/*

 * 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)

{

}