From 5cac33ef15c2f0769f0f0e85e02551732733cd0d Mon Sep 17 00:00:00 2001
From: Paul Duncan <pabs@pablotron.org>
Date: Tue, 5 Sep 2023 02:54:14 -0400
Subject: add content/posts/2023-09-05-c11-sha3.md

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+---
+slug: c11-sha3
+title: "C11 Sha3"
+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][] and [SP 800-185][800-185]:
+
+* SHA3-224
+* SHA3-256
+* SHA3-384
+* SHA3-512
+* HMAC-SHA3-224
+* HMAC-SHA3-256
+* HMAC-SHA3-384
+* HMAC-SHA3-512
+* SHAKE128 and SHAKE128-XOF
+* SHAKE256 and SHAKE256-XOF
+* cSHAKE128 and cSHAKE128-XOF
+* cSHAKE256 and cSHAKE256-XOF
+* KMAC128 and KMAC128-XOF
+* KMAC256 and KMAC256-XOF
+* TupleHash128 and TupleHash128-XOF
+* TupleHash256 and TupleHash256-XOF
+* ParallelHash128 and ParallelHash128-XOF
+* ParallelHash256 and ParallelHash256-XOF
+
+The code is available in the [Git repository][repo].
+
+## Features
+
+* [MIT licensed][mit]
+* Standard [C11][] with no external dependencies.
+* No allocations.
+* Easy to embed; drop `sha3.h` and `sha3.c` into your application.
+* Full Doxygen-friendly API documentation.
+* Full test suite based on test vectors from the [NIST CSRC Examples
+  with Intermediate Values][csrc-examples] page.
+
+## 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;
+}
+```
+
+Output:
+
+```sh
+> ./example asdf foo bar
+"asdf",dd2781f4c51bccdbe23e4d398b8a82261f585c278dbb4b84989fea70e76723a9
+"foo",76d3bc41c9f588f7fcd0d5bf4718f8f84b1c41b20882703100b9eb9413807c01
+"bar",cceefd7e0545bcf8b6d19f3b5750c8a3ee8350418877bc6fb12e32de28137355
+```
+
+[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"
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