SHA-2

SHA-2 is the family of cryptographic hash functions published by NIST in FIPS 180-4, comprising SHA-224, SHA-256, SHA-384, SHA-512, and two truncated variants. Built on the Merkle-Damgard construction, it is the most widely deployed hash family, securing TLS certificate signatures, software integrity checks, and the proof-of-work in many blockchains.

#Quantum impact

SHA-2 faces no exponential quantum attack. Grover's algorithm (Grover's algorithm) gives at most a quadratic speedup, lowering the preimage margin of SHA-256 from 2^256 to about 2^128 quantum operations. Collision resistance is set by the classical birthday bound (2^128 for SHA-256), and known quantum collision methods demand so much memory that they offer little real advantage. A SHA-2 function with adequate output size is therefore treated as post-quantum safe, which is why it appears inside conservative hash-based signatures.

#Relationship to SHA-3

SHA-2 and the later SHA-3 standard share no internal structure: SHA-3 uses a sponge construction and was standardized as an independent backup, not a replacement. Both remain approved for use.