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/*
* Copyright 2016-2024 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* https://www.openssl.org/source/license.html
* or in the file LICENSE in the source distribution.
*/
/*
* Confirm that a^b mod c agrees when calculated cleverly vs naively, for
* random a, b and c.
*/
#include <stdio.h>
#include <openssl/bn.h>
#include <openssl/err.h>
#include "fuzzer.h"
int FuzzerInitialize(int *argc, char ***argv)
{
OPENSSL_init_crypto(OPENSSL_INIT_LOAD_CRYPTO_STRINGS, NULL);
ERR_clear_error();
return 1;
}
int FuzzerTestOneInput(const uint8_t *buf, size_t len)
{
int success = 0;
size_t l1 = 0, l2 = 0, l3 = 0;
int s1 = 0, s3 = 0;
BN_CTX *ctx;
BIGNUM *b1;
BIGNUM *b2;
BIGNUM *b3;
BIGNUM *b4;
BIGNUM *b5;
b1 = BN_new();
b2 = BN_new();
b3 = BN_new();
b4 = BN_new();
b5 = BN_new();
ctx = BN_CTX_new();
/* Divide the input into three parts, using the values of the first two
* bytes to choose lengths, which generate b1, b2 and b3. Use three bits
* of the third byte to choose signs for the three numbers.
*/
if (len > 2) {
len -= 3;
/* limit l1, l2, and l3 to be no more than 512 bytes */
l1 = ((buf[0] * len) / 255) % 512;
++buf;
l2 = ((buf[0] * (len - l1)) / 255) % 512;
++buf;
l3 = (len - l1 - l2) % 512;
s1 = buf[0] & 1;
s3 = buf[0] & 4;
++buf;
}
OPENSSL_assert(BN_bin2bn(buf, l1, b1) == b1);
BN_set_negative(b1, s1);
OPENSSL_assert(BN_bin2bn(buf + l1, l2, b2) == b2);
OPENSSL_assert(BN_bin2bn(buf + l1 + l2, l3, b3) == b3);
BN_set_negative(b3, s3);
/* mod 0 is undefined */
if (BN_is_zero(b3)) {
success = 1;
goto done;
}
OPENSSL_assert(BN_mod_exp(b4, b1, b2, b3, ctx));
OPENSSL_assert(BN_mod_exp_simple(b5, b1, b2, b3, ctx));
success = BN_cmp(b4, b5) == 0;
if (!success) {
BN_print_fp(stdout, b1);
putchar('\n');
BN_print_fp(stdout, b2);
putchar('\n');
BN_print_fp(stdout, b3);
putchar('\n');
BN_print_fp(stdout, b4);
putchar('\n');
BN_print_fp(stdout, b5);
putchar('\n');
}
done:
OPENSSL_assert(success);
BN_free(b1);
BN_free(b2);
BN_free(b3);
BN_free(b4);
BN_free(b5);
BN_CTX_free(ctx);
ERR_clear_error();
return 0;
}
void FuzzerCleanup(void)
{
}
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