// Copyright (c) 2013 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/aes_128_gcm_decrypter.h"

#include <openssl/evp.h>

#include "base/memory/scoped_ptr.h"
#include "net/quic/crypto/scoped_evp_cipher_ctx.h"

using base::StringPiece;

namespace net {

namespace {

const size_t kKeySize = 16;
const size_t kNoncePrefixSize = 4;
const size_t kAuthTagSize = 16;

}  // namespace

Aes128GcmDecrypter::Aes128GcmDecrypter() {
}

// static
bool Aes128GcmDecrypter::IsSupported() {
  return true;
}

bool Aes128GcmDecrypter::SetKey(StringPiece key) {
  DCHECK_EQ(key.size(), sizeof(key_));
  if (key.size() != sizeof(key_)) {
    return false;
  }
  memcpy(key_, key.data(), key.size());
  return true;
}

bool Aes128GcmDecrypter::SetNoncePrefix(StringPiece nonce_prefix) {
  DCHECK_EQ(nonce_prefix.size(), kNoncePrefixSize);
  if (nonce_prefix.size() != kNoncePrefixSize) {
    return false;
  }
  memcpy(nonce_, nonce_prefix.data(), nonce_prefix.size());
  return true;
}

bool Aes128GcmDecrypter::Decrypt(StringPiece nonce,
                                 StringPiece associated_data,
                                 StringPiece ciphertext,
                                 unsigned char* output,
                                 size_t* output_length) {
  if (ciphertext.length() < kAuthTagSize ||
      nonce.size() != kNoncePrefixSize + sizeof(QuicPacketSequenceNumber)) {
    return false;
  }
  const size_t plaintext_size = ciphertext.length() - kAuthTagSize;
  // |len| is passed to an OpenSSL function to receive the output length.
  int len;

  ScopedEVPCipherCtx ctx;

  // Set the cipher type and the key. The IV (nonce) is set below.
  if (EVP_DecryptInit_ex(ctx.get(), EVP_aes_128_gcm(), NULL, key_,
                         NULL) == 0) {
    return false;
  }

  // Set the IV (nonce) length.
  if (EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_SET_IVLEN, nonce.size(),
                          NULL) == 0) {
    return false;
  }
  // Set the IV (nonce).
  if (EVP_DecryptInit_ex(ctx.get(), NULL, NULL, NULL,
                         reinterpret_cast<const unsigned char*>(
                             nonce.data())) == 0) {
    return false;
  }

  // Set the authentication tag.
  if (EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_SET_TAG, kAuthTagSize,
                          const_cast<char*>(ciphertext.data()) +
                          plaintext_size) == 0) {
    return false;
  }

  // If we pass a NULL, zero-length associated data to OpenSSL then it breaks.
  // Thus we only set non-empty associated data.
  if (!associated_data.empty()) {
    // Set the associated data. The second argument (output buffer) must be
    // NULL.
    if (EVP_DecryptUpdate(ctx.get(), NULL, &len,
                          reinterpret_cast<const unsigned char*>(
                              associated_data.data()),
                          associated_data.size()) == 0) {
      return false;
    }
  }

  if (EVP_DecryptUpdate(ctx.get(), output, &len,
                        reinterpret_cast<const unsigned char*>(
                            ciphertext.data()),
                        plaintext_size) == 0) {
    return false;
  }
  output += len;

  if (EVP_DecryptFinal_ex(ctx.get(), output, &len) == 0) {
    return false;
  }
  output += len;

  *output_length = plaintext_size;

  return true;
}

QuicData* Aes128GcmDecrypter::DecryptPacket(
    QuicPacketSequenceNumber sequence_number,
    StringPiece associated_data,
    StringPiece ciphertext) {
  COMPILE_ASSERT(sizeof(nonce_) == kNoncePrefixSize + sizeof(sequence_number),
                 incorrect_nonce_size);
  if (ciphertext.length() < kAuthTagSize) {
    return NULL;
  }
  size_t plaintext_size;
  scoped_ptr<char[]> plaintext(new char[ciphertext.length()]);

  memcpy(nonce_ + kNoncePrefixSize, &sequence_number, sizeof(sequence_number));
  if (!Decrypt(StringPiece(reinterpret_cast<char*>(nonce_), sizeof(nonce_)),
               associated_data, ciphertext,
               reinterpret_cast<unsigned char*>(plaintext.get()),
               &plaintext_size)) {
    return NULL;
  }
  return new QuicData(plaintext.release(), plaintext_size, true);
}

StringPiece Aes128GcmDecrypter::GetKey() const {
  return StringPiece(reinterpret_cast<const char*>(key_), sizeof(key_));
}

StringPiece Aes128GcmDecrypter::GetNoncePrefix() const {
  return StringPiece(reinterpret_cast<const char*>(nonce_), kNoncePrefixSize);
}

}  // namespace net