Re: [TLS] Rizzo claims implementation attach, should be interesting

Phillip Hallam-Baker <hallam@gmail.com> Tue, 20 September 2011 20:01 UTC

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Date: Tue, 20 Sep 2011 16:04:23 -0400
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From: Phillip Hallam-Baker <hallam@gmail.com>
To: mrex@sap.com
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Subject: Re: [TLS] Rizzo claims implementation attach, should be interesting
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On Tue, Sep 20, 2011 at 11:21 AM, Martin Rex <mrex@sap.com> wrote:

> Marsh Ray wrote:
> > But why split hairs over it? It breaks a basic security properties of
> > the system even if the application designer has done everything
> > according to the recommendations in the spec.
>
> Wrong.  I do not believe that it breaks any of the security properties.
> It does break some flawed assumptions.
>
> SSL was NEVER designed with a promise that you could multiplex
> data from an evil attack with data from a victim over the very same
> SSL connection and be secure against adaptive chose plaintext
> attacks trying to recover data from the victim.
>

SSL came before Javascript and even before cookies. So this is certainly
outside the model.

Adding AES in CBC mode probably came after the model had been changed
though.


If we want to avoid this type of attack we should probably change the
encryption mode. I don't like stream ciphers in general, but SSL was
designed round one and has been extensively verified when a stream cipher is
used.

>From a design point of view, re-use of the same key to encrypt each block is
bad news and turning a block cipher into a stream cipher is bad news. Anyone
know why CBC is so popular vs PCBC?


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