/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* Helper functions for MPI fuzzing targets. */

#include "mpi_helper.h"

#include <cstdlib>

#include <random>

char *to_char(const uint8_t *x) {

  return reinterpret_cast<char *>(const_cast<unsigned char *>(x));

}

void print_bn(std::string label, BIGNUM *x) {

  char *xc = BN_bn2hex(x);

  std::cout << label << ": " << std::hex << xc << std::endl;

  OPENSSL_free(xc);

}

// Check that the two numbers are equal.

void check_equal(BIGNUM *b, mp_int *m, size_t max_size) {

  char *bnBc = BN_bn2hex(b);

  char mpiMc[max_size];

  mp_tohex(m, mpiMc);

  std::string bnA(bnBc);

  std::string mpiA(mpiMc);

  OPENSSL_free(bnBc);

  // We have to strip leading zeros from bignums, ignoring the sign.

  if (bnA.at(0) != '-') {

    bnA.erase(0, std::min(bnA.find_first_not_of('0'), bnA.size() - 1));

  } else if (bnA.at(1) == '0') {

    bnA.erase(1, std::min(bnA.find_first_not_of('0', 1) - 1, bnA.size() - 1));

  }

  if (mpiA != bnA) {

    std::cout << "openssl: " << std::hex << bnA << std::endl;

    std::cout << "nss:     " << std::hex << mpiA << std::endl;

  }

  assert(mpiA == bnA);

}

// Parse data into two numbers for MPI and OpenSSL Bignum.

void parse_input(const uint8_t *data, size_t size, BIGNUM *A, BIGNUM *B,

                 mp_int *a, mp_int *b) {

  // Note that b might overlap a.

  size_t len = (size_t)size / 2;

  assert(mp_read_raw(a, to_char(data), len) == MP_OKAY);

  assert(mp_read_raw(b, to_char(data) + len, len) == MP_OKAY);

  // Force a positive sign.

  // TODO: add tests for negatives.

  MP_SIGN(a) = MP_ZPOS;

  MP_SIGN(b) = MP_ZPOS;

  // Skip the first byte as it's interpreted as sign by NSS.

  assert(BN_bin2bn(data + 1, len - 1, A) != nullptr);

  assert(BN_bin2bn(data + len + 1, len - 1, B) != nullptr);

  check_equal(A, a, 2 * size + 1);

  check_equal(B, b, 2 * size + 1);

}

// Parse data into a number for MPI and OpenSSL Bignum.

void parse_input(const uint8_t *data, size_t size, BIGNUM *A, mp_int *a) {

  assert(mp_read_raw(a, to_char(data), size) == MP_OKAY);

  // Force a positive sign.

  // TODO: add tests for negatives.

  MP_SIGN(a) = MP_ZPOS;

  // Skip the first byte as it's interpreted as sign by NSS.

  assert(BN_bin2bn(data + 1, size - 1, A) != nullptr);

  check_equal(A, a, 4 * size + 1);

}

// Take a chunk in the middle of data and use it as modulus.

std::tuple<BIGNUM *, mp_int> get_modulus(const uint8_t *data, size_t size,

                                         BN_CTX *ctx) {

  BIGNUM *r1 = BN_CTX_get(ctx);

  mp_int r2;

  assert(mp_init(&r2) == MP_OKAY);

  size_t len = static_cast<size_t>(size / 4);

  if (len != 0) {

    assert(mp_read_raw(&r2, to_char(data + len), len) == MP_OKAY);

    MP_SIGN(&r2) = MP_ZPOS;

    assert(BN_bin2bn(data + len + 1, len - 1, r1) != nullptr);

    check_equal(r1, &r2, 2 * len + 1);

  }

  // If we happen to get 0 for the modulus, take a random number.

  if (mp_cmp_z(&r2) == 0 || len == 0) {

    mp_zero(&r2);

    BN_zero(r1);

    std::mt19937 rng(data[0]);

    std::uniform_int_distribution<mp_digit> dist(1, MP_DIGIT_MAX);

    mp_digit x = dist(rng);

    mp_add_d(&r2, x, &r2);

    BN_add_word(r1, x);

  }

  return std::make_tuple(r1, r2);

}