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I was thinking whether or not you can find the hash function(s) used if you have the original message and the hash. So assume that no salt is used during the hashing process, just multiple hashing and concatenation, e.g.

hash = SHA512(MD5(original) || SHA512(original))

So how could you find the right hashing process, if really no salt is used and the process does not depend on other things like system time etc.? Remember that the original and the hash are given. Is the only way to find the right hashing sequence brute force?

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marked as duplicate by Steve, Rory Alsop May 19 '14 at 22:14

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

You can certainly narrow the possibilities down by just looking at the hash. MD5 spits out 128 bits and SHA-256, 256 bits. Beyond that, it would have to be brute force.

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