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      1 /*
      2  * Copyright 2021 The OpenSSL Project Authors. All Rights Reserved.
      3  *
      4  * Licensed under the Apache License 2.0 (the "License").  You may not use
      5  * this file except in compliance with the License.  You can obtain a copy
      6  * in the file LICENSE in the source distribution or at
      7  * https://www.openssl.org/source/license.html
      8  */
      9 
     10 #include <stdio.h>
     11 #include <stdlib.h>
     12 #include <openssl/core_names.h>
     13 #include <openssl/evp.h>
     14 #include <openssl/params.h>
     15 #include <openssl/err.h>
     16 
     17 /*
     18  * Taken from NIST's GCM Test Vectors
     19  * http://csrc.nist.gov/groups/STM/cavp/
     20  */
     21 
     22 /*
     23  * Hard coding the key into an application is very bad.
     24  * It is done here solely for educational purposes.
     25  */
     26 static unsigned char key[] = {
     27     0x77, 0xbe, 0x63, 0x70, 0x89, 0x71, 0xc4, 0xe2,
     28     0x40, 0xd1, 0xcb, 0x79, 0xe8, 0xd7, 0x7f, 0xeb
     29 };
     30 
     31 /*
     32  * The initialisation vector (IV) is better not being hard coded too.
     33  * Repeating password/IV pairs compromises the integrity of GMAC.
     34  * The IV is not considered secret information and is safe to store with
     35  * an encrypted password.
     36  */
     37 static unsigned char iv[] = {
     38     0xe0, 0xe0, 0x0f, 0x19, 0xfe, 0xd7, 0xba,
     39     0x01, 0x36, 0xa7, 0x97, 0xf3
     40 };
     41 
     42 static unsigned char data[] = {
     43     0x7a, 0x43, 0xec, 0x1d, 0x9c, 0x0a, 0x5a, 0x78,
     44     0xa0, 0xb1, 0x65, 0x33, 0xa6, 0x21, 0x3c, 0xab
     45 };
     46 
     47 static const unsigned char expected_output[] = {
     48     0x20, 0x9f, 0xcc, 0x8d, 0x36, 0x75, 0xed, 0x93,
     49     0x8e, 0x9c, 0x71, 0x66, 0x70, 0x9d, 0xd9, 0x46
     50 };
     51 
     52 /*
     53  * A property query used for selecting the GMAC implementation and the
     54  * underlying GCM mode cipher.
     55  */
     56 static char *propq = NULL;
     57 
     58 int main(int argc, char **argv)
     59 {
     60     int rv = EXIT_FAILURE;
     61     EVP_MAC *mac = NULL;
     62     EVP_MAC_CTX *mctx = NULL;
     63     unsigned char out[16];
     64     OSSL_PARAM params[4], *p = params;
     65     OSSL_LIB_CTX *library_context = NULL;
     66     size_t out_len = 0;
     67 
     68     library_context = OSSL_LIB_CTX_new();
     69     if (library_context == NULL) {
     70         fprintf(stderr, "OSSL_LIB_CTX_new() returned NULL\n");
     71         goto end;
     72     }
     73 
     74     /* Fetch the GMAC implementation */
     75     mac = EVP_MAC_fetch(library_context, "GMAC", propq);
     76     if (mac == NULL) {
     77         fprintf(stderr, "EVP_MAC_fetch() returned NULL\n");
     78         goto end;
     79     }
     80 
     81     /* Create a context for the GMAC operation */
     82     mctx = EVP_MAC_CTX_new(mac);
     83     if (mctx == NULL) {
     84         fprintf(stderr, "EVP_MAC_CTX_new() returned NULL\n");
     85         goto end;
     86     }
     87 
     88     /* GMAC requries a GCM mode cipher to be specified */
     89     *p++ = OSSL_PARAM_construct_utf8_string(OSSL_MAC_PARAM_CIPHER,
     90                                             "AES-128-GCM", 0);
     91 
     92     /*
     93      * If a non-default property query is required when fetching the GCM mode
     94      * cipher, it needs to be specified too.
     95      */
     96     if (propq != NULL)
     97         *p++ = OSSL_PARAM_construct_utf8_string(OSSL_MAC_PARAM_PROPERTIES,
     98                                                 propq, 0);
     99 
    100     /* Set the initialisation vector (IV) */
    101     *p++ = OSSL_PARAM_construct_octet_string(OSSL_CIPHER_PARAM_IV,
    102                                              iv, sizeof(iv));
    103     *p = OSSL_PARAM_construct_end();
    104 
    105     /* Initialise the GMAC operation */
    106     if (!EVP_MAC_init(mctx, key, sizeof(key), params)) {
    107         fprintf(stderr, "EVP_MAC_init() failed\n");
    108         goto end;
    109     }
    110 
    111     /* Make one or more calls to process the data to be authenticated */
    112     if (!EVP_MAC_update(mctx, data, sizeof(data))) {
    113         fprintf(stderr, "EVP_MAC_update() failed\n");
    114         goto end;
    115     }
    116 
    117     /* Make one call to the final to get the MAC */
    118     if (!EVP_MAC_final(mctx, out, &out_len, sizeof(out))) {
    119         fprintf(stderr, "EVP_MAC_final() failed\n");
    120         goto end;
    121     }
    122 
    123     printf("Generated MAC:\n");
    124     BIO_dump_indent_fp(stdout, out, out_len, 2);
    125     putchar('\n');
    126 
    127     if (out_len != sizeof(expected_output)) {
    128         fprintf(stderr, "Generated MAC has an unexpected length\n");
    129         goto end;
    130     }
    131 
    132     if (CRYPTO_memcmp(expected_output, out, sizeof(expected_output)) != 0) {
    133         fprintf(stderr, "Generated MAC does not match expected value\n");
    134         goto end;
    135     }
    136 
    137     rv = EXIT_SUCCESS;
    138 end:
    139     EVP_MAC_CTX_free(mctx);
    140     EVP_MAC_free(mac);
    141     OSSL_LIB_CTX_free(library_context);
    142     if (rv != EXIT_SUCCESS)
    143         ERR_print_errors_fp(stderr);
    144     return rv;
    145 }
    146