The usual process of signing a bunch of data is to hash it and then encrypt it with public key encryption, so the hash function is as important as the public ke

The usual process of signing a bunch of data is to hash it and then encrypt it with public key encryption, so the hash function is as important as the public key encryption scheme. If the hash is weak, an attacker may be able to construct compromised data that hashes to the same hash, and the whole signature becomes worthless.