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Network Working Group                                         P. HoffmanRequest for Comments: 3855                                           IMCCategory: Standards Track                                     C. Bonatti                                                                    IECA                                                               July 2004Transporting Secure/Multipurpose Internet MailExtensions (S/MIME) Objects in X.400Status 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 protocol options for conveying objects that   have been protected using the Cryptographic Message Syntax (CMS) and   Secure/Multipurpose Internet Mail Extensions (S/MIME) version 3.1   over an X.400 message transfer system.1. Introduction   The techniques described in the Cryptographic Message Syntax [CMS]   specification and message specifications can reasonably be   transported via a variety of electronic mail systems.  This   specification defines the options and values necessary to enable   interoperable transport of S/MIME messages over an X.400 system.   This document describes a mechanism for using CMS objects as the   message content of X.400 messages in a native X.400 environment.   This means that gateways or other functions that expect to deal with   IPMS, such as those specified in [MIXER] and [BODYMAP], cannot do   anything with these messages.  Note that cooperating S/MIME agents   must support common forms of message content in order to achieve   interoperability.   Definition of gateway services to support relay of CMS object between   X.400 and SMTP environments is beyond the scope of this document.Hoffman & Bonatti           Standards Track                     [Page 1]

RFC 3855          Transporting S/MIME Objects in X.400         July 20041.1.  Terminology   The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED",   and "MAY" in this document are to be interpreted as described inBCP14,RFC 2119 [MUSTSHOULD].1.2.  Definitions   For the purposes of this document, the following definitions apply.   ASN.1: Abstract Syntax Notation One, as defined in ISO/IEC 8824.   Object Identifier (OID): A globally unique identifier value   consisting of a sequence of integer values assigned through   distributed registration as specified by ISO/IEC 8824.   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.1.3.  Compatibility with Existing S/MIME Implementations   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.  S/MIME Packaging2.1.  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.   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.Hoffman & Bonatti           Standards Track                     [Page 2]

RFC 3855          Transporting S/MIME Objects in X.400         July 2004   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.   Some X.400 content types further refine the structure of content as a   set of heading elements and body parts.  An example of this is the   Interpersonal Messaging System (IPMS).  The IPMS content structure is   able to convey zero or more arbitrary body parts each identified by   the body part type.  The body part type is an ASN.1 OID or Integer   that denotes the syntax and semantics of the body part in question.2.2.  Carrying S/MIME as X.400 Content   When transporting a CMS-protected message in X.400, the preferred   approach (except as discussed insection 2.3 below) is to convey the   object as X.400 message content.  This section describes how S/MIME   CMS objects are conveyed as the content part of X.400 messages.  This   mechanism is suitable for transport of CMS-protected messages   regardless of the mail content that has been encapsulated.   Implementations MUST include the CMS object in the content field of   the X.400 message.   If the CMS object is covered by an outer MIME wrapper, the content-   type field of the P1 envelope MUST be set to the following CMS-   defined value:   id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)         rsadsi(113549) pkcs(1) pkcs7(7) 1 }   If the CMS object is not covered by an outer MIME wrapper, the   content-type field of the P1 envelope MUST be set to the following   CMS-defined value:   id-ct-contentInfo  OBJECT IDENTIFIER ::= { iso(1) member-body(2)         us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)         content-types(1) 6}2.2.1.  Carrying Plaintext MIME objects as X.400 Content   When transporting a plaintext MIME object in X.400, the preferred   approach is to convey the object as X.400 message content.  TheHoffman & Bonatti           Standards Track                     [Page 3]

RFC 3855          Transporting S/MIME Objects in X.400         July 2004   content-type field of the P1 envelope MUST be set to the following   CMS-defined value:   id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)         rsadsi(113549) pkcs(1) pkcs7(7) 1 }2.3.  Carrying S/MIME as IPMS Body Parts   Under some circumstances S/MIME CMS-protected messages can be   conveyed within select body parts of the content.  Implementations   generally SHOULD NOT embed CMS objects within X.400 body parts, but   should instead convey them as content as described insection 2.2.   Nevertheless, one notable exception is necessary for the case of   forwarding.   In instances when CMS objects are forwarded as part of a message   forwarding function, use of a body part is necessary.  When   forwarding a CMS object in an IPMS or IPMS-compatible body part,   implementations MUST use the content-body-part as formally defined by   [X.400], as shown below for reference.   content-body-part {ExtendedContentType:content-type}       EXTENDED-BODY-PART-TYPE ::= {           PARAMETERS {ForwardedContentParameters IDENTIFIED BY               {id-ep-content -- concatenated with content-type -- }},           DATA {Content IDENTIFIED BY               {id-et-content -- concatenated with content-type -- }} }   ForwardedContentParameters ::= SET {       delivery-time     [0] MessageDeliveryTime OPTIONAL,       delivery-envelope [1] OtherMessageDeliveryFields OPTIONAL,       mts-identifier    [2] MessageDeliveryIdentifier OPTIONAL }   id-ep-content ::= {joint-iso-itu-t(2) mhs(6) ipms(1) ep(11) 17}   id-et-content ::= {joint-iso-itu-t(2) mhs(6) ipms(1) et(4) 17}   The implementation MUST copy the CMS object to be forwarded into the   Content field of the content-body-part.  The direct-reference field   of the body part MUST include the OID formed by the concatenation of   the id-et-content value and the following CMS-defined value.   id-ct-contentInfo  OBJECT IDENTIFIER ::=         { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)         pkcs-9(9) smime(16) content-types(1) 6}   For example, to forward any CMS object the DATA component of the body   part would be identified by { 2 6 1 4 17 1 2 840 113549 1 9 16 1 6 }.Hoffman & Bonatti           Standards Track                     [Page 4]

RFC 3855          Transporting S/MIME Objects in X.400         July 2004   The ForwardedContentParameters are optional and MAY be supported at   the discretion of the implementor.  The OID value id-et-content MAY   also be included in the original-encoded-information-types field of   the X.400 message envelope at the discretion of the sending S/MIME   agent.   In this instance, the content-type field of the P1 envelope MUST be   set to the value associate with the forwarding content (e.g., integer   22 for IPMS).2.4.  Transfer Encoding   According to various S/MIME specifications for message wrapping, CMS   objects MAY optionally be wrapped in MIME to dynamically support 7-   bit transport.  This outer wrapping is not required for X.400   transport, and generally SHOULD NOT be applied in a homogeneous X.400   environment.  Heterogeneous mail systems or other factors MAY require   the presence of this outer MIME wrapper2.5.  Encoded Information Type Indication   In [MSG], the application/pkcs7-mime content type and optional   "smime-type" parameter are used to convey details about the security   applied (signed or enveloped) along with information about the   contained content.  This may aid receiving S/MIME implementations in   correctly processing the secured content.  Additional values of   smime-type are defined in [ESS].  In an X.400 transport environment,   MIME typing is not available.  Therefore the equivalent semantic is   conveyed using the Encoded Information Types (EITs).  The EITs are   conveyed in the original-encoded-information-types field of the X.400   message envelope.  This memo defines the following smime-types.Hoffman & Bonatti           Standards Track                     [Page 5]

RFC 3855          Transporting S/MIME Objects in X.400         July 2004   +-----------------------------------------------------+   |                                                     |   |     smime-type           EIT Value (OID)            |   | CMS protection type       Inner Content             |   |                                                     |   +-----------------------------------------------------+   |                                                     |   |  enveloped-data        id-eit-envelopedData         |   |  EnvelopedData         Data                         |   |                                                     |   |  signed-data           id-eit-signedData            |   |  SignedData            Data                         |   |                                                     |   |  certs-only            id-eit-certsOnly             |   |  SignedData            empty (zero-length content)  |   |                                                     |   |  signed-receipt        id-eit-signedReceipt         |   |  SignedData            Receipt                      |   |                                                     |   |  enveloped-x400        id-eit-envelopedx400         |   |  EnvelopedData         X.400 content                |   |                                                     |   |  signed-x400           id-eit-signedx400            |   |  SignedData            X.400 content                |   |                                                     |   |  compressed-data       id-eit-compressedData        |   |  CompressedDataRFC 3274 compression wrapper |   |                                                     |   +-----------------------------------------------------+   Sending agents SHOULD include the appropriate S/MIME EIT OID value.   Receiving agents SHOULD recognize S/MIME OID values in the EITs   field, and process the message appropriately according to local   procedures.   In order that consistency can be obtained in future S/MIME EIT   assignments, the following guidelines should be followed when   assigning new EIT values.  Values assigned for S/MIME EITs should   correspond to assigned smime-type values on a one-to-one basis.  The   restrictions of section 3.2.2 of [MSG] therefore apply.  S/MIME EIT   values may coexist with other EIT values intended to further qualify   the makeup of the protected content.Hoffman & Bonatti           Standards Track                     [Page 6]

RFC 3855          Transporting S/MIME Objects in X.400         July 20042.5.1.  Enveloped Data   The enveloped data EIT indicates that the X.400 content field   contains a MIME type that has been protected by the CMS enveloped-   data content type in accordance with [MSG].  The resulting enveloped   data CMS content is conveyed in accordance withsection 2.2.  This   EIT should be indicated by the following OID value:      id-eit-envelopedData  OBJECT IDENTIFIER ::=          { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)          pkcs-9(9) smime(16) id-eit(10) id-eit-envelopedData(1) }2.5.2.  Signed Data   The signed data EIT indicates that the X.400 content field contains a   MIME type that has been protected by the CMS signed-data content type   in accordance with [MSG].  The resulting signed data CMS content is   conveyed in accordance withsection 2.2.  This EIT should be   indicated by the following OID value:      id-eit-signedData  OBJECT IDENTIFIER ::=           { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)           pkcs-9(9) smime(16) id-eit(10) id-eit-signedData(2) }2.5.3.  Certs Only   The certs-only message is used to transport certificates and/or CRLs,   such as in response to a registration request.  This is described in   [CERT31].  The certs-only message consists of a single instance of   CMS content of type signed-data.  The encapContentInfo eContent field   MUST be absent and signerInfos field MUST be empty.  The resulting   certs-only CMS content is conveyed in accordance withsection 2.2.   This EIT should be indicated by the following OID value:      id-eit-certsOnly  OBJECT IDENTIFIER ::=          { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)          pkcs-9(9) smime(16) id-eit(10) id-eit-certsOnly(3) }2.5.4.  Signed Receipt   The signed receipt EIT indicates that the X.400 content field   contains a Receipt content that has been protected by the CMS   signed-data content type in accordance with [ESS].  The resulting CMS   signed-data content is conveyed in accordance withsection 2.2.  This   EIT should be indicated by the following OID value:Hoffman & Bonatti           Standards Track                     [Page 7]

RFC 3855          Transporting S/MIME Objects in X.400         July 2004      id-eit-signedReceipt  OBJECT IDENTIFIER ::=          { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)          pkcs-9(9) smime(16) id-eit(10) id-eit-signedReceipt(4) }2.5.5.  Enveloped X.400   The enveloped X.400 EIT indicates that the X.400 content field   contains X.400 content that has been protected by the CMS enveloped-   data content type in accordance with [X400WRAP].  The resulting   enveloped X.400 CMS content is conveyed in accordance withsection2.2.  This EIT should be indicated by the following OID value:      id-eit-envelopedX400  OBJECT IDENTIFIER ::=          { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)          pkcs-9(9) smime(16) id-eit(10) id-eit-envelopedX400(5) }2.5.6.  Signed X.400   The signed X.400 EIT indicates that the X.400 content field contains   X.400 content that has been protected by the CMS signed-data content   type in accordance with [X400WRAP].  The resulting signed X.400 CMS   content is conveyed in accordance withsection 2.2.  This EIT should   be indicated by the following OID value:      id-eit-signedX400  OBJECT IDENTIFIER ::=          { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)          pkcs-9(9) smime(16) id-eit(10) id-eit-signedX400(6) }2.5.7.  Compressed Data   The compressed data EIT indicates that the X.400 content field   contains a another type that has been compressed by the compressed-   data content type in accordance with [COMPRESS].  The resulting CMS   content is conveyed in accordance withsection 2.2.  This EIT should   be indicated by the following OID value:      id-eit-compressedData  OBJECT IDENTIFIER ::=          { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)          pkcs-9(9) smime(16) id-eit(10) id-eit-compressedData(7) }2.6.  Interaction with X.400 Elements of Service   Care should be taken in the selection of X.400 services to be used in   conjunction with CMS objects.  Services affecting conversion of the   content, expansion of Distribution Lists (DLs), and message   redirection can interact badly with services provided by the   "EnvelopedData" and "SignedData" CMS content types.Hoffman & Bonatti           Standards Track                     [Page 8]

RFC 3855          Transporting S/MIME Objects in X.400         July 20042.6.1.  MTS Conversion Services   MTS conversion is not applicable to the scenario of this document   because such conversion is incompatible with CMS protection   mechanisms.  X.400 systems that implement conversion services should   generally be unable to attempt conversion of CMS content types   because those types do not conform to X.420 structure rules.   Nevertheless, when transporting CMS objects within an X.400   environment, the Conversion Prohibition service SHOULD be selected.2.6.2.  Message Redirection Services   X.400 message redirection services can have an indirect impact on the   application of the CMS "EnvelopedData" content type.  Several   different forms of redirection are possible in X.400, including:   -  Originator Requested Alternate Recipient (ORAR)   -  Alternate Recipient Assignment   -  Redirection of Incoming Messages   In addition, any auto-forwarding services that are not security-aware   may share the same problem.  An auto-forwarding implementation that   removes the EnvelopedData and reapplies it for the forwarded   recipient is not affected by this problem.  The normal case is that   the private key is not available when the human user is not present,   thus decryption is not possible.  However, if the private key is   present, forwarding can be used instead.   When the "EnvelopedData" content type is used to protect message   contents, an instance of RecipientInfo is needed for each recipient   and alternate recipient in order to ensure the desired access to the   message.  A RecipientInfo for the originator is a good practice just   in case the MTS returns the whole message.   In the event that ORAR is used, the originator is aware of the   identity of the alternate recipient and SHOULD include a   corresponding RecipientInfo element.  For other forms of redirection   (including non-security-aware auto-forwarding) the alternate   recipient must either have access to the intended recipient's keys   (not recommended) or must relay the message to the intended recipient   by other means.2.6.3.  DL Expansion   X.400 DLs can have an indirect impact on the application of the CMS   "EnvelopedData" content type.  When the "EnvelopedData" content type   is used to protect message contents, an instance of RecipientInfo is   needed for each recipient in order to ensure the desired access toHoffman & Bonatti           Standards Track                     [Page 9]

RFC 3855          Transporting S/MIME Objects in X.400         July 2004   the message.  Messages to a DL would typically include only a single   RecipientInfo associated with the DL.  Unlike Mail Lists (MLs)   described in [ESS], however, X.400 DLs are not generally security-   aware and do not regenerate RecipientInfo elements for the DL   members.  It is recommended that a security-aware ML conforming to   [ESS] be used in preference to X.400 DLs.  When transporting CMS   objects within an X.400 environment, the DL Expansion Prohibited   service SHOULD be selected.3.  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].4.  References4.1.  Normative References   [MUSTSHOULD] Bradner, S., "Key words for use in RFCs to Indicate                Requirement Levels",BCP 14,RFC 2119, March 1997.   [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)",RFC3852, July 2004.   [COMPRESS]   Gutmann, P., "Compressed Data Content Type for                Cryptographic Message Syntax (CMS)",RFC 3274, June                2002.   [ESS]        Hoffman, P., Ed., "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.   [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.Hoffman & Bonatti           Standards Track                    [Page 10]

RFC 3855          Transporting S/MIME Objects in X.400         July 20044.2.  Informative References   [BODYMAP]    Alvestrand, H., "Mapping between X.400 andRFC-822/MIME                Message Bodies",RFC 2157, January 1998.   [MIXER]      Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay):                Mapping between X.400 andRFC 822/MIME",RFC 2156,                January 1998.   [X400WRAP]   Hoffman, P., Bonatti, C., and A. Eggen, "Securing X.400                Content with Secure/Multipurpose Internet Mail                Extensions (S/MIME),RFC 3854, July 2004.5.  Authors' 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.comHoffman & Bonatti           Standards Track                    [Page 11]

RFC 3855          Transporting S/MIME Objects in X.400         July 20046.  Full Copyright Statement   Copyright (C) The Internet Society (2004).  This document is subject   to the rights, licenses and restrictions contained inBCP 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 inBCP 78 andBCP 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 athttp://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 & Bonatti           Standards Track                    [Page 12]