util/encrypted_message_util.h

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This file contains two classes for working with EncryptedMessages.
//
// EncryptedMessageMaker is used by the Encoder to create EncryptedMessages
// by encrypting Observations, and Envelopes.
//
// MessageDecrypter is used by the Analyzer to decrypt EncryptedMessages
// containing Observations.

#ifndef COBALT_UTIL_ENCRYPTED_MESSAGE_UTIL_H_
#define COBALT_UTIL_ENCRYPTED_MESSAGE_UTIL_H_

#include <memory>
#include <string>
#include <vector>

#include "./encrypted_message.pb.h"
#include "google/protobuf/message_lite.h"
#include "third_party/statusor/statusor.h"
#include "third_party/tink/cc/hybrid_encrypt.h"
#include "util/crypto_util/cipher.h"

namespace cobalt {
namespace util {

// EncryptedMessageMaker is used by the Encoder to encrypt protocol buffer
// messages before sending them to the Shuffler (and then to the Analyzer).
//
// The Encoder should make two instances of this class:
// one constructed with the public key of the Analyzer used for encrypting
// Observations and one with the public key of the Shuffler used for
// encrypting Envelopes.
class EncryptedMessageMaker {
 public:
  // Encrypts a protocol buffer |message| and populates |encrypted_message|
  // with the result. Returns true for success or false on failure.
  virtual bool Encrypt(const google::protobuf::MessageLite& message,
                       EncryptedMessage* encrypted_message) const = 0;

  // Returns the EncryptionScheme used by the EncryptedMessageMaker.
  virtual EncryptedMessage::EncryptionScheme scheme() const = 0;

  // Make an EncryptedMessageMaker.
  //
  // |scheme| specifies which encryption scheme should be used.
  // The use of EncryptedMessage::NONE is disallowed.
  //
  // |public_key| must be appropriate to |scheme|. If |scheme| is
  // EncryptedMessage::NONE then |public_key| is ignored. If |scheme| is
  // EncryptedMessage::HYBRID_ECDH_V1 then |public_key| must be a PEM
  // encoding of a public key appropriate for that scheme. If |scheme| is
  // EncryptedMessage::HYBRID_TINK the |public_key| must be a base64-encoded
  // serialized tink Keyset protobuf message.
  static statusor::StatusOr<std::unique_ptr<EncryptedMessageMaker>> Make(
      const std::string& public_key, EncryptedMessage::EncryptionScheme scheme);

  // Make an EncryptedMessageMaker. (Do not use in production)
  //
  // |scheme| specifies which encryption scheme should be used. As of this
  // writing there are three schemes:
  //   - EncryptedMessage::NONE: See MakeUnencrypted below.
  //   - EncryptedMessage::HYBRID_ECDH_V1: See MakeHybridEcdh below.
  //   - EncryptedMessage::HYBRID_TINK: See MakeHybridTink below.
  //
  // |public_key| must be appropriate to |scheme|. If |scheme| is
  // EncryptedMessage::NONE then |public_key| is ignored. If |scheme| is
  // EncryptedMessage::HYBRID_ECDH_V1 then |public_key| must be a PEM
  // encoding of a public key appropriate for that scheme. If |scheme| is
  // EncryptedMessage::HYBRID_TINK the |public_key| must be a base64-encoded
  // serialized tink Keyset protobuf message.
  static statusor::StatusOr<std::unique_ptr<EncryptedMessageMaker>>
  MakeAllowUnencrypted(const std::string& public_key,
                       EncryptedMessage::EncryptionScheme scheme);

  // Make an UnencryptedMessageMaker.
  // Message will be serialized, but not encrypted: they will be sent in plain
  // text. This scheme must never be used in production Cobalt.
  static std::unique_ptr<EncryptedMessageMaker> MakeUnencrypted();

  // Make a HybridEcdhEncryptedMessageMaker.
  // Messages will be encrypted using version 1 of Cobalt's Elliptic-Curve
  // Diffie-Hellman-based hybrid public-key/private-key encryption scheme using
  // the |public_key_pem| that was passed in..
  static statusor::StatusOr<std::unique_ptr<EncryptedMessageMaker>>
  MakeHybridEcdh(const std::string& public_key_pem);

  // Make a HybridTinkEncryptedMessageMaker.
  // Messages will be encrypted using Tink's hybrid encryption scheme based on
  // the keyset passed in. |public_keyset_base64| is a tink::Keyset protobuf
  // message serialized and base64 encoded.
  static statusor::StatusOr<std::unique_ptr<EncryptedMessageMaker>>
  MakeHybridTink(const std::string& public_keyset_base64);

  virtual ~EncryptedMessageMaker() = default;
};

// HybridTinkEncryptedMessageMaker is an implementation of
// EncryptedMessageMaker. See EncryptedMessage::HYBRID_TINK for details.
class HybridTinkEncryptedMessageMaker : public EncryptedMessageMaker {
 public:
  explicit HybridTinkEncryptedMessageMaker(
      std::unique_ptr<::crypto::tink::HybridEncrypt> encrypter);

  bool Encrypt(const google::protobuf::MessageLite& message,
               EncryptedMessage* encrypted_message) const;

  EncryptedMessage::EncryptionScheme scheme() const {
    return EncryptedMessage::HYBRID_TINK;
  }

 private:
  std::unique_ptr<::crypto::tink::HybridEncrypt> encrypter_;
};

// HybridEcdhEncryptedMessageMaker is an implementation of
// EncryptedMessageMaker. See EncryptedMessage::HYBRID_ECDH_V1 for details.
class HybridEcdhEncryptedMessageMaker : public EncryptedMessageMaker {
 public:
  explicit HybridEcdhEncryptedMessageMaker(
      std::unique_ptr<crypto::HybridCipher> cipher);

  bool Encrypt(const google::protobuf::MessageLite& message,
               EncryptedMessage* encrypted_message) const;

  EncryptedMessage::EncryptionScheme scheme() const {
    return EncryptedMessage::HYBRID_ECDH_V1;
  }

 private:
  std::unique_ptr<crypto::HybridCipher> cipher_;
};

// UnencryptedMessageMaker is an implementation of EncryptedMessageMaker that
// does not perform any encryption.
class UnencryptedMessageMaker : public EncryptedMessageMaker {
 public:
  bool Encrypt(const google::protobuf::MessageLite& message,
               EncryptedMessage* encrypted_message) const;

  EncryptedMessage::EncryptionScheme scheme() const {
    return EncryptedMessage::NONE;
  }
};

class MessageDecrypter {
 public:
  // TODO(rudominer) For key-rotation support the MessageDecrypter
  // should accept multiple (public, private) key pairs and use the
  // fingerprint field of EncryptedMessage to select the appropriate private
  // key.
  explicit MessageDecrypter(const std::string& private_key_pem);

  bool DecryptMessage(const EncryptedMessage& encrypted_message,
                      google::protobuf::MessageLite* recovered_message) const;

 private:
  std::unique_ptr<crypto::HybridCipher> cipher_;
};

}  // namespace util
}  // namespace cobalt

#endif  // COBALT_UTIL_ENCRYPTED_MESSAGE_UTIL_H_