/* * 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 #include #include #include #include #include #include /* * 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 ret = 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; } ret = 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 (ret != EXIT_SUCCESS) ERR_print_errors_fp(stderr); return ret; }