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Re: [TLS] TLS1.3

"Paterson, Kenny" <Kenny.Paterson@rhul.ac.uk> Fri, 08 February 2013 13:03 UTC

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From: "Paterson, Kenny" <Kenny.Paterson@rhul.ac.uk>
To: Nikos Mavrogiannopoulos <nmav@gnutls.org>, "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] TLS1.3
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Date: Fri, 08 Feb 2013 13:03:40 +0000
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Subject: Re: [TLS] TLS1.3
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Nikos, all

> Using encrypt-then-MAC to counter the attack is as radical change as
> using the GCM or CCM modes. 

I agree. It will take work. But it's time for that kind of change.

> This isn't a small fix, it is an upgrade
> which changes the protocol semantics (e.g. MAC is no longer encrypted
> - whatever that may mean). Moreover, encrypt-then-MAC isn't a panacea.

It fixes every problem I can conceive of. And I've thought about the analysis of TLS's current MAC-pad-encrypt construction long and hard, believe me.

> There is nothing wrong with MAC-then-encrypt, 

I disagree. The paper by Bellare and Namprempre from Asiacrypt 2000 and Hugo Krawczyk's paper from Crypto 2001 both demonstrate good reasons to be suspicious of MAC-then-encrypt from a theoretical perspective. 

And in practice, time and again it's proven to be problematic. And not just in TLS (see for example my paper with Jean Paul Degabriele at ACM-CCS 2010 about MAC-then-encrypt configurations of IPsec. TL;DR: we broke them all).

Cheers

Kenny

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