Fast, pure and practical SHA-256 implementation

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LTS Haskell 22.26:
Stackage Nightly 2024-06-21:
Latest on Hackage:

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BSD-3-Clause licensed
This version can be pinned in stack with:cryptohash-sha256-,5417

Module documentation for

Depends on 2 packages(full list with versions):
Used by 3 packages in lts-12.14(full list with versions):

A practical incremental and one-pass, pure API to the SHA-256 cryptographic hash algorithm according to FIPS 180-4 with performance close to the fastest implementations available in other languages.

The core SHA-256 algorithm is implemented in C and is thus expected to be as fast as the standard sha256sum(1) tool; for instance, on an Intel Core i7-3770 at 3.40GHz this implementation can compute a SHA-256 hash over 230 MiB of data in under one second. (If, instead, you require a pure Haskell implementation and performance is secondary, please refer to the SHA package.)

Additionally, this package provides support for

conforming to RFC6234, RFC4231, RFC5869, et al..

Packages in the cryptohash-* family

Relationship to the cryptohash package and its API

This package has been originally a fork of cryptohash-0.11.7 because the cryptohash package had been deprecated and so this package continues to satisfy the need for a lightweight package providing the SHA-256 hash algorithm without any dependencies on packages other than base and bytestring. The API exposed by cryptohash-sha256-0.11.*'s Crypto.Hash.SHA256 module is guaranteed to remain a compatible superset of the API provided by the cryptohash-0.11.7's module of the same name.

Consequently, this package is designed to be used as a drop-in replacement for cryptohash-0.11.7's Crypto.Hash.SHA256 module, though with a clearly smaller footprint by almost 3 orders of magnitude.


  • Add hkdf function providing HKDF-SHA256 conforming to RFC5869

  • Declare Crypto.Hash.SHA256 module -XTrustworthy

  • Remove ineffective RULES

  • Convert to CApiFFI

  • Added ...AndLength variants of hashing functions:

    • finalizeAndLength
    • hashlazyAndLength
    • hmaclazyAndLength
  • Minor optimizations in hmac and hash

  • Use __builtin_bswap{32,64} only with GCC >= 4.3 (#1)

  • new hmac and hmaclazy functions providing HMAC-SHA256 computation conforming to RFC2104 and RFC4231
  • fix unaligned memory-accesses

  • switch to ‘safe’ FFI for calls where overhead becomes neglible
  • removed inline assembly in favour of portable C constructs
  • fix 32bit length overflow bug in hash function
  • fix inaccurate context-size
  • add context-size verification to incremental API operations

  • first version forked off cryptohash-0.11.7 release