1305153Sjkim/*
2305153Sjkim * Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
3299389Sjkim *
4299389Sjkim * Licensed under the Apache License 2.0 (the "License");
595967Speter * you may not use this file except in compliance with the License.
6238405Sjkim * You may obtain a copy of the License at
7238405Sjkim * https://www.openssl.org/source/license.html
8238405Sjkim * or in the file LICENSE in the source distribution.
995967Speter */
10238405Sjkim
1195967Speter/*
1295967Speter * Confirm that a^b mod c agrees when calculated cleverly vs naively, for
1395967Speter * random a, b and c.
1495967Speter */
15238405Sjkim
16238405Sjkim#include <stdio.h>
17127326Smarkm#include <openssl/bn.h>
18238405Sjkim#include <openssl/err.h>
19238405Sjkim#include "fuzzer.h"
2095967Speter
21238405Sjkim
22238405Sjkimint FuzzerInitialize(int *argc, char ***argv)
23238405Sjkim{
24238405Sjkim    OPENSSL_init_crypto(OPENSSL_INIT_LOAD_CRYPTO_STRINGS, NULL);
25238405Sjkim    ERR_clear_error();
26238405Sjkim
27238405Sjkim    return 1;
28238405Sjkim}
29238405Sjkim
30238405Sjkimint FuzzerTestOneInput(const uint8_t *buf, size_t len)
31238405Sjkim{
32238405Sjkim    int success = 0;
33238405Sjkim    size_t l1 = 0, l2 = 0, l3 = 0;
34238405Sjkim    int s1 = 0, s3 = 0;
35238405Sjkim    BN_CTX *ctx;
36238405Sjkim    BIGNUM *b1;
37238405Sjkim    BIGNUM *b2;
38238405Sjkim    BIGNUM *b3;
39238405Sjkim    BIGNUM *b4;
40238405Sjkim    BIGNUM *b5;
41238405Sjkim
42238405Sjkim    b1 = BN_new();
43238405Sjkim    b2 = BN_new();
44238405Sjkim    b3 = BN_new();
45238405Sjkim    b4 = BN_new();
46238405Sjkim    b5 = BN_new();
47238405Sjkim    ctx = BN_CTX_new();
48238405Sjkim
49238405Sjkim    /* Divide the input into three parts, using the values of the first two
50238405Sjkim     * bytes to choose lengths, which generate b1, b2 and b3. Use three bits
51238405Sjkim     * of the third byte to choose signs for the three numbers.
52238405Sjkim     */
53238405Sjkim    if (len > 2) {
54238405Sjkim        len -= 3;
55238405Sjkim        l1 = (buf[0] * len) / 255;
56238405Sjkim        ++buf;
57238405Sjkim        l2 = (buf[0] * (len - l1)) / 255;
58238405Sjkim        ++buf;
59238405Sjkim        l3 = len - l1 - l2;
60238405Sjkim
61238405Sjkim        s1 = buf[0] & 1;
62238405Sjkim        s3 = buf[0] & 4;
63238405Sjkim        ++buf;
64238405Sjkim    }
65238405Sjkim    OPENSSL_assert(BN_bin2bn(buf, l1, b1) == b1);
66238405Sjkim    BN_set_negative(b1, s1);
67238405Sjkim    OPENSSL_assert(BN_bin2bn(buf + l1, l2, b2) == b2);
68238405Sjkim    OPENSSL_assert(BN_bin2bn(buf + l1 + l2, l3, b3) == b3);
69238405Sjkim    BN_set_negative(b3, s3);
70238405Sjkim
71238405Sjkim    /* mod 0 is undefined */
72238405Sjkim    if (BN_is_zero(b3)) {
73238405Sjkim        success = 1;
74238405Sjkim        goto done;
75238405Sjkim    }
76238405Sjkim
77238405Sjkim    OPENSSL_assert(BN_mod_exp(b4, b1, b2, b3, ctx));
78238405Sjkim    OPENSSL_assert(BN_mod_exp_simple(b5, b1, b2, b3, ctx));
79238405Sjkim
80238405Sjkim    success = BN_cmp(b4, b5) == 0;
81238405Sjkim    if (!success) {
82238405Sjkim        BN_print_fp(stdout, b1);
83238405Sjkim        putchar('\n');
84238405Sjkim        BN_print_fp(stdout, b2);
85238405Sjkim        putchar('\n');
86238405Sjkim        BN_print_fp(stdout, b3);
87238405Sjkim        putchar('\n');
88238405Sjkim        BN_print_fp(stdout, b4);
89238405Sjkim        putchar('\n');
90238405Sjkim        BN_print_fp(stdout, b5);
91238405Sjkim        putchar('\n');
92238405Sjkim    }
93238405Sjkim
94238405Sjkim done:
95238405Sjkim    OPENSSL_assert(success);
96238405Sjkim    BN_free(b1);
97238405Sjkim    BN_free(b2);
98238405Sjkim    BN_free(b3);
99238405Sjkim    BN_free(b4);
100238405Sjkim    BN_free(b5);
101238405Sjkim    BN_CTX_free(ctx);
102238405Sjkim    ERR_clear_error();
103238405Sjkim
104238405Sjkim    return 0;
10595967Speter}
106238405Sjkim
107238405Sjkimvoid FuzzerCleanup(void)
108238405Sjkim{
109238405Sjkim}
110238405Sjkim