security: rename SignatureSha256 to DigestSha256

Change-Id: Idabb95222d86e2541372593698ed9754156a5df2
diff --git a/src/security/digest-sha256.hpp b/src/security/digest-sha256.hpp
new file mode 100644
index 0000000..19833e1
--- /dev/null
+++ b/src/security/digest-sha256.hpp
@@ -0,0 +1,65 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2014 Regents of the University of California.
+ *
+ * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
+ *
+ * ndn-cxx library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * ndn-cxx library 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 Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
+ */
+
+#ifndef NDN_SECURITY_DIGEST_SHA256_HPP
+#define NDN_SECURITY_DIGEST_SHA256_HPP
+
+#include "../data.hpp"
+#include "../encoding/tlv.hpp"
+
+namespace ndn {
+
+/**
+ * Represent a SHA256 digest.
+ */
+class DigestSha256 : public Signature
+{
+public:
+  class Error : public Signature::Error
+  {
+  public:
+    explicit
+    Error(const std::string& what)
+      : Signature::Error(what)
+    {
+    }
+  };
+
+  DigestSha256()
+  {
+    m_info = Block(Tlv::SignatureInfo);
+
+    m_type = Signature::Sha256;
+    m_info.push_back(nonNegativeIntegerBlock(Tlv::SignatureType, Tlv::DigestSha256));
+  }
+
+  explicit
+  DigestSha256(const Signature& signature)
+    : Signature(signature)
+  {
+    if (getType() != Signature::Sha256)
+      throw Error("Incorrect signature type");
+  }
+};
+
+} // namespace ndn
+
+#endif //NDN_SECURITY_DIGEST_SHA256_HPP