mbedtls/library/cmac.c

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/*
* NIST SP800-38B compliant CMAC implementation
*
* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* This file is part of mbed TLS (https://tls.mbed.org)
*/
/*
* Definition of CMAC:
* http://csrc.nist.gov/publications/nistpubs/800-38B/SP_800-38B.pdf
* RFC 4493 "The AES-CMAC Algorithm"
*/
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_CMAC_C)
#include "mbedtls/cmac.h"
#include <string.h>
#if defined(MBEDTLS_SELF_TEST) && defined(MBEDTLS_AES_C)
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdio.h>
#define mbedtls_printf printf
#endif /* MBEDTLS_PLATFORM_C */
#endif /* MBEDTLS_SELF_TEST && MBEDTLS_AES_C */
/* Implementation that should never be optimized out by the compiler */
static void mbedtls_zeroize( void *v, size_t n ) {
volatile unsigned char *p = v; while( n-- ) *p++ = 0;
}
/*
* Initialize context
*/
void mbedtls_cmac_init( mbedtls_cmac_context *ctx )
{
memset( ctx, 0, sizeof( mbedtls_cmac_context ) );
}
/*
* Multiply by u in GF(2^128)
*
* As explained in the paper, this can be achieved as
* If MSB(p) = 0, then p = (p << 1)
* If MSB(p) = 1, then p = (p << 1) ^ Rb
* with Rb = 0x87
*
* Input and output MUST not point to the same buffer
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*/
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static void cmac_multiply_by_u( unsigned char *output,
const unsigned char *input )
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{
const unsigned char Rb = 0x87; /* block size 16 only */
unsigned char mask;
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unsigned char overflow = 0;
int i;
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for( i = 15; i >= 0; i-- )
{
output[i] = input[i] << 1 | overflow;
overflow = input[i] >> 7;
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}
/* mask = ( input[0] >> 7 ) ? 0xff : 0x00
* using bit operations to avoid branches */
/* MSVC has a warning about unary minus on unsigned, but this is
* well-defined and precisely what we want to do here */
#if defined(_MSC_VER)
#pragma warning( push )
#pragma warning( disable : 4146 )
#endif
mask = - ( input[0] >> 7 );
#if defined(_MSC_VER)
#pragma warning( pop )
#endif
output[15] ^= Rb & mask;
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}
/*
* Generate subkeys
*/
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static int cmac_generate_subkeys( mbedtls_cmac_context *ctx )
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{
int ret;
unsigned char L[16];
size_t olen;
/* Calculate Ek(0) */
memset( L, 0, 16 );
if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx,
L, 16, L, &olen ) ) != 0 )
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{
return( ret );
}
/*
* Generate K1 and K2
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*/
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cmac_multiply_by_u( ctx->K1, L );
cmac_multiply_by_u( ctx->K2, ctx->K1 );
mbedtls_zeroize( L, sizeof( L ) );
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return( 0 );
}
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/*
* Set key and prepare context for use
*/
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int mbedtls_cmac_setkey( mbedtls_cmac_context *ctx,
mbedtls_cipher_id_t cipher,
const unsigned char *key,
unsigned int keybits )
{
int ret;
const mbedtls_cipher_info_t *cipher_info;
cipher_info = mbedtls_cipher_info_from_values( cipher, keybits,
MBEDTLS_MODE_ECB );
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if( cipher_info == NULL )
return( MBEDTLS_ERR_CMAC_BAD_INPUT );
if( cipher_info->block_size != 16 )
return( MBEDTLS_ERR_CMAC_BAD_INPUT );
mbedtls_cipher_free( &ctx->cipher_ctx );
if( ( ret = mbedtls_cipher_setup( &ctx->cipher_ctx, cipher_info ) ) != 0 )
return( ret );
if( ( ret = mbedtls_cipher_setkey( &ctx->cipher_ctx, key, keybits,
MBEDTLS_ENCRYPT ) ) != 0 )
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{
return( ret );
}
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return( cmac_generate_subkeys( ctx ) );
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}
/*
* Free context
*/
void mbedtls_cmac_free( mbedtls_cmac_context *ctx )
{
mbedtls_cipher_free( &ctx->cipher_ctx );
mbedtls_zeroize( ctx, sizeof( mbedtls_cmac_context ) );
}
/*
* Create padded last block from (partial) last block.
*
* We can't use the padding option from the cipher layer, as it only works for
* CBC and we use ECB mode, and anyway we need to XOR K1 or K2 in addition.
*/
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static void cmac_pad( unsigned char padded_block[16],
const unsigned char *last_block,
size_t length )
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{
size_t j;
for( j = 0; j < 16; j++ )
{
if( j < length )
padded_block[j] = last_block[j];
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else if( j == length )
padded_block[j] = 0x80;
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else
padded_block[j] = 0x00;
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}
}
/*
* XOR 128-bit
* Here, macro results in smaller compiled code than static inline function
*/
#define XOR_128( o, i1, i2 ) \
for( i = 0; i < 16; i++ ) \
( o )[i] = ( i1 )[i] ^ ( i2 )[i];
/*
* Update the CMAC state using an input block x
*/
#define UPDATE_CMAC( x ) \
do { \
XOR_128( state, ( x ), state ); \
if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx, \
state, 16, state, &olen ) ) != 0 ) \
return( ret ); \
} while( 0 )
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/*
* Generate tag on complete message
*/
int mbedtls_cmac_generate( mbedtls_cmac_context *ctx,
const unsigned char *input, size_t in_len,
unsigned char *tag, size_t tag_len )
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{
unsigned char state[16];
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unsigned char M_last[16];
int n, i, j, ret, needs_padding;
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size_t olen;
/*
* Check in_len requirements: SP800-38B A
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* 4 is a worst case bottom limit
*/
if( tag_len < 4 || tag_len > 16 || tag_len % 2 != 0 )
return( MBEDTLS_ERR_CMAC_BAD_INPUT );
if( in_len == 0 )
needs_padding = 1;
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else
needs_padding = in_len % 16 != 0;
n = in_len / 16 + needs_padding;
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/* Calculate last block */
if( needs_padding )
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{
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cmac_pad( M_last, input + 16 * ( n - 1 ), in_len % 16 );
XOR_128( M_last, M_last, ctx->K2 );
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}
else
{
/* Last block is complete block */
XOR_128( M_last, input + 16 * ( n - 1 ), ctx->K1 );
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}
memset( state, 0, 16 );
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for( j = 0; j < n - 1; j++ )
UPDATE_CMAC( input + 16 * j );
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UPDATE_CMAC( M_last );
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memcpy( tag, state, 16 );
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return( 0 );
}
#undef XOR_128
#undef UPDATE_CMAC
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/*
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* Verify tag on complete message
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*/
int mbedtls_cmac_verify( mbedtls_cmac_context *ctx,
const unsigned char *input, size_t in_len,
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const unsigned char *tag, size_t tag_len )
{
int ret;
unsigned char check_tag[16];
unsigned char i;
int diff;
if( ( ret = mbedtls_cmac_generate( ctx, input, in_len,
check_tag, tag_len ) ) != 0 )
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{
return ret;
}
/* Check tag in "constant-time" */
for( diff = 0, i = 0; i < tag_len; i++ )
diff |= tag[i] ^ check_tag[i];
if( diff != 0 )
return( MBEDTLS_ERR_CMAC_VERIFY_FAILED );
return( 0 );
}
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/*
* PRF based on CMAC with AES-128
* TODO: add reference to the standard
* TODO: do we need to take a cmac_context as an argument here?
*/
int mbedtls_aes_cmac_prf_128( mbedtls_cmac_context *ctx,
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const unsigned char *key, size_t key_length,
const unsigned char *input, size_t in_len,
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unsigned char *tag )
{
int ret;
unsigned char zero_key[16];
unsigned char int_key[16];
if( key_length == 16 )
{
/* Use key as is */
memcpy( int_key, key, 16 );
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}
else
{
mbedtls_cmac_context zero_ctx;
/* Key is AES_CMAC(0, key) */
mbedtls_cmac_init( &zero_ctx );
memset( zero_key, 0, 16 );
ret = mbedtls_cmac_setkey( &zero_ctx, MBEDTLS_CIPHER_ID_AES,
zero_key, 8 * sizeof zero_key );
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if( ret != 0 )
return( ret );
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ret = mbedtls_cmac_generate( &zero_ctx, key, key_length, int_key, 16 );
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if( ret != 0 )
return( ret );
}
ret = mbedtls_cmac_setkey( ctx, MBEDTLS_CIPHER_ID_AES,
int_key, 8 * sizeof int_key );
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if( ret != 0 )
return( ret );
mbedtls_zeroize( int_key, sizeof( int_key ) );
return( mbedtls_cmac_generate( ctx, input, in_len, tag, 16 ) );
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}
#if defined(MBEDTLS_SELF_TEST) && defined(MBEDTLS_AES_C)
/*
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* Examples 1 to 4 from SP800-38B corrected Appendix D.1
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* http://csrc.nist.gov/publications/nistpubs/800-38B/Updated_CMAC_Examples.pdf
*/
#define NB_CMAC_TESTS 4
#define NB_PRF_TESTS 3
/* Key */
static const unsigned char key[] = {
0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c
};
/* Assume we don't need to test Ek0 as this is a function of the cipher */
/* Subkey K1 */
static const unsigned char K1[] = {
0xfb, 0xee, 0xd6, 0x18, 0x35, 0x71, 0x33, 0x66,
0x7c, 0x85, 0xe0, 0x8f, 0x72, 0x36, 0xa8, 0xde
};
/* Subkey K2 */
static const unsigned char K2[] = {
0xf7, 0xdd, 0xac, 0x30, 0x6a, 0xe2, 0x66, 0xcc,
0xf9, 0x0b, 0xc1, 0x1e, 0xe4, 0x6d, 0x51, 0x3b
};
/* All Messages */
static const unsigned char M[] = {
0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96,
0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a,
0xae, 0x2d, 0x8a, 0x57, 0x1e, 0x03, 0xac, 0x9c,
0x9e, 0xb7, 0x6f, 0xac, 0x45, 0xaf, 0x8e, 0x51,
0x30, 0xc8, 0x1c, 0x46, 0xa3, 0x5c, 0xe4, 0x11,
0xe5, 0xfb, 0xc1, 0x19, 0x1a, 0x0a, 0x52, 0xef,
0xf6, 0x9f, 0x24, 0x45, 0xdf, 0x4f, 0x9b, 0x17,
0xad, 0x2b, 0x41, 0x7b, 0xe6, 0x6c, 0x37, 0x10
};
static const unsigned char T[NB_CMAC_TESTS][16] = {
{
0xbb, 0x1d, 0x69, 0x29, 0xe9, 0x59, 0x37, 0x28,
0x7f, 0xa3, 0x7d, 0x12, 0x9b, 0x75, 0x67, 0x46
},
{
0x07, 0x0a, 0x16, 0xb4, 0x6b, 0x4d, 0x41, 0x44,
0xf7, 0x9b, 0xdd, 0x9d, 0xd0, 0x4a, 0x28, 0x7c
},
{
0xdf, 0xa6, 0x67, 0x47, 0xde, 0x9a, 0xe6, 0x30,
0x30, 0xca, 0x32, 0x61, 0x14, 0x97, 0xc8, 0x27
},
{
0x51, 0xf0, 0xbe, 0xbf, 0x7e, 0x3b, 0x9d, 0x92,
0xfc, 0x49, 0x74, 0x17, 0x79, 0x36, 0x3c, 0xfe
}
};
/* Sizes in bytes */
static const size_t Mlen[NB_CMAC_TESTS] = {
0,
16,
40,
64
};
/* PRF K */
static const unsigned char PRFK[] = {
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
0xed, 0xcb
};
/* Sizes in bytes */
static const size_t PRFKlen[NB_PRF_TESTS] = {
18,
16,
10
};
/* PRF M */
static const unsigned char PRFM[] = {
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
0x10, 0x11, 0x12, 0x13
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};
static const unsigned char PRFT[NB_PRF_TESTS][16] = {
{
0x84, 0xa3, 0x48, 0xa4, 0xa4, 0x5d, 0x23, 0x5b,
0xab, 0xff, 0xfc, 0x0d, 0x2b, 0x4d, 0xa0, 0x9a
},
{
0x98, 0x0a, 0xe8, 0x7b, 0x5f, 0x4c, 0x9c, 0x52,
0x14, 0xf5, 0xb6, 0xa8, 0x45, 0x5e, 0x4c, 0x2d
},
{
0x29, 0x0d, 0x9e, 0x11, 0x2e, 0xdb, 0x09, 0xee,
0x14, 0x1f, 0xcf, 0x64, 0xc0, 0xb7, 0x2f, 0x3d
}
};
int mbedtls_cmac_self_test( int verbose )
{
mbedtls_cmac_context ctx;
unsigned char tag[16];
int i;
int ret;
mbedtls_cmac_init( &ctx );
if( mbedtls_cmac_setkey( &ctx, MBEDTLS_CIPHER_ID_AES, key, 8 * sizeof key ) != 0 )
{
if( verbose != 0 )
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mbedtls_printf( " CMAC: setup failed\n" );
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return( 1 );
}
if( ( memcmp( ctx.K1, K1, 16 ) != 0 ) ||
( memcmp( ctx.K2, K2, 16 ) != 0 ) )
{
if( verbose != 0 )
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mbedtls_printf( " CMAC: subkey generation failed\n" );
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return( 1 );
}
for( i = 0; i < NB_CMAC_TESTS; i++ )
{
mbedtls_printf( " AES-128-CMAC #%u: ", i );
ret = mbedtls_cmac_generate( &ctx, M, Mlen[i], tag, 16 );
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if( ret != 0 ||
memcmp( tag, T[i], 16 ) != 0 )
{
if( verbose != 0 )
mbedtls_printf( "failed\n" );
return( 1 );
}
ret = mbedtls_cmac_verify( &ctx, M, Mlen[i], T[i], 16 );
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if( ret != 0 )
{
if( verbose != 0 )
mbedtls_printf( "failed\n" );
return( 1 );
}
if( verbose != 0 )
mbedtls_printf( "passed\n" );
}
for( i = 0; i < NB_PRF_TESTS; i++ )
{
mbedtls_printf( " AES-CMAC-128-PRF #%u: ", i );
mbedtls_aes_cmac_prf_128( &ctx, PRFK, PRFKlen[i], PRFM, 20, tag );
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if( ret != 0 ||
memcmp( tag, PRFT[i], 16 ) != 0 )
{
if( verbose != 0 )
mbedtls_printf( "failed\n" );
return( 1 );
}
if( verbose != 0 )
mbedtls_printf( "passed\n" );
}
mbedtls_cmac_free( &ctx );
if( verbose != 0 )
mbedtls_printf( "\n" );
return( 0 );
}
#endif /* MBEDTLS_SELF_TEST && MBEDTLS_AES_C */
#endif /* MBEDTLS_CMAC_C */