[TLS] Comments/Questions on draft-gutmann-tls-encrypt-then-mac-00.txt

Eric Rescorla <ekr@rtfm.com> Fri, 20 September 2013 15:53 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 20 Sep 2013 08:52:58 -0700
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Subject: [TLS] Comments/Questions on draft-gutmann-tls-encrypt-then-mac-00.txt
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Peter,

After reviewing this document I have a few comments/questions:

- Because this draft relies on extensions, it seems not to resist
  active attack when clients do insecure version fallback
  (see for instance:
http://www.ietf.org/mail-archive/web/tls/current/msg09468.html)
  The existing attacks appear to principally be active attacks on the
browser
  environment, which is where fallback tends to happen.

- Maybe I am misreading the draft, but I'm unclear on how you get
   the TLSCompressed.length for the MAC computation in Section 3.
   Does this have the same issue as was raised for McGrew's CBC AEAD
   draft?

Am I missing something here?

Thanks,
-Ekr