1
vote
1answer
99 views

Is it possible to find a preimage for a reduced size hash?

Given a message $M$ and a 256 bit key $K$, perform HMAC($K$, $M$) with a 256 bit hash function resulting in: $a$ = ...
5
votes
2answers
257 views

Cost of attacking Mobile OTP with a fake server

You want to obtain a 74-bit secret $K$. There is an oracle that will provide you with the following value for several values of $T$: ...