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- /*-
- * Copyright 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 <string.h>
- #include <openssl/err.h>
- #include <openssl/evp.h>
- #include <openssl/core_names.h>
- /*
- * Example of using an extendable-output hash function (XOF). A XOF is a hash
- * function with configurable output length and which can generate an
- * arbitrarily large output.
- *
- * This example uses SHAKE256, an extendable output variant of SHA3 (Keccak).
- *
- * To generate different output lengths, you can pass a single integer argument
- * on the command line, which is the output size in bytes. By default, a 20-byte
- * output is generated and (for this length only) a known answer test is
- * performed.
- */
- /* Our input to the XOF hash function. */
- const char message[] = "This is a test message.";
- /* Expected output when an output length of 20 bytes is used. */
- static const char known_answer[] = {
- 0x52, 0x97, 0x93, 0x78, 0x27, 0x58, 0x7d, 0x62,
- 0x8b, 0x00, 0x25, 0xb5, 0xec, 0x39, 0x5e, 0x2d,
- 0x7f, 0x3e, 0xd4, 0x19
- };
- /*
- * A property query used for selecting the SHAKE256 implementation.
- */
- static const char *propq = NULL;
- int main(int argc, char **argv)
- {
- int rv = 1;
- OSSL_LIB_CTX *libctx = NULL;
- EVP_MD *md = NULL;
- EVP_MD_CTX *ctx = NULL;
- unsigned int digest_len = 20;
- int digest_len_i;
- unsigned char *digest = NULL;
- /* Allow digest length to be changed for demonstration purposes. */
- if (argc > 1) {
- digest_len_i = atoi(argv[1]);
- if (digest_len_i <= 0) {
- fprintf(stderr, "Specify a non-negative digest length\n");
- goto end;
- }
- digest_len = (unsigned int)digest_len_i;
- }
- /*
- * Retrieve desired algorithm. This must be a hash algorithm which supports
- * XOF.
- */
- md = EVP_MD_fetch(libctx, "SHAKE256", propq);
- if (md == NULL) {
- fprintf(stderr, "Failed to retrieve SHAKE256 algorithm\n");
- goto end;
- }
- /* Create context. */
- ctx = EVP_MD_CTX_new();
- if (ctx == NULL) {
- fprintf(stderr, "Failed to create digest context\n");
- goto end;
- }
- /* Initialize digest context. */
- if (EVP_DigestInit(ctx, md) == 0) {
- fprintf(stderr, "Failed to initialize digest\n");
- goto end;
- }
- /*
- * Feed our message into the digest function.
- * This may be called multiple times.
- */
- if (EVP_DigestUpdate(ctx, message, sizeof(message)) == 0) {
- fprintf(stderr, "Failed to hash input message\n");
- goto end;
- }
- /* Allocate enough memory for our digest length. */
- digest = OPENSSL_malloc(digest_len);
- if (digest == NULL) {
- fprintf(stderr, "Failed to allocate memory for digest\n");
- goto end;
- }
- /* Get computed digest. The digest will be of whatever length we specify. */
- if (EVP_DigestFinalXOF(ctx, digest, digest_len) == 0) {
- fprintf(stderr, "Failed to finalize hash\n");
- goto end;
- }
- printf("Output digest:\n");
- BIO_dump_indent_fp(stdout, digest, digest_len, 2);
- /* If digest length is 20 bytes, check it matches our known answer. */
- if (digest_len == 20) {
- /*
- * Always use a constant-time function such as CRYPTO_memcmp
- * when comparing cryptographic values. Do not use memcmp(3).
- */
- if (CRYPTO_memcmp(digest, known_answer, sizeof(known_answer)) != 0) {
- fprintf(stderr, "Output does not match expected result\n");
- goto end;
- }
- }
- rv = 0;
- end:
- OPENSSL_free(digest);
- EVP_MD_CTX_free(ctx);
- EVP_MD_free(md);
- OSSL_LIB_CTX_free(libctx);
- return rv;
- }
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