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+/*
+ * Copyright 2019 Google Inc.
+ * 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 OPEN_SOURCE_PRIVATE_INTERSECTION_SUM_SERVER_IMPL_H_
+#define OPEN_SOURCE_PRIVATE_INTERSECTION_SUM_SERVER_IMPL_H_
+
+#include "private_join_and_compute/crypto/context.h"
+#include "private_join_and_compute/crypto/ec_commutative_cipher.h"
+#include "private_join_and_compute/crypto/paillier.h"
+#include "private_join_and_compute/match.pb.h"
+#include "private_join_and_compute/message_sink.h"
+#include "private_join_and_compute/private_intersection_sum.pb.h"
+#include "private_join_and_compute/private_join_and_compute.pb.h"
+#include "private_join_and_compute/protocol_server.h"
+#include "private_join_and_compute/util/status.inc"
+
+namespace private_join_and_compute {
+
+// The "server side" of the intersection-sum protocol.  This represents the
+// party that will receive the size of the intersection as its output.  The
+// values that will be summed are supplied by the other party; this party will
+// only supply set elements as its inputs.
+class PrivateIntersectionSumProtocolServerImpl : public ProtocolServer {
+ public:
+  PrivateIntersectionSumProtocolServerImpl(
+      ::private_join_and_compute::Context* ctx, std::vector<std::string> inputs)
+      : ctx_(ctx), inputs_(std::move(inputs)) {}
+
+  ~PrivateIntersectionSumProtocolServerImpl() override = default;
+
+  // Executes the next Server round and creates a response.
+  //
+  // If the ClientMessage is StartProtocol, a ServerRoundOne will be sent to the
+  // message sink, containing the encrypted server identifiers.
+  //
+  // If the ClientMessage is ClientRoundOne, a ServerRoundTwo will be sent to
+  // the message sink, containing the intersection size, and encrypted
+  // intersection-sum.
+  //
+  // Fails with InvalidArgument if the message is not a
+  // PrivateIntersectionSumClientMessage of the expected round, or if the
+  // message is otherwise not as expected. Forwards all other failures
+  // encountered.
+  Status Handle(const ClientMessage& request,
+                MessageSink<ServerMessage>* server_message_sink) override;
+
+  bool protocol_finished() override { return protocol_finished_; }
+
+  // Utility function, used for testing.
+  ECCommutativeCipher* GetECCipher() { return ec_cipher_.get(); }
+
+ private:
+  // Encrypts the server's identifiers.
+  StatusOr<PrivateIntersectionSumServerMessage::ServerRoundOne> EncryptSet();
+
+  // Computes the intersection size and encrypted intersection_sum.
+  StatusOr<PrivateIntersectionSumServerMessage::ServerRoundTwo>
+  ComputeIntersection(const PrivateIntersectionSumClientMessage::ClientRoundOne&
+                          client_message);
+
+  Context* ctx_;  // not owned
+  std::unique_ptr<ECCommutativeCipher> ec_cipher_;
+
+  // inputs_ will first contain the plaintext server identifiers, and later
+  // contain the encrypted server identifiers.
+  std::vector<std::string> inputs_;
+  bool protocol_finished_ = false;
+};
+
+}  // namespace private_join_and_compute
+
+#endif  // OPEN_SOURCE_PRIVATE_INTERSECTION_SUM_SERVER_IMPL_H_