RFC 2311 (rfc2311) - Page 4 of 37

S/MIME Version 2 Message Specification

RFC 2311         S/MIME Version 2 Message Specification       March 1998


2. PKCS #7 Options

   The PKCS #7 message format allows for a wide variety of options in
   content and algorithm support. This section puts forth a number of
   support requirements and recommendations in order to achieve a base
   level of interoperability among all S/MIME implementations.

2.1 DigestAlgorithmIdentifier

   Receiving agents MUST support SHA-1 [SHA1] and MD5 [MD5].

   Sending agents SHOULD use SHA-1.

2.2 DigestEncryptionAlgorithmIdentifier

   Receiving agents MUST support rsaEncryption, defined in [PKCS-1].
   Receiving agents MUST support verification of signatures using RSA
   public key sizes from 512 bits to 1024 bits.

   Sending agents MUST support rsaEncryption. Outgoing messages are
   signed with a user's private key. The size of the private key is
   determined during key generation.

2.3 KeyEncryptionAlgorithmIdentifier

   Receiving agents MUST support rsaEncryption. Incoming encrypted
   messages contain symmetric keys which are to be decrypted with a
   user's private key.  The size of the private key is determined during
   key generation.

   Sending agents MUST support rsaEncryption. Sending agents MUST
   support encryption of symmetric keys with RSA public keys at key
   sizes from 512 bits to 1024 bits.

2.4 General Syntax

   The PKCS #7 defines six distinct content types: "data", "signedData",
   "envelopedData", "signedAndEnvelopedData", "digestedData", and
   "encryptedData". Receiving agents MUST support the "data",
   "signedData" and "envelopedData" content types. Sending agents may or
   may not send out any of the content types, depending on the services
   that the agent supports.

2.4.1 Data Content Type

   Sending agents MUST use the "data" content type as the content within
   other content types to indicate the message content which has had
   security services applied to it.



Dusse, et. al.               Informational