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/*
* Copyright 2021 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <stdio.h>
#include <stdlib.h>
#include <openssl/core_names.h>
#include <openssl/evp.h>
#include <openssl/params.h>
#include <openssl/err.h>
/*
* Taken from NIST's GCM Test Vectors
* http://csrc.nist.gov/groups/STM/cavp/
*/
/*
* Hard coding the key into an application is very bad.
* It is done here solely for educational purposes.
*/
static unsigned char key[] = {
0x77, 0xbe, 0x63, 0x70, 0x89, 0x71, 0xc4, 0xe2,
0x40, 0xd1, 0xcb, 0x79, 0xe8, 0xd7, 0x7f, 0xeb
};
/*
* The initialisation vector (IV) is better not being hard coded too.
* Repeating password/IV pairs compromises the integrity of GMAC.
* The IV is not considered secret information and is safe to store with
* an encrypted password.
*/
static unsigned char iv[] = {
0xe0, 0xe0, 0x0f, 0x19, 0xfe, 0xd7, 0xba,
0x01, 0x36, 0xa7, 0x97, 0xf3
};
static unsigned char data[] = {
0x7a, 0x43, 0xec, 0x1d, 0x9c, 0x0a, 0x5a, 0x78,
0xa0, 0xb1, 0x65, 0x33, 0xa6, 0x21, 0x3c, 0xab
};
static const unsigned char expected_output[] = {
0x20, 0x9f, 0xcc, 0x8d, 0x36, 0x75, 0xed, 0x93,
0x8e, 0x9c, 0x71, 0x66, 0x70, 0x9d, 0xd9, 0x46
};
/*
* A property query used for selecting the GMAC implementation and the
* underlying GCM mode cipher.
*/
static char *propq = NULL;
int main(int argc, char **argv)
{
int rv = EXIT_FAILURE;
EVP_MAC *mac = NULL;
EVP_MAC_CTX *mctx = NULL;
unsigned char out[16];
OSSL_PARAM params[4], *p = params;
OSSL_LIB_CTX *library_context = NULL;
size_t out_len = 0;
library_context = OSSL_LIB_CTX_new();
if (library_context == NULL) {
fprintf(stderr, "OSSL_LIB_CTX_new() returned NULL\n");
goto end;
}
/* Fetch the GMAC implementation */
mac = EVP_MAC_fetch(library_context, "GMAC", propq);
if (mac == NULL) {
fprintf(stderr, "EVP_MAC_fetch() returned NULL\n");
goto end;
}
/* Create a context for the GMAC operation */
mctx = EVP_MAC_CTX_new(mac);
if (mctx == NULL) {
fprintf(stderr, "EVP_MAC_CTX_new() returned NULL\n");
goto end;
}
/* GMAC requires a GCM mode cipher to be specified */
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_MAC_PARAM_CIPHER,
"AES-128-GCM", 0);
/*
* If a non-default property query is required when fetching the GCM mode
* cipher, it needs to be specified too.
*/
if (propq != NULL)
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_MAC_PARAM_PROPERTIES,
propq, 0);
/* Set the initialisation vector (IV) */
*p++ = OSSL_PARAM_construct_octet_string(OSSL_CIPHER_PARAM_IV,
iv, sizeof(iv));
*p = OSSL_PARAM_construct_end();
/* Initialise the GMAC operation */
if (!EVP_MAC_init(mctx, key, sizeof(key), params)) {
fprintf(stderr, "EVP_MAC_init() failed\n");
goto end;
}
/* Make one or more calls to process the data to be authenticated */
if (!EVP_MAC_update(mctx, data, sizeof(data))) {
fprintf(stderr, "EVP_MAC_update() failed\n");
goto end;
}
/* Make one call to the final to get the MAC */
if (!EVP_MAC_final(mctx, out, &out_len, sizeof(out))) {
fprintf(stderr, "EVP_MAC_final() failed\n");
goto end;
}
printf("Generated MAC:\n");
BIO_dump_indent_fp(stdout, out, out_len, 2);
putchar('\n');
if (out_len != sizeof(expected_output)) {
fprintf(stderr, "Generated MAC has an unexpected length\n");
goto end;
}
if (CRYPTO_memcmp(expected_output, out, sizeof(expected_output)) != 0) {
fprintf(stderr, "Generated MAC does not match expected value\n");
goto end;
}
rv = EXIT_SUCCESS;
end:
EVP_MAC_CTX_free(mctx);
EVP_MAC_free(mac);
OSSL_LIB_CTX_free(library_context);
if (rv != EXIT_SUCCESS)
ERR_print_errors_fp(stderr);
return rv;
}
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