HMAC?

[Amir Herzberg]

Perry E. Metzger wrote:
> So the question now arises, is HMAC using any of the broken hash
> functions vulnerable?
Considering that HMAC goal is `only` a MAC (shared key authentication), 
the existence of any collision is not very relevant to its use. But 
furthermore, what HMAC needs from the hash function is only that it will 
be hard to find collision when using an unknown, random key; clearly the 
current collisions are far off from this situation.

So, finding specific collisions in the hash function should not cause 
too much worry about its use in HMAC. Of course, if this would lead to 
finding many collisions easily, including to messages with random 
prefixes, this could be more worrying...

-- 
Best regards,

Amir Herzberg
Associate Professor, Computer Science Dept., Bar Ilan University
http://amirherzberg.com (information and lectures in cryptography & 
security)
Mirror site: http://www.mfn.org/~herzbea/
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