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      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 int FuzzerInitialize(int *argc, char ***argv)
     22 {
     23     OPENSSL_init_crypto(OPENSSL_INIT_LOAD_CRYPTO_STRINGS, NULL);
     24     ERR_clear_error();
     25 
     26     return 1;
     27 }
     28 
     29 int FuzzerTestOneInput(const uint8_t *buf, size_t len)
     30 {
     31     int success = 0;
     32     size_t l1 = 0, l2 = 0, l3 = 0;
     33     int s1 = 0, s3 = 0;
     34     BN_CTX *ctx;
     35     BIGNUM *b1;
     36     BIGNUM *b2;
     37     BIGNUM *b3;
     38     BIGNUM *b4;
     39     BIGNUM *b5;
     40 
     41     b1 = BN_new();
     42     b2 = BN_new();
     43     b3 = BN_new();
     44     b4 = BN_new();
     45     b5 = BN_new();
     46     ctx = BN_CTX_new();
     47 
     48     /* Divide the input into three parts, using the values of the first two
     49      * bytes to choose lengths, which generate b1, b2 and b3. Use three bits
     50      * of the third byte to choose signs for the three numbers.
     51      */
     52     if (len > 2) {
     53         len -= 3;
     54         /* limit l1, l2, and l3 to be no more than 512 bytes */
     55         l1 = ((buf[0] * len) / 255) % 512;
     56         ++buf;
     57         l2 = ((buf[0] * (len - l1)) / 255) % 512;
     58         ++buf;
     59         l3 = (len - l1 - l2) % 512;
     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 
    107 void FuzzerCleanup(void)
    108 {
    109 }
    110