1 /**
2 * PSA API multi-part HMAC demonstration.
3 *
4 * This programs computes the HMAC of two messages using the multi-part API.
5 *
6 * It comes with a companion program hash/md_hmac_demo.c, which does the same
7 * operations with the legacy MD API. The goal is that comparing the two
8 * programs will help people migrating to the PSA Crypto API.
9 *
10 * When it comes to multi-part HMAC operations, the `mbedtls_md_context`
11 * serves a dual purpose (1) hold the key, and (2) save progress information
12 * for the current operation. With PSA those roles are held by two disinct
13 * objects: (1) a psa_key_id_t to hold the key, and (2) a psa_operation_t for
14 * multi-part progress.
15 *
16 * This program and its companion hash/md_hmac_demo.c illustrate this by doing
17 * the same sequence of multi-part HMAC computation with both APIs; looking at
18 * the two side by side should make the differences and similarities clear.
19 */
20
21 /*
22 * Copyright The Mbed TLS Contributors
23 * SPDX-License-Identifier: Apache-2.0
24 *
25 * Licensed under the Apache License, Version 2.0 (the "License"); you may
26 * not use this file except in compliance with the License.
27 * You may obtain a copy of the License at
28 *
29 * http://www.apache.org/licenses/LICENSE-2.0
30 *
31 * Unless required by applicable law or agreed to in writing, software
32 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
33 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
34 * See the License for the specific language governing permissions and
35 * limitations under the License.
36 */
37
38 /* First include Mbed TLS headers to get the Mbed TLS configuration and
39 * platform definitions that we'll use in this program. Also include
40 * standard C headers for functions we'll use here. */
41 #include "mbedtls/build_info.h"
42
43 #include "psa/crypto.h"
44
45 #include "mbedtls/platform_util.h" // for mbedtls_platform_zeroize
46
47 #include <stdlib.h>
48 #include <stdio.h>
49
50 /* If the build options we need are not enabled, compile a placeholder. */
51 #if !defined(MBEDTLS_PSA_CRYPTO_C) || \
52 defined(MBEDTLS_PSA_CRYPTO_KEY_ID_ENCODES_OWNER)
main(void)53 int main( void )
54 {
55 printf( "MBEDTLS_PSA_CRYPTO_C not defined, "
56 "and/or MBEDTLS_PSA_CRYPTO_KEY_ID_ENCODES_OWNER defined\r\n" );
57 return( 0 );
58 }
59 #else
60
61 /* The real program starts here. */
62
63 /* Dummy inputs for HMAC */
64 const unsigned char msg1_part1[] = { 0x01, 0x02 };
65 const unsigned char msg1_part2[] = { 0x03, 0x04 };
66 const unsigned char msg2_part1[] = { 0x05, 0x05 };
67 const unsigned char msg2_part2[] = { 0x06, 0x06 };
68
69 /* Dummy key material - never do this in production!
70 * This example program uses SHA-256, so a 32-byte key makes sense. */
71 const unsigned char key_bytes[32] = { 0 };
72
73 /* Print the contents of a buffer in hex */
print_buf(const char * title,uint8_t * buf,size_t len)74 void print_buf( const char *title, uint8_t *buf, size_t len )
75 {
76 printf( "%s:", title );
77 for( size_t i = 0; i < len; i++ )
78 printf( " %02x", buf[i] );
79 printf( "\n" );
80 }
81
82 /* Run a PSA function and bail out if it fails.
83 * The symbolic name of the error code can be recovered using:
84 * programs/psa/psa_constant_name status <value> */
85 #define PSA_CHECK( expr ) \
86 do \
87 { \
88 status = ( expr ); \
89 if( status != PSA_SUCCESS ) \
90 { \
91 printf( "Error %d at line %d: %s\n", \
92 (int) status, \
93 __LINE__, \
94 #expr ); \
95 goto exit; \
96 } \
97 } \
98 while( 0 )
99
100 /*
101 * This function demonstrates computation of the HMAC of two messages using
102 * the multipart API.
103 */
hmac_demo(void)104 psa_status_t hmac_demo(void)
105 {
106 psa_status_t status;
107 const psa_algorithm_t alg = PSA_ALG_HMAC(PSA_ALG_SHA_256);
108 uint8_t out[PSA_MAC_MAX_SIZE]; // safe but not optimal
109 /* PSA_MAC_LENGTH(PSA_KEY_TYPE_HMAC, 8 * sizeof( key_bytes ), alg)
110 * should work but see https://github.com/Mbed-TLS/mbedtls/issues/4320 */
111
112 psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
113 psa_key_id_t key = 0;
114
115 /* prepare key */
116 psa_set_key_usage_flags( &attributes, PSA_KEY_USAGE_SIGN_MESSAGE );
117 psa_set_key_algorithm( &attributes, alg );
118 psa_set_key_type( &attributes, PSA_KEY_TYPE_HMAC );
119 psa_set_key_bits( &attributes, 8 * sizeof( key_bytes ) ); // optional
120
121 status = psa_import_key( &attributes,
122 key_bytes, sizeof( key_bytes ), &key );
123 if( status != PSA_SUCCESS )
124 return( status );
125
126 /* prepare operation */
127 psa_mac_operation_t op = PSA_MAC_OPERATION_INIT;
128 size_t out_len = 0;
129
130 /* compute HMAC(key, msg1_part1 | msg1_part2) */
131 PSA_CHECK( psa_mac_sign_setup( &op, key, alg ) );
132 PSA_CHECK( psa_mac_update( &op, msg1_part1, sizeof( msg1_part1 ) ) );
133 PSA_CHECK( psa_mac_update( &op, msg1_part2, sizeof( msg1_part2 ) ) );
134 PSA_CHECK( psa_mac_sign_finish( &op, out, sizeof( out ), &out_len ) );
135 print_buf( "msg1", out, out_len );
136
137 /* compute HMAC(key, msg2_part1 | msg2_part2) */
138 PSA_CHECK( psa_mac_sign_setup( &op, key, alg ) );
139 PSA_CHECK( psa_mac_update( &op, msg2_part1, sizeof( msg2_part1 ) ) );
140 PSA_CHECK( psa_mac_update( &op, msg2_part2, sizeof( msg2_part2 ) ) );
141 PSA_CHECK( psa_mac_sign_finish( &op, out, sizeof( out ), &out_len ) );
142 print_buf( "msg2", out, out_len );
143
144 exit:
145 psa_mac_abort( &op ); // needed on error, harmless on success
146 psa_destroy_key( key );
147 mbedtls_platform_zeroize( out, sizeof( out ) );
148
149 return( status );
150 }
151
main(void)152 int main(void)
153 {
154 psa_status_t status = PSA_SUCCESS;
155
156 /* Initialize the PSA crypto library. */
157 PSA_CHECK( psa_crypto_init( ) );
158
159 /* Run the demo */
160 PSA_CHECK( hmac_demo() );
161
162 /* Deinitialize the PSA crypto library. */
163 mbedtls_psa_crypto_free( );
164
165 exit:
166 return( status == PSA_SUCCESS ? EXIT_SUCCESS : EXIT_FAILURE );
167 }
168
169 #endif
170
