Re: [TLS] TLS 1.2 Long-term Support Profile draft posted

Wan-Teh Chang <wtc@google.com> Wed, 16 March 2016 15:31 UTC

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Date: Wed, 16 Mar 2016 08:31:06 -0700
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From: Wan-Teh Chang <wtc@google.com>
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
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Subject: Re: [TLS] TLS 1.2 Long-term Support Profile draft posted
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On Wed, Mar 16, 2016 at 5:36 AM, Peter Gutmann
<pgut001@cs.auckland.ac.nz>; wrote:
> After a number of, uh, gentle reminders from people who have been waiting for
> this, I've finally got around to posting the TLS-LTS draft I mentioned a while
> back.  It's now available as:
>
> http://www.ietf.org/id/draft-gutmann-tls-lts-00.txt

Section 3.4. "Implementation Issues" says:

   TLS-LTS requires that RSA signature verification be done as encode-
   then-compare, which fixes all known padding-manipulation issues:

   o  TLS-LTS implementations MUST verify RSA signatures by using
      encode-then-compare, meaning that they encode the expected
      signature result and perform a constant-time compare against the
      recovered signature data.

This is the procedure specified in PKCS #1 v2.1 (RFC 3447), Section
8.2.2, with the additional requirement that the comparison in Step 4
be constant-time, right?

https://tools.ietf.org/html/rfc3447#section-8.2.2

and the alternative procedure outlined in the Note at the end of that
section shall not be used?

   Note.  Another way to implement the signature verification operation
   is to apply a "decoding" operation (not specified in this document)
   to the encoded message to recover the underlying hash value, and then
   to compare it to a newly computed hash value.  This has the advantage
   that it requires less intermediate storage (two hash values rather
   than two encoded messages), but the disadvantage that it requires
   additional code.

Thanks,
Wan-Teh Chang