4 ms·
Well, if you have an internal collision hash(m1)=hash(m2) and both messages m1 and m2 are of the same size, then it seems that one would also get hash(m1|key|si
by more_original 14y ago
Well, if you have an internal collision hash(m1)=hash(m2) and both messages m1 and m2 are of the same size, then it seems that one would also get hash(m1|key|size) = hash(m2|key|size). So, I cannot really see how appending the size will help.
(All subject to optimistic assumptions about block sizes, etc.)
- tomp 14y agoIn this sense, every hash function is equally unsafe, even HMAC.
- more_original 14y agoPlease substantiate. An attacker knowing an internal collision of the hash algorithm for m1 and m2 (of the same size...) can construct HMAC(m2,key) from HMAC(m1,key) without knowing the key?