diff --git a/src/util/sha256.cpp b/src/util/sha256.cpp
new file mode 100644
index 0000000..7aeea64
--- /dev/null
+++ b/src/util/sha256.cpp
@@ -0,0 +1,152 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2013-2017 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.
+ */
+
+#include "sha256.hpp"
+#include "string-helper.hpp"
+#include "../security/detail/openssl.hpp"
+#include "../security/transform/digest-filter.hpp"
+#include "../security/transform/stream-sink.hpp"
+#include "../security/transform/stream-source.hpp"
+
+namespace ndn {
+namespace util {
+
+const size_t Sha256::DIGEST_SIZE;
+
+Sha256::Sha256()
+{
+  reset();
+}
+
+Sha256::Sha256(std::istream& is)
+  : m_output(make_unique<OBufferStream>())
+  , m_isEmpty(false)
+  , m_isFinalized(true)
+{
+  namespace tr = security::transform;
+
+  tr::streamSource(is) >> tr::digestFilter(DigestAlgorithm::SHA256) >> tr::streamSink(*m_output);
+}
+
+void
+Sha256::reset()
+{
+  namespace tr = security::transform;
+
+  m_input = make_unique<tr::StepSource>();
+  m_output = make_unique<OBufferStream>();
+  m_isEmpty = true;
+  m_isFinalized = false;
+
+  *m_input >> tr::digestFilter(DigestAlgorithm::SHA256) >> tr::streamSink(*m_output);
+}
+
+ConstBufferPtr
+Sha256::computeDigest()
+{
+  if (!m_isFinalized) {
+    BOOST_ASSERT(m_input != nullptr);
+    m_input->end();
+    m_isFinalized = true;
+  }
+
+  return m_output->buf();
+}
+
+bool
+Sha256::operator==(Sha256& digest)
+{
+  const Buffer& lhs = *computeDigest();
+  const Buffer& rhs = *digest.computeDigest();
+
+  if (lhs.size() != rhs.size()) {
+    return false;
+  }
+
+  // constant-time buffer comparison to mitigate timing attacks
+  return CRYPTO_memcmp(lhs.get(), rhs.get(), lhs.size()) == 0;
+}
+
+Sha256&
+Sha256::operator<<(Sha256& src)
+{
+  auto buf = src.computeDigest();
+  update(buf->get(), buf->size());
+  return *this;
+}
+
+Sha256&
+Sha256::operator<<(const std::string& str)
+{
+  update(reinterpret_cast<const uint8_t*>(str.data()), str.size());
+  return *this;
+}
+
+Sha256&
+Sha256::operator<<(const Block& block)
+{
+  update(block.wire(), block.size());
+  return *this;
+}
+
+Sha256&
+Sha256::operator<<(uint64_t value)
+{
+  update(reinterpret_cast<const uint8_t*>(&value), sizeof(uint64_t));
+  return *this;
+}
+
+void
+Sha256::update(const uint8_t* buffer, size_t size)
+{
+  if (m_isFinalized)
+    BOOST_THROW_EXCEPTION(Error("Digest has been already finalized"));
+
+  BOOST_ASSERT(m_input != nullptr);
+  m_input->write(buffer, size);
+  m_isEmpty = false;
+}
+
+std::string
+Sha256::toString()
+{
+  auto buf = computeDigest();
+  return toHex(*buf);
+}
+
+ConstBufferPtr
+Sha256::computeDigest(const uint8_t* buffer, size_t size)
+{
+  Sha256 sha256;
+  sha256.update(buffer, size);
+  return sha256.computeDigest();
+}
+
+std::ostream&
+operator<<(std::ostream& os, Sha256& digest)
+{
+  auto buf = digest.computeDigest();
+  printHex(os, *buf);
+  return os;
+}
+
+} // namespace util
+} // namespace ndn