One way hash functions, also called fingerprints or cryptographically secure checksums. A one-way function is one which is easy to compute but difficult (effectively impossible) to invert. The hash function maps data of arbitrary size into a string of fixed size, using a one-way compression function.
Ideally, a cryptographic hash function should be:
deterministic, the same message always results in the same hash
quick to compute
infeasible to generate a message from its hash
a small change to a message should change the hash value completely, so no correlations could be inferred
infeasible to find two different messages with the same hash value (collision)
The most common hash algorithms are MD5 (message-digest 5), which has been deprecated for SHA-1 (Secure Hash Algorithm), also phased out to SHA-2 and SHA-3. The algorithms above use the Merkle–Damgård construction, while SHA-3 uses Keccak (sponge construction). The newer BLAKE algorithm is based on ChaCha stream cipher. BLAKE is a faster algorithm when run on 64-bit and ARM architectures, used in the Equihash proof-of-work algorithm, and as a key derivation function.