Re: [TLS] Encrypt-then-MAC again (was Re: padding bug)

Peter Gutmann <p.gutmann@auckland.ac.nz> Thu, 05 December 2013 04:42 UTC

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From: Peter Gutmann <p.gutmann@auckland.ac.nz>
To: "<tls@ietf.org>" <tls@ietf.org>
Thread-Topic: [TLS] Encrypt-then-MAC again (was Re: padding bug)
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Date: Thu, 5 Dec 2013 04:41:57 +0000
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Subject: Re: [TLS] Encrypt-then-MAC again (was Re: padding bug)
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Martin Rex <mrex@sap.com> writes:

>Peter's proposal changes AtE to EtA, but does not currently address the 
>predictable IV for SSLv3 & TLSv1.0.  As it turns out, EtA will not protect 
>from BEAST, because it is "generically" secure only against decryption 
>oracles.  BEAST was exploiting an _encryption_ oracle.

The idea was to fix as much as possible with the least overhead possible.  In
my code I had to change four lines of code (exclusing the negotiate-EtA bits,
which mostly involve changing some lookup tables), which is about as low-
impact as you can get.  I can certainly add explicit-IV, but since you get
that in TLS 1.1 anyway it didn't seem like a good idea to start messing around
with other aspects of the protocol.

Peter.