Numerous protocols such as the Simple Mail Transport Protocol (SMTP, RFC 5821), the Session Initiation Protocol (SIP, RFC 3261), the Electronic Data Interchange (EDI) protocols, the Secure Inter-Domain Routing (SIDR) protocols, and some of the Public Key Information (PKI) certificate management protocols employ the CMS (Cryptographic Message Syntax) to protect their payloads. The IETF has revised the CMS and Secure Mail Internet Mail Extensions (S/MIME) specifications to add an additional content type, address protocol implementation issues, and to support additional algorithms:

• CMS has been published four times on the standards-track: RFC 2630, RFC 3369, RFC 3852, and RFC 5652. RFC 3852 addressed errata against RFC 3369, but more importantly progressed CMS from proposed to draft standard. RFC 5652 added a clarification about multiple signers (RFC 4853) and addressed errata against RFC 3852. In August, RFC 5652 was elevated to full standard (STD 70).
• S/MIME Version 3.2 Message Specification (RFC 5751) replaces S/MIME Version 3.1 Message Specification (RFC 3851). The mandatory content encryption algorithm is AES-128 CBC, the mandatory message digest algorithm is SHA-256, the mandatory digital signature algorithm and key exchange algorithm is still RSA, but the mandatory key size range is now 1024-bit to 2048-bit.
• S/MIME Version 3.2 Certificate Handling (RFC 5750) replaces S/MIME Version 3.1 Certificate Handling (RFC 3850). It updates the required digital signature algorithm to be RSA with SHA-256 and it increases the required key size range to be between 1024-bit and 4096-bit.
• The Cryptographic Message Syntax (CMS) Authenticated-Enveloped-Data Content Type (RFC 5083) specifies a content type for use by authenticated encryption algorithms.
• Using AES-CCM and AES-GCM Authenticated Encryption in the Cryptographic Message Syntax (CMS) specifies the use of two authenticated encryption algorithms, namely AES Counter Cipher Block Chaining-Message Authentication Code (AES-CCM) and AES-Galois/Counter Mode (GCM), as content-authenticated-encryption algorithms for use with the authenticated enveloped content type (RFC 5083).
• Using the GOST 28147-89, GOST R 34.11-94, GOST R 34.10-94, and GOST R 34.10-2001 Algorithms with Cryptographic Message Syntax (CMS), as its name implies, specifies how to use the GOST suite of cryptographic algorithms including GOST message digest algorithms, digital signature algorithms, key agreement algorithms, key transport algorithms, content encryption algorithm, and HMAC algorithms.
• Using the Boneh-Franklin and Boneh-Boyen Identity-Based Encryption Algorithms with the Cryptographic Message Syntax (CMS) (RRFC 5409) specifies the use of two identity-based encryption algorithms, Boneh-Franklin (BF) and Boneh-Boyen (BB1), that can be used to encrypt content-encryption keys.
• Using SHA2 Algorithms with Cryptographic Message Syntax (RFC 5754) specifies the conventions for use of SHA-224, SHA-256 SHA-384, and SHA-512 message digest algorithms as well as the use of the DSA with SHA-224 and SHA-256.
• Use of Elliptic Curve Cryptography (ECC) Algorithms in Cryptographic Message Syntax (CMS) (RFC 5753), which obsoletes RFC 3278, adds support for ECDSA with SHA-224, SHA-256, SHA-384, and SHA-512. It also specifies ECDH standard, ECDH co-factor, and 1-Pass ECMQV with SHA-224, SHA-256, SHA-384, and SHA-512 as the Key Derivation Functions and AES-128, -192, and -256 as the key wrap algorithms. This RFC also adds support for 1-Pass ECMQV when used with the authenticated enveloped content type (RFC 5083).

The S/MIME working group is slowly winding down. A draft that specifies the use of the RSA-KEM key transport algorithm in CMS is the remaining item and it should be published in the next month or two. After publication, chances are that the S/MIME working group will be closed, but the mailing list will remain active.

For more information, contact Blake Ramsdell (ramsdell@sendmail.com), Paul Hoffman (paul.hoffman@vpnc.org), Russ Housley (housley@vigilsec.com), Sean Turner (turners@ieca.com), or smime@ietf.org.

NIST requests comments on Draft SP 800-135, Recommendation for Application-Specific Key Derivation Functions.