Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message Specification
RFC 5751

Internet Engineering Task Force (IETF)                       B. Ramsdell
Request for Comments: 5751                              Brute Squad Labs
Obsoletes: 3851                                                S. Turner
Category: Standards Track                                           IECA
ISSN: 2070-1721                                             January 2010

   Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2
                         Message Specification

Abstract

   This document defines Secure/Multipurpose Internet Mail Extensions
   (S/MIME) version 3.2.  S/MIME provides a consistent way to send and
   receive secure MIME data.  Digital signatures provide authentication,
   message integrity, and non-repudiation with proof of origin.
   Encryption provides data confidentiality.  Compression can be used to
   reduce data size.  This document obsoletes RFC 3851.

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 5741.

   Information about the current status of this document, any
   errata, and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5751.

Ramsdell & Turner            Standards Track                    [Page 1]
RFC 5751            S/MIME 3.2 Message Specification        January 2010

Copyright Notice

   Copyright (c) 2010 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
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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Ramsdell & Turner            Standards Track                    [Page 2]
RFC 5751            S/MIME 3.2 Message Specification        January 2010

Table of Contents

   1. Introduction ....................................................4
      1.1. Specification Overview .....................................4
      1.2. Definitions ................................................5
      1.3. Conventions Used in This Document ..........................6
      1.4. Compatibility with Prior Practice of S/MIME ................7
      1.5. Changes from S/MIME v3 to S/MIME v3.1 ......................7
      1.6. Changes since S/MIME v3.1 ..................................7
   2. CMS Options .....................................................9
      2.1. DigestAlgorithmIdentifier ..................................9
      2.2. SignatureAlgorithmIdentifier ...............................9
      2.3. KeyEncryptionAlgorithmIdentifier ..........................10
      2.4. General Syntax ............................................11
      2.5. Attributes and the SignerInfo Type ........................12
      2.6. SignerIdentifier SignerInfo Type ..........................16
      2.7. ContentEncryptionAlgorithmIdentifier ......................16
   3. Creating S/MIME Messages .......................................18
      3.1. Preparing the MIME Entity for Signing, Enveloping,
           or Compressing ............................................19
      3.2. The application/pkcs7-mime Media Type .....................23
      3.3. Creating an Enveloped-Only Message ........................25
      3.4. Creating a Signed-Only Message ............................26
      3.5. Creating a Compressed-Only Message ........................30