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/*
* Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program 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 2 of the
* License, or any later version.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
FILE_LICENCE ( GPL2_OR_LATER );
/**
* @file
*
* Keyed-Hashing for Message Authentication
*/
#include <string.h>
#include <assert.h>
#include <ipxe/crypto.h>
#include <ipxe/hmac.h>
/**
* Reduce HMAC key length
*
* @v digest Digest algorithm to use
* @v digest_ctx Digest context
* @v key Key
* @v key_len Length of key
*/
static void hmac_reduce_key ( struct digest_algorithm *digest,
void *key, size_t *key_len ) {
uint8_t digest_ctx[digest->ctxsize];
digest_init ( digest, digest_ctx );
digest_update ( digest, digest_ctx, key, *key_len );
digest_final ( digest, digest_ctx, key );
*key_len = digest->digestsize;
}
/**
* Initialise HMAC
*
* @v digest Digest algorithm to use
* @v digest_ctx Digest context
* @v key Key
* @v key_len Length of key
*
* The length of the key should be less than the block size of the
* digest algorithm being used. (If the key length is greater, it
* will be replaced with its own digest, and key_len will be updated
* accordingly).
*/
void hmac_init ( struct digest_algorithm *digest, void *digest_ctx,
void *key, size_t *key_len ) {
unsigned char k_ipad[digest->blocksize];
unsigned int i;
/* Reduce key if necessary */
if ( *key_len > sizeof ( k_ipad ) )
hmac_reduce_key ( digest, key, key_len );
/* Construct input pad */
memset ( k_ipad, 0, sizeof ( k_ipad ) );
memcpy ( k_ipad, key, *key_len );
for ( i = 0 ; i < sizeof ( k_ipad ) ; i++ ) {
k_ipad[i] ^= 0x36;
}
/* Start inner hash */
digest_init ( digest, digest_ctx );
digest_update ( digest, digest_ctx, k_ipad, sizeof ( k_ipad ) );
}
/**
* Finalise HMAC
*
* @v digest Digest algorithm to use
* @v digest_ctx Digest context
* @v key Key
* @v key_len Length of key
* @v hmac HMAC digest to fill in
*
* The length of the key should be less than the block size of the
* digest algorithm being used. (If the key length is greater, it
* will be replaced with its own digest, and key_len will be updated
* accordingly).
*/
void hmac_final ( struct digest_algorithm *digest, void *digest_ctx,
void *key, size_t *key_len, void *hmac ) {
unsigned char k_opad[digest->blocksize];
unsigned int i;
/* Reduce key if necessary */
if ( *key_len > sizeof ( k_opad ) )
hmac_reduce_key ( digest, key, key_len );
/* Construct output pad */
memset ( k_opad, 0, sizeof ( k_opad ) );
memcpy ( k_opad, key, *key_len );
for ( i = 0 ; i < sizeof ( k_opad ) ; i++ ) {
k_opad[i] ^= 0x5c;
}
/* Finish inner hash */
digest_final ( digest, digest_ctx, hmac );
/* Perform outer hash */
digest_init ( digest, digest_ctx );
digest_update ( digest, digest_ctx, k_opad, sizeof ( k_opad ) );
digest_update ( digest, digest_ctx, hmac, digest->digestsize );
digest_final ( digest, digest_ctx, hmac );
}
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