demo: add GMAC demonstration program

Test vector from NIST's GCM mode suite.

Fixes #14123

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/16113)

2 files changed, 148 insertions, 0 deletions

diff --git a/demos/README.txt b/demos/README.txt
index 8adfdb774d..291094bf9d 100644
--- a/demos/README.txt
+++ b/demos/README.txt
@@ -23,6 +23,9 @@ hkdf.c                 Demonstration of HMAC based key derivation
 pbkdf2.c               Demonstration of PBKDF2 password based key derivation
 scrypt.c               Demonstration of SCRYPT password based key derivation
 
+mac:
+gmac.c                 Demonstration of GMAC message authentication
+
 pkey:
 EVP_PKEY_EC_keygen.c   Generate an EC key.
 
diff --git a/demos/mac/gmac.c b/demos/mac/gmac.c
new file mode 100644
index 0000000000..bdaa9b1daa
--- /dev/null
+++ b/demos/mac/gmac.c
@@ -0,0 +1,145 @@
+/*
+ * 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 requries 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;
+}