Subject: [Spasm] Change of Algorithms: Content Encryption Algorithms

From: Jim Schaad <[email-masked]>
Date: Sun, 31 Jul 2016 22:05:02 -0700

I am not back onto a normal daylight schedule and have gotten through a
couple of other documents so I am ready to start dealing with issues in the
S/MIME documents.  So this is the first of a series of open issue messages
that I will start dribbling out as things seem to come to a conclusion.

This message looks at Content Encryption Algorithms.  Please restrict your
discussions to this set of algorithms, I will be sending out messages on
other algorithm times over time.

Current Document for S/MIME 3.1

MUST: AES-128 CBC
SHOULD+: AES-192 CBC and AES-256 CBC
SHOULD-: DES EDE3 CBC (tripleDES)
Historic: RC2/40

Proposed for S/MIME 3.5

MUST:  AES-192 CBC, AES-256 CBC, AES-256 GCM
SHOULD+: ChaCha20/Poly1305 (256-bit)
SHOULD-: AES-128 CBC
Historic: RC2/40, DES EDE3 CBC (tripleDES)

Questions:
1.  The jump from MUST to SHOULD- may be too aggressive for AES-128 CBC, we
should potentially state this as MUST- but I think being aggressive makes
more sense as we want to go to all AEAD algorithms in next version.

2.  No recommendation for: AES-128 GCM or AES-192 GCM, should there be?  How
do people feel about 128 and 192 bit algorithms?

3.  Do we want to downgrade all of the CBC algorithms in favor of GCM
algorithms?

Jim