[cabfpub] SHA-1 Collision Found

Ryan Sleevi sleevi at google.com
Fri Feb 24 17:32:51 UTC 2017

On Fri, Feb 24, 2017 at 7:17 AM, philliph at comodo.com <philliph at comodo.com>

> * The lack of HSM support is not a concern as HSM manufacturers respond to
> the decisions of bodies like CABForum.

Hi Phillip,

I've snipped much of your email, since I believe it's neither appropriate
nor relevant for the list.

As you appear to have missed the point I was raising, which is unfortunate
given your knowledge of the Web PKI, I would simply again highlight that if
such a signature cannot be produced without exposing the key material, then
that is very much a concern for the CA/Browser Forum. We have already had
this discussion before, but I do not believe you chose to participate, so
it is unfortunate that you don't recognize the value in making productive,
collaborative progress.

This is the broader discussion, had during the last F2F (and some time
before) about what the intrinsic goals are with the CA/B Forum requiring
the use of a FIPS 140-2/3 Level 3 or CC EAL Level 4 key protection device.
If the intent is solely for key protection, then the points Peter raised
about utilizing 'raw' signing mode (whether PKCS#1 or literally raw RSA
signing) are relevant - it suggests that the key material can be protected
sufficiently (for RSA key sizes less than 4096 bits, assuming a
FIPS-approved mode of operation) while still producing these signatures. If
we take the view that such HSMs must operate in a FIPS-validated mode of
operation, then it's very relevant to understand what methods exist to
produce such signatures while still maintaining that operation (the method
Peter raised is generally not available in a FIPS-approved mode of
operation, depending on vendor, due to the fact that to maintain the FIPS
mode of operation, the HSM needs to produce the message digest itself using
an approved algorithm in an validated mode of operation). I realize that,
given your general lack of participation in the Forum, except for pointing
out when it's doing something you disagree with, you may not have followed
those discussions, and may not have been aware that it's still very much an
open and unresolved issue, with relevance to the operation of CAs today
(particularly those with >= 4096-bit keys) and tomorrow (for those that
would like to adopt EdDSA or SHA-3).

I do hope that, with some time to carefully reflect on the messages on the
thread, to recognize where confusion might exist and reconsider the
appropriateness of assuming you correctly understand the issue versus
asking questions to clarify, you might be able to make a productive
contribution to the discussion.
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