Re: [TLS] padding bug

Alfredo Pironti <alfredo@pironti.eu> Wed, 25 September 2013 10:49 UTC

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Date: Wed, 25 Sep 2013 12:48:55 +0200
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From: Alfredo Pironti <alfredo@pironti.eu>
To: "Lewis, Nick" <nick.lewis@usa.g4s.com>
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Subject: Re: [TLS] padding bug
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On Wed, Sep 25, 2013 at 10:32 AM, Lewis, Nick <nick.lewis@usa.g4s.com> wrote:
> Martin Rex wrote:
>
>> Where I agree is that it would be preferable to limit any fix to the exact
>> problem that has been identified (already by Vaudenay), which is in how
>> SSLv3&TLS use a Blockcipher in CBC mode with "authenticate-pad-encrypt"
>> rather than "pad-authenticate-encrypt".
>
>
>
> I agree that the fix should be limited to the exact problem. The fix could
> be a change from AtPtE to PtAtE
> using a greatly simplified version of
> http://tools.ietf.org/html/draft-pironti-tls-length-hiding-00  without
> the length hiding features

Indeed, I confirm a strict subset of
http://tools.ietf.org/html/draft-pironti-tls-length-hiding-02
(pointing to the latest version)
fixes the padding bug.

Once the padding bug is fixed according to this draft, my experience
implementing it in GnuTLS and miTLS is that it costs almost nothing to
implement the length-hiding features for the remaining stream and AEAD
ciphers.

Best,
Alfredo

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