---
slug: c11-sha3
title: "C11 SHA-3"
date: "2023-09-05T02:25:14-04:00"
---
This weekend I put together a [C11][] implementation of the following
[SHA-3][] algorithms from [FIPS 202][], [SP 800-185][800-185], and the
[draft KangarooTwelve and TurboSHAKE specification][turboshake-ietf]:

* SHA3-224, SHA3-256, SHA3-384, and SHA3-512
* SHAKE128 and SHAKE256
* HMAC-SHA3-224, HMAC-SHA3-256, HMAC-SHA3-384, and HMAC-SHA3-512
* cSHAKE128, cSHAKE128-XOF, cSHAKE256, and cSHAKE256-XOF
* KMAC128, KMAC128-XOF, KMAC256, and KMAC256-XOF
* TupleHash128, TupleHash128-XOF, TupleHash256, and TupleHash256-XOF
* ParallelHash128, ParallelHash128-XOF, ParallelHash256, and ParallelHash256-XOF
* TurboSHAKE128 and TurboSHAKE256
* KangarooTwelve

[Git Repository][repo], [API Documentation][api-docs]

## Features

* [MIT-0 licensed][mit]
* Standard [C11][] with no external dependencies.
* No allocations.
* Easy to embed: drop `sha3.h` and `sha3.c` into your application.
* Full Doxygen API documentation (available online [here][api-docs]).
* Full test suite based on test vectors from the [NIST Cryptographic Algorithm Validation Program (CAVP)][cavp], the [NIST CSRC Examples with Intermediate Values page][csrc-examples]. and the [Test Vectors section of the draft KangarooTwelve and TurboSHAKE specification][turboshake-ietf-test-vectors].

## Example

```c
// example.c: print hex-encode sha3-256 hash of each command-line argument
//
// build:
//   cc -o example -std=c11 -O3 -W -Wall -Wextra -Werror -pedantic -march=native -mtune=native example.c sha3.c
#include <stdint.h> // uint8_t
#include <stdio.h> // printf()
#include <string.h> // strlen()
#include "sha3.h" // sha3_256()

// print hex-encoded buffer to stdout.
static void print_hex(const uint8_t * const buf, const size_t len) {
  for (size_t i = 0; i < len; i++) {
    printf("%02x", buf[i]);
  }
}

int main(int argc, char *argv[]) {
  // loop over command-line arguments
  for (int i = 1; i < argc; i++) {
    // hash argument
    uint8_t buf[32] = { 0 };
    sha3_256((uint8_t*) argv[i], strlen(argv[i]), buf);

    // print argument and hex-encoded hash
    printf("\"%s\",", argv[i]);
    print_hex(buf, sizeof(buf));
    fputs("\n", stdout);
  }

  // return success
  return 0;
}
```
&nbsp;

Output:

```sh
> ./example asdf foo bar
"asdf",dd2781f4c51bccdbe23e4d398b8a82261f585c278dbb4b84989fea70e76723a9
"foo",76d3bc41c9f588f7fcd0d5bf4718f8f84b1c41b20882703100b9eb9413807c01
"bar",cceefd7e0545bcf8b6d19f3b5750c8a3ee8350418877bc6fb12e32de28137355
```
&nbsp;

**Update (2023-09-07):** Released v0.2 with TurboSHAKE128,
TurboSHAKE256, KangarooTwelve, and an `examples/` directory.

**Update (2023-09-18):** Released v0.3 with [AVX-512][] support (~3x
faster) and miscellaneous small fixes.

**Update (2023-10-15):** Released v0.4 with lots of documentation
improvements.

**Update (2023-10-19):** Released v0.5 with more documentation
improvements and additional examples.  added [online API
documentation][api-docs].

**Update (2024-03-02):** Released v0.6 with speed improvements,
simplified SHAKE API, and documentation updates. Added [CAVP][] test
vectors.

[C11]: https://en.wikipedia.org/wiki/C11_(C_standard_revision)
  "ISO/IEC 9899:2011"
[SHA-3]: https://en.wikipedia.org/wiki/SHA-3
  "Secure Hash Algorithm 3"
[FIPS 202]: https://csrc.nist.gov/pubs/fips/202/final
  "SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions"
[800-185]: https://csrc.nist.gov/pubs/sp/800/185/final
  "SHA-3 Derived Functions: cSHAKE, KMAC, TupleHash, and ParallelHash"
[repo]: https://github.com/pablotron/sha3
  "sha3 github repository"
[mit]: https://opensource.org/license/mit-0/
  "MIT No Attribution License"
[csrc-examples]: https://csrc.nist.gov/projects/cryptographic-standards-and-guidelines/example-values
  "NIST CSRC: Cryptographic Standards and Guidelines: Examples with Intermediate Values"
[avx-512]: https://en.wikipedia.org/wiki/AVX-512
  "AVX-512 x86-64 SIMD instructions."
[api-docs]: https://pmdn.org/api-docs/sha3/
  "online API documentation"
[cavp]: https://csrc.nist.gov/Projects/Cryptographic-Algorithm-Validation-Program/Secure-Hashing
  "NIST Cryptographic Algorithm Validation Program (CAVP)"
[turboshake]: https://eprint.iacr.org/2023/342.pdf
  "TurboSHAKE"
[turboshake-ietf]: https://www.ietf.org/archive/id/draft-irtf-cfrg-kangarootwelve-10.html
  "KangarooTwelve and TurboSHAKE"
[turboshake-ietf-test-vectors]: https://www.ietf.org/archive/id/draft-irtf-cfrg-kangarootwelve-10.html#name-test-vectors
  "KangarooTwelve and TurboSHAKE test vectors"