The cryptographic function used as the basis for Bitcoin’s proof-of-work
Malone, J.A (2015). Glossary of Bitcoin Terms and Definitions. United States: Lulu Press, Inc
Many hash functions exist but this is one Bitcoin uses primarily.
SHA-256 uses the Merkle-Damgard transform to return a fixed-length collision-resistant compression function into a hash function that accepts arbitary-length inputs. The input is padded, so that its length is a multiple of 512 bits.
SHA-256 uses a compression function that takes 768-bit input and produces 256-bit outputs. The block size is 512 bits.
Narayanan, Arvind, et al. (2017). Bitcoin and Cryptocurrency Technologies. United States: Princeton Press