1 /*
2 * Copyright 2016-2024 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 * https://www.openssl.org/source/license.html
8 * or in the file LICENSE in the source distribution.
9 */
10
11 /*
12 * Confirm that a^b mod c agrees when calculated cleverly vs naively, for
13 * random a, b and c.
14 */
15
16 #include <stdio.h>
17 #include <openssl/bn.h>
18 #include <openssl/err.h>
19 #include "fuzzer.h"
20
FuzzerInitialize(int * argc,char *** argv)21 int FuzzerInitialize(int *argc, char ***argv)
22 {
23 OPENSSL_init_crypto(OPENSSL_INIT_LOAD_CRYPTO_STRINGS, NULL);
24 ERR_clear_error();
25
26 return 1;
27 }
28
FuzzerTestOneInput(const uint8_t * buf,size_t len)29 int FuzzerTestOneInput(const uint8_t *buf, size_t len)
30 {
31 int success = 0;
32 size_t l1 = 0, l2 = 0, l3 = 0;
33 int s1 = 0, s3 = 0;
34 BN_CTX *ctx;
35 BIGNUM *b1;
36 BIGNUM *b2;
37 BIGNUM *b3;
38 BIGNUM *b4;
39 BIGNUM *b5;
40
41 b1 = BN_new();
42 b2 = BN_new();
43 b3 = BN_new();
44 b4 = BN_new();
45 b5 = BN_new();
46 ctx = BN_CTX_new();
47
48 /* Divide the input into three parts, using the values of the first two
49 * bytes to choose lengths, which generate b1, b2 and b3. Use three bits
50 * of the third byte to choose signs for the three numbers.
51 */
52 if (len > 2) {
53 len -= 3;
54 /* limit l1, l2, and l3 to be no more than 512 bytes */
55 l1 = ((buf[0] * len) / 255) % 512;
56 ++buf;
57 l2 = ((buf[0] * (len - l1)) / 255) % 512;
58 ++buf;
59 l3 = (len - l1 - l2) % 512;
60
61 s1 = buf[0] & 1;
62 s3 = buf[0] & 4;
63 ++buf;
64 }
65 OPENSSL_assert(BN_bin2bn(buf, l1, b1) == b1);
66 BN_set_negative(b1, s1);
67 OPENSSL_assert(BN_bin2bn(buf + l1, l2, b2) == b2);
68 OPENSSL_assert(BN_bin2bn(buf + l1 + l2, l3, b3) == b3);
69 BN_set_negative(b3, s3);
70
71 /* mod 0 is undefined */
72 if (BN_is_zero(b3)) {
73 success = 1;
74 goto done;
75 }
76
77 OPENSSL_assert(BN_mod_exp(b4, b1, b2, b3, ctx));
78 OPENSSL_assert(BN_mod_exp_simple(b5, b1, b2, b3, ctx));
79
80 success = BN_cmp(b4, b5) == 0;
81 if (!success) {
82 BN_print_fp(stdout, b1);
83 putchar('\n');
84 BN_print_fp(stdout, b2);
85 putchar('\n');
86 BN_print_fp(stdout, b3);
87 putchar('\n');
88 BN_print_fp(stdout, b4);
89 putchar('\n');
90 BN_print_fp(stdout, b5);
91 putchar('\n');
92 }
93
94 done:
95 OPENSSL_assert(success);
96 BN_free(b1);
97 BN_free(b2);
98 BN_free(b3);
99 BN_free(b4);
100 BN_free(b5);
101 BN_CTX_free(ctx);
102 ERR_clear_error();
103
104 return 0;
105 }
106
FuzzerCleanup(void)107 void FuzzerCleanup(void)
108 {
109 }
110