--- /dev/null
+/*
+ * Copyright 2021-2022 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 <string.h>
+#include <openssl/core_names.h>
+#include <openssl/evp.h>
+#include <openssl/params.h>
+#include <openssl/err.h>
+
+/*
+ * This is a demonstration of how to compute Poly1305-AES using the OpenSSL
+ * Poly1305 and AES providers and the EVP API.
+ *
+ * Please note that:
+ *
+ * - Poly1305 must never be used alone and must be used in conjunction with
+ * another primitive which processes the input nonce to be secure;
+ *
+ * - you must never pass a nonce to the Poly1305 primitive directly;
+ *
+ * - Poly1305 exhibits catastrophic failure (that is, can be broken) if a
+ * nonce is ever reused for a given key.
+ *
+ * If you are looking for a general purpose MAC, you should consider using a
+ * different MAC and looking at one of the other examples, unless you have a
+ * good familiarity with the details and caveats of Poly1305.
+ *
+ * This example uses AES, as described in the original paper, "The Poly1305-AES
+ * message authentication code":
+ * https://cr.yp.to/mac/poly1305-20050329.pdf
+ *
+ * The test vectors below are from that paper.
+ */
+
+/*
+ * Hard coding the key into an application is very bad.
+ * It is done here solely for educational purposes.
+ * These are the "r" and "k" inputs to Poly1305-AES.
+ */
+static const unsigned char test_r[] = {
+ 0x85, 0x1f, 0xc4, 0x0c, 0x34, 0x67, 0xac, 0x0b,
+ 0xe0, 0x5c, 0xc2, 0x04, 0x04, 0xf3, 0xf7, 0x00
+};
+
+static const unsigned char test_k[] = {
+ 0xec, 0x07, 0x4c, 0x83, 0x55, 0x80, 0x74, 0x17,
+ 0x01, 0x42, 0x5b, 0x62, 0x32, 0x35, 0xad, 0xd6
+};
+
+/*
+ * Hard coding a nonce must not be done under any circumstances and is done here
+ * purely for demonstration purposes. Please note that Poly1305 exhibits
+ * catastrophic failure (that is, can be broken) if a nonce is ever reused for a
+ * given key.
+ */
+static const unsigned char test_n[] = {
+ 0xfb, 0x44, 0x73, 0x50, 0xc4, 0xe8, 0x68, 0xc5,
+ 0x2a, 0xc3, 0x27, 0x5c, 0xf9, 0xd4, 0x32, 0x7e
+};
+
+/* Input message. */
+static const unsigned char test_m[] = {
+ 0xf3, 0xf6
+};
+
+static const unsigned char expected_output[] = {
+ 0xf4, 0xc6, 0x33, 0xc3, 0x04, 0x4f, 0xc1, 0x45,
+ 0xf8, 0x4f, 0x33, 0x5c, 0xb8, 0x19, 0x53, 0xde
+};
+
+/*
+ * A property query used for selecting the POLY1305 implementation.
+ */
+static char *propq = NULL;
+
+int main(int argc, char **argv)
+{
+ int rv = EXIT_FAILURE;
+ EVP_CIPHER *aes = NULL;
+ EVP_CIPHER_CTX *aesctx = NULL;
+ EVP_MAC *mac = NULL;
+ EVP_MAC_CTX *mctx = NULL;
+ unsigned char composite_key[32];
+ unsigned char out[16];
+ OSSL_LIB_CTX *library_context = NULL;
+ size_t out_len = 0;
+ int aes_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 Poly1305 implementation */
+ mac = EVP_MAC_fetch(library_context, "POLY1305", propq);
+ if (mac == NULL) {
+ fprintf(stderr, "EVP_MAC_fetch() returned NULL\n");
+ goto end;
+ }
+
+ /* Create a context for the Poly1305 operation */
+ mctx = EVP_MAC_CTX_new(mac);
+ if (mctx == NULL) {
+ fprintf(stderr, "EVP_MAC_CTX_new() returned NULL\n");
+ goto end;
+ }
+
+ /* Fetch the AES implementation */
+ aes = EVP_CIPHER_fetch(library_context, "AES-128-ECB", propq);
+ if (aes == NULL) {
+ fprintf(stderr, "EVP_CIPHER_fetch() returned NULL\n");
+ goto end;
+ }
+
+ /* Create a context for AES */
+ aesctx = EVP_CIPHER_CTX_new();
+ if (aesctx == NULL) {
+ fprintf(stderr, "EVP_CIPHER_CTX_new() returned NULL\n");
+ goto end;
+ }
+
+ /* Initialize the AES cipher with the 128-bit key k */
+ if (!EVP_EncryptInit_ex(aesctx, aes, NULL, test_k, NULL)) {
+ fprintf(stderr, "EVP_EncryptInit_ex() failed\n");
+ goto end;
+ }
+
+ /*
+ * Disable padding for the AES cipher. We do not strictly need to do this as
+ * we are encrypting a single block and thus there are no alignment or
+ * padding concerns, but this ensures that the operation below fails if
+ * padding would be required for some reason, which in this circumstance
+ * would indicate an implementation bug.
+ */
+ if (!EVP_CIPHER_CTX_set_padding(aesctx, 0)) {
+ fprintf(stderr, "EVP_CIPHER_CTX_set_padding() failed\n");
+ goto end;
+ }
+
+ /*
+ * Computes the value AES_k(n) which we need for our Poly1305-AES
+ * computation below.
+ */
+ if (!EVP_EncryptUpdate(aesctx, composite_key + 16, &aes_len,
+ test_n, sizeof(test_n))) {
+ fprintf(stderr, "EVP_EncryptUpdate() failed\n");
+ goto end;
+ }
+
+ /*
+ * The Poly1305 provider expects the key r to be passed as the first 16
+ * bytes of the "key" and the processed nonce (that is, AES_k(n)) to be
+ * passed as the second 16 bytes of the "key". We already put the processed
+ * nonce in the correct place above, so copy r into place.
+ */
+ memcpy(composite_key, test_r, 16);
+
+ /* Initialise the Poly1305 operation */
+ if (!EVP_MAC_init(mctx, composite_key, sizeof(composite_key), NULL)) {
+ 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, test_m, sizeof(test_m))) {
+ 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_CIPHER_CTX_free(aesctx);
+ EVP_CIPHER_free(aes);
+ 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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