NOTE:  the signer, verifier or both may obtain the time-stamp.

B.4.6.1 Time-Stamping the ES with Complete validation data

 When an OCSP response is used, it is necessary to time stamp in
 particular that response in the case the key from the responder would
 be compromised.  Since the information contained in the OCSP response

Pinkas, et al. Informational [Page 77] RFC 3126 Electronic Signature Formats September 2001

 is user specific and time specific, an individual time stamp is
 needed for every signature received.  Instead of placing the time
 stamp only over the certification path references and the revocation
 information references, which include the OCSP response, the time
 stamp is placed on the ES-C.  Since the certification path and
 revocation information references are included in the ES with
 Complete validation data they are also protected.  For the same
 cryptographic price, this provides an integrity mechanism over the ES
 with Complete validation data.  Any modification can be immediately
 detected.  It should be noticed that other means of
 protecting/detecting the integrity of the ES with Complete Validation
 Data exist and could be used.
 Although the technique requires a time stamp for every signature, it
 is well suited for individual users wishing to have an integrity
 protected copy of all the validated signatures they have received.
 By time-stamping the complete electronic signature, including the
 digital signature as well as the references to the certificates and
 revocation status information used to support validation of that
 signature, the time-stamp ensures that there is no ambiguity in the
 means of validating that signature.
 This technique is referred to as ES with eXtended validation data
 (ES-X), type 1 Time-Stamped in this document.
 NOTE:  Trust is achieved in the references by including a hash of the
 data being referenced.
 If it is desired for any reason to keep a copy of the additional data
 being referenced, the additional data may be attached to the
 electronic signature, in which case the electronic signature becomes
 a ES-X Long as defined by this document.
 A ES-X Long Time-Stamped is simply the concatenation of a ES-X Time-
 Stamped with a copy of the additional data being referenced.

B.4.6.2 Time-Stamping Certificates and Revocation Information

 References Time-Stamping each ES with Complete validation data as
 defined above may not be efficient, particularly when the same set of
 CA certificates and CRL information is used to validate many
 signatures.
 Time-Stamping CA certificates will stop any attacker from issuing
 bogus CA certificates that could be claimed to existing before the CA
 key was compromised.  Any bogus time-stamped CA certificates will
 show that the certificate was created after the legitimate CA key was

Pinkas, et al. Informational [Page 78] RFC 3126 Electronic Signature Formats September 2001

 compromised.  In the same way, time-stamping CA CRLs, will stop any
 attacker from issuing bogus CA CRLs which could be claimed to
 existing before the CA key was compromised.
 Time-Stamping of commonly used certificates and CRLs can be done
 centrally, e.g., inside a company or by a service provider.  This
 method reduces the amount of data the verifier has to time-stamp, for
 example it could reduce to just one time stamp per day (i.e., in the
 case were all the signers use the same CA and the CRL applies for the
 whole day).  The information that needs to be time stamped is not the
 actual certificates and CRLs but the unambiguous references to those
 certificates and CRLs.
 To comply with extended validation data, type 2 Time-stamped, this
 document requires the following:
  • All the CA certificates references and revocation information

references (i.e., CRLs) used in validating the ES-C are covered

       by one or more time-stamp.
 Thus a ES-C with a time-stamp signature value at time T1, can be
 proved valid if all the CA and CRL references are time-stamped at
 time T1+.

B.4.7 Time-Stamping for Long Life of Signature

 Advances in computing increase the probability of being able to break
 algorithms and compromise keys.  There is therefore a requirement to
 be able to protect electronic signatures against this probability.
 Over a period of time weaknesses may occur in the cryptographic
 algorithms used to create an electronic signature (e.g., due to the
 time available for cryptoanalysis, or improvements in
 cryptoanalytical techniques).  Before this such weaknesses become
 likely, a verifier should take extra measures to maintain the
 validity of the electronic signature.  Several techniques could be
 used to achieve this goal depending on the nature of the weakened
 cryptography.  In order to simplify, a single technique, called
 Archive validation data, covering all the cases is being used in this
 document.
 Archive validation data consists of the Complete validation data and
 the complete certificate and revocation data, time stamped together
 with the electronic signature.  The Archive validation data is
 necessary if the hash function and the crypto algorithms that were
 used to create the signature are no longer secure.  Also, if it

Pinkas, et al. Informational [Page 79] RFC 3126 Electronic Signature Formats September 2001

 cannot be assumed that the hash function used by the Time Stamping
 Authority is secure, then nested time-stamps of Archived Electronic
 Signature are required.
 The potential for Trusted Service Provider (TSP) key compromise
 should be significantly lower than user keys, because TSP(s) are
 expected to use stronger cryptography and better key protection.  It
 can be expected that new algorithms (or old ones with greater key
 lengths) will be used.  In such a case, a sequence of time-stamps
 will protect against forgery.  Each time-stamp needs to be affixed
 before either the compromise of the signing key or of the cracking of
 the algorithms used by the TSA.  TSAs (Time-Stamping Authorities)
 should have long keys (e.g., which at the time of drafting this
 document was 2048 bits for the signing RSA algorithm) and/or a "good"
 or different algorithm.
 Nested time-stamps will also protect the verifier against key
 compromise or cracking the algorithm on the old electronic
 signatures.
 The process will need to be performed and iterated before the
 cryptographic algorithms used for generating the previous time stamp
 are no longer secure.  Archive validation data may thus bear multiple
 embedded time stamps.

B.4.8 Reference to Additional Data

 Using type 1 or 2 of Time-Stamped extended validation data verifiers
 still needs to keep track of all the components that were used to
 validate the signature, in order to be able to retrieve them again
 later on.  These components may be archived by an external source
 like a trusted service provider, in which case referenced information
 that is provided as part of the ES with Complete validation data
 (ES-C) is adequate.  The actual certificates and CRL information
 reference in the ES-C can be gathered when needed for arbitration.

B.4.9 Time-Stamping for Mutual Recognition

 In some business scenarios both the signer and the verifier need to
 time-stamp their own copy of the signature value.  Ideally the two
 time-stamps should be as close as possible to each other.
 Example: A contract is signed by two parties A and B representing
 their respective organizations, to time-stamp the signer and verifier
 data two approaches are possible:
  • under the terms of the contract pre-defined common "trusted"

TSA may be used;

Pinkas, et al. Informational [Page 80] RFC 3126 Electronic Signature Formats September 2001

  • if both organizations run their own time-stamping services, A

and B can have the transaction time-stamped by these two time-

       stamping services.  In the latter case, the electronic
       signature will only be considered as valid, if both time-stamps
       were obtained in due time (i.e., there should not be a long
       delay between obtaining the two time-stamps).  Thus, neither A
       nor B can repudiate the signing time indicated by their own
       time-stamping service.
 Therefore, A and B do not need to agree on a common "trusted" TSA to
 get a valid transaction.
 It is important to note that signatures may be generated "off-line"
 and time-stamped at a later time by anyone, e.g., by the signer or
 any recipient interested in validating the signature.  The time-stamp
 over the signature from the signer can thus be provided by the signer
 together with the signed document, and /or obtained by the verifier
 following receipt of the signed document.
 The business scenarios may thus dictate that one or more of the
 long-term signature time-stamping methods describe above be used.
 This will need to be part of a mutually agreed the Signature
 Validation Policy with is part of the overall signature policy under
 which digital signature may be used to support the business
 relationship between the two parties.

B.4.10 TSA Key Compromise

 TSA servers should be built in such a way that once the private
 signature key is installed, that there is minimal likelihood of
 compromise over as long as possible period.  Thus the validity period
 for the TSA's keys should be as long as possible.
 Both the ES-T and the ES-C contain at least one time stamp over the
 signer's signature.  In order to protect against the compromise of
 the private signature key used to produce that time-stamp, the
 Archive validation data can be used when a different Time-Stamping
 Authority key is involved to produce the additional time-stamp.  If
 it is believed that the TSA key used in providing an earlier time-
 stamp may ever be compromised (e.g., outside its validity period),
 then the ES-A should be used.  For extremely long periods this may be
 applied repeatedly using new TSA keys.

B.5 Multiple Signatures

 Some electronic signatures may only be valid if they bear more than
 one signature.  This is the case generally when a contract is signed
 between two parties.  The ordering of the signatures may or may not

Pinkas, et al. Informational [Page 81] RFC 3126 Electronic Signature Formats September 2001

 be important, i.e., one may or may not need to be applied before the
 other. Several forms of multiple and counter signatures may need to
 be supported, which fall into two basic categories:
  • independent signatures;
  • embedded signatures.
 Independent signatures are parallel signatures where the ordering of
 the signatures is not important.  The capability to have more than
 one independent signature over the same data must be provided.
 Embedded signatures are applied one after the other and are used
 where the order the signatures are applied is important.  The
 capability to sign over signed data must be provided.
 These forms are described in clause 3.13.  All other multiple
 signature schemes, e.g., a signed document with a countersignature,
 double countersignatures or multiple signatures, can be reduced to
 one or more occurrence of the above two cases.

Annex C (informative): Identifiers and roles

C.1 Signer Name Forms

 The name used by the signer, held as the subject in the signer's
 certificate, must uniquely identify the entity.  The name must be
 allocated and verified on registration with the Certification
 Authority, either directly or indirectly through a Registration
 Authority, before being issued with a Certificate.
 This document places no restrictions on the form of the name.  The
 subject's name may be a distinguished name, as defined in [RFC2459],
 held in the subject field of the certificate, or any other name form
 held in the X.509 subjectAltName certificate extension field.  In the
 case that the subject has no distinguished name, the subject name can
 be an empty sequence and the subjectAltName extension must be
 critical.

C.2 TSP Name Forms

 All TSP name forms (Certification Authorities, Attribute Authorities
 and Time-Stamping Authorities) must be in the form of a distinguished
 name held in the subject field of the certificate.
 The TSP name form must include the legal jurisdiction (i.e., country)
 under which it operates and an identification for the organization
 providing the service.

Pinkas, et al. Informational [Page 82] RFC 3126 Electronic Signature Formats September 2001

C.3 Roles and Signer Attributes

 Where a signer signs as an individual but wishes to also identify
 him/herself as acting on behalf of an organization, it may be
 necessary to provide two independent forms of identification.  The
 first identity, with is directly associated with the signing key
 identifies him/her as an individual.  The second, which is managed
 independently, identifies that person acting as part of the
 organization, possibly with a given role.
 In this case the first identity is carried in the
 subject/subjectAltName field of the signer's certificate as described
 above.
 This document supports the following means of providing a second form
 of identification:
  • by placing a secondary name field containing a claimed role in

the CMS signed attributes field;

  • by placing an attribute certificate containing a certified role

in the CMS signed attributes field.

Pinkas, et al. Informational [Page 83] RFC 3126 Electronic Signature Formats September 2001

Full Copyright Statement

 Copyright (C) The Internet Society (2001).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Pinkas, et al. Informational [Page 84]

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