5 Cryptographic Hashes
5.1 Introduction
A hash function inputs an arbitrary-sized bitstring and outputs a fixed-size bitstring, ideally so that all output values are equally likely. A cryptographic hash (also known as a message digest) has some extra security properties:
preimage resistance: It should be computationally infeasible to find a message that has a given pre-specified hash.
collision resistance: It should be computationally infeasible to find two messages that have the same hash.
second preimage resistance: It should be computationally infeasible to find a second message that has the same hash as a given message.
The term message digest was originally more popular, but hash is more commonly used today. As evidence that the world ...
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