SHA2

SHA-2 is a family of cryptographic hash functions designed by the U.S. National Security Agency and published by NIST in 2001 as successors to SHA-1. The family includes six functions: SHA-224, SHA-256, SHA-384, SHA-512, and the truncated variants SHA-512/224 and SHA-512/256. Each function produces a fixed-size digest: 224, 256, 384, 512, or 224/256 bits respectively. The algorithms use the Merkle-Damgård construction with distinct word sizes and round counts: 32-bit words for the 224/256 variants and 64-bit words for the 384/512 variants, with 64 rounds in the 256-based functions and 80 rounds in the 512-based ones. Each function has its own initial hash values and a set of round constants.

SHA-2 is widely deployed for data integrity and authentication tasks. It is designed to address vulnerabilities discovered in SHA-1 and remains resistant to practical collision and preimage attacks according to current cryptanalysis. In practice, SHA-256 and SHA-512 are the most commonly used variants, supported by major security standards and software libraries. As with other Merkle-Damgård hashes, using a plain SHA-2 digest as a MAC is vulnerable to certain attack vectors, so HMAC-SHA-2 is preferred for message authentication.

Standardization and adoption: SHA-2 is formalized in NIST FIPS 180-4 and remains the recommended hash family for new systems, with broad hardware and software support. The choice among variants typically depends on security and performance considerations of the deployment environment. In response to later developments, SHA-3 was introduced as an alternative hash family, but SHA-2 remains widely trusted and in active use.

See also: SHA-3.