// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/quic/crypto/null_decrypter.h"
#include "net/quic/quic_utils.h"
#include "net/quic/quic_data_reader.h"

using base::StringPiece;
using std::string;

namespace net {

NullDecrypter::NullDecrypter() {}

bool NullDecrypter::SetKey(StringPiece key) { return key.empty(); }

bool NullDecrypter::SetNoncePrefix(StringPiece nonce_prefix) {
  return nonce_prefix.empty();
}

bool NullDecrypter::Decrypt(StringPiece /*nonce*/,
                            StringPiece associated_data,
                            StringPiece ciphertext,
                            unsigned char* output,
                            size_t* output_length) {
  QuicDataReader reader(ciphertext.data(), ciphertext.length());

  uint128 hash;
  if (!ReadHash(&reader, &hash)) {
    return false;
  }

  StringPiece plaintext = reader.ReadRemainingPayload();

  // TODO(rch): avoid buffer copy here
  string buffer = associated_data.as_string();
  plaintext.AppendToString(&buffer);
  if (hash != ComputeHash(buffer)) {
    return false;
  }
  memcpy(output, plaintext.data(), plaintext.length());
  *output_length = plaintext.length();
  return true;
}

QuicData* NullDecrypter::DecryptPacket(QuicPacketSequenceNumber /*seq_number*/,
                                       StringPiece associated_data,
                                       StringPiece ciphertext) {
  // It's worth duplicating |Decrypt|, above, in order to save a copy by using
  // the shared-data QuicData constructor directly.
  QuicDataReader reader(ciphertext.data(), ciphertext.length());

  uint128 hash;
  if (!ReadHash(&reader, &hash)) {
    return NULL;
  }

  StringPiece plaintext = reader.ReadRemainingPayload();

  // TODO(rch): avoid buffer copy here
  string buffer = associated_data.as_string();
  plaintext.AppendToString(&buffer);

  if (hash != ComputeHash(buffer)) {
    return NULL;
  }
  return new QuicData(plaintext.data(), plaintext.length());
}

StringPiece NullDecrypter::GetKey() const { return StringPiece(); }

StringPiece NullDecrypter::GetNoncePrefix() const { return StringPiece(); }

bool NullDecrypter::ReadHash(QuicDataReader* reader, uint128* hash) {
  uint64 lo;
  uint32 hi;
  if (!reader->ReadUInt64(&lo) ||
      !reader->ReadUInt32(&hi)) {
    return false;
  }
  *hash = hi;
  *hash <<= 64;
  *hash += lo;
  return true;
}

uint128 NullDecrypter::ComputeHash(const string& data) const {
  uint128 correct_hash = QuicUtils::FNV1a_128_Hash(data.data(), data.length());
  uint128 mask(GG_UINT64_C(0x0), GG_UINT64_C(0xffffffff));
  mask <<= 96;
  correct_hash &= ~mask;
  return correct_hash;
}

}  // namespace net