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

Eric Rescorla <ekr@rtfm.com> Tue, 24 September 2013 20:11 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Tue, 24 Sep 2013 13:11:00 -0700
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Subject: Re: [TLS] Comments/Questions on draft-gutmann-tls-encrypt-then-mac-00.txt
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Peter,

Do you think you could address the questions I asked below?

Thanks,
-Ekr



On Fri, Sep 20, 2013 at 8:52 AM, Eric Rescorla <ekr@rtfm.com> wrote:

> 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
>
>