/*

Copyright (c) 2007, Un Shyam

Copyright (c) 2011, 2014-2019, Arvid Norberg

Copyright (c) 2016-2018, Alden Torres

Copyright (c) 2016, Andrei Kurushin

Copyright (c) 2016, 2018, Steven Siloti

All rights reserved.

Redistribution and use in source and binary forms, with or without

modification, are permitted provided that the following conditions

are met:

    * Redistributions of source code must retain the above copyright

      notice, this list of conditions and the following disclaimer.

    * 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.

    * Neither the name of the author nor the names of its

      contributors may be used to endorse or promote products derived

      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT OWNER 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.

*/

#if !defined TORRENT_DISABLE_ENCRYPTION

#include <cstdint>

#include <algorithm>

#include <random>

#include "libtorrent/aux_/disable_warnings_push.hpp"

#include <boost/multiprecision/integer.hpp>

#include <boost/multiprecision/cpp_int.hpp>

#include "libtorrent/aux_/disable_warnings_pop.hpp"

#include "libtorrent/random.hpp"

#include "libtorrent/aux_/alloca.hpp"

#include "libtorrent/pe_crypto.hpp"

#include "libtorrent/hasher.hpp"

namespace libtorrent {

  namespace mp = boost::multiprecision;

  namespace {

    // TODO: it would be nice to get the literal working

    key_t const dh_prime

      ("0xFFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A63A36210000000000090563");

  }

  std::array<char, 96> export_key(key_t const& k)

  {

    std::array<char, 96> ret;

    auto* begin = reinterpret_cast<std::uint8_t*>(ret.data());

    std::uint8_t* end = mp::export_bits(k, begin, 8);

    // TODO: it would be nice to be able to export to a fixed width field, so

    // we wouldn't have to shift it later

    if (end < begin + 96)

    {

      int const len = int(end - begin);

#if defined __GNUC__ && __GNUC__ == 12

#pragma GCC diagnostic push

#pragma GCC diagnostic ignored "-Wstringop-overflow"

#endif

      std::memmove(begin + 96 - len, begin, aux::numeric_cast<std::size_t>(len));

#if defined __GNUC__ && __GNUC__ == 12

#pragma GCC diagnostic pop

#endif

      std::memset(begin, 0, aux::numeric_cast<std::size_t>(96 - len));

    }

    return ret;

  }

  void rc4_init(const unsigned char* in, std::size_t len, rc4 *state);

  std::size_t rc4_encrypt(unsigned char *out, std::size_t outlen, rc4 *state);

  // Set the prime P and the generator, generate local public key

  dh_key_exchange::dh_key_exchange()

  {

    aux::array<std::uint8_t, 96> random_key;

    aux::random_bytes({reinterpret_cast<char*>(random_key.data())

      , static_cast<std::ptrdiff_t>(random_key.size())});

    // create local key (random)

    mp::import_bits(m_dh_local_secret, random_key.begin(), random_key.end());

    // key = (2 ^ secret) % prime

    m_dh_local_key = mp::powm(key_t(2), m_dh_local_secret, dh_prime);

  }

  // compute shared secret given remote public key

  void dh_key_exchange::compute_secret(std::uint8_t const* remote_pubkey)

  {

    TORRENT_ASSERT(remote_pubkey);

    key_t key;

    mp::import_bits(key, remote_pubkey, remote_pubkey + 96);

    compute_secret(key);

  }

  void dh_key_exchange::compute_secret(key_t const& remote_pubkey)

  {

    // shared_secret = (remote_pubkey ^ local_secret) % prime

    m_dh_shared_secret = mp::powm(remote_pubkey, m_dh_local_secret, dh_prime);

    std::array<char, 96> buffer;

    mp::export_bits(m_dh_shared_secret, reinterpret_cast<std::uint8_t*>(buffer.data()), 8);

    static char const req3[4] = {'r', 'e', 'q', '3'};

    // calculate the xor mask for the obfuscated hash

    m_xor_mask = hasher(req3).update(buffer).final();

  }

  std::tuple<int, span<span<char const>>>

  encryption_handler::encrypt(

    span<span<char>> iovec)

  {

    TORRENT_ASSERT(!m_send_barriers.empty());

    TORRENT_ASSERT(m_send_barriers.front().enc_handler);

    int to_process = m_send_barriers.front().next;

    span<span<char>> bufs;

    bool need_destruct = false;

    if (to_process != INT_MAX)

    {

      TORRENT_ALLOCA(abufs, span<char>, iovec.size());

      bufs = abufs;

      need_destruct = true;

      int num_bufs = 0;

      for (int i = 0; to_process > 0 && i < iovec.size(); ++i)

      {

        ++num_bufs;

        int const size = int(iovec[i].size());

        if (to_process < size)

        {

          new (&bufs[i]) span<char>(

            iovec[i].data(), to_process);

          to_process = 0;

        }

        else

        {

          new (&bufs[i]) span<char>(iovec[i]);

          to_process -= size;

        }

      }

      bufs = bufs.first(num_bufs);

    }

    else

    {

      bufs = iovec;

    }

    int next_barrier = 0;

    span<span<char const>> out_iovec;

    if (!bufs.empty())

    {

      std::tie(next_barrier, out_iovec)

        = m_send_barriers.front().enc_handler->encrypt(bufs);

    }

    if (m_send_barriers.front().next != INT_MAX)

    {

      // to_process holds the difference between the size of the buffers

      // and the bytes left to the next barrier

      // if it's zero then pop the barrier

      // otherwise update the number of bytes remaining to the next barrier

      if (to_process == 0)

      {

        if (m_send_barriers.size() == 1)

        {

          // transitioning back to plaintext

          next_barrier = INT_MAX;

        }

        m_send_barriers.pop_front();

      }

      else

      {

        m_send_barriers.front().next = to_process;

      }

    }

#if TORRENT_USE_ASSERTS

    if (next_barrier != INT_MAX && next_barrier != 0)

    {

      int payload = 0;

      for (auto buf : bufs)

        payload += int(buf.size());

      int overhead = 0;

      for (auto buf : out_iovec)

        overhead += int(buf.size());

      TORRENT_ASSERT(overhead + payload == next_barrier);

    }

#endif

    if (need_destruct)

    {

      for (auto buf : bufs)

        buf.~span<char>();

    }

    return std::make_tuple(next_barrier, out_iovec);

  }

  int encryption_handler::decrypt(aux::crypto_receive_buffer& recv_buffer

    , std::size_t& bytes_transferred)

  {

    TORRENT_ASSERT(!is_recv_plaintext());

    int consume = 0;

    if (recv_buffer.crypto_packet_finished())

    {

      span<char> wr_buf = recv_buffer.mutable_buffer(int(bytes_transferred));

      int produce = 0;

      int packet_size = 0;

      std::tie(consume, produce, packet_size) = m_dec_handler->decrypt(wr_buf);

      TORRENT_ASSERT(packet_size || produce);

      TORRENT_ASSERT(packet_size >= 0);

      TORRENT_ASSERT(produce >= 0);

      bytes_transferred = std::size_t(produce);

      if (packet_size)

        recv_buffer.crypto_cut(consume, packet_size);

    }

    else

      bytes_transferred = 0;

    return consume;

  }

  bool encryption_handler::switch_send_crypto(std::shared_ptr<crypto_plugin> crypto

    , int pending_encryption)

  {

    bool place_barrier = false;

    if (!m_send_barriers.empty())

    {

      auto const end = std::prev(m_send_barriers.end());

      for (auto b = m_send_barriers.begin(); b != end; ++b)

        pending_encryption -= b->next;

      TORRENT_ASSERT(pending_encryption >= 0);

      m_send_barriers.back().next = pending_encryption;

    }

    else if (crypto)

      place_barrier = true;

    if (crypto)

      m_send_barriers.push_back(barrier(crypto, INT_MAX));

    return place_barrier;

  }

  void encryption_handler::switch_recv_crypto(std::shared_ptr<crypto_plugin> crypto

    , aux::crypto_receive_buffer& recv_buffer)

  {

    m_dec_handler = crypto;

    int packet_size = 0;

    if (crypto)

    {

      int consume = 0;

      int produce = 0;

      std::vector<span<char>> wr_buf;

      std::tie(consume, produce, packet_size) = crypto->decrypt(wr_buf);

      TORRENT_ASSERT(wr_buf.empty());

      TORRENT_ASSERT(consume == 0);

      TORRENT_ASSERT(produce == 0);

    }

    recv_buffer.crypto_reset(packet_size);

  }

  rc4_handler::rc4_handler()

    : m_encrypt(false)

    , m_decrypt(false)

  {

    m_rc4_incoming.x = 0;

    m_rc4_incoming.y = 0;

    m_rc4_outgoing.x = 0;

    m_rc4_outgoing.y = 0;

  }

  void rc4_handler::set_incoming_key(span<char const> key)

  {

    m_decrypt = true;

    rc4_init(reinterpret_cast<unsigned char const*>(key.data())

      , std::size_t(key.size()), &m_rc4_incoming);

    // Discard first 1024 bytes

    char buf[1024];

    span<char> vec(buf, sizeof(buf));

    decrypt(vec);

  }

  void rc4_handler::set_outgoing_key(span<char const> key)

  {

    m_encrypt = true;

    rc4_init(reinterpret_cast<unsigned char const*>(key.data())

      , std::size_t(key.size()), &m_rc4_outgoing);

    // Discard first 1024 bytes

    char buf[1024];

    span<char> vec(buf, sizeof(buf));

    encrypt(vec);

  }

  std::tuple<int, span<span<char const>>>

  rc4_handler::encrypt(span<span<char>> bufs)

  {

    span<span<char const>> empty;

    if (!m_encrypt) return std::make_tuple(0, empty);

    if (bufs.empty()) return std::make_tuple(0, empty);

    int bytes_processed = 0;

    for (auto& buf : bufs)

    {

      auto* const pos = reinterpret_cast<unsigned char*>(buf.data());

      int const len = int(buf.size());

      TORRENT_ASSERT(len >= 0);

      TORRENT_ASSERT(pos);

      bytes_processed += len;

      rc4_encrypt(pos, std::uint32_t(len), &m_rc4_outgoing);

    }

    return std::make_tuple(bytes_processed, empty);

  }

  std::tuple<int, int, int> rc4_handler::decrypt(span<span<char>> bufs)

  {

    if (!m_decrypt) return std::make_tuple(0, 0, 0);

    int bytes_processed = 0;

    for (auto& buf : bufs)

    {

      auto* const pos = reinterpret_cast<unsigned char*>(buf.data());

      int const len = int(buf.size());

      TORRENT_ASSERT(len >= 0);

      TORRENT_ASSERT(pos);

      bytes_processed += len;

      rc4_encrypt(pos, std::uint32_t(len), &m_rc4_incoming);

    }

    return std::make_tuple(0, bytes_processed, 0);

  }

// All this code is based on libTomCrypt (http://www.libtomcrypt.com/)

// this library is public domain and has been specially

// tailored for libtorrent by Arvid Norberg

void rc4_init(const unsigned char* in, std::size_t len, rc4 *state)

{

  std::size_t const key_size = sizeof(state->buf);

  aux::array<std::uint8_t, key_size> key;

  std::uint8_t tmp, *s;

  int keylen, x, y, j;

  TORRENT_ASSERT(state != nullptr);

  TORRENT_ASSERT(len <= key_size);

  if (len > key_size) len = key_size;

  state->x = 0;

  while (len--) {

    state->buf[state->x++] = *in++;

  }

  /* extract the key */

  s = state->buf.data();

  std::memcpy(key.data(), s, key_size);

  keylen = state->x;

  /* make RC4 perm and shuffle */

  for (x = 0; x < int(key_size); ++x) {

    s[x] = x & 0xff;

  }

  for (j = x = y = 0; x < int(key_size); x++) {

    y = (y + state->buf[x] + key[j++]) & 255;

    if (j == keylen) {

      j = 0;

    }

    tmp = s[x]; s[x] = s[y]; s[y] = tmp;

  }

  state->x = 0;

  state->y = 0;

}

std::size_t rc4_encrypt(unsigned char *out, std::size_t outlen, rc4 *state)

{

  std::uint8_t x, y, *s, tmp;

  std::size_t n;

  TORRENT_ASSERT(out != nullptr);

  TORRENT_ASSERT(state != nullptr);

  n = outlen;

  x = state->x & 0xff;

  y = state->y & 0xff;

  s = state->buf.data();

  while (outlen--) {

    x = (x + 1) & 255;

    y = (y + s[x]) & 255;

    tmp = s[x]; s[x] = s[y]; s[y] = tmp;

    tmp = (s[x] + s[y]) & 255;

    *out++ ^= s[tmp];

  }

  state->x = x;

  state->y = y;

  return n;

}

} // namespace libtorrent

#endif // TORRENT_DISABLE_ENCRYPTION