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Cryptographic hash function

A cryptographic hash function deterministically produces a digest and is designed to resist preimage, second-preimage and collision attacks.

Related Observatory article: Cryptographic hash function on hesela.com

Preimage search starts from a target digest; second-preimage search starts from a specified input; collision search may choose both distinct inputs. Designed resistance is not a promise that collisions do not exist. [1] An unkeyed digest does not authenticate its own origin: replacing both data and the expected digest can preserve a match. HMAC adds a shared secret to authentication; hashing is not encryption. [2]

Relations

related

checksum, hash-collision, merkle-tree, deduplication

Limitations

• Algorithm choice, output length and known attacks determine useful security; a matching digest is not proof of storage durability. [1, 3]

Citations

1. NIST CSRC glossary: cryptographic hash function and security properties (accessed 2026-10-12)
2. RFC 2104: HMAC, sections 1-2 (construction, not current algorithm selection advice) (accessed 2026-10-12)
3. Hesela: Why a valid checksum can still return the wrong data (accessed 2026-10-12)

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