136 lines
4.6 KiB
C
136 lines
4.6 KiB
C
/**
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* MD API multi-part HMAC demonstration.
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*
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* This programs computes the HMAC of two messages using the multi-part API.
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*
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* This is a companion to psa/hmac_demo.c, doing the same operations with the
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* legacy MD API. The goal is that comparing the two programs will help people
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* migrating to the PSA Crypto API.
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*
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* When it comes to multi-part HMAC operations, the `mbedtls_md_context`
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* serves a dual purpose (1) hold the key, and (2) save progress information
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* for the current operation. With PSA those roles are held by two disinct
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* objects: (1) a psa_key_id_t to hold the key, and (2) a psa_operation_t for
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* multi-part progress.
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*
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* This program and its companion psa/hmac_demo.c illustrate this by doing the
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* same sequence of multi-part HMAC computation with both APIs; looking at the
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* two side by side should make the differences and similarities clear.
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*/
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/*
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* Copyright The Mbed TLS Contributors
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* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
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*/
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/* First include Mbed TLS headers to get the Mbed TLS configuration and
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* platform definitions that we'll use in this program. Also include
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* standard C headers for functions we'll use here. */
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#include "mbedtls/build_info.h"
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#include "mbedtls/md.h"
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#include "mbedtls/platform_util.h" // for mbedtls_platform_zeroize
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#include <stdlib.h>
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#include <stdio.h>
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/* If the build options we need are not enabled, compile a placeholder. */
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#if !defined(MBEDTLS_MD_C)
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int main(void)
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{
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printf("MBEDTLS_MD_C not defined\r\n");
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return 0;
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}
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#else
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/* The real program starts here. */
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/* Dummy inputs for HMAC */
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const unsigned char msg1_part1[] = { 0x01, 0x02 };
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const unsigned char msg1_part2[] = { 0x03, 0x04 };
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const unsigned char msg2_part1[] = { 0x05, 0x05 };
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const unsigned char msg2_part2[] = { 0x06, 0x06 };
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/* Dummy key material - never do this in production!
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* This example program uses SHA-256, so a 32-byte key makes sense. */
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const unsigned char key_bytes[32] = { 0 };
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/* Print the contents of a buffer in hex */
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void print_buf(const char *title, unsigned char *buf, size_t len)
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{
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printf("%s:", title);
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for (size_t i = 0; i < len; i++) {
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printf(" %02x", buf[i]);
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}
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printf("\n");
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}
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/* Run an Mbed TLS function and bail out if it fails.
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* A string description of the error code can be recovered with:
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* programs/util/strerror <value> */
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#define CHK(expr) \
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do \
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{ \
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ret = (expr); \
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if (ret != 0) \
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{ \
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printf("Error %d at line %d: %s\n", \
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ret, \
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__LINE__, \
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#expr); \
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goto exit; \
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} \
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} while (0)
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/*
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* This function demonstrates computation of the HMAC of two messages using
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* the multipart API.
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*/
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int hmac_demo(void)
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{
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int ret;
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const mbedtls_md_type_t alg = MBEDTLS_MD_SHA256;
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unsigned char out[MBEDTLS_MD_MAX_SIZE]; // safe but not optimal
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mbedtls_md_context_t ctx;
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mbedtls_md_init(&ctx);
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/* prepare context and load key */
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// the last argument to setup is 1 to enable HMAC (not just hashing)
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const mbedtls_md_info_t *info = mbedtls_md_info_from_type(alg);
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CHK(mbedtls_md_setup(&ctx, info, 1));
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CHK(mbedtls_md_hmac_starts(&ctx, key_bytes, sizeof(key_bytes)));
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/* compute HMAC(key, msg1_part1 | msg1_part2) */
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CHK(mbedtls_md_hmac_update(&ctx, msg1_part1, sizeof(msg1_part1)));
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CHK(mbedtls_md_hmac_update(&ctx, msg1_part2, sizeof(msg1_part2)));
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CHK(mbedtls_md_hmac_finish(&ctx, out));
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print_buf("msg1", out, mbedtls_md_get_size(info));
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/* compute HMAC(key, msg2_part1 | msg2_part2) */
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CHK(mbedtls_md_hmac_reset(&ctx)); // prepare for new operation
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CHK(mbedtls_md_hmac_update(&ctx, msg2_part1, sizeof(msg2_part1)));
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CHK(mbedtls_md_hmac_update(&ctx, msg2_part2, sizeof(msg2_part2)));
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CHK(mbedtls_md_hmac_finish(&ctx, out));
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print_buf("msg2", out, mbedtls_md_get_size(info));
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exit:
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mbedtls_md_free(&ctx);
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mbedtls_platform_zeroize(out, sizeof(out));
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return ret;
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}
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int main(void)
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{
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int ret;
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CHK(hmac_demo());
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exit:
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return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
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}
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#endif
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