/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */
/* ====================================================================
 * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
 *
 * Portions of the attached software ("Contribution") are developed by
 * SUN MICROSYSTEMS, INC., and are contributed to the OpenSSL project.
 *
 * The Contribution is licensed pursuant to the Eric Young open source
 * license provided above.
 *
 * The binary polynomial arithmetic software is originally written by
 * Sheueling Chang Shantz and Douglas Stebila of Sun Microsystems
 * Laboratories. */

/* For BIGNUM format macros. */
#if !defined(__STDC_FORMAT_MACROS)
#define __STDC_FORMAT_MACROS
#endif

#include <errno.h>
#include <stdio.h>
#include <string.h>

#include <utility>

#include <openssl/bn.h>
#include <openssl/crypto.h>
#include <openssl/err.h>
#include <openssl/mem.h>

#include "../crypto/test/scoped_types.h"
#include "../crypto/test/test_util.h"


// This program tests the BIGNUM implementation. It takes an optional -bc
// argument to write a transcript compatible with the UNIX bc utility.
//
// TODO(davidben): Rather than generate random inputs and depend on bc to check
// the results, most of these tests should use known answers.

static const int num0 = 100; // number of tests
static const int num1 = 50;  // additional tests for some functions
static const int num2 = 5;   // number of tests for slow functions

static bool test_add(FILE *fp);
static bool test_sub(FILE *fp);
static bool test_lshift1(FILE *fp);
static bool test_lshift(FILE *fp, BN_CTX *ctx, ScopedBIGNUM a);
static bool test_rshift1(FILE *fp);
static bool test_rshift(FILE *fp, BN_CTX *ctx);
static bool test_sqr(FILE *fp, BN_CTX *ctx);
static bool test_mul(FILE *fp);
static bool test_div(FILE *fp, BN_CTX *ctx);
static int rand_neg();

static bool test_div_word(FILE *fp);
static bool test_mont(FILE *fp, BN_CTX *ctx);
static bool test_mod(FILE *fp, BN_CTX *ctx);
static bool test_mod_mul(FILE *fp, BN_CTX *ctx);
static bool test_mod_exp(FILE *fp, BN_CTX *ctx);
static bool test_mod_exp_mont_consttime(FILE *fp, BN_CTX *ctx);
static bool test_exp(FILE *fp, BN_CTX *ctx);
static bool test_mod_sqrt(FILE *fp, BN_CTX *ctx);
static bool test_exp_mod_zero(void);
static bool test_small_prime(FILE *fp, BN_CTX *ctx);
static bool test_mod_exp_mont5(FILE *fp, BN_CTX *ctx);
static bool test_sqrt(FILE *fp, BN_CTX *ctx);
static bool test_bn2bin_padded(BN_CTX *ctx);
static bool test_dec2bn(BN_CTX *ctx);
static bool test_hex2bn(BN_CTX *ctx);
static bool test_asc2bn(BN_CTX *ctx);
static bool test_mpi();
static bool test_rand();
static bool test_asn1();

static const uint8_t kSample[] =
    "\xC6\x4F\x43\x04\x2A\xEA\xCA\x6E\x58\x36\x80\x5B\xE8\xC9"
    "\x9B\x04\x5D\x48\x36\xC2\xFD\x16\xC9\x64\xF0";

// A wrapper around puts that takes its arguments in the same order as our *_fp
// functions.
static void puts_fp(FILE *out, const char *m) {
  if (out != nullptr) {
    fputs(m, out);
  }
}

static void flush_fp(FILE *out) {
  if (out != nullptr) {
    fflush(out);
  }
}

static void message(FILE *out, const char *m) {
  puts_fp(out, "print \"test ");
  puts_fp(out, m);
  puts_fp(out, "\\n\"\n");
}

int main(int argc, char *argv[]) {
  CRYPTO_library_init();

  ScopedFILE bc_file;
  argc--;
  argv++;
  while (argc >= 1) {
    if (strcmp(*argv, "-bc") == 0) {
      if (argc < 2) {
        fprintf(stderr, "Missing parameter to -bc\n");
        return 1;
      }
      bc_file.reset(fopen(argv[1], "w+"));
      if (!bc_file) {
        fprintf(stderr, "Failed to open %s: %s\n", argv[1], strerror(errno));
      }
      argc--;
      argv++;
    } else {
      fprintf(stderr, "Unknown option: %s\n", argv[0]);
      return 1;
    }
    argc--;
    argv++;
  }


  ScopedBN_CTX ctx(BN_CTX_new());
  if (!ctx) {
    return 1;
  }

  puts_fp(bc_file.get(), "/* This script, when run through the UNIX bc utility, "
                         "should produce a sequence of zeros. */\n");
  puts_fp(bc_file.get(), "/* tr a-f A-F < bn_test.out | sed s/BAsE/base/ | bc "
                         "| grep -v 0 */\n");
  puts_fp(bc_file.get(), "obase=16\nibase=16\n");

  message(bc_file.get(), "BN_add");
  if (!test_add(bc_file.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_sub");
  if (!test_sub(bc_file.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_lshift1");
  if (!test_lshift1(bc_file.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_lshift (fixed)");
  ScopedBIGNUM sample(BN_bin2bn(kSample, sizeof(kSample) - 1, NULL));
  if (!sample) {
    return 1;
  }
  if (!test_lshift(bc_file.get(), ctx.get(), std::move(sample))) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_lshift");
  if (!test_lshift(bc_file.get(), ctx.get(), nullptr)) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_rshift1");
  if (!test_rshift1(bc_file.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_rshift");
  if (!test_rshift(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_sqr");
  if (!test_sqr(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_mul");
  if (!test_mul(bc_file.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_div");
  if (!test_div(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_div_word");
  if (!test_div_word(bc_file.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_mod");
  if (!test_mod(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_mod_mul");
  if (!test_mod_mul(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_mont");
  if (!test_mont(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_mod_exp");
  if (!test_mod_exp(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_mod_exp_mont_consttime");
  if (!test_mod_exp_mont_consttime(bc_file.get(), ctx.get()) ||
      !test_mod_exp_mont5(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_exp");
  if (!test_exp(bc_file.get(), ctx.get()) ||
      !test_exp_mod_zero()) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_mod_sqrt");
  if (!test_mod_sqrt(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "Small prime generation");
  if (!test_small_prime(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  message(bc_file.get(), "BN_sqrt");
  if (!test_sqrt(bc_file.get(), ctx.get())) {
    return 1;
  }
  flush_fp(bc_file.get());

  if (!test_bn2bin_padded(ctx.get()) ||
      !test_dec2bn(ctx.get()) ||
      !test_hex2bn(ctx.get()) ||
      !test_asc2bn(ctx.get()) ||
      !test_mpi() ||
      !test_rand() ||
      !test_asn1()) {
    return 1;
  }

  printf("PASS\n");
  return 0;
}

static bool test_add(FILE *fp) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  if (!a || !b || !c || !BN_rand(a.get(), 512, 0, 0)) {
    return false;
  }

  for (int i = 0; i < num0; i++) {
    if (!BN_rand(b.get(), 450 + i, 0, 0)) {
      return false;
    }
    a->neg = rand_neg();
    b->neg = rand_neg();
    if (!BN_add(c.get(), a.get(), b.get())) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " + ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, "\n");
    }
    a->neg = !a->neg;
    b->neg = !b->neg;
    if (!BN_add(c.get(), c.get(), b.get()) ||
        !BN_add(c.get(), c.get(), a.get())) {
      return false;
    }
    if (!BN_is_zero(c.get())) {
      fprintf(stderr, "Add test failed!\n");
      return false;
    }
  }
  return true;
}

static bool test_sub(FILE *fp) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  if (!a || !b || !c) {
    return false;
  }

  for (int i = 0; i < num0 + num1; i++) {
    if (i < num1) {
      if (!BN_rand(a.get(), 512, 0, 0) ||
          !BN_copy(b.get(), a.get()) ||
          !BN_set_bit(a.get(), i) ||
          !BN_add_word(b.get(), i)) {
        return false;
      }
    } else {
      if (!BN_rand(b.get(), 400 + i - num1, 0, 0)) {
        return false;
      }
      a->neg = rand_neg();
      b->neg = rand_neg();
    }
    if (!BN_sub(c.get(), a.get(), b.get())) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, "\n");
    }
    if (!BN_add(c.get(), c.get(), b.get()) ||
        !BN_sub(c.get(), c.get(), a.get())) {
      return false;
    }
    if (!BN_is_zero(c.get())) {
      fprintf(stderr, "Subtract test failed!\n");
      return false;
    }
  }
  return true;
}

static bool test_div(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !b || !c || !d || !e) {
    return false;
  }

  if (!BN_one(a.get())) {
    return false;
  }
  BN_zero(b.get());
  if (BN_div(d.get(), c.get(), a.get(), b.get(), ctx)) {
    fprintf(stderr, "Division by zero succeeded!\n");
    return false;
  }
  ERR_clear_error();

  for (int i = 0; i < num0 + num1; i++) {
    if (i < num1) {
      if (!BN_rand(a.get(), 400, 0, 0) ||
          !BN_copy(b.get(), a.get()) ||
          !BN_lshift(a.get(), a.get(), i) ||
          !BN_add_word(a.get(), i)) {
        return false;
      }
    } else if (!BN_rand(b.get(), 50 + 3 * (i - num1), 0, 0)) {
      return false;
    }
    a->neg = rand_neg();
    b->neg = rand_neg();
    if (!BN_div(d.get(), c.get(), a.get(), b.get(), ctx)) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " / ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, d.get());
      puts_fp(fp, "\n");

      BN_print_fp(fp, a.get());
      puts_fp(fp, " % ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, "\n");
    }
    if (!BN_mul(e.get(), d.get(), b.get(), ctx) ||
        !BN_add(d.get(), e.get(), c.get()) ||
        !BN_sub(d.get(), d.get(), a.get())) {
      return false;
    }
    if (!BN_is_zero(d.get())) {
      fprintf(stderr, "Division test failed!\n");
      return false;
    }
  }

  // Test that BN_div never gives negative zero in the quotient.
  if (!BN_set_word(a.get(), 1) ||
      !BN_set_word(b.get(), 2)) {
    return false;
  }
  BN_set_negative(a.get(), 1);
  if (!BN_div(d.get(), c.get(), a.get(), b.get(), ctx)) {
    return false;
  }
  if (!BN_is_zero(d.get()) || BN_is_negative(d.get())) {
    fprintf(stderr, "Division test failed!\n");
    return false;
  }

  // Test that BN_div never gives negative zero in the remainder.
  if (!BN_set_word(b.get(), 1)) {
    return false;
  }
  if (!BN_div(d.get(), c.get(), a.get(), b.get(), ctx)) {
    return false;
  }
  if (!BN_is_zero(c.get()) || BN_is_negative(c.get())) {
    fprintf(stderr, "Division test failed!\n");
    return false;
  }

  return true;
}

static bool test_lshift1(FILE *fp) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  if (!a || !b || !c || !BN_rand(a.get(), 200, 0, 0)) {
    return false;
  }
  a->neg = rand_neg();
  for (int i = 0; i < num0; i++) {
    if (!BN_lshift1(b.get(), a.get())) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " * 2");
      puts_fp(fp, " - ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, "\n");
    }
    if (!BN_add(c.get(), a.get(), a.get()) ||
        !BN_sub(a.get(), b.get(), c.get())) {
      return false;
    }
    if (!BN_is_zero(a.get())) {
      fprintf(stderr, "Left shift one test failed!\n");
      return false;
    }

    if (!BN_copy(a.get(), b.get())) {
      return false;
    }
  }
  return true;
}

static bool test_rshift(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !b || !c || !d || !e || !BN_one(c.get()) ||
      !BN_rand(a.get(), 200, 0, 0)) {
    return false;
  }
  a->neg = rand_neg();
  for (int i = 0; i < num0; i++) {
    if (!BN_rshift(b.get(), a.get(), i + 1) ||
        !BN_add(c.get(), c.get(), c.get())) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " / ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, "\n");
    }
    if (!BN_div(d.get(), e.get(), a.get(), c.get(), ctx) ||
        !BN_sub(d.get(), d.get(), b.get())) {
      return false;
    }
    if (!BN_is_zero(d.get())) {
      fprintf(stderr, "Right shift test failed!\n");
      return false;
    }
  }
  return true;
}

static bool test_rshift1(FILE *fp) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  if (!a || !b || !c || !BN_rand(a.get(), 200, 0, 0)) {
    return false;
  }
  a->neg = rand_neg();

  for (int i = 0; i < num0; i++) {
    if (!BN_rshift1(b.get(), a.get())) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " / 2");
      puts_fp(fp, " - ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, "\n");
    }
    if (!BN_sub(c.get(), a.get(), b.get()) ||
        !BN_sub(c.get(), c.get(), b.get())) {
      return false;
    }
    if (!BN_is_zero(c.get()) && !BN_abs_is_word(c.get(), 1)) {
      fprintf(stderr, "Right shift one test failed!\n");
      return false;
    }
    if (!BN_copy(a.get(), b.get())) {
      return false;
    }
  }
  return true;
}

static bool test_lshift(FILE *fp, BN_CTX *ctx, ScopedBIGNUM a) {
  if (!a) {
    a.reset(BN_new());
    if (!a || !BN_rand(a.get(), 200, 0, 0)) {
      return false;
    }
    a->neg = rand_neg();
  }

  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  if (!b || !c || !d || !BN_one(c.get())) {
    return false;
  }

  for (int i = 0; i < num0; i++) {
    if (!BN_lshift(b.get(), a.get(), i + 1) ||
        !BN_add(c.get(), c.get(), c.get())) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " * ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, "\n");
    }
    if (!BN_mul(d.get(), a.get(), c.get(), ctx) ||
        !BN_sub(d.get(), d.get(), b.get())) {
      return false;
    }
    if (!BN_is_zero(d.get())) {
      fprintf(stderr, "Left shift test failed!\n");
      fprintf(stderr, "a=");
      BN_print_fp(stderr, a.get());
      fprintf(stderr, "\nb=");
      BN_print_fp(stderr, b.get());
      fprintf(stderr, "\nc=");
      BN_print_fp(stderr, c.get());
      fprintf(stderr, "\nd=");
      BN_print_fp(stderr, d.get());
      fprintf(stderr, "\n");
      return false;
    }
  }
  return true;
}

static bool test_mul(FILE *fp) {
  ScopedBN_CTX ctx(BN_CTX_new());
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!ctx || !a || !b || !c || !d || !e) {
    return false;
  }

  for (int i = 0; i < num0 + num1; i++) {
    if (i <= num1) {
      if (!BN_rand(a.get(), 100, 0, 0) ||
          !BN_rand(b.get(), 100, 0, 0)) {
        return false;
      }
    } else if (!BN_rand(b.get(), i - num1, 0, 0)) {
      return false;
    }
    a->neg = rand_neg();
    b->neg = rand_neg();
    if (!BN_mul(c.get(), a.get(), b.get(), ctx.get())) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " * ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, "\n");
    }
    if (!BN_div(d.get(), e.get(), c.get(), a.get(), ctx.get()) ||
        !BN_sub(d.get(), d.get(), b.get())) {
      return false;
    }
    if (!BN_is_zero(d.get()) || !BN_is_zero(e.get())) {
      fprintf(stderr, "Multiplication test failed!\n");
      return false;
    }
  }

  // Test that BN_mul never gives negative zero.
  if (!BN_set_word(a.get(), 1)) {
    return false;
  }
  BN_set_negative(a.get(), 1);
  BN_zero(b.get());
  if (!BN_mul(c.get(), a.get(), b.get(), ctx.get())) {
    return false;
  }
  if (!BN_is_zero(c.get()) || BN_is_negative(c.get())) {
    fprintf(stderr, "Multiplication test failed!\n");
    return false;
  }

  return true;
}

static bool test_sqr(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !c || !d || !e) {
    return false;
  }

  for (int i = 0; i < num0; i++) {
    if (!BN_rand(a.get(), 40 + i * 10, 0, 0)) {
      return false;
    }
    a->neg = rand_neg();
    if (!BN_sqr(c.get(), a.get(), ctx)) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " * ");
      BN_print_fp(fp, a.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, "\n");
    }
    if (!BN_div(d.get(), e.get(), c.get(), a.get(), ctx) ||
        !BN_sub(d.get(), d.get(), a.get())) {
      return false;
    }
    if (!BN_is_zero(d.get()) || !BN_is_zero(e.get())) {
      fprintf(stderr, "Square test failed!\n");
      return false;
    }
  }

  // Regression test for a BN_sqr overflow bug.
  BIGNUM *a_raw = a.get();
  if (!BN_hex2bn(
          &a_raw,
          "80000000000000008000000000000001FFFFFFFFFFFFFFFE0000000000000000") ||
      !BN_sqr(c.get(), a.get(), ctx)) {
    return false;
  }
  if (fp != NULL) {
    BN_print_fp(fp, a.get());
    puts_fp(fp, " * ");
    BN_print_fp(fp, a.get());
    puts_fp(fp, " - ");
    BN_print_fp(fp, c.get());
    puts_fp(fp, "\n");
  }
  if (!BN_mul(d.get(), a.get(), a.get(), ctx)) {
    return false;
  }
  if (BN_cmp(c.get(), d.get())) {
    fprintf(stderr,
            "Square test failed: BN_sqr and BN_mul produce "
            "different results!\n");
    return false;
  }

  // Regression test for a BN_sqr overflow bug.
  a_raw = a.get();
  if (!BN_hex2bn(
          &a_raw,
          "80000000000000000000000080000001FFFFFFFE000000000000000000000000") ||
      !BN_sqr(c.get(), a.get(), ctx)) {
    return false;
  }
  if (fp != NULL) {
    BN_print_fp(fp, a.get());
    puts_fp(fp, " * ");
    BN_print_fp(fp, a.get());
    puts_fp(fp, " - ");
    BN_print_fp(fp, c.get());
    puts_fp(fp, "\n");
  }
  if (!BN_mul(d.get(), a.get(), a.get(), ctx)) {
    return false;
  }
  if (BN_cmp(c.get(), d.get())) {
    fprintf(stderr,
            "Square test failed: BN_sqr and BN_mul produce "
            "different results!\n");
    return false;
  }

  return true;
}


static int rand_neg() {
  static unsigned int neg = 0;
  static const int sign[8] = {0, 0, 0, 1, 1, 0, 1, 1};

  return sign[(neg++) % 8];
}

static void print_word(FILE *fp, BN_ULONG w) {
  fprintf(fp, BN_HEX_FMT1, w);
}

static bool test_div_word(FILE *fp) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  if (!a || !b) {
    return false;
  }

  for (int i = 0; i < num0; i++) {
    do {
      if (!BN_rand(a.get(), 512, -1, 0) ||
          !BN_rand(b.get(), BN_BITS2, -1, 0)) {
        return false;
      }
    } while (BN_is_zero(b.get()));

    if (!BN_copy(b.get(), a.get())) {
      return false;
    }
    BN_ULONG s = b->d[0];
    BN_ULONG r = BN_div_word(b.get(), s);
    if (r == (BN_ULONG)-1) {
      return false;
    }

    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " / ");
      print_word(fp, s);
      puts_fp(fp, " - ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, "\n");

      BN_print_fp(fp, a.get());
      puts_fp(fp, " % ");
      print_word(fp, s);
      puts_fp(fp, " - ");
      print_word(fp, r);
      puts_fp(fp, "\n");
    }
    if (!BN_mul_word(b.get(), s) ||
        !BN_add_word(b.get(), r) ||
        !BN_sub(b.get(), a.get(), b.get())) {
      return false;
    }
    if (!BN_is_zero(b.get())) {
      fprintf(stderr, "Division (word) test failed!\n");
      return false;
    }
  }
  return true;
}

static bool test_mont(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM A(BN_new());
  ScopedBIGNUM B(BN_new());
  ScopedBIGNUM n(BN_new());
  ScopedBN_MONT_CTX mont(BN_MONT_CTX_new());
  if (!a || !b || !c || !d || !A || !B || !n || !mont) {
    return false;
  }

  BN_zero(n.get());
  if (BN_MONT_CTX_set(mont.get(), n.get(), ctx)) {
    fprintf(stderr, "BN_MONT_CTX_set succeeded for zero modulus!\n");
    return false;
  }
  ERR_clear_error();

  if (!BN_set_word(n.get(), 16)) {
    return false;
  }
  if (BN_MONT_CTX_set(mont.get(), n.get(), ctx)) {
    fprintf(stderr, "BN_MONT_CTX_set succeeded for even modulus!\n");
    return false;
  }
  ERR_clear_error();

  if (!BN_rand(a.get(), 100, 0, 0) ||
      !BN_rand(b.get(), 100, 0, 0)) {
    return false;
  }

  for (int i = 0; i < num2; i++) {
    int bits = (200 * (i + 1)) / num2;

    if (bits == 0) {
      continue;
    }
    if (!BN_rand(n.get(), bits, 0, 1) ||
        !BN_MONT_CTX_set(mont.get(), n.get(), ctx) ||
        !BN_nnmod(a.get(), a.get(), n.get(), ctx) ||
        !BN_nnmod(b.get(), b.get(), n.get(), ctx) ||
        !BN_to_montgomery(A.get(), a.get(), mont.get(), ctx) ||
        !BN_to_montgomery(B.get(), b.get(), mont.get(), ctx) ||
        !BN_mod_mul_montgomery(c.get(), A.get(), B.get(), mont.get(), ctx) ||
        !BN_from_montgomery(A.get(), c.get(), mont.get(), ctx)) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " * ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " % ");
      BN_print_fp(fp, &mont->N);
      puts_fp(fp, " - ");
      BN_print_fp(fp, A.get());
      puts_fp(fp, "\n");
    }
    if (!BN_mod_mul(d.get(), a.get(), b.get(), n.get(), ctx) ||
        !BN_sub(d.get(), d.get(), A.get())) {
      return false;
    }
    if (!BN_is_zero(d.get())) {
      fprintf(stderr, "Montgomery multiplication test failed!\n");
      return false;
    }
  }

  return true;
}

static bool test_mod(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !b || !c || !d || !e ||
      !BN_rand(a.get(), 1024, 0, 0)) {
    return false;
  }

  for (int i = 0; i < num0; i++) {
    if (!BN_rand(b.get(), 450 + i * 10, 0, 0)) {
      return false;
    }
    a->neg = rand_neg();
    b->neg = rand_neg();
    if (!BN_mod(c.get(), a.get(), b.get(), ctx)) {
      return false;
    }
    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " % ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, "\n");
    }
    if (!BN_div(d.get(), e.get(), a.get(), b.get(), ctx) ||
        !BN_sub(e.get(), e.get(), c.get())) {
      return false;
    }
    if (!BN_is_zero(e.get())) {
      fprintf(stderr, "Modulo test failed!\n");
      return false;
    }
  }
  return true;
}

static bool test_mod_mul(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !b || !c || !d || !e) {
    return false;
  }

  if (!BN_one(a.get()) || !BN_one(b.get())) {
    return false;
  }
  BN_zero(c.get());
  if (BN_mod_mul(e.get(), a.get(), b.get(), c.get(), ctx)) {
    fprintf(stderr, "BN_mod_mul with zero modulus succeeded!\n");
    return false;
  }
  ERR_clear_error();

  for (int j = 0; j < 3; j++) {
    if (!BN_rand(c.get(), 1024, 0, 0)) {
      return false;
    }
    for (int i = 0; i < num0; i++) {
      if (!BN_rand(a.get(), 475 + i * 10, 0, 0) ||
          !BN_rand(b.get(), 425 + i * 11, 0, 0)) {
        return false;
      }
      a->neg = rand_neg();
      b->neg = rand_neg();
      if (!BN_mod_mul(e.get(), a.get(), b.get(), c.get(), ctx)) {
        ERR_print_errors_fp(stderr);
        return false;
      }
      if (fp != NULL) {
        BN_print_fp(fp, a.get());
        puts_fp(fp, " * ");
        BN_print_fp(fp, b.get());
        puts_fp(fp, " % ");
        BN_print_fp(fp, c.get());
        if (a->neg != b->neg && !BN_is_zero(e.get())) {
          // If  (a*b) % c  is negative,  c  must be added
          // in order to obtain the normalized remainder
          // (new with OpenSSL 0.9.7, previous versions of
          // BN_mod_mul could generate negative results)
          puts_fp(fp, " + ");
          BN_print_fp(fp, c.get());
        }
        puts_fp(fp, " - ");
        BN_print_fp(fp, e.get());
        puts_fp(fp, "\n");
      }
      if (!BN_mul(d.get(), a.get(), b.get(), ctx) ||
          !BN_sub(d.get(), d.get(), e.get()) ||
          !BN_div(a.get(), b.get(), d.get(), c.get(), ctx)) {
        return false;
      }
      if (!BN_is_zero(b.get())) {
        fprintf(stderr, "Modulo multiply test failed!\n");
        ERR_print_errors_fp(stderr);
        return false;
      }
    }
  }
  return true;
}

static bool test_mod_exp(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !b || !c || !d || !e) {
    return false;
  }

  if (!BN_one(a.get()) || !BN_one(b.get())) {
    return false;
  }
  BN_zero(c.get());
  if (BN_mod_exp(d.get(), a.get(), b.get(), c.get(), ctx)) {
    fprintf(stderr, "BN_mod_exp with zero modulus succeeded!\n");
    return 0;
  }
  ERR_clear_error();

  if (!BN_rand(c.get(), 30, 0, 1)) {  // must be odd for montgomery
    return false;
  }
  for (int i = 0; i < num2; i++) {
    if (!BN_rand(a.get(), 20 + i * 5, 0, 0) ||
        !BN_rand(b.get(), 2 + i, 0, 0) ||
        !BN_mod_exp(d.get(), a.get(), b.get(), c.get(), ctx)) {
      return false;
    }

    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " ^ ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " % ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, d.get());
      puts_fp(fp, "\n");
    }
    if (!BN_exp(e.get(), a.get(), b.get(), ctx) ||
        !BN_sub(e.get(), e.get(), d.get()) ||
        !BN_div(a.get(), b.get(), e.get(), c.get(), ctx)) {
      return false;
    }
    if (!BN_is_zero(b.get())) {
      fprintf(stderr, "Modulo exponentiation test failed!\n");
      return false;
    }
  }
  return true;
}

static bool test_mod_exp_mont_consttime(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM c(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !b || !c || !d || !e) {
    return false;
  }

  if (!BN_one(a.get()) || !BN_one(b.get())) {
    return false;
  }
  BN_zero(c.get());
  if (BN_mod_exp_mont_consttime(d.get(), a.get(), b.get(), c.get(), ctx,
                                nullptr)) {
    fprintf(stderr, "BN_mod_exp_mont_consttime with zero modulus succeeded!\n");
    return 0;
  }
  ERR_clear_error();

  if (!BN_set_word(c.get(), 16)) {
    return false;
  }
  if (BN_mod_exp_mont_consttime(d.get(), a.get(), b.get(), c.get(), ctx,
                                nullptr)) {
    fprintf(stderr, "BN_mod_exp_mont_consttime with even modulus succeeded!\n");
    return 0;
  }
  ERR_clear_error();

  if (!BN_rand(c.get(), 30, 0, 1)) {  // must be odd for montgomery
    return false;
  }
  for (int i = 0; i < num2; i++) {
    if (!BN_rand(a.get(), 20 + i * 5, 0, 0) ||
        !BN_rand(b.get(), 2 + i, 0, 0) ||
        !BN_mod_exp_mont_consttime(d.get(), a.get(), b.get(), c.get(), ctx,
                                   NULL)) {
      return false;
    }

    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " ^ ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " % ");
      BN_print_fp(fp, c.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, d.get());
      puts_fp(fp, "\n");
    }
    if (!BN_exp(e.get(), a.get(), b.get(), ctx) ||
        !BN_sub(e.get(), e.get(), d.get()) ||
        !BN_div(a.get(), b.get(), e.get(), c.get(), ctx)) {
      return false;
    }
    if (!BN_is_zero(b.get())) {
      fprintf(stderr, "Modulo exponentiation test failed!\n");
      return false;
    }
  }
  return true;
}

// Test constant-time modular exponentiation with 1024-bit inputs,
// which on x86_64 cause a different code branch to be taken.
static bool test_mod_exp_mont5(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM p(BN_new());
  ScopedBIGNUM m(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !p || !m || !d || !e ||
      !BN_rand(m.get(), 1024, 0, 1) ||  // must be odd for montgomery
      !BN_rand(a.get(), 1024, 0, 0)) {
    return false;
  }
  // Zero exponent.
  BN_zero(p.get());
  if (!BN_mod_exp_mont_consttime(d.get(), a.get(), p.get(), m.get(), ctx,
                                 NULL)) {
    return false;
  }
  if (!BN_is_one(d.get())) {
    fprintf(stderr, "Modular exponentiation test failed!\n");
    return false;
  }
  if (!BN_rand(p.get(), 1024, 0, 0)) {
    return false;
  }
  // Zero input.
  BN_zero(a.get());
  if (!BN_mod_exp_mont_consttime(d.get(), a.get(), p.get(), m.get(), ctx,
                                 NULL)) {
    return false;
  }
  if (!BN_is_zero(d.get())) {
    fprintf(stderr, "Modular exponentiation test failed!\n");
    return false;
  }
  // Craft an input whose Montgomery representation is 1, i.e., shorter than the
  // modulus m, in order to test the const time precomputation
  // scattering/gathering.
  ScopedBN_MONT_CTX mont(BN_MONT_CTX_new());
  if (!mont || !BN_one(a.get()) ||
      !BN_MONT_CTX_set(mont.get(), m.get(), ctx) ||
      !BN_from_montgomery(e.get(), a.get(), mont.get(), ctx) ||
      !BN_mod_exp_mont_consttime(d.get(), e.get(), p.get(), m.get(), ctx,
                                 NULL) ||
      !BN_mod_exp(a.get(), e.get(), p.get(), m.get(), ctx)) {
    return false;
  }
  if (BN_cmp(a.get(), d.get()) != 0) {
    fprintf(stderr, "Modular exponentiation test failed!\n");
    return false;
  }
  // Finally, some regular test vectors.
  if (!BN_rand(e.get(), 1024, 0, 0) ||
      !BN_mod_exp_mont_consttime(d.get(), e.get(), p.get(), m.get(), ctx,
                                 NULL) ||
      !BN_mod_exp(a.get(), e.get(), p.get(), m.get(), ctx)) {
    return false;
  }
  if (BN_cmp(a.get(), d.get()) != 0) {
    fprintf(stderr, "Modular exponentiation test failed!\n");
    return false;
  }

  return true;
}

static bool test_exp(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM b(BN_new());
  ScopedBIGNUM d(BN_new());
  ScopedBIGNUM e(BN_new());
  if (!a || !b || !d || !e) {
    return false;
  }

  for (int i = 0; i < num2; i++) {
    if (!BN_rand(a.get(), 20 + i * 5, 0, 0) ||
        !BN_rand(b.get(), 2 + i, 0, 0) ||
        !BN_exp(d.get(), a.get(), b.get(), ctx)) {
      return false;
    }

    if (fp != NULL) {
      BN_print_fp(fp, a.get());
      puts_fp(fp, " ^ ");
      BN_print_fp(fp, b.get());
      puts_fp(fp, " - ");
      BN_print_fp(fp, d.get());
      puts_fp(fp, "\n");
    }
    if (!BN_one(e.get())) {
      return false;
    }
    while (!BN_is_zero(b.get())) {
      if (!BN_mul(e.get(), e.get(), a.get(), ctx) ||
          !BN_sub(b.get(), b.get(), BN_value_one())) {
        return false;
      }
    }
    if (!BN_sub(e.get(), e.get(), d.get())) {
      return false;
    }
    if (!BN_is_zero(e.get())) {
      fprintf(stderr, "Exponentiation test failed!\n");
      return false;
    }
  }
  return true;
}

// test_exp_mod_zero tests that 1**0 mod 1 == 0.
static bool test_exp_mod_zero(void) {
  ScopedBIGNUM zero(BN_new());
  if (!zero) {
    return false;
  }
  BN_zero(zero.get());

  ScopedBN_CTX ctx(BN_CTX_new());
  ScopedBIGNUM r(BN_new());
  if (!ctx || !r ||
      !BN_mod_exp(r.get(), BN_value_one(), zero.get(), BN_value_one(), ctx.get())) {
    return false;
  }

  if (!BN_is_zero(r.get())) {
    fprintf(stderr, "1**0 mod 1 = ");
    BN_print_fp(stderr, r.get());
    fprintf(stderr, ", should be 0\n");
    return false;
  }

  return true;
}

static bool test_mod_sqrt(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM a(BN_new());
  ScopedBIGNUM p(BN_new());
  ScopedBIGNUM r(BN_new());
  if (!a || !p || !r) {
    return false;
  }

  for (int i = 0; i < 16; i++) {
    if (i < 8) {
      const unsigned kPrimes[8] = {2, 3, 5, 7, 11, 13, 17, 19};
      if (!BN_set_word(p.get(), kPrimes[i])) {
        return false;
      }
    } else {
      if (!BN_set_word(a.get(), 32) ||
          !BN_set_word(r.get(), 2 * i + 1) ||
          !BN_generate_prime_ex(p.get(), 256, 0, a.get(), r.get(), nullptr)) {
        return false;
      }
    }
    p->neg = rand_neg();

    for (int j = 0; j < num2; j++) {
      // construct 'a' such that it is a square modulo p, but in general not a
      // proper square and not reduced modulo p
      if (!BN_rand(r.get(), 256, 0, 3) ||
          !BN_nnmod(r.get(), r.get(), p.get(), ctx) ||
          !BN_mod_sqr(r.get(), r.get(), p.get(), ctx) ||
          !BN_rand(a.get(), 256, 0, 3) ||
          !BN_nnmod(a.get(), a.get(), p.get(), ctx) ||
          !BN_mod_sqr(a.get(), a.get(), p.get(), ctx) ||
          !BN_mul(a.get(), a.get(), r.get(), ctx)) {
        return false;
      }
      if (rand_neg() && !BN_sub(a.get(), a.get(), p.get())) {
        return false;
      }

      if (!BN_mod_sqrt(r.get(), a.get(), p.get(), ctx) ||
          !BN_mod_sqr(r.get(), r.get(), p.get(), ctx) ||
          !BN_nnmod(a.get(), a.get(), p.get(), ctx)) {
        return false;
      }

      if (BN_cmp(a.get(), r.get()) != 0) {
        fprintf(stderr, "BN_mod_sqrt failed: a = ");
        BN_print_fp(stderr, a.get());
        fprintf(stderr, ", r = ");
        BN_print_fp(stderr, r.get());
        fprintf(stderr, ", p = ");
        BN_print_fp(stderr, p.get());
        fprintf(stderr, "\n");
        return false;
      }
    }
  }
  return true;
}

static bool test_small_prime(FILE *fp, BN_CTX *ctx) {
  static const unsigned kBits = 10;

  ScopedBIGNUM r(BN_new());
  if (!r || !BN_generate_prime_ex(r.get(), static_cast<int>(kBits), 0, NULL,
                                  NULL, NULL)) {
    return false;
  }
  if (BN_num_bits(r.get()) != kBits) {
    fprintf(fp, "Expected %u bit prime, got %u bit number\n", kBits,
            BN_num_bits(r.get()));
    return false;
  }

  return true;
}

static bool test_sqrt(FILE *fp, BN_CTX *ctx) {
  ScopedBIGNUM n(BN_new());
  ScopedBIGNUM nn(BN_new());
  ScopedBIGNUM sqrt(BN_new());
  if (!n || !nn || !sqrt) {
    return false;
  }

  // Test some random squares.
  for (int i = 0; i < 100; i++) {
    if (!BN_rand(n.get(), 1024 /* bit length */,
                 -1 /* no modification of top bits */,
                 0 /* don't modify bottom bit */) ||
        !BN_mul(nn.get(), n.get(), n.get(), ctx) ||
        !BN_sqrt(sqrt.get(), nn.get(), ctx)) {
      ERR_print_errors_fp(stderr);
      return false;
    }
    if (BN_cmp(n.get(), sqrt.get()) != 0) {
      fprintf(stderr, "Bad result from BN_sqrt.\n");
      return false;
    }
  }

  // Test some non-squares.
  for (int i = 0; i < 100; i++) {
    if (!BN_rand(n.get(), 1024 /* bit length */,
                 -1 /* no modification of top bits */,
                 0 /* don't modify bottom bit */) ||
        !BN_mul(nn.get(), n.get(), n.get(), ctx) ||
        !BN_add(nn.get(), nn.get(), BN_value_one())) {
      ERR_print_errors_fp(stderr);
      return false;
    }

    if (BN_sqrt(sqrt.get(), nn.get(), ctx)) {
      char *nn_str = BN_bn2dec(nn.get());
      fprintf(stderr, "BIO_sqrt didn't fail on a non-square: %s\n", nn_str);
      OPENSSL_free(nn_str);
    }
  }

  return true;
}

static bool test_bn2bin_padded(BN_CTX *ctx) {
  uint8_t zeros[256], out[256], reference[128];

  memset(zeros, 0, sizeof(zeros));

  // Test edge case at 0.
  ScopedBIGNUM n(BN_new());
  if (!n || !BN_bn2bin_padded(NULL, 0, n.get())) {
    fprintf(stderr,
            "BN_bn2bin_padded failed to encode 0 in an empty buffer.\n");
    return false;
  }
  memset(out, -1, sizeof(out));
  if (!BN_bn2bin_padded(out, sizeof(out), n.get())) {
    fprintf(stderr,
            "BN_bn2bin_padded failed to encode 0 in a non-empty buffer.\n");
    return false;
  }
  if (memcmp(zeros, out, sizeof(out))) {
    fprintf(stderr, "BN_bn2bin_padded did not zero buffer.\n");
    return false;
  }

  // Test a random numbers at various byte lengths.
  for (size_t bytes = 128 - 7; bytes <= 128; bytes++) {
    if (!BN_rand(n.get(), bytes * 8, 0 /* make sure top bit is 1 */,
                 0 /* don't modify bottom bit */)) {
      ERR_print_errors_fp(stderr);
      return false;
    }
    if (BN_num_bytes(n.get()) != bytes ||
        BN_bn2bin(n.get(), reference) != bytes) {
      fprintf(stderr, "Bad result from BN_rand; bytes.\n");
      return false;
    }
    // Empty buffer should fail.
    if (BN_bn2bin_padded(NULL, 0, n.get())) {
      fprintf(stderr,
              "BN_bn2bin_padded incorrectly succeeded on empty buffer.\n");
      return false;
    }
    // One byte short should fail.
    if (BN_bn2bin_padded(out, bytes - 1, n.get())) {
      fprintf(stderr, "BN_bn2bin_padded incorrectly succeeded on short.\n");
      return false;
    }
    // Exactly right size should encode.
    if (!BN_bn2bin_padded(out, bytes, n.get()) ||
        memcmp(out, reference, bytes) != 0) {
      fprintf(stderr, "BN_bn2bin_padded gave a bad result.\n");
      return false;
    }
    // Pad up one byte extra.
    if (!BN_bn2bin_padded(out, bytes + 1, n.get()) ||
        memcmp(out + 1, reference, bytes) || memcmp(out, zeros, 1)) {
      fprintf(stderr, "BN_bn2bin_padded gave a bad result.\n");
      return false;
    }
    // Pad up to 256.
    if (!BN_bn2bin_padded(out, sizeof(out), n.get()) ||
        memcmp(out + sizeof(out) - bytes, reference, bytes) ||
        memcmp(out, zeros, sizeof(out) - bytes)) {
      fprintf(stderr, "BN_bn2bin_padded gave a bad result.\n");
      return false;
    }
  }

  return true;
}

static int DecimalToBIGNUM(ScopedBIGNUM *out, const char *in) {
  BIGNUM *raw = NULL;
  int ret = BN_dec2bn(&raw, in);
  out->reset(raw);
  return ret;
}

static bool test_dec2bn(BN_CTX *ctx) {
  ScopedBIGNUM bn;
  int ret = DecimalToBIGNUM(&bn, "0");
  if (ret != 1 || !BN_is_zero(bn.get()) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_dec2bn gave a bad result.\n");
    return false;
  }

  ret = DecimalToBIGNUM(&bn, "256");
  if (ret != 3 || !BN_is_word(bn.get(), 256) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_dec2bn gave a bad result.\n");
    return false;
  }

  ret = DecimalToBIGNUM(&bn, "-42");
  if (ret != 3 || !BN_abs_is_word(bn.get(), 42) || !BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_dec2bn gave a bad result.\n");
    return false;
  }

  ret = DecimalToBIGNUM(&bn, "-0");
  if (ret != 2 || !BN_is_zero(bn.get()) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_dec2bn gave a bad result.\n");
    return false;
  }

  ret = DecimalToBIGNUM(&bn, "42trailing garbage is ignored");
  if (ret != 2 || !BN_abs_is_word(bn.get(), 42) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_dec2bn gave a bad result.\n");
    return false;
  }

  return true;
}

static int HexToBIGNUM(ScopedBIGNUM *out, const char *in) {
  BIGNUM *raw = NULL;
  int ret = BN_hex2bn(&raw, in);
  out->reset(raw);
  return ret;
}

static bool test_hex2bn(BN_CTX *ctx) {
  ScopedBIGNUM bn;
  int ret = HexToBIGNUM(&bn, "0");
  if (ret != 1 || !BN_is_zero(bn.get()) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_hex2bn gave a bad result.\n");
    return false;
  }

  ret = HexToBIGNUM(&bn, "256");
  if (ret != 3 || !BN_is_word(bn.get(), 0x256) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_hex2bn gave a bad result.\n");
    return false;
  }

  ret = HexToBIGNUM(&bn, "-42");
  if (ret != 3 || !BN_abs_is_word(bn.get(), 0x42) || !BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_hex2bn gave a bad result.\n");
    return false;
  }

  ret = HexToBIGNUM(&bn, "-0");
  if (ret != 2 || !BN_is_zero(bn.get()) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_hex2bn gave a bad result.\n");
    return false;
  }

  ret = HexToBIGNUM(&bn, "abctrailing garbage is ignored");
  if (ret != 3 || !BN_is_word(bn.get(), 0xabc) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_hex2bn gave a bad result.\n");
    return false;
  }

  return true;
}

static ScopedBIGNUM ASCIIToBIGNUM(const char *in) {
  BIGNUM *raw = NULL;
  if (!BN_asc2bn(&raw, in)) {
    return nullptr;
  }
  return ScopedBIGNUM(raw);
}

static bool test_asc2bn(BN_CTX *ctx) {
  ScopedBIGNUM bn = ASCIIToBIGNUM("0");
  if (!bn || !BN_is_zero(bn.get()) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_asc2bn gave a bad result.\n");
    return false;
  }

  bn = ASCIIToBIGNUM("256");
  if (!bn || !BN_is_word(bn.get(), 256) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_asc2bn gave a bad result.\n");
    return false;
  }

  bn = ASCIIToBIGNUM("-42");
  if (!bn || !BN_abs_is_word(bn.get(), 42) || !BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_asc2bn gave a bad result.\n");
    return false;
  }

  bn = ASCIIToBIGNUM("0x1234");
  if (!bn || !BN_is_word(bn.get(), 0x1234) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_asc2bn gave a bad result.\n");
    return false;
  }

  bn = ASCIIToBIGNUM("0X1234");
  if (!bn || !BN_is_word(bn.get(), 0x1234) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_asc2bn gave a bad result.\n");
    return false;
  }

  bn = ASCIIToBIGNUM("-0xabcd");
  if (!bn || !BN_abs_is_word(bn.get(), 0xabcd) || !BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_asc2bn gave a bad result.\n");
    return false;
  }

  bn = ASCIIToBIGNUM("-0");
  if (!bn || !BN_is_zero(bn.get()) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_asc2bn gave a bad result.\n");
    return false;
  }

  bn = ASCIIToBIGNUM("123trailing garbage is ignored");
  if (!bn || !BN_is_word(bn.get(), 123) || BN_is_negative(bn.get())) {
    fprintf(stderr, "BN_asc2bn gave a bad result.\n");
    return false;
  }

  return true;
}

struct MPITest {
  const char *base10;
  const char *mpi;
  size_t mpi_len;
};

static const MPITest kMPITests[] = {
  { "0", "\x00\x00\x00\x00", 4 },
  { "1", "\x00\x00\x00\x01\x01", 5 },
  { "-1", "\x00\x00\x00\x01\x81", 5 },
  { "128", "\x00\x00\x00\x02\x00\x80", 6 },
  { "256", "\x00\x00\x00\x02\x01\x00", 6 },
  { "-256", "\x00\x00\x00\x02\x81\x00", 6 },
};

static bool test_mpi() {
  uint8_t scratch[8];

  for (size_t i = 0; i < sizeof(kMPITests) / sizeof(kMPITests[0]); i++) {
    const MPITest &test = kMPITests[i];
    ScopedBIGNUM bn(ASCIIToBIGNUM(test.base10));
    const size_t mpi_len = BN_bn2mpi(bn.get(), NULL);
    if (mpi_len > sizeof(scratch)) {
      fprintf(stderr, "MPI test #%u: MPI size is too large to test.\n",
              (unsigned)i);
      return false;
    }

    const size_t mpi_len2 = BN_bn2mpi(bn.get(), scratch);
    if (mpi_len != mpi_len2) {
      fprintf(stderr, "MPI test #%u: length changes.\n", (unsigned)i);
      return false;
    }

    if (mpi_len != test.mpi_len ||
        memcmp(test.mpi, scratch, mpi_len) != 0) {
      fprintf(stderr, "MPI test #%u failed:\n", (unsigned)i);
      hexdump(stderr, "Expected: ", test.mpi, test.mpi_len);
      hexdump(stderr, "Got:      ", scratch, mpi_len);
      return false;
    }

    ScopedBIGNUM bn2(BN_mpi2bn(scratch, mpi_len, NULL));
    if (bn2.get() == nullptr) {
      fprintf(stderr, "MPI test #%u: failed to parse\n", (unsigned)i);
      return false;
    }

    if (BN_cmp(bn.get(), bn2.get()) != 0) {
      fprintf(stderr, "MPI test #%u: wrong result\n", (unsigned)i);
      return false;
    }
  }

  return true;
}

static bool test_rand() {
  ScopedBIGNUM bn(BN_new());
  if (!bn) {
    return false;
  }

  // Test BN_rand accounts for degenerate cases with |top| and |bottom|
  // parameters.
  if (!BN_rand(bn.get(), 0, 0 /* top */, 0 /* bottom */) ||
      !BN_is_zero(bn.get())) {
    fprintf(stderr, "BN_rand gave a bad result.\n");
    return false;
  }
  if (!BN_rand(bn.get(), 0, 1 /* top */, 1 /* bottom */) ||
      !BN_is_zero(bn.get())) {
    fprintf(stderr, "BN_rand gave a bad result.\n");
    return false;
  }

  if (!BN_rand(bn.get(), 1, 0 /* top */, 0 /* bottom */) ||
      !BN_is_word(bn.get(), 1)) {
    fprintf(stderr, "BN_rand gave a bad result.\n");
    return false;
  }
  if (!BN_rand(bn.get(), 1, 1 /* top */, 0 /* bottom */) ||
      !BN_is_word(bn.get(), 1)) {
    fprintf(stderr, "BN_rand gave a bad result.\n");
    return false;
  }
  if (!BN_rand(bn.get(), 1, -1 /* top */, 1 /* bottom */) ||
      !BN_is_word(bn.get(), 1)) {
    fprintf(stderr, "BN_rand gave a bad result.\n");
    return false;
  }

  if (!BN_rand(bn.get(), 2, 1 /* top */, 0 /* bottom */) ||
      !BN_is_word(bn.get(), 3)) {
    fprintf(stderr, "BN_rand gave a bad result.\n");
    return false;
  }

  return true;
}

struct ASN1Test {
  const char *value_ascii;
  const char *der;
  size_t der_len;
};

static const ASN1Test kASN1Tests[] = {
    {"0", "\x02\x01\x00", 3},
    {"1", "\x02\x01\x01", 3},
    {"127", "\x02\x01\x7f", 3},
    {"128", "\x02\x02\x00\x80", 4},
    {"0xdeadbeef", "\x02\x05\x00\xde\xad\xbe\xef", 7},
    {"0x0102030405060708",
     "\x02\x08\x01\x02\x03\x04\x05\x06\x07\x08", 10},
    {"0xffffffffffffffff",
      "\x02\x09\x00\xff\xff\xff\xff\xff\xff\xff\xff", 11},
};

struct ASN1InvalidTest {
  const char *der;
  size_t der_len;
};

static const ASN1InvalidTest kASN1InvalidTests[] = {
    // Bad tag.
    {"\x03\x01\x00", 3},
    // Empty contents.
    {"\x02\x00", 2},
};

// kASN1BuggyTests are incorrect encodings and how |BN_cbs2unsigned_buggy|
// should interpret them.
static const ASN1Test kASN1BuggyTests[] = {
    // Negative numbers.
    {"128", "\x02\x01\x80", 3},
    {"255", "\x02\x01\xff", 3},
    // Unnecessary leading zeros.
    {"1", "\x02\x02\x00\x01", 4},
};

static bool test_asn1() {
  for (const ASN1Test &test : kASN1Tests) {
    ScopedBIGNUM bn = ASCIIToBIGNUM(test.value_ascii);
    if (!bn) {
      return false;
    }

    // Test that the input is correctly parsed.
    ScopedBIGNUM bn2(BN_new());
    if (!bn2) {
      return false;
    }
    CBS cbs;
    CBS_init(&cbs, reinterpret_cast<const uint8_t*>(test.der), test.der_len);
    if (!BN_cbs2unsigned(&cbs, bn2.get()) || CBS_len(&cbs) != 0) {
      fprintf(stderr, "Parsing ASN.1 INTEGER failed.\n");
      return false;
    }
    if (BN_cmp(bn.get(), bn2.get()) != 0) {
      fprintf(stderr, "Bad parse.\n");
      return false;
    }

    // Test the value serializes correctly.
    CBB cbb;
    uint8_t *der;
    size_t der_len;
    CBB_zero(&cbb);
    if (!CBB_init(&cbb, 0) ||
        !BN_bn2cbb(&cbb, bn.get()) ||
        !CBB_finish(&cbb, &der, &der_len)) {
      CBB_cleanup(&cbb);
      return false;
    }
    ScopedOpenSSLBytes delete_der(der);
    if (der_len != test.der_len ||
        memcmp(der, reinterpret_cast<const uint8_t*>(test.der), der_len) != 0) {
      fprintf(stderr, "Bad serialization.\n");
      return false;
    }

    // |BN_cbs2unsigned_buggy| parses all valid input.
    CBS_init(&cbs, reinterpret_cast<const uint8_t*>(test.der), test.der_len);
    if (!BN_cbs2unsigned_buggy(&cbs, bn2.get()) || CBS_len(&cbs) != 0) {
      fprintf(stderr, "Parsing ASN.1 INTEGER failed.\n");
      return false;
    }
    if (BN_cmp(bn.get(), bn2.get()) != 0) {
      fprintf(stderr, "Bad parse.\n");
      return false;
    }
  }

  for (const ASN1InvalidTest &test : kASN1InvalidTests) {
    ScopedBIGNUM bn(BN_new());
    if (!bn) {
      return false;
    }
    CBS cbs;
    CBS_init(&cbs, reinterpret_cast<const uint8_t*>(test.der), test.der_len);
    if (BN_cbs2unsigned(&cbs, bn.get())) {
      fprintf(stderr, "Parsed invalid input.\n");
      return false;
    }
    ERR_clear_error();

    // All tests in kASN1InvalidTests are also rejected by
    // |BN_cbs2unsigned_buggy|.
    CBS_init(&cbs, reinterpret_cast<const uint8_t*>(test.der), test.der_len);
    if (BN_cbs2unsigned_buggy(&cbs, bn.get())) {
      fprintf(stderr, "Parsed invalid input.\n");
      return false;
    }
    ERR_clear_error();
  }

  for (const ASN1Test &test : kASN1BuggyTests) {
    // These broken encodings are rejected by |BN_cbs2unsigned|.
    ScopedBIGNUM bn(BN_new());
    if (!bn) {
      return false;
    }

    CBS cbs;
    CBS_init(&cbs, reinterpret_cast<const uint8_t*>(test.der), test.der_len);
    if (BN_cbs2unsigned(&cbs, bn.get())) {
      fprintf(stderr, "Parsed invalid input.\n");
      return false;
    }
    ERR_clear_error();

    // However |BN_cbs2unsigned_buggy| accepts them.
    ScopedBIGNUM bn2 = ASCIIToBIGNUM(test.value_ascii);
    if (!bn2) {
      return false;
    }

    CBS_init(&cbs, reinterpret_cast<const uint8_t*>(test.der), test.der_len);
    if (!BN_cbs2unsigned_buggy(&cbs, bn.get()) || CBS_len(&cbs) != 0) {
      fprintf(stderr, "Parsing (invalid) ASN.1 INTEGER failed.\n");
      return false;
    }

    if (BN_cmp(bn.get(), bn2.get()) != 0) {
      fprintf(stderr, "\"Bad\" parse.\n");
      return false;
    }
  }

  // Serializing negative numbers is not supported.
  ScopedBIGNUM bn = ASCIIToBIGNUM("-1");
  if (!bn) {
    return false;
  }
  CBB cbb;
  CBB_zero(&cbb);
  if (!CBB_init(&cbb, 0) ||
      BN_bn2cbb(&cbb, bn.get())) {
    fprintf(stderr, "Serialized negative number.\n");
    CBB_cleanup(&cbb);
    return false;
  }
  CBB_cleanup(&cbb);

  return true;
}