Re: [TLS] Are the AEAD cipher suites a security trade-off win with TLS1.2?

Peter Gutmann <pgut001@cs.auckland.ac.nz> Fri, 18 March 2016 23:54 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: "mrex@sap.com" <mrex@sap.com>, =?iso-8859-1?Q?Colm_MacC=E1rthaigh?= <colm@allcosts.net>
Thread-Topic: [TLS] Are the AEAD cipher suites a security trade-off win with TLS1.2?
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Date: Fri, 18 Mar 2016 23:53:44 +0000
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Subject: Re: [TLS] Are the AEAD cipher suites a security trade-off win with TLS1.2?
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Martin Rex <mrex@sap.com>; writes:

>Though it is a pretty flawed assumption.
>
>I've seen an AEAD cipher implementation fail badly just recently (resulting
>in corrupted plaintext that went unnoticed within TLS--MACing the ciphertext
>is obviously a pretty dumb idea), something that is *MUCH* more unlikely to
>happen to any cipher suites using GenericBlockCipher PDU.

There have been many more failures with GCM, the most notorious being Colin
Percival's tarsnap, where a single missed operation (increment the IV)
resulted in a total loss of security.  Colin is a very experienced crypto
developer, so its not like this was some beginner mistake.  This is why I
referred to GCM as "brittle", you can be about as abusive as you like with CBC
and the worst you get is degradation to ECB, while with GCM you make one
mistake and you get a catastrophic loss of security.

Peter.