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rfc:rfc3854

Network Working Group P. Hoffman Request for Comments: 3854 IMC Category: Standards Track C. Bonatti

                                                                  IECA
                                                              A. Eggen
                                                                   FFI
                                                             July 2004
   Securing X.400 Content with Secure/Multipurpose Internet Mail
                        Extensions (S/MIME)

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2004).

Abstract

 This document describes a protocol for adding cryptographic signature
 and encryption services to X.400 content with Secure/Multipurpose
 Internet Mail Extensions (S/MIME).

1. Introduction

 The techniques described in the Cryptographic Message Syntax [CMS]
 specification are general enough to support many different content
 types.  The [CMS] specification thus provides many options for
 providing different security mechanisms.  In order to ensure
 interoperability of systems within the X.400 community, it is
 necessary to specify the use of CMS features to protect X.400 content
 (called "CMS-X.400" in this document).

1.1. Specification Overview

 This document is intended to be similar to the S/MIME Version 3.1
 Message Specification [MSG] except that it is tailored to the
 requirements of X.400 content rather than Multipurpose Internet Mail
 Extensions (MIME).

Hoffman, et al. Standards Track [Page 1] RFC 3854 Securing X.400 with S/MIME July 2004

 This document defines how to create an X.400 content type that has
 been cryptographically enhanced according to [CMS].  In order to
 create S/MIME messages carrying X.400 content, an S/MIME agent has to
 follow specifications in this document, as well as the specifications
 listed in [CMS].  This memo also defines new parameter values for the
 application/pkcs7-mime MIME type that can be used to transport those
 body parts.
 Throughout this document, there are requirements and recommendations
 made for how receiving agents handle incoming messages.  There are
 separate requirements and recommendations for how sending agents
 create outgoing messages.  In general, the best strategy is to "be
 liberal in what you receive and conservative in what you send".  Most
 of the requirements are placed on the handling of incoming messages
 while the recommendations are mostly on the creation of outgoing
 messages.
 This document does not address transport of CMS-X.400 content.  It is
 assumed that CMS-X.400 content would be transported by Internet mail
 systems, X.400, or other suitable transport.
 This document describes applying security services to the content of
 entire X.400 messages, which may or may not be IPMS messages.  These
 objects can be carried by several means, including SMTP-based mail
 and X.400 mail.  Note that cooperating S/MIME agents must support
 common forms of message content in order to achieve interoperability.
 If the CMS objects are sent as parts of an RFC 822 message, a
 standard MIXER gateway [MIXER] will most likely choose to encapsulate
 the message.  This is not likely to be a format that is usable by an
 X.400 recipient.  MIXER is specifically focused on translation
 between X.420 Interpersonal Messages and non-secure RFC822/MIME
 messages.  The discussion of security-related body parts in sections
 7.3 and 7.4 of [BODYMAP] is relevant to CMS messages.
 Definition of gateway services to support relay of CMS object between
 X.400 and SMTP environments is beyond the scope of this document.

1.2. Terminology

 The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED",
 and "MAY" in this document are to be interpreted as described in BCP
 14, RFC 2119 [MUSTSHOULD].

Hoffman, et al. Standards Track [Page 2] RFC 3854 Securing X.400 with S/MIME July 2004

1.3. Definitions

 For the purposes of this document, the following definitions apply.
 ASN.1:             Abstract Syntax Notation One, as defined in
                    ISO/IEC 8824.
 BER:               Basic Encoding Rules for ASN.1, as defined in
                    ISO/IEC 8825-1.
 Certificate:       A type that binds an entity's distinguished name
                    to a public key with a digital signature.
 DER:               Distinguished Encoding Rules for ASN.1, as defined
                    in ISO/IEC 8825-1.
 7-bit data:        Text data with lines less than 998 characters
                    long, where none of the characters have the 8th
                    bit set, and there are no NULL characters.  <CR>
                    and <LF> occur only as part of a <CR><LF> end of
                    line delimiter.
 8-bit data:        Text data with lines less than 998 characters, and
                    where none of the characters are NULL characters.
                    <CR> and <LF> occur only as part of a <CR><LF> end
                    of line delimiter.
 Binary data:       Arbitrary data.
 Transfer Encoding: A reversible transformation made on data so 8-bit
                    or binary data may be sent via a channel that only
                    transmits 7-bit data.
 Receiving agent:   Software that interprets and processes S/MIME CMS
                    objects.
 Sending agent:     Software that creates S/MIME CMS objects.
 S/MIME agent:      User software that is a receiving agent, a sending
                    agent, or both.

1.4. Compatibility with Prior Practice of S/MIME

 There are believed to be no existing X.400 implementations that
 support S/MIME version 2.  Further, signed interoperability between
 X.400 and MIME systems that support S/MIME version 2 is not believed

Hoffman, et al. Standards Track [Page 3] RFC 3854 Securing X.400 with S/MIME July 2004

 to be easily achievable.  Therefore backward compatibility with
 S/MIME version 2 is not considered to be a requirement for this
 document.
 It is a goal of this document to, if possible, maintain backward
 compatibility with existing X.400 implementations that employ S/MIME
 v3.1 wrappers.

2. CMS Options

 CMS allows for a wide variety of options in content and algorithm
 support.  This section puts forth a number of support requirements
 and recommendations in order to achieve a base level of
 interoperability among all CMS-X.400 implementations.  [CMS] provides
 additional details regarding the use of the cryptographic algorithms.

2.1. DigestAlgorithmIdentifier

 Sending and receiving agents MUST support SHA-1 [CMSALG].

2.2. SignatureAlgorithmIdentifier

 Receiving agents MUST support id-dsa-with-sha1 defined in [CMSALG].
 The algorithm parameters MUST be absent (not encoded as NULL).
 Receiving agents MUST support rsaEncryption, defined in [CMSALG].
 Sending agents MUST support either id-dsa-with-sha1 or rsaEncryption.

2.3. KeyEncryptionAlgorithmIdentifier

 Sending and receiving agents MUST support rsaEncryption, defined in
 [CMSALG].
 Sending and receiving agents SHOULD support Diffie-Hellman defined in
 [CMSALG].

2.4. General Syntax

 The general syntax of CMS objects consist of an instance of the
 ContentInfo structure containing one of several defined CMS content
 types.  CMS defines multiple content types.  Of these, only the
 SignedData and EnvelopedData content types are used for CMS-X.400.

2.4.1. SignedData Content Type

 Sending agents MUST use the signedData content type to apply a
 digital signature to a message or, in a degenerate case where there
 is no signature information, to convey certificates.

Hoffman, et al. Standards Track [Page 4] RFC 3854 Securing X.400 with S/MIME July 2004

2.4.2. EnvelopedData Content Type

 Senders MUST use the envelopedData content type to apply privacy
 protection to a message.  A sender needs to have access to a public
 key for each intended message recipient to use this service.  This
 content type does not provide authentication.

2.5. Attribute SignerInfo Type

 The SignerInfo type allows the inclusion of unsigned and signed
 attributes to be included along with a signature.
 Receiving agents MUST be able to handle zero or one instance of each
 of the signed attributes listed here.  Sending agents SHOULD generate
 one instance of each of the following signed attributes in each CMS-
 X400 message:
  1. signingTime
  2. sMIMECapabilities
  3. sMIMEEncryptionKeyPreference
 Requirements for processing of these attributes MUST be in accordance
 with the S/MIME Message Specification [MSG].  Handling of the
 signingTime attribute MUST comply with clause 2.5.1 of [MSG].
 Handling of the sMIMECapabilities attribute MUST comply with clause
 2.5.2 of [MSG].  Handling of the sMIMEEncryptionKeyPreference
 attribute MUST comply with clause 2.5.3 of [MSG].
 Further, receiving agents SHOULD be able to handle zero or one
 instance in the signed attributes of the signingCertificate attribute
 [ESS].
 Sending agents SHOULD generate one instance of the signingCertificate
 signed attribute in each CMS-X400 message.
 Additional attributes and values for these attributes may be defined
 in the future.  Receiving agents SHOULD handle attributes or values
 that they do not recognize in a graceful manner.
 Sending agents that include signed attributes that are not listed
 here SHOULD display those attributes to the user, so that the user is
 aware of all of the data being signed.

Hoffman, et al. Standards Track [Page 5] RFC 3854 Securing X.400 with S/MIME July 2004

2.6. ContentEncryptionAlgorithmIdentifier

 Sending and receiving agents MUST support encryption and decryption
 with DES EDE3 CBC, hereinafter called "tripleDES" [CMSALG].  Sending
 and receiving agents SHOULD support encryption and decryption with
 AES [CMSAES] at a key size of 128, 192 and 256 bits.

3. Creating S/MIME Messages

 This section describes the S/MIME message formats and how they can be
 used to secure X.400 contents.  The S/MIME messages are a combination
 of X.400 contents and CMS objects (i.e., a ContentInfo structure
 containing one of the CMS-defined content types).  The X.400 content
 and other data, such as certificates and algorithm identifiers, are
 given to CMS processing facilities which produces a CMS object.  This
 document also describes how nested, secured S/MIME messages should be
 formatted when encapsulating an X.400 content, and provides an
 example of how a triple-wrapped S/MIME message over X.400 content
 should be created if backwards compatibility with S/MIME version 2 is
 of no concern.
 S/MIME provides one format for enveloped-only data, several formats
 for signed-only data, and several formats for signed and enveloped
 data.  The different formats are required to accommodate several
 environments, in particular for signed messages.  Only one of these
 signed formats is applicable to X.400.
 Note that canonicalization is not required for X.400 content because
 it is a binary rather than text encoding, and only the "embedded"
 content version is used.  These dramatically simplify the description
 of S/MIME productions.
 The reader of this section is expected to understand X.400 as
 described in [X.400] and S/MIME as described in [CMS] and [ESS].

3.1. The X.400 Message Structure

 This section reviews the X.400 message format.  An X.400 message has
 two parts, the envelope and the content, as described in X.402
 [X.400]:
 Envelope --  An information object whose composition varies from one
 transmittal step to another and that variously identifies the
 message's originator and potential recipients, documents its previous
 conveyance and directs its subsequent conveyance by the Message
 Transfer System (MTS), and characterizes its content.

Hoffman, et al. Standards Track [Page 6] RFC 3854 Securing X.400 with S/MIME July 2004

 Content -- The content is the piece of information that the
 originating User Agent wants to be delivered to one or more
 recipients.  The MTS neither examines nor modifies the content,
 except for conversion, during its conveyance of the message.  MTS
 conversion is not applicable to the scenario of this document because
 such conversion is incompatible with CMS protection mechanisms.
 One piece of information borne by the envelope identifies the type of
 the content.  The content type is an identifier (an ASN.1 OID or
 Integer) that denotes the syntax and semantics of the content
 overall.  This identifier enables the MTS to determine the message's
 deliverability to particular users, and enables User Agents and
 Message Stores to interpret and process the content.
 Another piece of information borne by the envelope identifies the
 types of encoded information represented in the content.  An encoded
 information type (EIT) is an identifier (an ASN.1 Object Identifier
 or Integer) that denotes the medium and format (e.g., IA5 text or
 Group 3 facsimile) of individual portions of the content.  It further
 enables the MTS to determine the message's deliverability to
 particular users, and to identify opportunities for it to make the
 message deliverable by converting a portion of the content from one
 EIT to another.
 This document describes how S/MIME CMS is used to secure the content
 part of X.400 messages.

3.2. Creating a Signed-only Message with X.400 Content

 The SignedData format as described in the Cryptographic Message
 Syntax [CMS] MUST be used for signing of X.400 contents.
 The X.400 content to be protected MUST be placed in the SignedData
 encapContentInfo eContent field.  Note that this X.400 content SHOULD
 maintain the encoding defined by the content type, but SHOULD NOT be
 MIME wrapped.  The object identifier for the content type of the
 protected X.400 content MUST be placed in the SignedData
 encapContentInfo eContentType field.
 The signedData object is encapsulated by a ContentInfo SEQUENCE with
 a contentType of id-signedData.
 Note that if SMTP [SMTP] is used to transport the resulting signed-
 only message then the optional MIME encoding SHOULD be used.  If
 binary transports such as X.400 are used then the optional MIME
 encoding SHOULD NOT be used.

Hoffman, et al. Standards Track [Page 7] RFC 3854 Securing X.400 with S/MIME July 2004

 There are many reasons for this requirement.  An outer MIME wrapper
 should not be used in X.400.  Further, there are places where X.400
 systems will interact with SMTP/MIME systems where the outer MIME
 wrapper might be necessary.  Because this wrapping is outside the
 security wrappers, any gateway system that might bridge the gap
 between the two systems will be smart enough to apply or remove the
 outer MIME wrapper as appropriate.

3.2.1. MIME Wrapping to Dynamically Support 7-bit Transport

 The signedData object MAY optionally be wrapped in MIME.  This allows
 the system to support 7-bit transport when required.  This outer MIME
 wrapper MAY be dynamically added or removed throughout the delivery
 path since it is outside the signature and encryption wrappers.  In
 this case the application/pkcs7-mime type as defined in S/MIME
 Version 3.1 Message Specification [MSG] SHOULD be used with the
 following parameters:
 Content-Type: application/pkcs7-mime; smime-type=signed-x400
 Content-Transfer-Encoding: base64
 If the application/pkcs7-mime MIME type is used to support 7-bit
 transport, the steps to create this format are:
 Step 1.  The X.400 content to be signed is ASN.1 encoded.
 Step 2.  The ASN.1 encoded X.400 content and other required data is
 processed into a CMS object of type SignedData.  The SignedData
 structure is encapsulated by a ContentInfo SEQUENCE with a
 contentType of id-signedData.
 Step 3.  The CMS object is inserted into an application/pkcs7-mime
 MIME entity.
 The smime-type parameter for messages using application/pkcs7-mime
 with SignedData is "signed-x400" as defined in [TRANSPORT].

3.3. Creating an Enveloped-only Message with X.400 Content

 This section describes the format for enveloping an X.400 content
 without signing it.  It is important to note that sending enveloped
 but not signed messages does not provide for data integrity.  It is
 possible to replace ciphertext in such a way that the processed
 message will still be valid, but the meaning is altered.
 The EnvelopedData format as described in [CMS] is used for
 confidentiality of the X.400 contents.

Hoffman, et al. Standards Track [Page 8] RFC 3854 Securing X.400 with S/MIME July 2004

 The X.400 content to be protected MUST be placed in the EnvelopedData
 encryptedContentInfo encryptedContent field.  Note that this X.400
 content SHOULD maintain the encoding defined by the content type, but
 SHOULD NOT be MIME wrapped.  The object identifier for content type
 of the protected X.400 content MUST be placed in the EnvelopedData
 encryptedContentInfo contentType field.
 The envelopedData object is encapsulated by a ContentInfo SEQUENCE
 with a contentType of id-envelopedData.
 Note that if SMTP is used to transport the resulting enveloped-only
 message then the optional MIME encoding SHOULD be used.  If other
 transport (e.g., X.400) that is optimized for binary content is used
 then the optional MIME encoding SHOULD NOT be used.

3.3.1. MIME Wrapping to Dynamically Support 7-bits Transport

 The envelopedData object MAY optionally be wrapped in MIME.  This
 allows the system to support 7-bit transport when required.  This
 outer MIME wrapper MAY be dynamically added or removed throughout the
 delivery path since it is outside the signature and encryption
 wrappers.  In this case, the application/pkcs7-mime type as defined
 in S/MIME Version 3.1 Message Specification [MSG] SHOULD be used with
 the following parameters:
 Content-Type: application/pkcs7-mime; smime-type=enveloped-x400
 Content-Transfer-Encoding: base64
 If the application/pkcs7-mime MIME type is used to support 7-bit
 transport, the steps to create this format are:
 Step 1.  The X.400 content to be enveloped is ASN.1 encoded.
 Step 2.  The ASN.1 encoded X.400 content and other required data is
 processed into a CMS object of type EnvelopedData.  In addition to
 encrypting a copy of the content-encryption key for each recipient, a
 copy of the content encryption key SHOULD be encrypted for the
 originator and included in the EnvelopedData (see [CMS] Section 6).
 The EnvelopedData structure is encapsulated by a ContentInfo SEQUENCE
 with a contentType of id-envelopedData.
 Step 3.  The CMS object is inserted into an application/pkcs7-mime
 MIME entity to allow for 7-bit transport.
 If the application/pkcs7-mime MIME entity is used, the smime-type
 parameter for enveloped-only messages is "enveloped-x400" as defined
 in [TRANSPORT].

Hoffman, et al. Standards Track [Page 9] RFC 3854 Securing X.400 with S/MIME July 2004

3.4. Nested CMS Structures

 To achieve signing and enveloping, any of the signed-only and
 encrypted-only CMS objects may be nested.
 When nesting is used, backwards compatibility with S/MIME version 2
 requires that each layer of the nested message are identified with
 the OID id-data, and when id-data is used a MIME wrapper is required.
 This can potentially lead to an enormous amount of overhead and
 should be avoided.  Because S/MIME version 2 compatibility is of no
 concern, implementations SHOULD directly encode the encapsulated
 object as the eContent of the current structure.
 MIME wrapping to support 7-bit transport is optional and need only be
 used around the outermost CMS structure.  In this case, the
 application/pkcs7 content type MUST be used.
 An S/MIME implementation MUST be able to receive and process
 arbitrarily nested CMS structures within reasonable resource limits
 of the recipient computer.

3.4.1. Creating a Triple Wrapped Message With an X.400 Content

 The Enhanced Security Services for S/MIME [ESS] document provides
 examples of how nested, secured S/MIME messages are formatted.  ESS
 provides an example of how a triple-wrapped S/MIME message is
 formatted using application/pkcs7-mime for the signatures.
 This section explains how an X.400 content may be conveyed within a
 Triple Wrapped Message because S/MIME version 2 compatibility is of
 no concern:
 Step 1.  Start with the X.400 content (called the "original
 content").  The X.400 content MUST be ASN.1 encoded, but SHOULD NOT
 be MIME wrapped.
 Step 2.  Place the ASN.1 encoded X.400 content to be protected in the
 SignedData encapContentInfo eContent field.  Add any attributes that
 are to be signed.
 Step 3.  Sign the result of step 2 (the original content).  The
 SignedData encapContentInfo eContentType MUST contain the object
 identifier of the X.400 content.
 Step 4.  Encrypt the result of step 3 as a single block.  The
 EnvelopedData encryptedContentInfo contentType MUST be set to id-
 signedData.  This is called the "encrypted body".

Hoffman, et al. Standards Track [Page 10] RFC 3854 Securing X.400 with S/MIME July 2004

 Step 5.  Using the same logic as in step 2 and 3 above, sign the
 result of step 4 (the encrypted body) as a single block.  The
 SignedData encapContentInfo eContentType MUST be set to id-
 envelopedData.  The outer SignedData structure is encapsulated by a
 ContentInfo SEQUENCE with a contentType of id-signedData.
 Step 6.  The resulting message is called the "outer signature", and
 is also the triple wrapped message.
 MIME wrapping to support 7-bit transport is optional and MUST only be
 used around the outermost CMS structure.  In this case, the
 application/pkcs7-mime content type MUST be used.  The smime-type in
 the case of adding a MIME wrapper MUST be consistent with that
 appropriate to the innermost protection layer.
 In some instances, an smime-type will be created that only reflects
 one security service (such as certs-only, which applies only to
 signed-only messages).  However, as new layers are wrapped, this
 smime-type SHOULD be propagated upwards.  Thus if a certs-only
 message were to be encrypted, or wrapped in a new SignedData
 structure, the smime-type of certs-only should be propagated up to
 the next MIME wrapper.  In other words, the innermost type is
 reflected outwards.

3.5. Carrying Plaintext X.400 Content in SMTP

 While the objectives of this document focus on protecting X.400
 content with CMS wrappers, it is a reality that users do not
 generally send all message using security.  It therefore stands to
 reason that a means to carry non-secured X.400 content over the
 chosen transport system must be seamlessly provided.  While
 transporting X.400 content in an X.400 system is trivial, carrying
 X.400 content in SMTP requires additional definition.
 Content-Type: application/x400-content; content-type = 1*DIGIT *( "."
 1*DIGIT)
 where the content-type parameter value is either a single integer
 (for a built-in content-type) or an OID in dotted notation (for an
 extended content-type).

Hoffman, et al. Standards Track [Page 11] RFC 3854 Securing X.400 with S/MIME July 2004

4. Use of Certificates

4.1. Certificate Enrollment

 S/MIME v3.1 does not specify how to get a certificate from a
 certificate authority, but instead mandates that every sending agent
 already has a certificate.  The PKIX Working Group has, at the time
 of this writing, produced two separate standards for certificate
 enrollment: CMP (RFC 2510) and CMC (RFC 2792).

4.2. Certificate Processing

 A receiving agent MUST provide some certificate retrieval mechanism
 in order to gain access to certificates for recipients of digital
 envelopes.  This document does not cover how S/MIME agents handle
 certificates, only what they do after a certificate has been
 validated or rejected.  S/MIME certification issues are covered in
 [CERT31].
 At a minimum, for initial S/MIME deployment, a user agent could
 automatically generate a message to an intended recipient requesting
 that recipient's certificate in a signed return message.  Receiving
 and sending agents SHOULD also provide a mechanism to allow a user to
 "store and protect" certificates for correspondents in such a way so
 as to guarantee their later retrieval.

4.3. Certificate Name Use for X.400 Content

 End-entity certificates used in the context of this document MAY
 contain an X.400 address as described in [X.400].  The address must
 be in the form of an "ORAddress".  The X.400 address SHOULD be in the
 subjectAltName extension, and SHOULD NOT be in the subject
 distinguished name.
 Sending agents SHOULD make the originator address in the X.400
 content (e.g., the "originator" field in P22) match an X.400 address
 in the signer's certificate.
 Receiving agents MUST recognize X.400 addresses in the subjectAltName
 field.
 Receiving agents SHOULD check that the originator address in the
 X.400 content matches an X.400 address in the signer's certificate,
 if X.400 addresses are present in the certificate and an originator
 address is available in the content.  A receiving agent SHOULD
 provide some explicit alternate processing of the message if this

Hoffman, et al. Standards Track [Page 12] RFC 3854 Securing X.400 with S/MIME July 2004

 comparison fails, which may be to display a message that shows the
 recipient the addresses in the certificate or other certificate
 details.
 The subject alternative name extension is used in S/MIME as the
 preferred means to convey the X.400 address(es) that correspond to
 the entity for this certificate.  Any X.400 addresses present MUST be
 encoded using the x400Address CHOICE of the GeneralName type.  Since
 the SubjectAltName type is a SEQUENCE OF GeneralName, multiple X.400
 addresses MAY be present.

5. Security Considerations

 This specification introduces no new security concerns to the CMS or
 S/MIME models.  Security issues are identified in section 5 of [MSG],
 section 6 of [ESS] and the Security Considerations section of [CMS].

6. References

6.1. Normative References

 [CERT31]     Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
              Extensions (S/MIME) Version 3.1 Certificate Handling",
              RFC 3850, July 2004.
 [CMS]        Housley, R., "Cryptographic Message Syntax (CMS)", RFC
              3852, July 2004.
 [CMSAES]     Schaad, J., "Use of the AES Encryption Algorithm in
              CMS", RFC 3565, July 2003.
 [CMSALG]     Housley, R., "Cryptographic Message Syntax (CMS)
              Algorithms", RFC 3370, August 2002.
 [ESS]        Hoffman, P., Editor "Enhanced Security Services for
              S/MIME", RFC 2634, June 1999.
 [MSG]        Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
              Extensions (S/MIME) Version 3.1 Message Specification",
              RFC 3851, July 2004.
 [MUSTSHOULD] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [TRANSPORT]  Hoffman, P. and C. Bonatti, "Transporting
              Secure/Multipurpose Internet Mail Extensions (S/MIME)
              Objects in X.400", RFC 3855, July 2004.

Hoffman, et al. Standards Track [Page 13] RFC 3854 Securing X.400 with S/MIME July 2004

 [X.400]      ITU-T X.400 Series of Recommendations, Information
              technology - Message Handling Systems (MHS).  X.400:
              System and Service Overview; X.402: Overall
              Architecture; X.411: Message Transfer System: Abstract
              Service Definition and Procedures; X.420: Interpersonal
              Messaging System; 1996.

6.2. Informative References

 [BODYMAP]    Alvestrand, H., Ed., "Mapping between X.400 and RFC-
              822/MIME Message Bodies", RFC 2157, January 1998.
 [MIXER]      Kille, S., Ed., "MIXER (Mime Internet X.400 Enhanced
              Relay): Mapping between X.400 and RFC 822/MIME", RFC
              2156, January 1998.
 [SMTP]       Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
              April, 2001.

7. Editors' Addresses

 Paul Hoffman
 Internet Mail Consortium
 127 Segre Place
 Santa Cruz, CA  95060  USA
 EMail: phoffman@imc.org
 Chris Bonatti
 IECA, Inc.
 15309 Turkey Foot Road
 Darnestown, MD  20878-3640  USA
 EMail: bonattic@ieca.com
 Anders Eggen
 Forsvarets Forskningsinstitutt
 Postboks 25
 2027 Kjeller, Norway
 EMail: anders.eggen@ffi.no

Hoffman, et al. Standards Track [Page 14] RFC 3854 Securing X.400 with S/MIME July 2004

8. Full Copyright Statement

 Copyright (C) The Internet Society (2004).  This document is subject
 to the rights, licenses and restrictions contained in BCP 78, and
 except as set forth therein, the authors retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at ietf-
 ipr@ietf.org.

Acknowledgement

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

Hoffman, et al. Standards Track [Page 15]

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