SHA0

SHA-0, short for Secure Hash Algorithm 0, is the original member of the SHA cryptographic hash family. It produces a 160-bit hash value and was published in 1993 as part of FIPS 180. Designed for digital fingerprints and data integrity, SHA-0 was intended to be a fast, secure one-way function that processes input in 512-bit blocks and compresses information into a fixed-size digest.

Cryptographic details: SHA-0 uses a five-word (160-bit) state and an 80-round compression function similar to later SHA designs, but it lacks one small change found in SHA-1. Specifically, the message schedule in SHA-0 computes the expanded words as W_t = W_{t-3} XOR W_{t-8} XOR W_{t-14} XOR W_{t-16} for t from 16 to 79, with no additional rotation. SHA-1 adds a left-rotate by 1 bit during this expansion. This subtle difference alters the algebraic structure of the algorithm.

Security and history: In the mid-1990s, researchers demonstrated cryptanalytic weaknesses in SHA-0, including practical collision attacks. In response, NIST adopted SHA-1, introducing the rotation and other refinements, and SHA-0 was phased out of use. Today SHA-0 is considered insecure for modern cryptographic deployments and is largely of historical interest.

Legacy and context: SHA-0’s significance lies in its role as the precursor to SHA-1 and the broader SHA family. The field later expanded with SHA-2 and SHA-3 to address stronger security goals, and contemporary standards for digital signatures and integrity rely on SHA-2 or SHA-3 rather than SHA-0.