RFC 1847 (rfc1847) - Page 2 of 11
Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted
Alternative Format: Original Text Document
RFC 1847 Security Multiparts October 1995 1. Introduction An Internet electronic mail message consists of two parts: the headers and the body. The headers form a collection of field/value pairs structured according to STD 11, RFC 822 [1], whilst the body, if structured, is defined according to MIME [2]. The basic MIME specification does not provide specific security protection. This document defines a framework whereby security protection provided by other protocols may be used with MIME in a complementary fashion. By itself, it does not specify security protection. A MIME agent must include support for both the framework defined here and a mechanism to interact with a security protocol defined in a separate document. The resulting combined service provides security for single-part and multi-part textual and non-textual messages. The framework is provided by defining two new security subtypes of the MIME multipart content type: signed and encrypted. In each of the security subtypes, there are exactly two related body parts: one for the protected data and one for the control information. The type and contents of the control information body parts are determined by the value of the protocol parameter of the enclosing multipart/signed or multipart/encrypted content type, which is required to be present. By registering new values for the required protocol parameter, the framework is easily extended to accommodate a variety of protocols. A MIME agent that includes support for this framework will be able to recognize a security multipart body part and to identify its protected data and control information body parts. If the value of the protocol parameter is unrecognized the MIME agent will not be able to process the security multipart. However, a MIME agent may continue to process any other body parts that may be present. 2. Definition of Security Subtypes of Multipart The multipart/signed content type specifies how to support authentication and integrity services via digital signature. The control information is carried in the second of the two required body parts. The multipart/encrypted content type specifies how to support confidentiality via encryption. The control information is carried in the first of the two required body parts. A three-step process is described for the origination and reception of the multipart/signed and multipart/encrypted contents. The details of the processing performed during each step is left to be specified by the security protocol being used. Galvin, et al Standards Track
