SIP-Based Messaging with S/MIME
RFC 8591

Document Type RFC - Proposed Standard (April 2019; No errata)
Was draft-campbell-sip-messaging-smime (individual in art area)
Last updated 2019-04-30
Stream IETF
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Document shepherd Sean Turner
Shepherd write-up Show (last changed 2018-09-11)
IESG IESG state RFC 8591 (Proposed Standard)
Consensus Boilerplate Yes
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Responsible AD Alexey Melnikov
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IANA IANA review state Version Changed - Review Needed
IANA action state No IANA Actions
Internet Engineering Task Force (IETF)                       B. Campbell
Request for Comments: 8591                             Standard Velocity
Updates: 3261, 3428, 4975                                     R. Housley
Category: Standards Track                                 Vigil Security
ISSN: 2070-1721                                               April 2019

                    SIP-Based Messaging with S/MIME

Abstract

   Mobile messaging applications used with the Session Initiation
   Protocol (SIP) commonly use some combination of the SIP MESSAGE
   method and the Message Session Relay Protocol (MSRP).  While these
   provide mechanisms for hop-by-hop security, neither natively provides
   end-to-end protection.  This document offers guidance on how to
   provide end-to-end authentication, integrity protection, and
   confidentiality using the Secure/Multipurpose Internet Mail
   Extensions (S/MIME).  It updates and provides clarifications for RFCs
   3261, 3428, and 4975.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8591.

Campbell & Housley           Standards Track                    [Page 1]
RFC 8591                S/MIME for SIP Messaging              April 2019

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Campbell & Housley           Standards Track                    [Page 2]
RFC 8591                S/MIME for SIP Messaging              April 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Problem Statement and Scope . . . . . . . . . . . . . . . . .   5
   4.  Applicability of S/MIME . . . . . . . . . . . . . . . . . . .   6
     4.1.  Signed Messages . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Encrypted Messages  . . . . . . . . . . . . . . . . . . .   7
     4.3.  Signed and Encrypted Messages . . . . . . . . . . . . . .   9
     4.4.  Certificate Handling  . . . . . . . . . . . . . . . . . .   9
       4.4.1.  Subject Alternative Name  . . . . . . . . . . . . . .   9
       4.4.2.  Certificate Validation  . . . . . . . . . . . . . . .   9
   5.  Transfer Encoding . . . . . . . . . . . . . . . . . . . . . .   9
   6.  User Agent Capabilities . . . . . . . . . . . . . . . . . . .  10
   7.  Using S/MIME with the SIP MESSAGE Method  . . . . . . . . . .  11
     7.1.  Size Limit  . . . . . . . . . . . . . . . . . . . . . . .  11
     7.2.  SIP User Agent Capabilities . . . . . . . . . . . . . . .  11
     7.3.  Failure Cases . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Using S/MIME with MSRP  . . . . . . . . . . . . . . . . . . .  12
     8.1.  Chunking  . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.2.  Streamed Data . . . . . . . . . . . . . . . . . . . . . .  13
     8.3.  Indicating Support for S/MIME . . . . . . . . . . . . . .  14
     8.4.  MSRP URIs . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.5.  Failure Cases . . . . . . . . . . . . . . . . . . . . . .  15
   9.  S/MIME Interaction with Other SIP Messaging Features  . . . .  15
     9.1.  Common Profile for Instant Messaging  . . . . . . . . . .  15
     9.2.  Instant Message Disposition Notifications . . . . . . . .  16
   10. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Signed Message in SIP including the Sender's Certificate  17
     10.2.  Signed Message in SIP with No Certificate  . . . . . . .  19
     10.3.  MSRP Signed and Encrypted Message in a Single Chunk  . .  20
     10.4.  MSRP Signed and Encrypted Message Sent in Multiple
            Chunks . . . . . . . . . . . . . . . . . . . . . . . . .  21
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  23
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