Hot answers tagged preimage-resistance
The question "why is preimage resistance needed for hash functions" is not really relevant. This is because collision resistance implies preimage resistance. Thus, it is just a fact that if you have collision resistance then you must have preimage resistance. So, instead, I will relate to what preimage resistance is good for at all. In more technical ...
There are a lot of other uses for hash functions than signature algorithms. For example, when used as a MAC – whether directly or in HMAC – a preimage attack would recover the key and allow forgery for arbitrary messages. Even specifically in signature algorithms there's the Lamport signature which requires preimage resistance.
Only top voted, non community-wiki answers of a minimum length are eligible