hmac_demo.c (5696B)
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) 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 */ 62 static 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 */ 93 static 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 } 141 142 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