---
date: "2019-08-25T07:35:23Z"
title: Self-Contained C11 SHA-2 Implementation
---

Last month I wrote a [C11][] [SHA-2][] implementation.

Features:
* Self-contained (no external dependencies)
* C11 only (platform-agnostic)
* MIT-licensed
* Includes [test vectors][] (via `make test`).

The code is available [here][].

It includes implementations of the following:
* SHA-224
* SHA-256
* SHA-384
* SHA-512
* HMAC-SHA256
* HMAC-SHA512

This implementation is faster than [coreutils][], but slower than the
[assembly-optimized, processor family-specific OpenSSL SHA-2
implementation][openssl-asm-sha]:

```
> time -p ./sha256 ~/Videos/8x*avi > /dev/null
rleal 9.39
user 9.10
sys 0.29
> time -p sha256sum ~/Videos/8x*avi > /dev/null
real 12.04
user 11.73
sys 0.31
> time -p openssl sha256 ~/Videos/8x*avi > /dev/null
real 6.36
user 6.01
sys 0.32
```

[sha-2]: https://en.wikipedia.org/wiki/SHA-2
  "Secure Hash Algorithm 2"
[c11]: https://en.wikipedia.org/wiki/C11_(C_standard_revision)
  "C11 standard of the C programming language"
[coreutils]: https://www.gnu.org/software/coreutils/
  "GNU core utilities"
[openssl-asm-sha]: https://github.com/openssl/openssl/tree/master/crypto/sha/asm
  "assembly-optimized OpenSSL SHA-2 implementation."
[here]: https://github.com/pablotron/sha2
  "C11 SHA-2 implementation."
[test vectors]: https://www.di-mgt.com.au/sha_testvectors.html
  "SHA test vectors."