The Fiat-Shamir heuristic may be applied to transform a Sigma-Protocol on
R(x,w) into a ZKPoK.
Let's call the prover's first message
a and the verifier challenge
It is said that given a secure hash function
H, one could have
e = H(x,a) for Random-Oracle security.
But what happens if only
a is hashed? What known attacks are made possible, or how is a proof of security made impossible?