Overview

FIPS PUB 180-4, the Secure Hash Standard (SHS), is a U.S. Federal Information Processing Standard published by the National Institute of Standards and Technology (NIST), U.S. Department of Commerce, in August 2015. It specifies cryptographic hash algorithms that compute a fixed-length message digest from an arbitrary-length input message. These digests are used to detect whether a message has been altered since the digest was generated, and they underpin authentication, digital signatures, and data-integrity applications.

Key points

• Specifies seven secure hash algorithms: SHA-1 and the SHA-2 family, comprising SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, and SHA-512/256.
• SHA-256 produces a 256-bit (32-byte) digest, operating on 512-bit message blocks using 32-bit words and 64 rounds of compression.
• Each algorithm is iterative and one-way: it is computationally infeasible to recover the input from a digest or to find two distinct inputs that hash to the same digest (collision resistance).
• Defines the message padding, parsing, initial hash values, and the round functions and constants for each variant.
• Published under DOI 10.6028/NIST.FIPS.180-4.

Relevance to Truestamp

This standard defines SHA-256, the hash function Truestamp uses throughout its system, applied with RFC 6962-style byte-prefix domain separation as recorded in the byte-prefix registry. It is cited in the Truestamp whitepaper.

Citations

1. Secure Hash Standard (SHS). National Institute of Standards and Technology (NIST), U.S. Department of Commerce, FIPS PUB 180-4, August 2015.