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)
53int 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 */
64const unsigned char msg1_part1[] = { 0x01, 0x02 };
65const unsigned char msg1_part2[] = { 0x03, 0x04 };
66const unsigned char msg2_part1[] = { 0x05, 0x05 };
67const 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. */
71const unsigned char key_bytes[32] = { 0 };
72
73/* Print the contents of a buffer in hex */
74void 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 */
105psa_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
146exit:
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
154int 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
167exit:
168    return status == PSA_SUCCESS ? EXIT_SUCCESS : EXIT_FAILURE;
169}
170
171#endif
172