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 }
80 printf("\n");
81 }
82
83 /* Run a PSA function and bail out if it fails.
84 * The symbolic name of the error code can be recovered using:
85 * programs/psa/psa_constant_name status <value> */
86 #define PSA_CHECK(expr) \
87 do \
88 { \
89 status = (expr); \
90 if (status != PSA_SUCCESS) \
91 { \
92 printf("Error %d at line %d: %s\n", \
93 (int) status, \
94 __LINE__, \
95 #expr); \
96 goto exit; \
97 } \
98 } \
99 while (0)
100
101 /*
102 * This function demonstrates computation of the HMAC of two messages using
103 * the multipart API.
104 */
hmac_demo(void)105 psa_status_t hmac_demo(void)
106 {
107 psa_status_t status;
108 const psa_algorithm_t alg = PSA_ALG_HMAC(PSA_ALG_SHA_256);
109 uint8_t out[PSA_MAC_MAX_SIZE]; // safe but not optimal
110 /* PSA_MAC_LENGTH(PSA_KEY_TYPE_HMAC, 8 * sizeof( key_bytes ), alg)
111 * should work but see https://github.com/Mbed-TLS/mbedtls/issues/4320 */
112
113 psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
114 psa_key_id_t key = 0;
115
116 /* prepare key */
117 psa_set_key_usage_flags(&attributes, PSA_KEY_USAGE_SIGN_MESSAGE);
118 psa_set_key_algorithm(&attributes, alg);
119 psa_set_key_type(&attributes, PSA_KEY_TYPE_HMAC);
120 psa_set_key_bits(&attributes, 8 * sizeof(key_bytes)); // optional
121
122 status = psa_import_key(&attributes,
123 key_bytes, sizeof(key_bytes), &key);
124 if (status != PSA_SUCCESS) {
125 return status;
126 }
127
128 /* prepare operation */
129 psa_mac_operation_t op = PSA_MAC_OPERATION_INIT;
130 size_t out_len = 0;
131
132 /* compute HMAC(key, msg1_part1 | msg1_part2) */
133 PSA_CHECK(psa_mac_sign_setup(&op, key, alg));
134 PSA_CHECK(psa_mac_update(&op, msg1_part1, sizeof(msg1_part1)));
135 PSA_CHECK(psa_mac_update(&op, msg1_part2, sizeof(msg1_part2)));
136 PSA_CHECK(psa_mac_sign_finish(&op, out, sizeof(out), &out_len));
137 print_buf("msg1", out, out_len);
138
139 /* compute HMAC(key, msg2_part1 | msg2_part2) */
140 PSA_CHECK(psa_mac_sign_setup(&op, key, alg));
141 PSA_CHECK(psa_mac_update(&op, msg2_part1, sizeof(msg2_part1)));
142 PSA_CHECK(psa_mac_update(&op, msg2_part2, sizeof(msg2_part2)));
143 PSA_CHECK(psa_mac_sign_finish(&op, out, sizeof(out), &out_len));
144 print_buf("msg2", out, out_len);
145
146 exit:
147 psa_mac_abort(&op); // needed on error, harmless on success
148 psa_destroy_key(key);
149 mbedtls_platform_zeroize(out, sizeof(out));
150
151 return status;
152 }
153
main(void)154 int main(void)
155 {
156 psa_status_t status = PSA_SUCCESS;
157
158 /* Initialize the PSA crypto library. */
159 PSA_CHECK(psa_crypto_init());
160
161 /* Run the demo */
162 PSA_CHECK(hmac_demo());
163
164 /* Deinitialize the PSA crypto library. */
165 mbedtls_psa_crypto_free();
166
167 exit:
168 return status == PSA_SUCCESS ? EXIT_SUCCESS : EXIT_FAILURE;
169 }
170
171 #endif
172
