xref: /openssl/demos/mac/gmac.c (revision da1c088f)
1 /*
2  * Copyright 2021-2023 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 
main(int argc,char ** argv)58 int main(int argc, char **argv)
59 {
60     int ret = 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 requires 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     ret = EXIT_SUCCESS;
138 end:
139     EVP_MAC_CTX_free(mctx);
140     EVP_MAC_free(mac);
141     OSSL_LIB_CTX_free(library_context);
142     if (ret != EXIT_SUCCESS)
143         ERR_print_errors_fp(stderr);
144     return ret;
145 }
146