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
21
FuzzerInitialize(int * argc,char *** argv)22 int FuzzerInitialize(int *argc, char ***argv)
23 {
24 OPENSSL_init_crypto(OPENSSL_INIT_LOAD_CRYPTO_STRINGS, NULL);
25 ERR_clear_error();
26
27 return 1;
28 }
29
FuzzerTestOneInput(const uint8_t * buf,size_t len)30 int FuzzerTestOneInput(const uint8_t *buf, size_t len)
31 {
32 int success = 0;
33 size_t l1 = 0, l2 = 0, l3 = 0;
34 int s1 = 0, s3 = 0;
35 BN_CTX *ctx;
36 BIGNUM *b1;
37 BIGNUM *b2;
38 BIGNUM *b3;
39 BIGNUM *b4;
40 BIGNUM *b5;
41
42 b1 = BN_new();
43 b2 = BN_new();
44 b3 = BN_new();
45 b4 = BN_new();
46 b5 = BN_new();
47 ctx = BN_CTX_new();
48
49 /* Divide the input into three parts, using the values of the first two
50 * bytes to choose lengths, which generate b1, b2 and b3. Use three bits
51 * of the third byte to choose signs for the three numbers.
52 */
53 if (len > 2) {
54 len -= 3;
55 /* limit l1, l2, and l3 to be no more than 512 bytes */
56 l1 = ((buf[0] * len) / 255) % 512;
57 ++buf;
58 l2 = ((buf[0] * (len - l1)) / 255) % 512;
59 ++buf;
60 l3 = (len - l1 - l2) % 512;
61
62 s1 = buf[0] & 1;
63 s3 = buf[0] & 4;
64 ++buf;
65 }
66 OPENSSL_assert(BN_bin2bn(buf, l1, b1) == b1);
67 BN_set_negative(b1, s1);
68 OPENSSL_assert(BN_bin2bn(buf + l1, l2, b2) == b2);
69 OPENSSL_assert(BN_bin2bn(buf + l1 + l2, l3, b3) == b3);
70 BN_set_negative(b3, s3);
71
72 /* mod 0 is undefined */
73 if (BN_is_zero(b3)) {
74 success = 1;
75 goto done;
76 }
77
78 OPENSSL_assert(BN_mod_exp(b4, b1, b2, b3, ctx));
79 OPENSSL_assert(BN_mod_exp_simple(b5, b1, b2, b3, ctx));
80
81 success = BN_cmp(b4, b5) == 0;
82 if (!success) {
83 BN_print_fp(stdout, b1);
84 putchar('\n');
85 BN_print_fp(stdout, b2);
86 putchar('\n');
87 BN_print_fp(stdout, b3);
88 putchar('\n');
89 BN_print_fp(stdout, b4);
90 putchar('\n');
91 BN_print_fp(stdout, b5);
92 putchar('\n');
93 }
94
95 done:
96 OPENSSL_assert(success);
97 BN_free(b1);
98 BN_free(b2);
99 BN_free(b3);
100 BN_free(b4);
101 BN_free(b5);
102 BN_CTX_free(ctx);
103 ERR_clear_error();
104
105 return 0;
106 }
107
FuzzerCleanup(void)108 void FuzzerCleanup(void)
109 {
110 }
111
