/*
hmac_sha256.c
Originally written by https://github.com/h5p9sl
*/

#include "hmac_sha256.h"

#include "sha256crypt.h"

#include <stdlib.h>
#include <string.h>

#define SHA256_BLOCK_SIZE	64

static void*	H(const void* x, const size_t xlen,const void* y, const size_t ylen, void* out, const size_t outlen);

size_t	hmac_sha256(const void* key, const size_t keylen, const void* data, const size_t datalen, void* out,
		const size_t outlen)
{
	uint8_t	k[SHA256_BLOCK_SIZE], k_ipad[SHA256_BLOCK_SIZE], k_opad[SHA256_BLOCK_SIZE],
		ihash[ZBX_SHA256_DIGEST_SIZE], ohash[ZBX_SHA256_DIGEST_SIZE];
	size_t	sz;
	int	i;

	memset(k, 0, sizeof(k));
	memset(k_ipad, 0x36, SHA256_BLOCK_SIZE);
	memset(k_opad, 0x5c, SHA256_BLOCK_SIZE);

	if (keylen > SHA256_BLOCK_SIZE)
	{
		/* If the key is larger than the hash algorithm's
		block size, we must digest it first.
		sha256(key, keylen, k, sizeof(k));*/
		zbx_sha256_hash_for_hmac(key, keylen, k, sizeof(k));
	}
	else
		memcpy(k, key, keylen);

	for (i = 0; i < SHA256_BLOCK_SIZE; i++)
	{
		k_ipad[i] ^= k[i];
		k_opad[i] ^= k[i];
	}

	/* Perform HMAC algorithm: ( https://tools.ietf.org/html/rfc2104 )
	`H(K XOR opad, H(K XOR ipad, data))` */
	H(k_ipad, sizeof(k_ipad), data, datalen, ihash, sizeof(ihash));
	H(k_opad, sizeof(k_opad), ihash, sizeof(ihash), ohash, sizeof(ohash));

	sz = (outlen > ZBX_SHA256_DIGEST_SIZE) ? ZBX_SHA256_DIGEST_SIZE : outlen;
	memcpy(out, ohash, sz);

	return sz;
}

static void*	H(const void* x, const size_t xlen, const void* y, const size_t ylen, void* out, const size_t outlen)
{
	void*		result;
	size_t		buflen = (xlen + ylen);
	uint8_t*	buf = (uint8_t*)malloc(buflen);

	memcpy(buf, x, xlen);
	memcpy(buf + xlen, y, ylen);
	result = zbx_sha256_hash_for_hmac(buf, buflen, out, outlen);
	free(buf);

	return result;
}