RFC 2311 (rfc2311) - Page 2 of 37

S/MIME Version 2 Message Specification

RFC 2311         S/MIME Version 2 Message Specification       March 1998


   Please note: The information in this document is historical material
   being published for the public record. It is not an IETF standard.
   The use of the word "standard" in this document indicates a standard
   for adopters of S/MIME version 2, not an IETF standard.

1.1 Specification Overview

   This document describes a protocol for adding cryptographic signature
   and encryption services to MIME data. The MIME standard [MIME-SPEC]
   provides a general structure for the content type of Internet
   messages and allows extensions for new content type applications.

   This memo defines how to create a MIME body part that has been
   cryptographically enhanced according to PKCS #7 [PKCS-7]. This memo
   also defines the application/pkcs7-mime MIME type that can be used to
   transport those body parts. This memo also defines how to create
   certification requests that conform to PKCS #10 [PKCS-10], and the
   application/pkcs10 MIME type for transporting those requests.

   This memo also discusses how to use the multipart/signed MIME type
   defined in [MIME-SECURE] to transport S/MIME signed messages. This
   memo also defines the application/pkcs7-signature MIME type, which is
   also used to transport S/MIME signed messages. This specification is
   compatible with PKCS #7 in that it uses the data types defined by
   PKCS #7.

   In order to create S/MIME messages, an agent has to follow
   specifications in this memo, as well as some of the specifications
   listed in the following documents:

    - "PKCS #1: RSA Encryption", [PKCS-1]
    - "PKCS #7: Cryptographic Message Syntax", [PKCS-7]
    - "PKCS #10: Certification Request Syntax", [PKCS-10]

   Throughout this memo, 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.

   The separation for requirements on receiving agents and sending
   agents also derives from the likelihood that there will be S/MIME
   systems that involve software other than traditional Internet mail
   clients. S/MIME can be used with any system that transports MIME





Dusse, et. al.               Informational