2.5.7 S/MIME Mail Security (smime)

Chair(s):

Security Area Director(s):

Security Area Advisor:

Mailing Lists:

Description of Working Group:

The use of Diffie-Hellman Key Agreement as the mandatory to implement key establishment mechanism may expose some implementations to vulnerabilities based on "small subgroup" attacks. An informational document will be prepared describing techniques that can be used to avoid these attacks.

The Cryptographic Message Syntax (CMS) is cryptographic algorithm independent, yet there is always more than one way to use any algorithm. To ensure interoperability, each algorithm should have a specification that describes its use with CMS. Specifications for the use of additional cryptographic algorithms will be developed. An additional suite of 'mandatory to implement' algorithms may be selected.

To aid implementers, documents containing example output for CMS will be collected and published. Some of the examples will include structures and signed attributed defined in the Enhanced Security Services (ESS) document.

Current methods of publishing certificates in the Directory do not allow the inclusion of secondary support information such as the SMimeCapabilities attribute. A method of publishing certificates along with authenticated secondary support information will be defined.

In some situations it would be advantageous for the CMS RecipientInfo structure to support additional key management techniques, including cryptographic keys derived from passwords. A mechanism to facilitate the definition of additional key management techniques will be defined. S/MIME version 3 permits the use of previously distributed symmetric key-encryption keys. Specifications for the distribution of symmetric key-encryption keys to mmultiple message recipients will be developed. Mail List Agents (MLAs) are one user of symmetric key-encryption keys. The specification will be cryptographic algorithm independent.

S/MIME version 3 supports security labels. Specifications that show how this feature can be used to implement an organizational security policy will be developed. Security policies from large organizations will be used as examples.

S/MIME version 3 can be used to protect electronic mail to and from a domain. In such an environment, S/MIME v3 processing is performed by message transfer agents, guards, and gateways in order to provide "Domain Security Services." Mechanisms are needed to solve a number of interoperability problems and technical limitations that arise when domains supporting different security policies wish to interoperate.

The S/MIME Working Group will attempt to coordinate its efforts with the OpenPGP Working Group in areas where the work of the two groups overlap.

Goals and Milestones:

Internet-Drafts:

• - Examples of S/MIME Messages
• - Use of ECC Algorithms in CMS
• - Compressed Data Content Type for CMS
• - Implementing Company Classification Policy with the S/MIME Security Label
• - CMS Symmetric Key Management and Distribution
• - Transporting S/MIME Objects in X.400
• - Securing X.400 Content with S/MIME
• - Use of the AES Encryption Algorithm and RSA-OAEP Key Transport in CMS
• - Cryptographic Message Syntax
• - Cryptographic Message Syntax (CMS) Algorithms
• - Intended Recipients Attribute for the Cryptographic Message Syntax (CMS)
• - Sender Authentication and the Surreptitious Forwarding Attack in CMS and S/MIME
• - Wrapping an HMAC key with a Triple-DES Key or an AES Key
• - AES Key Wrap Algorithm
• - S/MIME Version 3.1 Certificate Handling
• - S/MIME Version 3.1 Message Specification

Request For Comments: