Subject: Re: [CGA-EXT] WGLC for draft-ietf-csi-hash-threat-05.txt

From: Ana Kukec <[email-masked]>
Date: Fri, 12 Feb 2010 14:51:29 +0100

Hi Jean-Michel,

Thanks for the comments, they are very useful. While addressing your 
comments in the new version of the draft, i noticed your question.

Jean-Michel Combes wrote:
>    ... non-repudiation feature, while collision attacks are mainly about
>    affecting the non-repudiation feature, i.e. in the collision attack
>    against the CGA both of the CGA Parameters sets are choosen by an
>    attacker, which is not useful in the real-world scenarios.
>
> <JMC>
> "which is not useful in the real-world scenarios"
> Out of curiosity, may you explain to me why you have such a conclusion?
> <JMC>
>   

AFAIU, that conclusion is the consequence of two things:
=> CGA does is that it proves that the sender of the message is the same 
as the one from the previous message.
=> In the collision attack against CGA in SEND, the attacker itself 
produces both (colliding) CGAs and both sets of CGA Parameters sets.

This basically means that CGAs do not deal with the non-repudiation. So, 
what are the benefits of such attack? I mean, CGA and SEND did what they 
were supposed to do, no matter of circumstances.

Ana