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 OR GPL-2.0-or-later
24 */
25
26 /* First include Mbed TLS headers to get the Mbed TLS configuration and
27 * platform definitions that we'll use in this program. Also include
28 * standard C headers for functions we'll use here. */
29 #include "mbedtls/build_info.h"
30
31 #include "psa/crypto.h"
32
33 #include "mbedtls/platform_util.h" // for mbedtls_platform_zeroize
34
35 #include <stdlib.h>
36 #include <stdio.h>
37
38 /* If the build options we need are not enabled, compile a placeholder. */
39 #if !defined(MBEDTLS_PSA_CRYPTO_C) || \
40 defined(MBEDTLS_PSA_CRYPTO_KEY_ID_ENCODES_OWNER)
main(void)41 int main(void)
42 {
43 printf("MBEDTLS_PSA_CRYPTO_C not defined, "
44 "and/or MBEDTLS_PSA_CRYPTO_KEY_ID_ENCODES_OWNER defined\r\n");
45 return 0;
46 }
47 #else
48
49 /* The real program starts here. */
50
51 /* Dummy inputs for HMAC */
52 const unsigned char msg1_part1[] = { 0x01, 0x02 };
53 const unsigned char msg1_part2[] = { 0x03, 0x04 };
54 const unsigned char msg2_part1[] = { 0x05, 0x05 };
55 const unsigned char msg2_part2[] = { 0x06, 0x06 };
56
57 /* Dummy key material - never do this in production!
58 * This example program uses SHA-256, so a 32-byte key makes sense. */
59 const unsigned char key_bytes[32] = { 0 };
60
61 /* Print the contents of a buffer in hex */
print_buf(const char * title,uint8_t * buf,size_t len)62 void print_buf(const char *title, uint8_t *buf, size_t len)
63 {
64 printf("%s:", title);
65 for (size_t i = 0; i < len; i++) {
66 printf(" %02x", buf[i]);
67 }
68 printf("\n");
69 }
70
71 /* Run a PSA function and bail out if it fails.
72 * The symbolic name of the error code can be recovered using:
73 * programs/psa/psa_constant_name status <value> */
74 #define PSA_CHECK(expr) \
75 do \
76 { \
77 status = (expr); \
78 if (status != PSA_SUCCESS) \
79 { \
80 printf("Error %d at line %d: %s\n", \
81 (int) status, \
82 __LINE__, \
83 #expr); \
84 goto exit; \
85 } \
86 } \
87 while (0)
88
89 /*
90 * This function demonstrates computation of the HMAC of two messages using
91 * the multipart API.
92 */
hmac_demo(void)93 psa_status_t hmac_demo(void)
94 {
95 psa_status_t status;
96 const psa_algorithm_t alg = PSA_ALG_HMAC(PSA_ALG_SHA_256);
97 uint8_t out[PSA_MAC_MAX_SIZE]; // safe but not optimal
98 /* PSA_MAC_LENGTH(PSA_KEY_TYPE_HMAC, 8 * sizeof( key_bytes ), alg)
99 * should work but see https://github.com/Mbed-TLS/mbedtls/issues/4320 */
100
101 psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
102 psa_key_id_t key = 0;
103
104 /* prepare key */
105 psa_set_key_usage_flags(&attributes, PSA_KEY_USAGE_SIGN_MESSAGE);
106 psa_set_key_algorithm(&attributes, alg);
107 psa_set_key_type(&attributes, PSA_KEY_TYPE_HMAC);
108 psa_set_key_bits(&attributes, 8 * sizeof(key_bytes)); // optional
109
110 status = psa_import_key(&attributes,
111 key_bytes, sizeof(key_bytes), &key);
112 if (status != PSA_SUCCESS) {
113 return status;
114 }
115
116 /* prepare operation */
117 psa_mac_operation_t op = PSA_MAC_OPERATION_INIT;
118 size_t out_len = 0;
119
120 /* compute HMAC(key, msg1_part1 | msg1_part2) */
121 PSA_CHECK(psa_mac_sign_setup(&op, key, alg));
122 PSA_CHECK(psa_mac_update(&op, msg1_part1, sizeof(msg1_part1)));
123 PSA_CHECK(psa_mac_update(&op, msg1_part2, sizeof(msg1_part2)));
124 PSA_CHECK(psa_mac_sign_finish(&op, out, sizeof(out), &out_len));
125 print_buf("msg1", out, out_len);
126
127 /* compute HMAC(key, msg2_part1 | msg2_part2) */
128 PSA_CHECK(psa_mac_sign_setup(&op, key, alg));
129 PSA_CHECK(psa_mac_update(&op, msg2_part1, sizeof(msg2_part1)));
130 PSA_CHECK(psa_mac_update(&op, msg2_part2, sizeof(msg2_part2)));
131 PSA_CHECK(psa_mac_sign_finish(&op, out, sizeof(out), &out_len));
132 print_buf("msg2", out, out_len);
133
134 exit:
135 psa_mac_abort(&op); // needed on error, harmless on success
136 psa_destroy_key(key);
137 mbedtls_platform_zeroize(out, sizeof(out));
138
139 return status;
140 }
141
main(void)142 int main(void)
143 {
144 psa_status_t status = PSA_SUCCESS;
145
146 /* Initialize the PSA crypto library. */
147 PSA_CHECK(psa_crypto_init());
148
149 /* Run the demo */
150 PSA_CHECK(hmac_demo());
151
152 /* Deinitialize the PSA crypto library. */
153 mbedtls_psa_crypto_free();
154
155 exit:
156 return status == PSA_SUCCESS ? EXIT_SUCCESS : EXIT_FAILURE;
157 }
158
159 #endif
160
