Hash Function
Definition
A hash function deterministically maps input data to a value of fixed or defined length.
Hash functions assign hash values to input data or keys, for example, for mapping in a hash table. Cryptographic hash functions are a subclass with additional security goals such as collision and preimage resistance. Hashing is not encryption because no decryption is intended.
Simply explained
Like a digital fingerprint: identical data produce the same imprint, small changes usually produce a different one.
Why it matters in practice
Relevant for integrity checks, signatures, content addressing, and secure protocols.
Example from business
A downloaded file is hashed after transfer and compared with a published SHA-256 value.
Limits and pitfalls
- Confusing hashing with encryption; using insecure legacy algorithms; storing passwords only with fast standard hashes instead of password hashing/KDF.
Origin & history
SHA families are specified in NIST standards. FIPS 180-4 defines several Secure Hash Algorithms; SHA-3 is separately standardized in FIPS 202.
Use in mid-sized companies
- Possible applications: file integrity, digital signatures, deduplicating content IDs, and security protocols.
Frequently asked questions
Can a hash be decrypted?
A cryptographic hash function is not defined as reversible encryption. Are all hash functions cryptographically secure? No.
Sources
- Secure Hash Standard · NIST FIPS 180-4, Secure Hash Standard
- hash · NIST DADS, hash
- cryptographic hash function · NIST, cryptographic hash function
- SHA-3 · NIST FIPS 202, SHA-3
Source verification: 10./11.10.2026.
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