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rfc:rfc3628

Network Working Group D. Pinkas Request for Comments: 3628 Bull Category: Informational N. Pope

                                                               J. Ross
                                                  Security & Standards
                                                         November 2003
      Policy Requirements for Time-Stamping Authorities (TSAs)

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 (2003).  All Rights Reserved.

Abstract

 This document defines requirements for a baseline time-stamp policy
 for Time-Stamping Authorities (TSAs) issuing time-stamp tokens,
 supported by public key certificates, with an accuracy of one second
 or better.  A TSA may define its own policy which enhances the policy
 defined in this document.  Such a policy shall incorporate or further
 constrain the requirements identified in this document.

Table of Contents

 1.  Introduction. . . . . . . . . . . . . . . . . . . . . . . . .  3
 2.  Overview. . . . . . . . . . . . . . . . . . . . . . . . . . .  4
 3.  Definitions and Abbreviations . . . . . . . . . . . . . . . .  5
     3.1. Definitions. . . . . . . . . . . . . . . . . . . . . . .  5
     3.2. Abbreviations. . . . . . . . . . . . . . . . . . . . . .  6
 4.  General Concepts. . . . . . . . . . . . . . . . . . . . . . .  6
     4.1. Time-Stamping Services . . . . . . . . . . . . . . . . .  6
     4.2. Time-Stamping Authority. . . . . . . . . . . . . . . . .  7
     4.3. Subscriber . . . . . . . . . . . . . . . . . . . . . . .  7
     4.4. Time-Stamp Policy and TSA Practice Statement . . . . . .  8
          4.4.1.  Purpose. . . . . . . . . . . . . . . . . . . . .  8
          4.4.2.  Level of Specificity . . . . . . . . . . . . . .  8
          4.4.3.  Approach . . . . . . . . . . . . . . . . . . . .  8
 5.  Time-Stamp Policies . . . . . . . . . . . . . . . . . . . . .  9
     5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.2. Identification . . . . . . . . . . . . . . . . . . . . .  9
     5.3. User Community and Applicability . . . . . . . . . . . . 10

Pinkas, et al. Informational [Page 1] RFC 3628 Requirements for Time-Stamping Authorities November 2003

     5.4. Conformance. . . . . . . . . . . . . . . . . . . . . . . 10
 6.  Obligations and Liability . . . . . . . . . . . . . . . . . . 10
     6.1. TSA Obligations. . . . . . . . . . . . . . . . . . . . . 10
          6.1.1.  General. . . . . . . . . . . . . . . . . . . . . 10
          6.1.2.  TSA Obligations Towards Subscribers. . . . . . . 11
     6.2. Subscriber Obligations . . . . . . . . . . . . . . . . . 11
     6.3. Relying Party Obligations. . . . . . . . . . . . . . . . 11
     6.4. Liability. . . . . . . . . . . . . . . . . . . . . . . . 11
 7.  Requirements on TSA Practices . . . . . . . . . . . . . . . . 12
     7.1. Practice and Disclosure Statements . . . . . . . . . . . 12
          7.1.1.  TSA Practice Statement . . . . . . . . . . . . . 12
          7.1.2.  TSA Disclosure Statement . . . . . . . . . . . . 13
     7.2. Key Management Life Cycle. . . . . . . . . . . . . . . . 15
          7.2.1.  TSU Key Generation . . . . . . . . . . . . . . . 15
          7.2.2.  TSU Private Key Protection . . . . . . . . . . . 15
          7.2.3.  TSU Public Key Distribution. . . . . . . . . . . 16
          7.2.4.  Rekeying TSU's Key . . . . . . . . . . . . . . . 17
          7.2.5.  End of TSU Key Life Cycle. . . . . . . . . . . . 17
          7.2.6.  Life Cycle Management of the Cryptographic Module
                  used to Sign Time-Stamps . . . . . . . . . . . . 17
     7.3. Time-Stamping. . . . . . . . . . . . . . . . . . . . . . 18
          7.3.1.  Time-Stamp Token . . . . . . . . . . . . . . . . 18
          7.3.2.  Clock Synchronization with UTC . . . . . . . . . 19
     7.4. TSA Management and Operation . . . . . . . . . . . . . . 20
          7.4.1.  Security Management. . . . . . . . . . . . . . . 20
          7.4.2.  Asset Classification and Management. . . . . . . 21
          7.4.3.  Personnel Security . . . . . . . . . . . . . . . 22
          7.4.4.  Physical and Environmental Security. . . . . . . 23
          7.4.5.  Operations Management. . . . . . . . . . . . . . 25
          7.4.6.  System Access Management . . . . . . . . . . . . 26
          7.4.7.  Trustworthy Systems Deployment and Maintenance . 27
          7.4.8.  Compromise of TSA Services . . . . . . . . . . . 28
          7.4.9.  TSA Termination. . . . . . . . . . . . . . . . . 29
          7.4.10. Compliance with Legal Requirements . . . . . . . 29
          7.4.11. Recording of Information Concerning Operation
                  of Time-Stamping Services. . . . . . . . . . . . 30
     7.5. Organizational . . . . . . . . . . . . . . . . . . . . . 31
 8.  Security Considerations . . . . . . . . . . . . . . . . . . . 32
 9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
 10. References. . . . . . . . . . . . . . . . . . . . . . . . . . 33
     10.1. Normative References. . . . . . . . . . . . . . . . . . 33
     10.2. Informative References. . . . . . . . . . . . . . . . . 34
 Annex A (informative): Coordinated Universal Time . . . . . . . . 35
 Annex B (informative): Possible for Implementation Architectures
                        and Time-Stamping Services . . . . . . . . 36
 Annex C (informative): Long Term Verification of Time-Stamp
                        Tokens . . . . . . . . . . . . . . . . . . 38
 Annex D (informative): Model TSA Disclosure Statement . . . . . . 39

Pinkas, et al. Informational [Page 2] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 42
 Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 43

1. Introduction

 The contents of this Informational RFC is technically equivalent to
 ETSI TS 102 023 V 1.2.1 (2002-06) [TS 102023].  The ETSI TS is under
 the ETSI Copyright (C).  Individual copies of this ETSI deliverable
 can be downloaded from http://www.etsi.org
 In creating reliable and manageable digital evidence it is necessary
 to have an agreed upon method of associating time data to transaction
 so that they might be compared to each other at a later time.  The
 quality of this evidence is based on creating and managing the data
 structure that represent the events and the quality of the parametric
 data points that anchor them to the real world.  In this instance
 this being the time data and how it was applied.
 A typical transaction is a digitally signed document, where it is
 necessary to prove that the digital signature from the signer was
 applied when the signer's certificate was valid.
 A timestamp or a time mark (which is an audit record kept in a secure
 audit trail from a trusted third party) applied to a digital
 signature value proves that the digital signature was created before
 the date included in the time-stamp or time mark.
 To prove the digital signature was generated while the signer's
 certificate was valid, the digital signature must be verified and the
 following conditions satisfied:
    1. the time-stamp (or time mark) was applied before the end of the
       validity period of the signer's certificate,
    2. the time-stamp (or time mark) was applied either while the
       signer's certificate was not revoked or before the revocation
       date of the certificate.
 Thus a time-stamp (or time mark) applied in this manner proves that
 the digital signature was created while the signer's certificate was
 valid. This concept proves the validity of a digital signature over
 the whole of any certificate chain.
 Policy requirements to cover that case is the primary reason of this
 document.  However, it should be observed that these policy
 requirements can be used to address other needs.

Pinkas, et al. Informational [Page 3] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 The electronic time stamp is gaining interest from the business
 sector as an important component of electronic signatures.  It is
 also featured by the ETSI Electronic Signature Format standard [TS
 101733] or Electronic Signature Formats for long term electronic
 signatures [RFC 3126], built upon the Time-Stamp Protocol [RFC 3161].
 Agreed minimum security and quality requirements are necessary in
 order to ensure trustworthy validation of long-term electronic
 signatures.
 The European Directive 1999/93/EC [Dir 99/93/EC] defines
 certification service provider as "an entity or a legal or natural
 person who issues certificates or provides other services related to
 electronic signatures".  One example of a certification-service-
 provider is a Time-Stamping Authority.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14, RFC 2119
 [RFC 2119].

2. Overview

 These policy requirements are aimed at time-stamping services used in
 support of qualified electronic signatures (i.e., in line with
 article 5.1 of the European Directive on a community framework for
 electronic signatures) but may be applied to any application
 requiring to prove that a datum existed before a particular time.
 These policy requirements are based on the use of public key
 cryptography, public key certificates and reliable time sources. The
 present document may be used by independent bodies as the basis for
 confirming that a TSA may be trusted for providing time-stamping
 services.
 This document addresses requirements for synchronizing TSAs issuing
 time-stamp tokens with Coordinated universal time (UTC) and digitally
 signed by TSUs.
 Subscriber and relying parties should consult the TSA's practice
 statement to obtain further details of precisely how this time-stamp
 policy is implemented by the particular TSA (e.g., protocols used in
 providing this service).
 This document does not specify:
  1. protocols used to access the TSUs;

Pinkas, et al. Informational [Page 4] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 NOTE 1: A time-stamping protocol is defined in RFC 3161 [RFC 3161]
 and profiled in TS 101 861 [TS 101861].
  1. how the requirements identified herein may be assessed by an

independent body;

  1. requirements for information to be made available to such

independent bodies;

  1. requirements on such independent bodies.
 NOTE 2: See CEN Workshop Agreement 14172 "EESSI Conformity Assessment
 Guidance" [CWA 14172].

3. Definitions and Abbreviations

3.1. Definitions

 For the purposes of the present document, the following terms and
 definitions apply:
 NOTE: Where a definition is copied from a referenced document this is
 indicated by inclusion of the reference identifier number at the end
 of the definition.
 relying party: recipient of a time-stamp token who relies on that
       time-stamp token.
 subscriber: entity requiring the services provided by a TSA and which
       has explicitly or implicitly agreed to its terms and
       conditions.
 time-stamp token: data object that binds a representation of a datum
       to a particular time, thus establishing evidence that the datum
       existed before that time.
 time-stamping authority: authority which issues time-stamp tokens.
 TSA Disclosure statement: set of statements about the policies and
       practices of a TSA that particularly require emphasis or
       disclosure to subscribers and relying parties, for example to
       meet regulatory requirements.
 TSA practice statement: statement of the practices that a TSA employs
       in issuing time-stamp tokens.
 TSA system: composition of IT products and components organized to
       support the provision of time-stamping services.

Pinkas, et al. Informational [Page 5] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 time-stamp policy: named set of rules that indicates the
       applicability of a time-stamp token to a particular community
       and/or class of application with common security requirements.
 time-stamping unit: set of hardware and software which is managed as
       a unit and has a single time-stamp token signing key active at
       a time.
 Coordinated Universal Time (UTC): Time scale based on the second as
       defined in ITU-R Recommendation TF.460-5 [TF.460-5].
       NOTE: For most practical purposes UTC is equivalent to mean
       solar time at the prime meridian.  More specifically, UTC is a
       compromise between the highly stable atomic time (Temps
       Atomique International
        - TAI) and solar time derived from the irregular Earth
       rotation (related to the Greenwich mean sidereal time (GMST) by
       a conventional relationship).  (See annex A for more details).
 UTC(k): Time-scale realized by the laboratory "k" and kept in close
       agreement with UTC, with the goal to reach plus or minus 100
       ns. (See ITU-R Recommendation TF.536-1 [TF.536-1]).
       NOTE:  A list of UTC(k) laboratories is given in section 1 of
       Circular T disseminated by BIPM and available from the BIPM
       website (http://www.bipm.org/).

3.2. Abbreviations

 For the purposes of the present document, the following abbreviations
 apply:
    TSA  Time-Stamping Authority
    TSU  Time-Stamping Unit
    TST  Time-Stamp Token
    UTC  Coordinated Universal Time

4. General Concepts

4.1. Time-Stamping Services

 The provision of time-stamping services is broken down into the
 following component services for the purposes of classifying
 requirements:
  1. Time-stamping provision: This service component generates

time-stamp tokens.

Pinkas, et al. Informational [Page 6] RFC 3628 Requirements for Time-Stamping Authorities November 2003

  1. Time-stamping management: The service component that monitors and

controls the operation of the time-stamping services to ensure

    that the service is provided as specified by the TSA.  This
    service component is responsibile  for the installation and
    de-installation of the time-stamping provision service. For
    example, time-stamping management ensures that the clock used for
    time-stamping is correctly synchronized with UTC.
 This subdivision of services is only for the purposes of clarifying
 the requirements specified in the current document and places no
 restrictions on any subdivision of an implementation of time-stamping
 services.

4.2. Time-Stamping Authority

 The authority to issue time-stamp tokens, trusted by the users of the
 time-stamping services, i.e., subscribers and relying parties, is
 called the Time-Stamping Authority (TSA).  TSA has overall
 responsibility for time-stamping services identified in clause 4.1.
 The TSA has responsibility for the operation of one or more TSU's
 which creates and signs on behalf of the TSA.  The TSA responsible
 for issuing a time-stamp token is identifiable (see 7.3.1 h).
 The TSA may use other parties to provide parts of the Time-Stamping
 Services.  However, the TSA always maintains overall responsibility
 and ensures that the policy requirements identified in the present
 document are met.  For example, a TSA may sub-contract all the
 component services, including the services which generate time-stamp
 tokens using the TSU's keys.  However, the private key or keys used
 to generate the time-stamp tokens belong to the TSA which maintains
 overall responsibility for meeting the requirements in this document.
 A TSA may operate several identifiable time-stamping units.  Each
 unit has a different key.  See Annex B for possible implementations.
 A TSA is a certification-service-provider, as defined in the EU
 Directive on Electronic Signatures (see article 2(11)), which issues
 time-stamp tokens.

4.3. Subscriber

 The subscriber may be an organization comprising several end-users or
 an individual end-user.
 When the subscriber is an organization, some of the obligations that
 apply to that organization will have to apply as well to the end-
 users. In any case the organization will be held responsible if the

Pinkas, et al. Informational [Page 7] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 obligations from the end-users are not correctly fulfilled and
 therefore the organization is expected to suitably inform its end
 users.
 When the subscriber is an end-user, the end-user will be held
 directly responsible if its obligations are not correctly fulfilled.

4.4. Time-Stamp Policy and TSA Practice Statement

 This section explains the relative roles of Time-stamp policy and TSA
 practice statement.  It places no restriction on the form of a time-
 stamp policy or practice statement specification.

4.4.1. Purpose

 In general, the time-stamp policy states "what is to be adhered to,"
 while a TSA practice statement states "how it is adhered to", i.e.,
 the processes it will use in creating time-stamps and maintaining the
 accuracy of its clock.  The relationship between the time-stamp
 policy and TSA practice statement is similar in nature to the
 relationship of other business policies which state the requirements
 of the business, while operational units define the practices and
 procedures of how these policies are to be carried out.
 The present document specifies a time-stamp policy to meet general
 requirements for trusted time-stamping services.  TSAs specify in TSA
 practice statements how these requirements are met.

4.4.2. Level of Specificity

 The TSA practice statement is more specific than a time-stamp policy.
 A TSA practice statement is a more detailed description of the terms
 and conditions as well as business and operational practices of a TSA
 in issuing and otherwise managing time-stamping services.  The TSA
 practice statement of a TSA enforces the rules established by a
 time-stamp policy.  A TSA practice statement defines how a specific
 TSA meets the technical, organizational and procedural requirements
 identified in a time-stamp policy.
 NOTE: Even lower-level internal documentation may be appropriate for
 a TSA detailing the specific procedures necessary to complete the
 practices identified in the TSA practice statement.

4.4.3. Approach

 The approach of a time-stamp policy is significantly different from a
 TSA practice statement.  A time-stamp policy is defined independently
 of the specific details of the specific operating environment of a

Pinkas, et al. Informational [Page 8] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 TSA, whereas a TSA practice statement is tailored to the
 organizational structure, operating procedures, facilities, and
 computing environment of a TSA.  A time-stamp policy may be defined
 by the user of times-stamp services, whereas the TSA practice
 statement is always defined by the provider.

5. Time-Stamp Policies

5.1. Overview

 A time-stamp policy is a "named set of rules that indicates the
 applicability of a time-stamp token to a particular community and/or
 class of application with common security requirements" (see clauses
 3.1 and 4.4).
 The present document defines requirements for a baseline time-stamp
 policy for TSAs issuing time-stamp tokens, supported by public key
 certificates, with an accuracy of 1 second or better.
 NOTE 1: Without additional measures the relying party may not be able
 to ensure the validity of a time-stamp token beyond the end of the
 validity period of the supporting certificate.  See Annex C on
 verification of the validity of a time-stamp token beyond the
 validity period of the TSU's certificate.
 A TSA may define its own policy which enhances the policy defined in
 this document.  Such a policy shall incorporate or further constrain
 the requirements identified in this document.
 If an accuracy of better than 1 second is provided by a TSA and if
 all the TSUs have that same characteristics, then the accuracy shall
 be indicated in the TSA's disclosure statement (see section 7.1.2)
 that  each time-stamp token is issued with an accuracy of better than
 1 second.
 NOTE 2: It is required that a time-stamp token includes an identifier
 for the applicable policy (see section 7.3.1).

5.2. Identification

 The object-identifier [X.208] of the baseline time-stamp policy is:
 itu-t(0) identified-organization(4) etsi(0) time-stamp-policy(2023)
 policy-identifiers(1) baseline-ts-policy (1)
 In the TSA disclosure statement made available to subscribers and
 relying parties, a TSA shall also include the identifier for the
 time-stamp policy to indicate its conformance.

Pinkas, et al. Informational [Page 9] RFC 3628 Requirements for Time-Stamping Authorities November 2003

5.3. User Community and Applicability

 This policy is aimed at meeting the requirements of time-stamping
 qualified electronic signatures (see European Directive on Electronic
 Signatures) for long term validity (e.g., as defined in TS 101 733
 [TS 101733]), but is generally applicable to any requirement for an
 equivalent quality.
 This policy may be used for public time-stamping services or time-
 stamping services used within a closed community.

5.4. Conformance

 The TSA shall use the identifier for the time-stamp policy in time-
 stamp tokens as given in section 5.2, or define its own time-stamp
 policy that incorporates or further constrains the requirements
 identified in the present document:
 a) if the TSA claims conformance to the identified time-stamp policy
    and makes available to subscribers and relying parties on request
    the evidence to support the claim of conformance; or
 b) if the TSA has been assessed to conform to the identified time-
    stamp policy by an independent party.
 A conformant TSA must demonstrate that:
 a) it meets its obligations as defined in section 6.1;
 b) it has implemented controls which meet the requirements specified
    in section 7.

6. Obligations and Liability

6.1. TSA Obligations

6.1.1. General

 The TSA shall ensure that all requirements on TSA, as detailed in
 section 7, are implemented as applicable to the selected trusted
 time-stamp policy.
 The TSA shall ensure conformance with the procedures prescribed in
 this policy, even when the TSA functionality is undertaken by sub-
 contractors.
 The TSA shall also ensure adherence to any additional obligations
 indicated in the time-stamp either directly or incorporated by
 reference.

Pinkas, et al. Informational [Page 10] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 The TSA shall provide all its time-stamping services consistent with
 its practice statement.

6.1.2. TSA Obligations Towards Subscribers

 The TSA shall meet its claims as given in its terms and conditions
 including the availability and accuracy of its service.

6.2. Subscriber Obligations

 The current document places no specific obligations on the subscriber
 beyond any TSA specific requirements stated in the TSA's terms and
 condition.
 NOTE:  It is advisable that, when obtaining a time-stamp token, the
 subscriber verifies that the time-stamp token has been correctly
 signed and that the private key used to sign the time-stamp token has
 not been compromised.

6.3. Relying Party Obligations

 The terms and conditions made available to relying parties (see
 section 7.1.2) shall include an obligation on the relying party that,
 when relying on a time-stamp token, it shall:
 a) verify that the time-stamp token has been correctly signed and
    that the private key used to sign the time-stamp has not been
    compromised until the time of the verification;
    NOTE: During the TSU's certificate validity period, the validity
    of the signing key can be checked using current revocation status
    for the TSU's certificate.  If the time of verification exceeds
    the end of the validity period of the corresponding certificate,
    see annex C for guidance.
 b) take into account any limitations on the usage of the time-stamp
    indicated by the time-stamp policy;
 c) take into account any other precautions prescribed in agreements
    or elsewhere.

6.4. Liability

 The present document does not specify any requirement on liability.
 In particular, it should be noticed that a TSA may disclaim or limit
 any liability unless otherwise stipulated by the applicable law.

Pinkas, et al. Informational [Page 11] RFC 3628 Requirements for Time-Stamping Authorities November 2003

7. Requirements on TSA Practices

 The TSA shall implement the controls that meet the following
 requirements.
 These policy requirements are not meant to imply any restrictions on
 charging for TSA services.
 The requirements are indicated in terms of the security objectives,
 followed by more specific requirements for controls to meet those
 objectives where it is necessary to provide confidence that those
 objective will be met.
    NOTE: The details of controls required to meet an objective is a
    balance between achieving the necessary confidence whilst
    minimizing the restrictions on the techniques that a TSA may
    employ in issuing time-stamp tokens.  In the case of section 7.4
    (TSA management and operation), a reference is made to a source of
    more detailed control requirements.  Due to these factors the
    specificity of the requirements given under a given topic may
    vary.
 The provision of a time-stamp token in response to a request is at
 the discretion of the TSA depending on any service level agreements
 with the subscriber.

7.1. Practice and Disclosure Statements

7.1.1. TSA Practice Statement

 The TSA shall ensure that it demonstrates the reliability necessary
 for providing time-stamping services.
 In particular:
 a) The TSA shall have a risk assessment carried out in order to
    evaluate business assets and threats to those assets in order to
    determine the necessary security controls and operational
    procedures.
 b) The TSA shall have a statement of the practices and procedures
    used to address all the requirements identified in this time-stamp
    policy.
    NOTE 1: This policy makes no requirement as to the structure of
    the TSA practice statement.

Pinkas, et al. Informational [Page 12] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 c) The TSA's practice statement shall identify the obligations of all
    external organizations supporting the TSA services including the
    applicable policies and practices.
 d) The TSA shall make available to subscribers and relying parties
    its practice statement, and other relevant documentation, as
    necessary, to assess conformance to the time-stamp policy.
    NOTE 2: The TSA is not generally required to make all the details
    of its practices public.
 e) The TSA shall disclose to all subscribers and potential relying
    parties the terms and conditions regarding use of its time-
    stamping services as specified in section 7.1.2.
 f) The TSA shall have a high level management body with final
    authority for approving the TSA practice statement.
 g) The senior management of the TSA shall ensure that the practices
    are properly implemented.
 h) The TSA shall define a review process for the practices including
    responsibilities for maintaining the TSA practice statement.
 i) The TSA shall give due notice of changes it intends to make in its
    practice statement and shall, following approval as in (f) above,
    make the revised TSA practice statement immediately available as
    required under (d) above.

7.1.2. TSA Disclosure Statement

 The TSA shall disclose to all subscribers and potential relying
 parties the terms and conditions regarding use of its time-stamping
 services.  This statement shall at least specify for each time-stamp
 policy supported by the TSA:
 a) The TSA contact information.
 b) The time-stamp policy being applied.
 c) At least one hashing algorithm which may be used to represent the
    datum being time-stamped. (No hash algorithm is mandated).
 d) The expected life-time of the signature used to sign the time-
    stamp token (depends on the hashing algorithm being used, the
    signature algorithm being used and the private key length).

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 e) The accuracy of the time in the time-stamp tokens with respect to
    UTC.
 f) Any limitations on the use of the time-stamping service.
 g) The subscriber's obligations as defined in section 6.2, if any.
 h) The relying party's obligations as defined in section 6.3.
 i) Information on how to verify the time-stamp token such that the
    relying party is considered to "reasonably rely" on the time-stamp
    token (see section 6.3) and any possible limitations on the
    validity period.
 j) The period of time during which TSA event logs (see section
    7.4.10) are retained.
 k) The applicable legal system, including any claim to meet the
    requirements on time-stamping services under national law.
 l) Limitations of liability.
 m) Procedures for complaints and dispute settlement.
 n) If the TSA has been assessed to be conformant with the identified
    time-stamp policy, and if so by which independent body.
    NOTE 1: It is also recommended that the TSA includes in its
    time-stamping disclosure statement availability of its service,
    for example the expected mean time between failure of the time-
    stamping service, the mean time to recovery following a failure,
    and provisions made for disaster recovery including back-up
    services;
    This information shall be available through a durable means of
    communication.  This information shall be available in a readily
    understandable language.  It may be transmitted electronically.
    NOTE 2: A model TSA disclosure statement which may be used as the
    basis of such a communication is given in annex D. Alternatively
    this may be provided as part of a subscriber / relying party
    agreement.  These TSA disclosure statements may be included in a
    TSA practice statement provided that they are conspicuous to the
    reader.

Pinkas, et al. Informational [Page 14] RFC 3628 Requirements for Time-Stamping Authorities November 2003

7.2. Key Management Life Cycle

7.2.1. TSA Key Generation

 The TSA shall ensure that any cryptographic keys are generated in
 under controlled circumstances.
 In particular:
 a) The generation of the TSU's signing key(s) shall be undertaken in
    a physically secured environment (see section 7.4.4) by personnel
    in trusted roles (see section 7.4.3) under, at least, dual
    control.  The personnel authorized to carry out this function
    shall be limited to those requiring to do so under the TSA's
    practices.
 b) The generation of the TSU's signing key(s) shall be carried out
    within a cryptographic module(s) which either:
  1. meets the requirements identified in FIPS 140-1 [FIPS 140-1]

level 3 or higher, or

  1. meets the requirements identified in CEN Workshop Agreement

14167-2 [CWA 14167-2], or

  1. is a trustworthy system which is assured to EAL 4 or higher in

accordance to ISO 15408 [ISO 15408], or equivalent security

       criteria.  This shall be to a security target or protection
       profile which meets the requirements of the current document,
       based on a risk analysis and taking into account physical and
       other non-technical security measures.
 c) The TSU key generation algorithm, the resulting signing key length
    and signature algorithm used for signing time-stamp tokens key
    shall be recognized by any national supervisory body, or in
    accordance with existing current state of art, as being fit for
    the purposes of time-stamp tokens as issued by the TSA.

7.2.2. TSU Private Key Protection

 The TSA shall ensure that TSU private keys remain confidential and
 maintain their integrity.
 In particular:
 a) The TSU private signing key shall be held and used within a
    cryptographic module which:

Pinkas, et al. Informational [Page 15] RFC 3628 Requirements for Time-Stamping Authorities November 2003

  1. meets the requirements identified in FIPS 140-1 [FIPS 140-1]

level 3 or higher; or

  1. meets the requirements identified in CEN Workshop Agreement

14167-2 [CWA 14167-2]; or

  1. is a trustworthy system which is assured to EAL 4 or higher in

accordance to ISO 15408 [ISO 15408], or equivalent security

       criteria. This shall be a security target or protection profile
       which meets the requirements of the current document, based on
       a risk analysis and taking into account physical and other
       non-technical security measures.
    NOTE: Backup of TSU private keys is deprecated in order to
    minimize risk of key compromise.
 b) If TSU private keys are backed up, they shall be copied, stored
    and recovered only by personnel in trusted roles using, at least,
    dual control in a physically secured environment. (see section
    7.4.4).  The personnel authorized to carry out this function shall
    be limited to those requiring to do so under the TSA's practices.
 c) Any backup copies of the TSU private signing keys shall be
    protected to ensure its confidentiality by the cryptographic
    module before being stored outside that device.

7.2.3. TSU Public Key Distribution

 The TSA shall ensure that the integrity and authenticity of the TSU
 signature verification (public) keys and any associated parameters
 are maintained during its distribution to relying parties.
 In particular:
 a) TSU signature verification (public) keys shall be made available
    to relying parties in a public key certificate.
    NOTE: For example, TSU's certificates may be issued by a
    certification authority operated by the same organization as the
    TSA, or issued by another authority.
 b) The TSU's signature verification (public) key certificate shall be
    issued by a certification authority operating under a certificate
    policy which provides a level of security equivalent to, or higher
    than, this time-stamping policy.

Pinkas, et al. Informational [Page 16] RFC 3628 Requirements for Time-Stamping Authorities November 2003

7.2.4. Rekeying TSU's Key

 The life-time of TSU's certificate shall be not longer than the
 period of time that the chosen algorithm and key length is recognized
 as being fit for purpose (see section 7.2.1c)).
 NOTE 1: The following additional considerations apply when limiting
 that lifetime:
  1. Section 7.4.10 requires that records concerning time-stamping

services shall be held for a period of time,as appropriate, for at

    least 1 year after the expiration of the validity of the TSU's
    signing keys.  The longer the validity period of the TSU
    certificates will be, the longer the size of the records to be
    kept will be.
  1. Should a TSU private key be compromised, then the longer the

life-time, the more affected time-stamp tokens there will be.

 NOTE 2: TSU key compromise does not only depend on the
 characteristics of the cryptographic module being used but also on
 the procedures being used at system initialization and key export
 (when that function is supported).

7.2.5. End of TSU Key Life Cycle

 The TSA shall ensure that TSU private signing keys are not used
 beyond the end of their life cycle.
 In particular:
 a) Operational or technical procedures shall be in place to ensure
    that a new key is put in place when a TSU's key expires.
 b) The TSU private signing keys, or any key part, including any
    copies shall be destroyed such that the private keys cannot be
    retrieved.
 c) The TST generation system SHALL reject any attempt to issue TSTs
    if the signing private key has expired.

7.2.6. Life Cycle Management of the Cryptographic Module used to Sign

      Time-Stamps
 The TSA shall ensure the security of cryptographic hardware
 throughout its lifecycle.

Pinkas, et al. Informational [Page 17] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 In particular the TSA shall ensure that:
 a) Time-stamp token signing cryptographic hardware is not tampered
    with during shipment;
 b) Time-stamp token signing cryptographic hardware is not tampered
    with while stored;
 c) Installation, activation and duplication of TSU's signing keys in
    cryptographic hardware shall be done only by personnel in trusted
    roles using, at least, dual control in a physically secured
    environment. (see section 7.4.4);
 d) Time-stamp token signing cryptographic hardware is functioning
    correctly; and
 e) TSU private signing keys stored on TSU cryptographic module are
    erased upon device retirement.

7.3. Time-Stamping

7.3.1. Time-Stamp Token

 The TSA shall ensure that time-stamp tokens are issued securely and
 include the correct time.
 In particular:
 a) The time-stamp token shall include an identifier for the time-
    stamp policy;
 b) Each time-stamp token shall have a unique identifier;
 c) The time values the TSU uses in the time-stamp token shall be
    traceable to at least one of the real time values distributed by a
    UTC(k) laboratory.
    NOTE 1: The Bureau International des Poids et Mesures (BIPM)
    computes UTC on the basis of its local representations UTC(k) from
    a large ensemble of atomic clocks in national metrology institutes
    and national astronomical observatories round the world.  The BIPM
    disseminates UTC through its monthly Circular T [list 1].  This is
    available on the BIPM website (www.bipm.org) and it officially
    identifies all those institutes having recognized UTC(k) time
    scales.

Pinkas, et al. Informational [Page 18] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 d) The time included in the time-stamp token shall be synchronized
    with UTC within the accuracy defined in this policy and, if
    present, within the accuracy defined in the time-stamp token
    itself;
 e) If the time-stamp provider's clock is detected (see section
    7.3.2c)) as being out of the stated accuracy (see section 7.1.2e))
    then time-stamp tokens shall not be issued.
 f) The time-stamp token shall include a representation (e.g., hash
    value) of the datum being time-stamped as provided by the
    requestor;
 g) The time-stamp token shall be signed using a key generated
    exclusively for this purpose.
    NOTE 2: A protocol for a time-stamp token is defined in RFC 3631
    and profiled in TS 101 861 [TS 101861].
    NOTE 3: In the case of a number of requests at approximately the
    same time, the ordering of the time within the accuracy of the TSU
    clock is not mandated.
 h) The time-stamp token shall include:
  1. where applicable, an identifier for the country in which the

TSA is established;

  1. an identifier for the TSA;
  1. an identifier for the unit which issues the time-stamps.

7.3.2. Clock Synchronization with UTC

 The TSA shall ensure that its clock is synchronized with UTC within
 the declared accuracy.
 In particular:
 a) The calibration of the TSU clocks shall be maintained such that
    the clocks shall not be expected to drift outside the declared
    accuracy.
 b) The TSU clocks shall be protected against threats which could
    result in an undetected change to the clock that takes it outside
    its calibration.

Pinkas, et al. Informational [Page 19] RFC 3628 Requirements for Time-Stamping Authorities November 2003

    NOTE 1: Threats may include tampering by unauthorized personnel,
    radio or electrical shocks.
 c) The TSA shall ensure that, if the time that would be indicated in
    a time-stamp token drifts or jumps out of synchronization with
    UTC, this will be detected (see also 7.3.1e)).
    NOTE 2: Relying parties are required to be informed of such events
    (see section 7.4.8).
 d) The TSA shall ensure that clock synchronization is maintained when
    a leap second occurs as notified by the appropriate body.  The
    change to take account of the leap second shall occur during the
    last minute of the day when the leap second is scheduled to occur.
    A record shall be maintained of the exact time (within the
    declared accuracy) when this change occurred.  See annex A for
    more details.
    NOTE 3: A leap second is an adjustment to UTC by skipping or
    adding an extra second on the last second of a UTC month.  First
    preference is given to the end of December and June, and second
    preference is given to the end of March and September.

7.4. TSA Management and Operation

7.4.1. Security Management

 The TSA shall ensure that the administrative and management
 procedures applied are adequate and correspond to recognized best
 practice.
 In particular:
 TSA General
 a) The TSA shall retain responsibility for all aspects of the
    provision of time-stamping services within the scope of this
    time-stamp policy, whether or not functions are outsourced to
    subcontractors.  Responsibilities of third parties shall be
    clearly defined by the TSA and appropriate arrangements made to
    ensure that third parties are bound to implement any controls
    required by the TSA.  The TSA shall retain responsibility for the
    disclosure of relevant practices of all parties.

Pinkas, et al. Informational [Page 20] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 b) The TSA management shall provide direction on information security
    through a suitable high level steering forum that is responsible
    for defining the TSA's information security policy.  The TSA shall
    ensure publication and communication of this policy to all
    employees who are impacted by it.
 c) The information security infrastructure necessary to manage the
    security within the TSA shall be maintained at all times.  Any
    changes that will impact on the level of security provided shall
    be approved by the TSA management forum.
    NOTE 1: See ISO/IEC 17799 [ISO 17799] for guidance on information
    security management including information security infrastructure,
    management information security forum and information security
    policies.
 d) The security controls and operating procedures for TSA facilities,
    systems and information assets providing the time-stamping
    services shall be documented, implemented and maintained.
    NOTE 2: The present documentation (commonly called a system
    security policy or manual) should identify all relevant targets,
    objects and potential threats related to the services provided and
    the safeguards required to avoid or limit the effects of those
    threats, consistent with the Risk Assessment required under
    section 7.1.1a).  It should describe the rules, directives and
    procedures regarding how the specified services and the associated
    security assurance are granted in addition to stating policy on
    incidents and disasters.
 e) TSA shall ensure that the security of information is maintained
    when the responsibility for TSA functions has been outsourced to
    another organization or entity.

7.4.2. Asset Classification and Management

 The TSA shall ensure that its information and other assets receive an
 appropriate level of protection.
 In particular:
  1. The TSA shall maintain an inventory of all assets and shall assign

a classification for the protection requirements to those assets

    consistent with the risk analysis.

Pinkas, et al. Informational [Page 21] RFC 3628 Requirements for Time-Stamping Authorities November 2003

7.4.3. Personnel Security

 The TSA shall ensure that personnel and hiring practices enhance and
 support the trustworthiness of the TSA's operations.
 In particular (TSA general):
 a) The TSA shall employ personnel which possess the expert knowledge,
    experience and qualifications necessary for the offered services
    and as appropriate to the job function.
    NOTE 1: TSA personnel should be able to fulfill the requirement of
    "expert knowledge, experience and qualifications" through formal
    training and credentials, actual experience, or a combination of
    the two.
    NOTE 2: Personnel employed by a TSA include individual personnel
    contractually engaged in performing functions in support of the
    TSA's time-stamping services.  Personnel who may be involved in
    monitoring the TSA services need not be TSA personnel.
 b) Security roles and responsibilities, as specified in the TSA's
    security policy, shall be documented in job descriptions.  Trusted
    roles, on which the security of the TSA's operation is dependent,
    shall be clearly identified.
 c) TSA personnel (both temporary and permanent) shall have job
    descriptions defined from the view point of separation of duties
    and least privilege, determining position sensitivity based on the
    duties and access levels, background screening and employee
    training and awareness.  Where appropriate, these shall
    differentiate between general functions and TSA specific
    functions.  These should include skills and experience
    requirements.
 d) Personnel shall exercise administrative and management procedures
    and processes that are in line with the TSA's information security
    management procedures (see section 7.4.1).
    NOTE 3: See ISO/IEC 17799 [ISO 17799] for guidance.
    The following additional controls shall be applied to time-
    stamping management:
 e) Managerial personnel shall be employed who possess:
  1. knowledge of time-stamping technology; and
  2. knowledge of digital signature technology; and

Pinkas, et al. Informational [Page 22] RFC 3628 Requirements for Time-Stamping Authorities November 2003

  1. knowledge of mechanisms for calibration or synchronization the

TSU clocks with UTC; and

  1. familiarity with security procedures for personnel with security

responsibilities; and

  1. experience with information security and risk assessment.
 f) All TSA personnel in trusted roles shall be free from conflict of
    interest that might prejudice the impartiality of the TSA
    operations.
 g) Trusted roles include roles that involve the following
    responsibilities:
  1. Security Officers: Overall responsibility for administering the

implementation of the security practices.

  1. System Administrators: Authorized to install, configure and

maintain the TSA trustworthy systems for time-stamping

       management.
  1. System Operators: Responsible for operating the TSA trustworthy

systems on a day-to-day basis. Authorized to perform system

       backup and recovery.
  1. System Auditors: Authorized to view archives and audit logs of

the TSA trustworthy systems.

 h) TSA personnel shall be formally appointed to trusted roles by
    senior management responsible for security.
 i) The TSA shall not appoint to trusted roles or management any
    person who is known to have a conviction for a serious crime or
    other offense which affects his/her suitability for the position.
    Personnel shall not have access to the trusted functions until any
    necessary checks are completed.
    NOTE 4: In some countries it may not be possible for TSA to obtain
    information on past convictions without the collaboration of the
    candidate employee.

7.4.4. Physical and Environmental Security

 The TSA shall ensure that physical access to critical services is
 controlled and physical risks to its assets minimized.

Pinkas, et al. Informational [Page 23] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 In particular (general):
 a) For both the time-stamping provision and the time-stamping
    management:
  1. physical access to facilities concerned with time-stamping

services shall be limited to properly authorized individuals;

  1. controls shall be implemented to avoid loss, damage or

compromise of assets and interruption to business activities;

       and
    -  controls shall be implemented to avoid compromise or theft of
       information and information processing facilities.
 b) Access controls shall be applied to the cryptographic module to
    meet the requirements of security of cryptographic modules as
    identified in clauses 7.2.1 and 7.2.2.
 c) The following additional controls shall be applied to time-
    stamping management:
  1. The time-stamping management facilities shall be operated in an

environment which physically protects the services from

       compromise through unauthorized access to systems or data.
  1. Physical protection shall be achieved through the creation of

clearly defined security perimeters (i.e., physical barriers)

       around the time-stamping management.  Any parts of the premises
       shared with other organizations shall be outside this
       perimeter.
  1. Physical and environmental security controls shall be

implemented to protect the facility that houses system

       resources, the system resources themselves, and the facilities
       used to support their operation.  The TSA's physical and
       environmental security policy for systems concerned with time-
       stamping management shall address as a minimum the physical
       access control, natural disaster protection, fire safety
       factors, failure of supporting utilities (e.g., power,
       telecommunications), structure collapse, plumbing leaks,
       protection against theft, breaking and entering, and disaster
       recovery.
  1. Controls shall be implemented to protect against equipment,

information, media and software relating to the time-stamping

       services being taken off-site without authorization.
    NOTE 1: See ISO/IEC 17799 [ISO 17799] for guidance on physical and
    environmental security.

Pinkas, et al. Informational [Page 24] RFC 3628 Requirements for Time-Stamping Authorities November 2003

    NOTE 2: Other functions may be supported within the same secured
    area provided that the access is limited to authorized personnel.

7.4.5. Operations Management

 The TSA shall ensure that the TSA system components are secure and
 correctly operated, with minimal risk of failure:
 In particular (general):
 a) The integrity of TSA system components and information shall be
    protected against viruses, malicious and unauthorized software.
 b) Incident reporting and response procedures shall be employed in
    such a way that damage from security incidents and malfunctions
    shall be minimized.
 c) Media used within the TSA trustworthy systems shall be securely
    handled to protect media from damage, theft, unauthorized access
    and obsolescence.
    NOTE 1: Every member of personnel with management responsibilities
    is responsible for planning and effectively implementing the
    time-stamp policy and associated practices as documented in the
    TSA practice statement.
 d) Procedures shall be established and implemented for all trusted
    and administrative roles that impact on the provision of time-
    stamping services.
 Media handling and security
 e) All media shall be handled securely in accordance with
    requirements of the information classification scheme (see section
    7.4.2).  Media containing sensitive data shall be securely
    disposed of when no longer required.
 System Planning
 f) Capacity demands shall be monitored and projections of future
    capacity requirements made to ensure that adequate processing
    power and storage are available.

Pinkas, et al. Informational [Page 25] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 Incident reporting and response
 g) The TSA shall act in a timely and coordinated manner in order to
    respond quickly to incidents and to limit the impact of breaches
    of security.  All incidents shall be reported as soon as possible
    after the incident.
 The following additional controls shall be applied to time-stamping
 management:
 Operations procedures and responsibilities
 h) TSA security operations shall be separated from other operations.
    NOTE 2: TSA security operations' responsibilities include:
  1. operational procedures and responsibilities;
  2. secure systems planning and acceptance;
  3. protection from malicious software;
  4. housekeeping;
  5. network management;
  6. active monitoring of audit journals, event analysis and

follow-up;

  1. media handling and security;
  2. data and software exchange.
 These operations shall be managed by TSA trusted personnel, but, may
 actually be performed by, non-specialist, operational personnel
 (under supervision), as defined within the appropriate security
 policy, and, roles and responsibility documents.

7.4.6. System Access Management

 The TSA shall ensure that TSA system access is limited to properly
 authorized individuals.
 In particular (general):
 a) Controls (e.g., firewalls) shall be implemented to protect the
    TSA's internal network domains from unauthorized access including
    access by subscribers and third parties.
    NOTE 1: Firewalls should also be configured to prevent all
    protocols and accesses not required for the operation of the TSA.

Pinkas, et al. Informational [Page 26] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 b) The TSA shall ensure effective administration of user (this
    includes operators, administrators and auditors) access to
    maintain system security, including user account management,
    auditing and timely modification or removal of access.
 c) The TSA shall ensure that access to information and application
    system functions is restricted in accordance with the access
    control policy and that the TSA system provides sufficient
    computer security controls for the separation of trusted roles
    identified in TSA's practices, including the separation of
    security administrator and operation functions.  Particularly, use
    of system utility programs is restricted and tightly controlled.
 d) TSA personnel shall be properly identified and authenticated
    before using critical applications related to time-stamping.
 e) TSA personnel shall be accountable for their activities, for
    example by retaining event logs (see section 7.4.10).
 The following additional controls shall be applied to time-stamping
 management:
 f) The TSA shall ensure that local network components (e.g., routers)
 are kept in a physically secure environment and that their
 configurations are periodically audited for compliance with the
 requirements specified by the TSA.
 g) Continuous monitoring and alarm facilities shall be provided to
 enable the TSA to detect, register and react in a timely manner upon
 any unauthorized and/or irregular attempts to access its resources.
 NOTE 2: This may use, for example, an intrusion detection system,
 access control monitoring and alarm facilities.

7.4.7. Trustworthy Systems Deployment and Maintenance

 The TSA shall use trustworthy systems and products that are protected
 against modification.
 NOTE: The risk analysis carried out on the TSA's services (see
 section 7.1.1) should identify its critical services requiring
 trustworthy systems and the levels of assurance required.

Pinkas, et al. Informational [Page 27] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 In particular:
 a) An analysis of security requirements shall be carried out at the
    design and requirements specification stage of any systems
    development project undertaken by the TSA or on behalf of the TSA
    to ensure that security is built into IT systems.
 b) Change control procedures shall be applied for releases,
    modifications and emergency software fixes of any operational
    software.

7.4.8. Compromise of TSA Services

 The TSA shall ensure in the case of events which affect the security
 of the TSA's services, including compromise of TSU's private signing
 keys or detected loss of calibration, that relevant information is
 made available to subscribers and relying parties.
 In particular:
 a) The TSA's disaster recovery plan shall address the compromise or
    suspected compromise of TSU's private signing keys or loss of
    calibration of a TSU clock, which may have affected time-stamp
    tokens which have been issued.
 b) In the case of a compromise, or suspected compromise or loss of
    calibration the TSA shall make available to all subscribers and
    relying parties a description of compromise that occurred.
 c) In the case of compromise to a TSU's operation (e.g., TSU key
    compromise), suspected compromise or loss of calibration the TSU
    shall not issue time-stamp tokens until steps are taken to recover
    from the compromise
 d) In case of major compromise of the TSA's operation or loss of
    calibration, wherever possible, the TSA shall make available to
    all subscribers and relying parties information which may be used
    to identify the time-stamp tokens which may have been affected,
    unless this breaches the privacy of the TSAs users or the security
    of the TSA services.
    NOTE:  In case the private key does become compromised, an audit
    trail of all tokens generated by the TSA may provide a means to
    discriminate between genuine and false backdated tokens.  Two
    time-stamp tokens from two different TSAs may be another way to
    address this issue.

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7.4.9. TSA Termination

 The TSA shall ensure that potential disruptions to subscribers and
 relying parties are minimized as a result of the cessation of the
 TSA's time-stamping services, and in particular ensure continued
 maintenance of information required to verify the correctness of
 time-stamp tokens.
 In particular:
 a) Before the TSA terminates its time-stamping services the following
    procedures shall be executed as a minimum:
  1. the TSA shall make available to all subscribers and relying

parties information concerning its termination;

  1. TSA shall terminate authorization of all subcontractors to act

on behalf of the TSA in carrying out any functions relating to

       the process of issuing time-stamp tokens;
  1. the TSA shall transfer obligations to a reliable party for

maintaining event log and audit archives (see section 7.4.10)

       necessary to demonstrate the correct operation of the TSA for a
       reasonable period;
  1. the TSA shall maintain or transfer to a reliable party its

obligations to make available its public key or its

       certificates to relying parties for a reasonable period;
  1. TSU private keys, including backup copies, shall be destroyed

in a manner such that the private keys cannot be retrieved.

 b) The TSA shall have an arrangement to cover the costs to fulfill
    these minimum requirements in case the TSA becomes bankrupt or for
    other reasons is unable to cover the costs by itself.
 c) The TSA shall state in its practices the provisions made for
    termination of service.  This shall include:
  1. notification of affected entities;
  2. transferring the TSA obligations to other parties.
 d) The TSA shall take steps to have the TSU's certificates revoked.

7.4.10. Compliance with Legal Requirements

 The TSA shall ensure compliance with legal requirements.

Pinkas, et al. Informational [Page 29] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 In particular:
 a) The TSA shall ensure that the requirements of the European data
    protection Directive [Dir 95/46/EC], as implemented through
    national legislation, are met.
 b) Appropriate technical and organizational measures shall be taken
    against unauthorized or unlawful processing of personal data and
    against accidental loss or destruction of, or damage to, personal
    data.
 c) The information contributed by users to the TSA shall be
    completely protected from disclosure unless with their agreement
    or by court order or other legal requirement.

7.4.11. Recording of Information Concerning Operation of Time-Stamping

       Services
 The TSA shall ensure that all relevant information concerning the
 operation of time-stamping services is recorded for a defined period
 of time, in particular for the purpose of providing evidence for the
 purposes of legal proceedings.
 In particular:
 General
 a) The specific events and data to be logged shall be documented by
    the TSA.
 b) The confidentiality and integrity of current and archived records
    concerning operation of time-stamping services shall be
    maintained.
 c) Records concerning the operation of time-stamping services shall
    be completely and confidentially archived in accordance with
    disclosed business practices.
 d) Records concerning the operation of time-stamping services shall
    be made available if required for the purposes of providing
    evidence of the correct operation of the time-stamping services
    for the purpose of legal proceedings.
 e) The precise time of significant TSA environmental, key management
    and clock synchronization events shall be recorded.
 f) Records concerning time-stamping services shall be held for a
    period of time after the expiration of the validity of the TSU's

Pinkas, et al. Informational [Page 30] RFC 3628 Requirements for Time-Stamping Authorities November 2003

    signing keys as appropriate for providing necessary legal evidence
    and as notified in the TSA disclosure statement (see section
    7.1.2).
 g) The events shall be logged in a way that they cannot be easily
    deleted or destroyed (except if reliably transferred to long-term
    media) within the period of time that they are required to be
    held.
    NOTE: This may be achieved, for example, through the use of
    write-only media, a record of each removable media used and the
    use of off-site backup.
 h) Any information recorded about subscribers shall be kept
    confidential except as where agreement is obtained from the
    subscriber for its wider publication.
 TSU key management
 i) Records concerning all events relating to the life-cycle of TSU
    keys shall be logged.
 j) Records concerning all events relating to the life-cycle of TSU
    certificates (if appropriate) shall be logged.
 Clock Synchronization
 k) Records concerning all events relating to synchronization of a
    TSU's clock to UTC shall be logged.  This shall include
    information concerning normal re-calibration or synchronization of
    clocks use in time-stamping.
 l) Records concerning all events relating to detection of loss of
    synchronization shall be logged.

7.5. Organizational

 The TSA shall ensure that its organization is reliable.
 In particular that:
 a) Policies and procedures under which the TSA operates shall be
    non-discriminatory.
 b) The TSA shall make its services accessible to all applicants whose
    activities fall within its declared field of operation and that
    agree to abide by their obligations as specified in the TSA
    disclosure statement.

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 c) The TSA is a legal entity according to national law.
 d) The TSA has a system or systems for quality and information
    security management appropriate for the time-stamping services it
    is providing.
 e) The TSA has adequate arrangements to cover liabilities arising
    from its operations and/or activities.
 f) It has the financial stability and resources required to operate
    in conformity with this policy.
    NOTE 1: This includes requirements for TSA termination identified
    in section 7.4.9.
 g) It employs a sufficient number of personnel having the necessary
    education, training, technical knowledge and experience relating
    to the type, range and volume of work necessary to provide time-
    stamping services.
    NOTE 2: Personnel employed by a TSA include individual personnel
    contractually engaged in performing functions in support of the
    TSA's time-stamping services.  Personnel who may be involved only
    in monitoring the TSA services need not be TSA personnel.
 h) It has policies and procedures for the resolution of complaints
    and disputes received from customers or other parties about the
    provisioning of the time-stamping services or any other related
    matters.
 i) It has a properly documented agreement and contractual
    relationship in place where the provisioning of services involves
    subcontracting, outsourcing or other third party arrangements.

8. Security Considerations

 When verifying time-stamp tokens it is necessary for the verifier to
 ensure that the TSU certificate is trusted and not revoked.  This
 means that the security is dependent upon the security of the CA that
 has issued the TSU certificate for both issuing the certificate and
 providing accurate revocation status information for that
 certificate.
 When a time-stamp is verified as valid at a given point of time, this
 does not mean that it will necessarily remain valid later on.  Every
 time, a time-stamp token is verified during the validity period of
 the TSU certificate, it must be verified again against the current
 revocation status information, since in case of compromise of a TSU

Pinkas, et al. Informational [Page 32] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 private key, all the time-stamp tokens generated by that TSU become
 invalid.  Annex C provides guidance about the long term verification
 of time-stamp tokens.
 In applying time-stamping to applications, consideration also needs
 to be given to the security of the application.  In particular, when
 applying time-stamps it is necessary to ensure that the integrity of
 data is maintained before the time-stamp is applied.  The requester
 ought to really make sure that the hash value included in the time-
 stamp token matches with the hash of the data.

9. Acknowledgments

 The development of this document was supported by ETSI and the
 European Commission.  Special thanks are due to Franco Ruggieri for
 his valuable inputs.

10. References

10.1. Normative References

 [RFC 2119]     Bradner, S. "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.
 [TF.460-5]     ITU-R Recommendation TF.460-5 (1997): Standard-
                frequency and time-signal emissions.
 [TF.536-1]     ITU-R Recommendation TF.536-1 (1998): Time-scale
                notations.
 [CWA 14167-2]  CEN Workshop Agreement 14167-2: Cryptographic Module
                for CSP Signing Operations - Protection Profile
                (MCSO-PP).
 [FIPS 140-1]   FIPS PUB 140-1 (1994): Security Requirements for
                Cryptographic Modules.
 [ISO 15408]    ISO/IEC 15408 (1999) (parts 1 to 3): Information
                technology - Security techniques and Evaluation
                criteria for IT security.

Pinkas, et al. Informational [Page 33] RFC 3628 Requirements for Time-Stamping Authorities November 2003

10.2. Informative References

 [CWA 14172]    CEN Workshop Agreement 14172: EESSI Conformity
                Assessment Guidance.
 [Dir 95/46/EC] Directive 95/46/EC of the European Parliament and of
                the Council of 24 October 1995 on the protection of
                individuals with regard to the processing of personal
                data and on the free movement of such data.
 [Dir 99/93/EC] Directive 1999/93/EC of the European Parliament and of
                the Council of 13 December 1999 on a Community
                framework for electronic signatures.
 [ISO 17799]    ISO/IEC 17799: Information technology Code of practice
                for information security management
 [RFC 3126]     Pinkas, D., Ross, J. and N. Pope, "Electronic
                Signature Formats for long term electronic
                signatures", RFC 3126, September 2001.
 [RFC 3161]     Adams, C., Cain, P., Pinkas, D. and R. Zuccherato,
                "Internet X.509 Public Key Infrastructure Time-Stamp
                Protocol (TSP)", RFC 3161, August 2001.
 [TS 101733]    ETSI Technical Specification 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.
 [TS 101861]    ETSI Technical Specification TS 101 861 V1.2.1.
                (2001-11).  Time stamping profile.  Note: copies of
                ETSI TS 101 861 can be freely downloaded from the ETSI
                web site www.etsi.org.
 [TS 102023]    ETSI Technical Specification TS 102 023.  Policy
                requirements for Time-Stamping Authorities.  Note:
                copies of ETSI TS 102 023 can be freely downloaded
                from the ETSI web site www.etsi.org.
 [X.208]        CCITT Recommendation X.208: Specification of Abstract
                Syntax Notation One (ASN.1), 1988.

Pinkas, et al. Informational [Page 34] RFC 3628 Requirements for Time-Stamping Authorities November 2003

Annex A (informative): Coordinated Universal Time

 Coordinated Universal Time (UTC) is the international time standard
 that became effective on January 1, 1972.  UTC has superseded
 Greenwich Mean Time (GMT), but in practice they are never more than 1
 second different.  Hence many people continue to refer to GMT when in
 fact they operate to UTC.
 Zero (0) hours UTC is midnight in Greenwich, England, which lies on
 the zero longitudinal meridian.  Universal time is based on a 24 hour
 clock, therefore, afternoon hours such as 4 pm UTC are expressed as
 16:00 UTC (sixteen hours, zero minutes).
 International Atomic Time (TAI) is calculated by the Bureau
 International des Poids et Mesures (BIPM) from the readings of more
 than 200 atomic clocks located in metrology institutes and
 observatories in more than 30 countries around the world.
 Information on TAI is made available every month in the BIPM Circular
 T (ftp://62.161.69.5/pub/tai/publication).  It is that TAI does not
 lose or gain with respect to an imaginary perfect clock by more than
 about one tenth of a microsecond (0.0000001 second) per year.
 Coordinated Universal Time (UTC): Time scale, based on the second, as
 defined and recommended by the International Telecommunications Radio
 Committee (ITU-R), and maintained by the Bureau International des
 Poids et Mesures (BIPM).  The maintenance by BIPM includes
 cooperation among various national laboratories around the world.
 The full definition of UTC is contained in ITU-R Recommendation
 TF.460-4.
 Atomic Time, with the unit of duration the Systeme International (SI)
 second defined as the duration of 9 192 631 770 cycles of radiation,
 corresponds to the transition between two hyperfine levels of the
 ground state of caesium 133.  TAI is the International Atomic Time
 scale, a statistical timescale based on a large number of atomic
 clocks.
 Universal Time (UT) is counted from 0 hours at midnight, with unit of
 duration the mean solar day, defined to be as uniform as possible
 despite variations in the rotation of the Earth.
  1. UT0 is the rotational time of a particular place of

observation. It is observed as the diurnal motion of stars or

       extraterrestrial radio sources.
  1. UT1 is computed by correcting UT0 for the effect of polar

motion on the longitude of the observing site. It varies from

       uniformity because of the irregularities in the Earth's

Pinkas, et al. Informational [Page 35] RFC 3628 Requirements for Time-Stamping Authorities November 2003

       rotation. UT1, is based on the somewhat irregular rotation of
       the Earth. Rotational irregularities usually result in a net
       decrease in the Earth's average rotational velocity, and
       ensuing lags of UT1 with respect to UTC.
 Coordinated Universal Time (UTC) is the basis for international
 time-keeping and follows TAI exactly except for an integral number of
 seconds, 32 in year 2001.  These leap seconds are inserted on the
 advice of the International Earth Rotation Service (IERS)
 (http://hpiers.obspm.fr/) to ensure that, having taken into account
 irregularities, the Sun is overhead within 0,9 seconds of 12:00:00
 UTC on the meridian of Greenwich.  UTC is thus the modern successor
 of Greenwich Mean Time, GMT, which was used when the unit of time was
 the mean solar day.
 Adjustments to the atomic, i.e., UTC, time scale consist of an
 occasional addition or deletion of one full second, which is called a
 leap second.  Twice yearly, during the last minute of the day of June
 30 and December 31, Universal Time, adjustments may be made to ensure
 that the accumulated difference between UTC and UT1 will not exceed
 0,9 s before the next scheduled adjustment.  Historically,
 adjustments, when necessary, have usually consisted of adding an
 extra second to the UTC time scale in order to allow the rotation of
 the Earth to "catch up". Therefore, the last minute of the UTC time
 scale, on the day when an adjustment is made, will have 61 seconds.
 Adjustments dates are typically announced several months in advance
 in IERS Bulletin C:
 ftp://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat.
 Coordinated Universal Time (UTC) differs thus from TAI by an integral
 number of seconds.  UTC is kept within 0,9 s of UT1 by the
 introduction of one-second steps to UTC, the "leap second".  To date
 these steps have always been positive.

Annex B (informative): Possible for Implementation Architectures

      and Time-Stamping Services

B.1. Managed Time-Stamping Service

 Some organizations may be willing to host one or more Time-Stamping
 Units in order to take advantage of both the proximity and the
 quality of the Time-Stamping Service, without being responsible for
 the installation, operation and management of these Time-Stamping
 Units.

Pinkas, et al. Informational [Page 36] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 This can be achieved by using units that are installed in the
 premises from the hosting organization and then remotely managed by a
 Time-Stamping Authority that takes the overall responsibility of the
 quality of the service delivered to the hosting organization.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+                                                                   +
+                      Time-Stamping Authority                      +
+_____________              _____________              _____________+

|+ | | | | +| |+| | | | Time - | | | |+| |+| Time - |←————| Stamping |————→| Time - |+| |+| Stamping | | Install. | Management | Install. | | Stamping |+| |+| Unit | | Management | | Management | | Unit |+| |+|| | |_| | ||+| |+ | | +| |+ | | +| |+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++| | Hosting | | Hosting | | Organization | | Organization | || ||

             Figure B.1: Managed Time-stamping Service
 The requirements for time-stamping services described in the current
 document includes requirements on both the time-stamping management
 and for the operation of the unit which issues the time-stamp tokens.
 The TSA, as identified in the time-stamp token, has the
 responsibility to ensure that these requirements are met (for example
 through contractual obligations).
 It should be clear that the hosting organization will generally want
 to be able to monitor the use of the service and, at a minimum, know
 whether the service is working or not and even be able to measure the
 performances of the service, e.g., the number of time-stamps
 generated during some period of time.  Such monitoring can be
 considered to be outside of TSA's time-stamping authority.
 Therefore the description of the management operation described in
 the main body of the document is not limitative.  Monitoring
 operations, if performed directly on the unit, may be permitted by
 the Time-Stamping service provider.

Pinkas, et al. Informational [Page 37] RFC 3628 Requirements for Time-Stamping Authorities November 2003

B.2. Selective Alternative Quality

 Some relying parties may be willing to take advantage of particular
 characteristics from a time-stamp token such as a specific signature
 algorithm and/or key length or a specific accuracy for the time
 contained in the time stamp token.  These parameters can be
 considered as specifying a "quality" for the time stamp token.
 Time stamp tokens with various qualities may be issued by different
 time-stamping units operated by the same or different TSAs.
 A particular time-stamping unit will only provide one combination of
 algorithm and key length (since a time-stamping unit is a set of
 hardware and software which is managed as a unit and has a single
 time-stamp token signing key).  In order to obtain different
 combinations of algorithm and key length, different time-stamping
 units shall be used.
 A particular time-stamping unit may provide a fixed accuracy for the
 time contained in the time stamp token or different accuracy if
 instructed to do so either by using a specific mode of access (e.g.,
 e-mail or http) or by using specific parameters in the request.

Annex C (informative): Long Term Verification of Time-Stamp Tokens

 Usually, a time-stamp token becomes unverifiable beyond the end of
 the validity period of the certificate from the TSU, because the CA
 that has issued the certificate does not warrant any more that it
 will publish revocation data, including data about revocations due to
 key compromises.  However, verification of a time-stamp token might
 still be performed beyond the end of the validity period of the
 certificate from the TSU, if, at the time of verification, it can be
 known that:
  1. the TSU private key has not been compromised at any time up to

the time that a relying part verifies a time-stamp token;

  1. the hash algorithms used in the time-stamp token exhibits no

collisions at the time of verification;

  1. the signature algorithm and signature key size under which the

time-stamp token has been signed is still beyond the reach of

      cryptographic attacks at the time of verification.
 If these conditions cannot be met, then the validity may be
 maintained by applying an additional time-stamp to protect the
 integrity of the previous one.

Pinkas, et al. Informational [Page 38] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 The present document does not specify the details of how such
 protection may be obtained.  For the time being, and until some
 enhancements are defined to support these features, the information
 may be obtained using-out-of bands means or alternatively in the
 context of closed environments.  As an example, should a CA guaranty
 to maintain the revocation status of TSU certificates after the end
 of its validity period, this would fulfill the first requirement.
 NOTE 1: An alternative to Time-Stamping is for a Trusted Service
 Provider to record a representation of a datum bound to a particular
 time in an audit trail, thus establishing evidence that the datum
 existed before that time.  This technique, which is called Time-
 Marking, can be a valuable alternative for checking the long term
 validity of signatures.
 NOTE 2: The TSA or other trusted third party service provider may
 support the verification of time-stamp tokens.

Annex D (informative): Model TSA Disclosure Statement Structure.

 The TSA disclosure statement contains a section for each defined
 statement type.  Each section of a TSA disclosure statement contains
 a descriptive statement, which MAY include hyperlinks to the relevant
 certificate policy/certification practice statement sections.
 D.1.  STATEMENT TYPE: Entire agreement
       STATEMENT DESCRIPTION: A statement indicating that the
       disclosure statement is not the entire agreement, but only a
       part of it.
 D.2.  STATEMENT TYPE: TSA contact info
       STATEMENT DESCRIPTION: The name, location and relevant contact
       information for the TSA.
 D.3.  STATEMENT TYPE: time-stamp token types and usage
       STATEMENT DESCRIPTION: A description of each class/type of
       time-stamp tokens issued by the TSA (in accordance with each
       time-stamp policy) and any restrictions on time-stamp usage.
       SPECIFIC REQUIREMENT: Indication of the policy being applied,
       including the contexts for which the time-stamp token can be
       used (e.g., only for use with electronic signatures), the
       hashing algorithms, the expected life time of the time-stamp
       token signature, any limitations on the use of the time-stamp
       token and information on how to verify the time-stamp token.

Pinkas, et al. Informational [Page 39] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 D.4.  STATEMENT TYPE: Reliance limits.
       STATEMENT DESCRIPTION: reliance limits, if any.
       SPECIFIC REQUIREMENT: Indication of the accuracy of the time in
       the time-stamp token, and the period of time for which TSA
       event logs (see section 7.4.10) are maintained (and hence are
       available to provide supporting evidence).
 D.5.  STATEMENT TYPE: Obligations of subscribers.
       STATEMENT DESCRIPTION: The description of, or reference to, the
       critical subscriber obligations.
       SPECIFIC REQUIREMENT: No specific requirements identified in
       the current document.  Where applicable the TSA may specify
       additional obligations.
 D.6.  STATEMENT TYPE: TSU public key status checking obligations of
       relying parties.
       STATEMENT DESCRIPTION: The extent to which relying parties are
       obligated to check the TSU public key status, and references to
       further explanation.
       SPECIFIC REQUIREMENT: Information on how to validate the TSU
       public key status, including requirements to check the
       revocation status of TSU public key, such that the relying
       party is considered to "reasonably rely" on the time-stamp
       token (see section 6.3).
 D.7.  STATEMENT TYPE: Limited warranty and disclaimer/Limitation of
       liability.
       STATEMENT DESCRIPTION: Summary of the warranty, disclaimers,
       limitations of liability and any applicable warranty or
       insurance programs
       SPECIFIC REQUIREMENT: Limitations of liability (see section
       6.4).
 D.8.  STATEMENT TYPE: Applicable agreements and practice statement.
       STATEMENT DESCRIPTION: Identification and references to
       applicable agreements, practice statement, time-stamp policy
       and other relevant documents.

Pinkas, et al. Informational [Page 40] RFC 3628 Requirements for Time-Stamping Authorities November 2003

 D.9.  STATEMENT TYPE: Privacy policy.
       STATEMENT DESCRIPTION: A description of and reference to the
       applicable privacy policy.
       SPECIFIC REQUIREMENT: Note: TSA's under this policy are
       required to comply with the requirements of Data Protection
       Legislation.
 D.10. STATEMENT TYPE: Refund policy
       STATEMENT DESCRIPTION: A description of and reference to the
       applicable refund policy.
 D.11. STATEMENT TYPE: Applicable law, complaints and dispute
       resolution mechanisms.
       STATEMENT DESCRIPTION: Statement of the choice of law,
       complaints procedure and dispute resolution mechanisms.
       SPECIFIC REQUIREMENT: The procedures for complaints and dispute
       settlements.  The applicable legal system.
 D.12. STATEMENT TYPE: TSA and repository licenses, trust marks, and
       audit.
       STATEMENT DESCRIPTION: Summary of any governmental licenses,
       seal programs; and a description of the audit process and if
       applicable the audit firm.
       SPECIFIC REQUIREMENT: If the TSA has been assessed to be
       conformant with the identified time-stamp policy, and if so
       through which independent party.

Pinkas, et al. Informational [Page 41] RFC 3628 Requirements for Time-Stamping Authorities November 2003

Authors' Addresses

 Denis Pinkas
 Bull
 Rue Jean Jaures,
 78340 Les Clayes CEDEX
 FRANCE
 EMail: Denis.Pinkas@bull.net
 Nick Pope
 Security & Standards
 192 Moulsham Street
 Chelmsford, Essex
 CM2 0LG
 United Kingdom
 EMail: pope@secstan.com
 John Ross
 Security & Standards
 192 Moulsham Street
 Chelmsford, Essex
 CM2 0LG
 United Kingdom
 EMail: ross@secstan.com
 This Informational RFC has been produced in ETSI ESI.
 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
 Claire d'Esclercs
 ETSI
 650 Route des Lucioles
 F-06921 Sophia Antipolis, Cedex
 FRANCE
 EMail: claire.desclercs@etsi.org

Pinkas, et al. Informational [Page 42] RFC 3628 Requirements for Time-Stamping Authorities November 2003

Full Copyright Statement

 Copyright (C) The Internet Society (2003).  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 assignees.
 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 43]

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