/* This file is part of Eclat
   Copyright (C) 2012-2023 Sergey Poznyakoff
 
   Eclat is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.
 
   Eclat is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
 
   You should have received a copy of the GNU General Public License
   along with Eclat.  If not, see <http://www.gnu.org/licenses/>. */

#include <config.h>
#include "libeclat.h"
#include "sha1.h"
#include <string.h>

#define IPAD 0x36
#define OPAD 0x5c

void
hmac_sha1(const void *text, size_t textlen,
	  const void *key, size_t keylen,
	  void *digest)
{
	size_t i;
	struct sha1_ctx ctx;
	char innerhash[20];
	char keybuf[20];
	unsigned char ipad[64];    /* inner padding - key ^ ipad[64] */
        unsigned char opad[64];    /* outer padding - key ^ opad[64] */
	unsigned char *kp = (unsigned char *)key;
	
	/* if key is longer than 64 bytes reset it to key=SHA1(key) */
	if (keylen > 64) {
		struct sha1_ctx keyhash;

		sha1_init_ctx(&keyhash);
		sha1_process_bytes(key, keylen, &keyhash);
		sha1_finish_ctx(&keyhash, keybuf);
		key = keybuf;
		keylen = sizeof(keybuf);
	}

	/* Compute SHA1(K XOR opad, SHA1(K XOR ipad, text)),
	   where
	     K is an key, padded to 64 bytes with zeros,
	     ipad and opad are the respective defines above repeated 64 times
	     text is the text argument (textlen bytes long)
         */
	memset(ipad, IPAD,  sizeof(ipad));
	memset(opad, OPAD, sizeof(opad));

	for (i = 0; i < keylen; i++, kp++) {
		ipad[i] ^= *kp;
		opad[i] ^= *kp;
	}

	/* Compute inner hash */
	sha1_init_ctx(&ctx);
	sha1_process_block(ipad, sizeof(ipad), &ctx);
	sha1_process_bytes(text, textlen, &ctx);
	sha1_finish_ctx(&ctx, innerhash);

	/* Compute outer hash */
	sha1_init_ctx(&ctx);
	sha1_process_block(opad, sizeof(opad), &ctx);
	sha1_process_bytes(innerhash, sizeof(innerhash), &ctx);
	sha1_finish_ctx(&ctx, digest);
}