1/*
2 * Copyright 2016 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
22int 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
30int 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        l1 = (buf[0] * len) / 255;
56        ++buf;
57        l2 = (buf[0] * (len - l1)) / 255;
58        ++buf;
59        l3 = len - l1 - l2;
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
107void FuzzerCleanup(void)
108{
109}
110