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diff --git a/src/main/cpp/include/securegcm/d2d_connection_context_v1.h b/src/main/cpp/include/securegcm/d2d_connection_context_v1.h
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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_