1

From the definition, a collision would mean you would have to find any two arbitrary x and y such that h(x) = h(y) where h is some cryptographic hash function. This is different from a second pre-image which means you have to find some y such that given some specific x, h(y) = h(x) (where x != y). The key difference being that x is fixed upfront.

I can make many cases why weak second pre-image resistance can hurt you (e.g. replace a known-to-be-good hash of a message/file with a malicious message/file that has the same hash), but I can't immediately come up with an attack where a collision would help you much. What are some real-world or theoretical attack vectors where abusing a weak collision resistant hash could cause harm?

2

Hash collision in a signature is for example a problem in document signing if the attacker can provide both signed documents. Just imagine a case where somebody orders you to do some work and the conditions are inside a signed document. Once you are ready they present you with a different version of the document which contains a lower pay for you but which still matches the signature.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.