// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:nil -*-
// vim: ts=8 sw=2 sts=2 expandtab

#include "crypto_onwire.h"
#include "common/debug.h"
#include "common/ceph_crypto.h"
#include "include/buffer.h"
#include "include/types.h"

#include <openssl/evp.h>

#include <array>
#include <numeric> // for std::accumulate()

#define dout_subsys ceph_subsys_ms

namespace ceph::crypto::onwire {

static constexpr const std::size_t AESGCM_KEY_LEN{16};
static constexpr const std::size_t AESGCM_IV_LEN{12};
static constexpr const std::size_t AESGCM_TAG_LEN{16};
static constexpr const std::size_t AESGCM_BLOCK_LEN{16};

struct nonce_t {
  ceph_le32 fixed;
  ceph_le64 counter;

  bool operator==(const nonce_t& rhs) const {
    return !memcmp(this, &rhs, sizeof(*this));
  }
} __attribute__((packed));
static_assert(sizeof(nonce_t) == AESGCM_IV_LEN);

using key_t = std::array<std::uint8_t, AESGCM_KEY_LEN>;

// http://www.mindspring.com/~dmcgrew/gcm-nist-6.pdf
// https://www.openssl.org/docs/man1.0.2/crypto/EVP_aes_128_gcm.html#GCM-mode
// https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption
// https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf
class AES128GCM_OnWireTxHandler : public ceph::crypto::onwire::TxHandler {
  CephContext* const cct;
  std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)> ectx;
  ceph::bufferlist buffer;
  nonce_t nonce, initial_nonce;
  bool used_initial_nonce;
  bool new_nonce_format;  // 64-bit counter?
  static_assert(sizeof(nonce) == AESGCM_IV_LEN);

public:
  AES128GCM_OnWireTxHandler(CephContext* const cct,
			    const key_t& key,
			    const nonce_t& nonce,
			    bool new_nonce_format)
    : cct(cct),
      ectx(EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free),
      nonce(nonce), initial_nonce(nonce), used_initial_nonce(false),
      new_nonce_format(new_nonce_format) {
    ceph_assert_always(ectx);
    ceph_assert_always(key.size() * CHAR_BIT == 128);

    if (1 != EVP_EncryptInit_ex(ectx.get(), EVP_aes_128_gcm(),
			        nullptr, nullptr, nullptr)) {
      throw std::runtime_error("EVP_EncryptInit_ex failed");
    }

    if(1 != EVP_EncryptInit_ex(ectx.get(), nullptr, nullptr,
			       key.data(), nullptr)) {
      throw std::runtime_error("EVP_EncryptInit_ex failed");
    }
  }

  ~AES128GCM_OnWireTxHandler() override {
    ::TOPNSPC::crypto::zeroize_for_security(&nonce, sizeof(nonce));
    ::TOPNSPC::crypto::zeroize_for_security(&initial_nonce, sizeof(initial_nonce));
  }

  void reset_tx_handler(const uint32_t* first, const uint32_t* last) override;

  void authenticated_encrypt_update(const ceph::bufferlist& plaintext) override;
  ceph::bufferlist authenticated_encrypt_final() override;

  std::string_view cipher_name() const override {
    return "AES-128-GCM";
  };
};

void AES128GCM_OnWireTxHandler::reset_tx_handler(const uint32_t* first,
                                                 const uint32_t* last)
{
  if (nonce == initial_nonce) {
    if (used_initial_nonce) {
      throw ceph::crypto::onwire::TxHandlerError("out of nonces");
    }
    used_initial_nonce = true;
  }

  if(1 != EVP_EncryptInit_ex(ectx.get(), nullptr, nullptr, nullptr,
      reinterpret_cast<const unsigned char*>(&nonce))) {
    throw std::runtime_error("EVP_EncryptInit_ex failed");
  }

  ceph_assert(buffer.get_append_buffer_unused_tail_length() == 0);
  buffer.reserve(std::accumulate(first, last, AESGCM_TAG_LEN));

  if (!new_nonce_format) {
    // msgr2.0: 32-bit counter followed by 64-bit fixed field,
    // susceptible to overflow!
    nonce.fixed = nonce.fixed + 1;
  } else {
    nonce.counter = nonce.counter + 1;
  }
}

void AES128GCM_OnWireTxHandler::authenticated_encrypt_update(
  const ceph::bufferlist& plaintext)
{
  ceph_assert(buffer.get_append_buffer_unused_tail_length() >=
              plaintext.length());
  auto filler = buffer.append_hole(plaintext.length());

  for (const auto& plainbuf : plaintext.buffers()) {
    int update_len = 0;

    if(1 != EVP_EncryptUpdate(ectx.get(),
	reinterpret_cast<unsigned char*>(filler.c_str()),
	&update_len,
	reinterpret_cast<const unsigned char*>(plainbuf.c_str()),
	plainbuf.length())) {
      throw std::runtime_error("EVP_EncryptUpdate failed");
    }
    ceph_assert_always(update_len >= 0);
    ceph_assert(static_cast<unsigned>(update_len) == plainbuf.length());
    filler.advance(update_len);
  }

  ldout(cct, 15) << __func__
		 << " plaintext.length()=" << plaintext.length()
		 << " buffer.length()=" << buffer.length()
		 << dendl;
}

ceph::bufferlist AES128GCM_OnWireTxHandler::authenticated_encrypt_final()
{
  int final_len = 0;
  ceph_assert(buffer.get_append_buffer_unused_tail_length() ==
              AESGCM_BLOCK_LEN);
  auto filler = buffer.append_hole(AESGCM_BLOCK_LEN);
  if(1 != EVP_EncryptFinal_ex(ectx.get(),
	reinterpret_cast<unsigned char*>(filler.c_str()),
	&final_len)) {
    throw std::runtime_error("EVP_EncryptFinal_ex failed");
  }
  ceph_assert_always(final_len == 0);

  static_assert(AESGCM_BLOCK_LEN == AESGCM_TAG_LEN);
  if(1 != EVP_CIPHER_CTX_ctrl(ectx.get(),
	EVP_CTRL_GCM_GET_TAG, AESGCM_TAG_LEN,
	filler.c_str())) {
    throw std::runtime_error("EVP_CIPHER_CTX_ctrl failed");
  }

  ldout(cct, 15) << __func__
		 << " buffer.length()=" << buffer.length()
		 << " final_len=" << final_len
		 << dendl;
  return std::move(buffer);
}

// RX PART
class AES128GCM_OnWireRxHandler : public ceph::crypto::onwire::RxHandler {
  std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)> ectx;
  nonce_t nonce;
  bool new_nonce_format;  // 64-bit counter?
  static_assert(sizeof(nonce) == AESGCM_IV_LEN);

public:
  AES128GCM_OnWireRxHandler(CephContext* const cct,
			    const key_t& key,
			    const nonce_t& nonce,
			    bool new_nonce_format)
    : ectx(EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free),
      nonce(nonce), new_nonce_format(new_nonce_format) {
    ceph_assert_always(ectx);
    ceph_assert_always(key.size() * CHAR_BIT == 128);

    if (1 != EVP_DecryptInit_ex(ectx.get(), EVP_aes_128_gcm(),
			        nullptr, nullptr, nullptr)) {
      throw std::runtime_error("EVP_DecryptInit_ex failed");
    }

    if(1 != EVP_DecryptInit_ex(ectx.get(), nullptr, nullptr,
			       key.data(), nullptr)) {
      throw std::runtime_error("EVP_DecryptInit_ex failed");
    }
  }

  ~AES128GCM_OnWireRxHandler() override {
    ::TOPNSPC::crypto::zeroize_for_security(&nonce, sizeof(nonce));
  }

  std::uint32_t get_extra_size_at_final() override {
    return AESGCM_TAG_LEN;
  }
  void reset_rx_handler() override;
  void authenticated_decrypt_update(ceph::bufferlist& bl) override;
  void authenticated_decrypt_update_final(ceph::bufferlist& bl) override;

  std::string_view cipher_name() const override {
    return "AES-128-GCM";
  };
};

void AES128GCM_OnWireRxHandler::reset_rx_handler()
{
  if(1 != EVP_DecryptInit_ex(ectx.get(), nullptr, nullptr, nullptr,
	reinterpret_cast<const unsigned char*>(&nonce))) {
    throw std::runtime_error("EVP_DecryptInit_ex failed");
  }

  if (!new_nonce_format) {
    // msgr2.0: 32-bit counter followed by 64-bit fixed field,
    // susceptible to overflow!
    nonce.fixed = nonce.fixed + 1;
  } else {
    nonce.counter = nonce.counter + 1;
  }
}

void AES128GCM_OnWireRxHandler::authenticated_decrypt_update(
  ceph::bufferlist& bl)
{
  // discard cached crcs as we will be writing through c_str()
  bl.invalidate_crc();
  for (auto& buf : bl.buffers()) {
    auto p = reinterpret_cast<unsigned char*>(const_cast<char*>(buf.c_str()));
    int update_len = 0;

    if (1 != EVP_DecryptUpdate(ectx.get(), p, &update_len, p, buf.length())) {
      throw std::runtime_error("EVP_DecryptUpdate failed");
    }
    ceph_assert_always(update_len >= 0);
    ceph_assert(static_cast<unsigned>(update_len) == buf.length());
  }
}

void AES128GCM_OnWireRxHandler::authenticated_decrypt_update_final(
  ceph::bufferlist& bl)
{
  unsigned orig_len = bl.length();
  ceph_assert(orig_len >= AESGCM_TAG_LEN);

  // decrypt optional data. Caller is obliged to provide only signature but it
  // may supply ciphertext as well. Combining the update + final is reflected
  // combined together.
  ceph::bufferlist auth_tag;
  bl.splice(orig_len - AESGCM_TAG_LEN, AESGCM_TAG_LEN, &auth_tag);
  if (bl.length() > 0) {
    authenticated_decrypt_update(bl);
  }

  // we need to ensure the tag is stored in continuous memory.
  if (1 != EVP_CIPHER_CTX_ctrl(ectx.get(), EVP_CTRL_GCM_SET_TAG,
	AESGCM_TAG_LEN, auth_tag.c_str())) {
    throw std::runtime_error("EVP_CIPHER_CTX_ctrl failed");
  }

  // I expect that 0 bytes will be appended. The call is supposed solely to
  // authenticate the message.
  {
    int final_len = 0;
    if (0 >= EVP_DecryptFinal_ex(ectx.get(), nullptr, &final_len)) {
      throw MsgAuthError();
    }
    ceph_assert_always(final_len == 0);
    ceph_assert(bl.length() + AESGCM_TAG_LEN == orig_len);
  }
}

ceph::crypto::onwire::rxtx_t ceph::crypto::onwire::rxtx_t::create_handler_pair(
  CephContext* cct,
  const AuthConnectionMeta& auth_meta,
  bool new_nonce_format,
  bool crossed)
{
  if (auth_meta.is_mode_secure()) {
    ceph_assert_always(auth_meta.connection_secret.length() >= \
      sizeof(key_t) + 2 * sizeof(nonce_t));
    const char* secbuf = auth_meta.connection_secret.c_str();

    key_t key;
    {
      ::memcpy(key.data(), secbuf, sizeof(key));
      secbuf += sizeof(key);
    }

    nonce_t rx_nonce;
    {
      ::memcpy(&rx_nonce, secbuf, sizeof(rx_nonce));
      secbuf += sizeof(rx_nonce);
    }

    nonce_t tx_nonce;
    {
      ::memcpy(&tx_nonce, secbuf, sizeof(tx_nonce));
      secbuf += sizeof(tx_nonce);
    }

    return {
      std::make_unique<AES128GCM_OnWireRxHandler>(
	cct, key, crossed ? tx_nonce : rx_nonce, new_nonce_format),
      std::make_unique<AES128GCM_OnWireTxHandler>(
	cct, key, crossed ? rx_nonce : tx_nonce, new_nonce_format)
    };
  } else {
    return { nullptr, nullptr };
  }
}

} // namespace ceph::crypto::onwire
