# Tag Info

3

The key thing you're missing here is that collision resistant hash functions ("CRHFs," what we normally call just "crypto hashes") and message authentication codes ("MACs") have substantially different security goals. CRHFs must meet these goals: Collision resistance: Attacker can't easily find two messages that hash to the same value. Preimage resistance:...

5

It is widely known, generally, that a MAC is a HASH with key. Nope; there are plenty of perfectly good MACs that, if you know the key, aren't very good hashes at all. Examples of this would include CMAC and GMAC; in both cases, if you know the key, it's easy to generate an image that MACs to a specific value. However, lets assume that you're talking ...

4

Does many:1 mean two different inputs would have the same hash outputs? Yes. This is a consequence of the pidgeonhole principle: as MD5 has a much larger number of potential inputs ($2^{2^{64}}$ or so) than outputs ($2^{128}$), some inputs must lead to the same output, i.e. collide. Cryptographic hashes all have this "limitation", because they have a ...

3

By trying all the 128 different bit position on the state, 19 rounds (over the 64) are required for a full avalanche effect (source code). round 0: 00000000000000000000000000000001 00000000000000000000000010000000 00000000000000000000000000000000 00000000000000000000000000000000 round 1: 00000000000000000000000000000000 00000000000000010000001000000000 ...

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