I'm more or less attempting to determine crypography algoirthms and how they work. I'm a little confused on proving how one is trivial.
For example:
MAC(xbit_key,Message) = xbit_hash(Message) XOR xbit_key
A:
Take a look at this for a general explanation and that for a good example. If it's still not clear, come back with a more specific question.
Steven Sudit
2010-09-11 10:23:06
I still find it slightly confusing. The question I posed was equivalent to the mathematical equivalence of a specific MAC algorithm. For example as shown in HMAC, the mathematical equivalence is: HMAC(K,m) = H((K ⊕ opad) ∥ H((K ⊕ ipad) ∥ m)). I'm trying to determine why my example Algorithm can be trivially broken, which I believe would make use of the birthday attack (http://en.wikipedia.org/wiki/Birthday_attack), in proving that there is a likely chance of collision. Or maybe the issue is that my algorithm merely XOR's the K w/ Hashed Message, which might not be secure.
DJPlayer
2010-09-12 15:12:45
@DJPlayer: No need for birthdays. The only secret component is the xbit_key. So given a message M "secured" with your MAC, all the attacker does is XOR your MAC with xbit_hash(M) and, voila, out pops the xbit_key.
GregS
2010-09-12 15:56:48
@GregS: Yes, this is just a reinvention of the "ultra-secure" technique of XORing with a password. Scare quotes intentional!
Steven Sudit
2010-09-12 21:03:05