baseline CPIM security

I believe that without a mandatory-to-implement baseline security mechanism,
including a ciphersuite, the prospects of CPIM passing the IESG are slim.
Moreover, if different presence protocols/applications do not use common
security mechanisms to apply to security properties to MSGFMT and PIDF, the
prospects for interoperability through CPIM gateways are equally slim. It is
also desirable, I think, to use the same mechanism to secure MSGFMT and
PIDF, in order to minimize the number of security mechanisms that
CPIM-compliant applications and protocols must support.

Since both PIDF and MSGFMT are MIME-based, I'd like to suggest that S/MIME
should be the mandatory-to-implement security mechanism for CPIM-compliant
devices. In my experience, this option is currently preferred by the
Security ADs to the alternatives.

If we grant that S/MIME should be the mandatory-to-implement security
mechanism, we must also select a minimum ciphersuite. Today, 3DES is most
commonly used for this purpose. However, an S/MIME ciphersuite for AES is
also underway; for example, see:

http://www.ietf.org/internet-drafts/draft-ietf-smime-aes-alg-04.txt

Ultimately, I think it is probably the right choice for CPIM to normatively
depend on AES rather than 3DES, even those the CMS AES work is mostly still
at the I-D stage.

In terms of textual changes, I'd further like to suggest that the baseline
CPIM specification is the appropriate place to declare the
mandatory-to-implement security mechanism, and that both the PIDF document
and the MSGFMT document should normatively reference the security
requirements in CPIM.

Comments? If not, this will be added to impp-cpim-04.

Jon Peterson
NeuStar, Inc.



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