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/*
* cifra - embedded cryptography library
* Written in 2014 by Joseph Birr-Pixton <jpixton@gmail.com>
*
* To the extent possible under law, the author(s) have dedicated all
* copyright and related and neighboring rights to this software to the
* public domain worldwide. This software is distributed without any
* warranty.
*
* You should have received a copy of the CC0 Public Domain Dedication
* along with this software. If not, see
* <http://creativecommons.org/publicdomain/zero/1.0/>.
*/
#include "hmac.h"
#include "chash.h"
#include "bitops.h"
#include "handy.h"
#include "tassert.h"
#include <string.h>
void cf_hmac_init(cf_hmac_ctx *ctx,
const cf_chash *hash,
const uint8_t *key, size_t nkey)
{
assert(ctx);
assert(hash);
mem_clean(ctx, sizeof *ctx);
ctx->hash = hash;
/* Prepare key: */
uint8_t k[CF_CHASH_MAXBLK];
/* Shorten long keys. */
if (nkey > hash->blocksz)
{
/* Standard doesn't cover case where blocksz < hashsz.
* FIPS186-1 seems to want to append a negative number of zero bytes.
* In any case, we only have a k buffer of CF_CHASH_MAXBLK! */
assert(hash->hashsz <= hash->blocksz);
cf_hash(hash, key, nkey, k);
key = k;
nkey = hash->hashsz;
}
/* Right zero-pad short keys. */
if (k != key)
memcpy(k, key, nkey);
if (hash->blocksz > nkey)
memset(k + nkey, 0, hash->blocksz - nkey);
/* Start inner hash computation */
uint8_t blk[CF_CHASH_MAXBLK];
xor_b8(blk, k, 0x36, hash->blocksz);
hash->init(&ctx->inner);
hash->update(&ctx->inner, blk, hash->blocksz);
/* And outer. */
xor_b8(blk, k, 0x5c, hash->blocksz);
hash->init(&ctx->outer);
hash->update(&ctx->outer, blk, hash->blocksz);
mem_clean(blk, sizeof blk);
mem_clean(k, sizeof k);
}
void cf_hmac_update(cf_hmac_ctx *ctx, const void *data, size_t ndata)
{
assert(ctx && ctx->hash);
ctx->hash->update(&ctx->inner, data, ndata);
}
void cf_hmac_finish(cf_hmac_ctx *ctx, uint8_t *out)
{
assert(ctx && ctx->hash);
assert(out);
uint8_t innerh[CF_MAXHASH];
ctx->hash->digest(&ctx->inner, innerh);
ctx->hash->update(&ctx->outer, innerh, ctx->hash->hashsz);
ctx->hash->digest(&ctx->outer, out);
mem_clean(ctx, sizeof *ctx);
}
void cf_hmac(const uint8_t *key, size_t nkey,
const uint8_t *msg, size_t nmsg,
uint8_t *out,
const cf_chash *hash)
{
cf_hmac_ctx ctx;
assert(out);
assert(hash);
cf_hmac_init(&ctx, hash, key, nkey);
cf_hmac_update(&ctx, msg, nmsg);
cf_hmac_finish(&ctx, out);
}
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