Re: [Cfrg] A little room for AES-192 in TLS?

‎Dear colleagues,

Thank you for this discussion!

To be honest, I cannot imagine an adversary model (with any relation to practice) for TLS, for which AES-192 would be useful - I agree with Kenny about related-key attacks here.

So I don't see any strong points to add AES-192 to 1.3 too. 

Best regards,
Stanislav Smyshlyaev

‎
  Исходное сообщение  
От: Paterson, Kenny
Отправлено: понедельник, 16 января 2017 г., 20:37
Кому: Eric Rescorla; John Mattsson
Копия: cfrg@irtf.org; Leonard den Ottolander
Тема: Re: [Cfrg] A little room for AES-192 in TLS?

Hi,

On 16/01/2017 16:27, "Cfrg on behalf of Eric Rescorla"
<cfrg-bounces@irtf.org on behalf of ekr@rtfm.com> wrote:

>Generally, I think the sense of the WG is to try to minimize the number
>of ciphers/suits.
>
>
>Speaking personally, what would make me be in favor of adding AES-192
>would be
>some statement from CFRG that they thought that it was significantly
>stronger than
>AES-256. Absent that, I think it would be better to leave it out of TLS.

Speaking without my co-chair's hat on...

I don't think related-key attacks are a particular concern for TLS. So I
don't think there's a strong argument for supporting AES-192 in the TLS
1.3 protocol specification.

Anyone else from CFRG have an opinion on this?

Cheers

Kenny 

>
>
>-Ekr
>
>
>
>
>On Mon, Jan 16, 2017 at 7:59 AM, John Mattsson
><john.mattsson@ericsson.com> wrote:
>
>Note that there are trivial generic related-key attacks on AES-192 with #K
>= D = T = M = 2^96
>
>http://dx.doi.org/10.1080/0161-118791861749
>
>Regards,
>John
>
>
>On 2017-01-16, 15:43, "Cfrg on behalf of Leonard den Ottolander"
><cfrg-bounces@irtf.org on behalf of
>leonard-lists@den.ottolander.nl> wrote:
>
>>On Sun, 2017-01-15 at 20:59 +0000, Taylor R Campbell wrote:
>>> Only very unusual protocols ever use related keys. In sensible
>>> protocols, every key is drawn independently uniformly at random.
>>
>>Protocols that are designed to use related keys? I hope not!
>>
>>Compare 
>http://eprint.iacr.org/2009/317 <http://eprint.iacr.org/2009/317> 4.1
>Related-key attack model:
>>
>>"Compared to other cryptanalytic attacks in which the attacker can
>>manipu-
>>late only the plaintexts and/or the ciphertexts the choice of the
>>relation between
>>secret keys gives additional degree of freedom to the attacker. The
>>downside of
>>this freedom is that such attacks might be harder to mount in practice.
>>Still,
>>designers usually try to build "ideal" primitives which can be
>>automatically used
>>without further analysis in the widest possible set of applications,
>>protocols, or
>>modes of operation. Thus resistance to such attacks is an important
>>design goal
>>for block ciphers, and in fact it was one of the stated design goals of
>>the Rijndael
>>algorithm, which was selected as the Advanced Encryption Standard."
>>
>>So the question remains if indeed AES-192 is inherently more resistant
>>to this kind of attack (more of an "ideal primitive" in this respect)
>>than AES-256 or do I read too much in the remark "the key schedule of
>>AES-192 has better diffusion" in 6 Attack on AES-192?
>>
>>Regards,
>>Leonard.
>>
>>--
>>mount -t life -o ro /dev/dna /genetic/research
>>
>>
>>
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