1 /*-
2 * Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10 #include <stdio.h>
11 #include <string.h>
12 #include <openssl/err.h>
13 #include <openssl/evp.h>
14 #include <openssl/core_names.h>
15
16 /*
17 * Example of using an extendable-output hash function (XOF). A XOF is a hash
18 * function with configurable output length and which can generate an
19 * arbitrarily large output.
20 *
21 * This example uses SHAKE256, an extendable output variant of SHA3 (Keccak).
22 *
23 * To generate different output lengths, you can pass a single integer argument
24 * on the command line, which is the output size in bytes. By default, a 20-byte
25 * output is generated and (for this length only) a known answer test is
26 * performed.
27 */
28
29 /* Our input to the XOF hash function. */
30 const char message[] = "This is a test message.";
31
32 /* Expected output when an output length of 20 bytes is used. */
33 static const char known_answer[] = {
34 0x52, 0x97, 0x93, 0x78, 0x27, 0x58, 0x7d, 0x62,
35 0x8b, 0x00, 0x25, 0xb5, 0xec, 0x39, 0x5e, 0x2d,
36 0x7f, 0x3e, 0xd4, 0x19
37 };
38
39 /*
40 * A property query used for selecting the SHAKE256 implementation.
41 */
42 static const char *propq = NULL;
43
main(int argc,char ** argv)44 int main(int argc, char **argv)
45 {
46 int rv = 1;
47 OSSL_LIB_CTX *libctx = NULL;
48 EVP_MD *md = NULL;
49 EVP_MD_CTX *ctx = NULL;
50 unsigned int digest_len = 20;
51 int digest_len_i;
52 unsigned char *digest = NULL;
53
54 /* Allow digest length to be changed for demonstration purposes. */
55 if (argc > 1) {
56 digest_len_i = atoi(argv[1]);
57 if (digest_len_i <= 0) {
58 fprintf(stderr, "Specify a non-negative digest length\n");
59 goto end;
60 }
61
62 digest_len = (unsigned int)digest_len_i;
63 }
64
65 /*
66 * Retrieve desired algorithm. This must be a hash algorithm which supports
67 * XOF.
68 */
69 md = EVP_MD_fetch(libctx, "SHAKE256", propq);
70 if (md == NULL) {
71 fprintf(stderr, "Failed to retrieve SHAKE256 algorithm\n");
72 goto end;
73 }
74
75 /* Create context. */
76 ctx = EVP_MD_CTX_new();
77 if (ctx == NULL) {
78 fprintf(stderr, "Failed to create digest context\n");
79 goto end;
80 }
81
82 /* Initialize digest context. */
83 if (EVP_DigestInit(ctx, md) == 0) {
84 fprintf(stderr, "Failed to initialize digest\n");
85 goto end;
86 }
87
88 /*
89 * Feed our message into the digest function.
90 * This may be called multiple times.
91 */
92 if (EVP_DigestUpdate(ctx, message, sizeof(message)) == 0) {
93 fprintf(stderr, "Failed to hash input message\n");
94 goto end;
95 }
96
97 /* Allocate enough memory for our digest length. */
98 digest = OPENSSL_malloc(digest_len);
99 if (digest == NULL) {
100 fprintf(stderr, "Failed to allocate memory for digest\n");
101 goto end;
102 }
103
104 /* Get computed digest. The digest will be of whatever length we specify. */
105 if (EVP_DigestFinalXOF(ctx, digest, digest_len) == 0) {
106 fprintf(stderr, "Failed to finalize hash\n");
107 goto end;
108 }
109
110 printf("Output digest:\n");
111 BIO_dump_indent_fp(stdout, digest, digest_len, 2);
112
113 /* If digest length is 20 bytes, check it matches our known answer. */
114 if (digest_len == 20) {
115 /*
116 * Always use a constant-time function such as CRYPTO_memcmp
117 * when comparing cryptographic values. Do not use memcmp(3).
118 */
119 if (CRYPTO_memcmp(digest, known_answer, sizeof(known_answer)) != 0) {
120 fprintf(stderr, "Output does not match expected result\n");
121 goto end;
122 }
123 }
124
125 rv = 0;
126 end:
127 OPENSSL_free(digest);
128 EVP_MD_CTX_free(ctx);
129 EVP_MD_free(md);
130 OSSL_LIB_CTX_free(libctx);
131 return rv;
132 }
133
