Definition
SHA-256 is a cryptographic hash algorithm in the SHA-2 family that produces a 256-bit digest. The output is commonly displayed as 64 hexadecimal characters. Bitcoin uses two successive SHA-256 operations when hashing block headers for proof of work, and related hashing constructions appear elsewhere in its data structures. The algorithm maps input data to a digest; it does not encrypt the data or provide a decryption operation. Miners do not break SHA-256 when they discover a block. They search through varying candidate headers until a resulting hash meets the required numerical target. The ability to verify a result quickly is different from the difficulty of finding one. SHA-256 should also be distinguished from the elliptic-curve signature algorithms that authorize Bitcoin spending. Hashing and digital signatures serve complementary roles, but possessing a transaction hash does not grant access to its funds.
Source references
References accompanying this glossary entry:
- https://csrc.nist.gov/pubs/fips/180-4/upd1/final
- https://developer.bitcoin.org/reference/block_chain.html
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