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// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef SECURITY_CRYPTAUTH_LIB_SECUREGCM_D2D_CONNECTION_CONTEXT_V1_H_
#define SECURITY_CRYPTAUTH_LIB_SECUREGCM_D2D_CONNECTION_CONTEXT_V1_H_
#include <memory>
#include <string>
#include "securemessage/crypto_ops.h"
namespace securegcm {
// The full context of a secure connection. This class has methods to encode and
// decode messages that are to be sent to another device.
//
// This class should be kept compatible with the Java implementation in
// java/com/google/security/cryptauth/lib/securegcm/D2DConnectionContextV1.java
class D2DConnectionContextV1 {
public:
D2DConnectionContextV1(const securemessage::CryptoOps::SecretKey& encode_key,
const securemessage::CryptoOps::SecretKey& decode_key,
uint32_t encode_sequence_number,
uint32_t decode_sequence_number);
// Once the initiator and responder have negotiated a secret key, use this
// method to encrypt and sign |payload|. Both initiator and responder devices
// can use this message.
//
// On failure, nullptr is returned.
std::unique_ptr<string> EncodeMessageToPeer(const string& payload);
// Once the initiator and responder have negotiated a secret key, use this
// method to decrypt and verify a |message| received from the other device.
// Both initiator and responder devices can use this message.
//
// On failure, nullptr is returned.
std::unique_ptr<string> DecodeMessageFromPeer(const string& message);
// Returns a cryptographic digest (SHA256) of the session keys prepended by
// the SHA256 hash of the ASCII string "D2D".
//
// On failure, nullptr is returned.
std::unique_ptr<string> GetSessionUnique();
// Creates a saved session that can be later used for resumption. Note,
// this must be stored in a secure location.
std::unique_ptr<string> SaveSession();
// Parse a saved session info and attempt to construct a resumed context.
//
// The session info passed to this method should be one that was generated
// by |SaveSession|.
//
// On failure, nullptr is returned.
static std::unique_ptr<D2DConnectionContextV1> FromSavedSession(
const string& savedSessionInfo);
private:
// The key used to encode payloads.
const securemessage::CryptoOps::SecretKey encode_key_;
// The key used to decode received messages.
const securemessage::CryptoOps::SecretKey decode_key_;
// The current sequence number for encoding.
uint32_t encode_sequence_number_;
// The current sequence number for decoding.
uint32_t decode_sequence_number_;
// A friend to access private variables for testing.
friend class D2DConnectionContextV1Peer;
};
} // namespace securegcm
#endif // SECURITY_CRYPTAUTH_LIB_SECUREGCM_D2D_CONNECTION_CONTEXT_V1_H_
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