[Isis-wg] draft-bhatia-manral-crypto-req-isis-01.txt

[Tony Li <[e-mail]>]

Hi,

I'd like to take exception to some language found in this draft.  I  
quote:

   The HMAC-MD5 scheme is also not good enough as there have recently
    been reports about attacks on the collision resistance properties of
    MD5 [MD5-attack]. MD5CRK, was a distributed computing project to
    break the MD5 hash algorithm in a short period of time. The project
    closed down with the publication of the paper [MD5-attack].

    It was discovered that collisions can be found in MD5 algorithm in
    less than 24 hours, making MD5 very insecure.

I find this language to simply be irresponsible in that it  
misconstrues an attack vector and then draws a completely incorrect  
conclusion and reports it using the most incendiary language possible.

It is correct that it is possible to quickly find a collision for an  
MD5 hash.  However, just finding a collision does not give an  
attacker a mechanism to compute a correct hash for an arbitrary  
packet.  Thus, the attacker does not have a mechanism to forge  
arbitrary packets and have them injected into IS-IS.  In fact, the  
most that this process will do is allow the attacker to calculate  
some other, effectively pseudo-random packet that would have an  
identical hash.  The odds of such a packet being a syntactically  
correct IS-IS PDU are long indeed (e.g., is the Fletcher checksum  
correct?), and the odds of it further performing some attack  of  
interest within an IS-IS domain are longer still.

Note that I do not disagree that there is a need for replacement  
algorithms.  Experience has shown that all cryptographic algorithms  
will eventually be compromised in serious ways.  However, the attack  
cited is simply not in that category and it is wholly unreasonable to  
claim that the sky is falling.

I recommend that the WG not accept this draft until this language is  
revised.

Regards,
Tony

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