fuzz/bignum.c

   1 /*
   2  * Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the OpenSSL licenses, (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 "fuzzer.h"
  19
  20 static BN_CTX *ctx;
  21 static BIGNUM *b1;
  22 static BIGNUM *b2;
  23 static BIGNUM *b3;
  24 static BIGNUM *b4;
  25 static BIGNUM *b5;
  26
  27 int FuzzerInitialize(int *argc, char ***argv)
  28 {
  29     b1 = BN_new();
  30     b2 = BN_new();
  31     b3 = BN_new();
  32     b4 = BN_new();
  33     b5 = BN_new();
  34     ctx = BN_CTX_new();
  35
  36     return 1;
  37 }
  38
  39 int FuzzerTestOneInput(const uint8_t *buf, size_t len)
  40 {
  41     int success = 0;
  42     size_t l1 = 0, l2 = 0, l3 = 0;
  43     int s1 = 0, s2 = 0, s3 = 0;
  44
  45     /* Divide the input into three parts, using the values of the first two
  46      * bytes to choose lengths, which generate b1, b2 and b3. Use three bits
  47      * of the third byte to choose signs for the three numbers.
  48      */
  49     if (len > 2) {
  50         len -= 3;
  51         l1 = (buf[0] * len) / 255;
  52         ++buf;
  53         l2 = (buf[0] * (len - l1)) / 255;
  54         ++buf;
  55         l3 = len - l1 - l2;
  56
  57         s1 = buf[0] & 1;
  58         s2 = buf[0] & 2;
  59         s3 = buf[0] & 4;
  60         ++buf;
  61     }
  62     OPENSSL_assert(BN_bin2bn(buf, l1, b1) == b1);
  63     BN_set_negative(b1, s1);
  64     OPENSSL_assert(BN_bin2bn(buf + l1, l2, b2) == b2);
  65     BN_set_negative(b2, s2);
  66     OPENSSL_assert(BN_bin2bn(buf + l1 + l2, l3, b3) == b3);
  67     BN_set_negative(b3, s3);
  68
  69     /* mod 0 is undefined */
  70     if (BN_is_zero(b3)) {
  71         success = 1;
  72         goto done;
  73     }
  74
  75     OPENSSL_assert(BN_mod_exp(b4, b1, b2, b3, ctx));
  76     OPENSSL_assert(BN_mod_exp_simple(b5, b1, b2, b3, ctx));
  77
  78     success = BN_cmp(b4, b5) == 0;
  79     if (!success) {
  80         BN_print_fp(stdout, b1);
  81         putchar('\n');
  82         BN_print_fp(stdout, b2);
  83         putchar('\n');
  84         BN_print_fp(stdout, b3);
  85         putchar('\n');
  86         BN_print_fp(stdout, b4);
  87         putchar('\n');
  88         BN_print_fp(stdout, b5);
  89         putchar('\n');
  90     }
  91
  92  done:
  93     OPENSSL_assert(success);
  94
  95     return 0;
  96 }
  97
  98 void FuzzerCleanup(void)
  99 {
 100     BN_free(b1);
 101     BN_free(b2);
 102     BN_free(b3);
 103     BN_free(b4);
 104     BN_free(b5);
 105     BN_CTX_free(ctx);
 106 }