diff --git a/model/sync-digest.h b/model/sync-digest.h
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+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2012 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Zhenkai Zhu <zhenkai@cs.ucla.edu>
+ *         卞超轶 Chaoyi Bian <bcy@pku.edu.cn>
+ *	   Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ */
+
+#ifndef SYNC_DIGEST_H
+#define SYNC_DIGEST_H
+
+#include <boost/exception/all.hpp>
+#include <openssl/evp.h>
+#include <boost/cstdint.hpp>
+
+namespace ns3 {
+namespace Sync {
+
+const std::size_t HASH_SIZE = 160;
+
+/**
+ * @ingroup sync
+ * @brief A simple wrapper for libcrypto hash functions
+ */
+class Digest
+{
+public:
+  /**
+   * @brief Default constructor.  Will initialize internal libssl structures
+   */
+  Digest ();
+
+  /**
+   * @brief Destructor
+   */
+  ~Digest ();
+
+  // Digest &
+  // operator << (
+
+  /**
+   * @brief Obtain a short version of the hash (just first sizeof(size_t) bytes
+   *
+   * Side effect: Finalize will be called on `this'
+   */
+  std::size_t
+  getHash ();
+
+  /**
+   * @brief Compare two full digests
+   *
+   * Side effect: Finalize will be called on `this' and `digest'
+   */
+  bool
+  operator == (Digest &digest);
+
+private:
+  /**
+   * @brief Finalize digest. All subsequent calls to "operator <<" will fire an exception
+   */
+  void Finalize ();
+  
+private:
+  EVP_MD_CTX *m_context;
+  uint8_t *m_buffer;
+  uint32_t m_hashLength;
+};
+
+struct DigestCalculationError : virtual boost::exception { };
+
+} // Sync
+} // ns3
+
+#endif // SYNC_DIGEST_H