diff --git a/src/encoding/tlv.hpp b/src/encoding/tlv.hpp
index 1c4851a..7d7461f 100644
--- a/src/encoding/tlv.hpp
+++ b/src/encoding/tlv.hpp
@@ -106,7 +106,12 @@
   // SignatureInfo TLVs
   ValidityPeriod = 253,
   NotBefore = 254,
-  NotAfter = 255
+  NotAfter = 255,
+
+  AdditionalDescription = 258,
+  DescriptionEntry = 512,
+  DescriptionKey = 513,
+  DescriptionValue = 514
 };
 
 /** @brief indicates a possible value of ContentType field
diff --git a/src/security/additional-description.cpp b/src/security/additional-description.cpp
new file mode 100644
index 0000000..6aed34a
--- /dev/null
+++ b/src/security/additional-description.cpp
@@ -0,0 +1,197 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2015 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 "additional-description.hpp"
+#include "../util/concepts.hpp"
+#include "../encoding/block-helpers.hpp"
+
+namespace ndn {
+namespace security {
+
+BOOST_CONCEPT_ASSERT((boost::EqualityComparable<AdditionalDescription>));
+BOOST_CONCEPT_ASSERT((WireEncodable<AdditionalDescription>));
+BOOST_CONCEPT_ASSERT((WireEncodableWithEncodingBuffer<AdditionalDescription>));
+BOOST_CONCEPT_ASSERT((WireDecodable<AdditionalDescription>));
+static_assert(std::is_base_of<tlv::Error, AdditionalDescription::Error>::value,
+              "AdditionalDescription::Error must inherit from tlv::Error");
+
+static const size_t KEY_OFFSET = 0;
+static const size_t VALUE_OFFSET = 1;
+
+AdditionalDescription::AdditionalDescription(const Block& block)
+{
+  wireDecode(block);
+}
+
+const std::string&
+AdditionalDescription::get(const std::string& key) const
+{
+  auto it = m_info.find(key);
+  if (it == m_info.end())
+    throw Error("Entry does not exist for key (" + key + ")");
+
+  return it->second;
+}
+
+void
+AdditionalDescription::set(const std::string& key, const std::string& value)
+{
+  m_info[key] = value;
+}
+
+bool
+AdditionalDescription::has(const std::string& key) const
+{
+  return (m_info.find(key) != m_info.end());
+}
+
+AdditionalDescription::iterator
+AdditionalDescription::begin()
+{
+  return m_info.begin();
+}
+
+AdditionalDescription::iterator
+AdditionalDescription::end()
+{
+  return m_info.end();
+}
+
+AdditionalDescription::const_iterator
+AdditionalDescription::begin() const
+{
+  return m_info.begin();
+}
+
+AdditionalDescription::const_iterator
+AdditionalDescription::end() const
+{
+  return m_info.end();
+}
+
+template<encoding::Tag TAG>
+size_t
+AdditionalDescription::wireEncode(EncodingImpl<TAG>& encoder) const
+{
+  size_t totalLength = 0;
+
+  for (auto it = m_info.rbegin(); it != m_info.rend(); it++) {
+    size_t entryLength = 0;
+    entryLength += prependStringBlock(encoder, tlv::DescriptionValue, it->second);
+    entryLength += prependStringBlock(encoder, tlv::DescriptionKey, it->first);
+    entryLength += encoder.prependVarNumber(entryLength);
+    entryLength += encoder.prependVarNumber(tlv::DescriptionEntry);
+
+    totalLength += entryLength;
+  }
+
+  totalLength += encoder.prependVarNumber(totalLength);
+  totalLength += encoder.prependVarNumber(tlv::AdditionalDescription);
+  return totalLength;
+}
+
+template size_t
+AdditionalDescription::wireEncode<encoding::EncoderTag>(EncodingImpl<encoding::EncoderTag>& encoder) const;
+
+template size_t
+AdditionalDescription::wireEncode<encoding::EstimatorTag>(EncodingImpl<encoding::EstimatorTag>& encoder) const;
+
+const Block&
+AdditionalDescription::wireEncode() const
+{
+  if (m_wire.hasWire())
+    return m_wire;
+
+  EncodingEstimator estimator;
+  size_t estimatedSize = wireEncode(estimator);
+
+  EncodingBuffer buffer(estimatedSize, 0);
+  wireEncode(buffer);
+
+  m_wire = buffer.block();
+  m_wire.parse();
+
+  return m_wire;
+}
+
+void
+AdditionalDescription::wireDecode(const Block& wire)
+{
+   if (!wire.hasWire()) {
+    throw Error("The supplied block does not contain wire format");
+  }
+
+  m_wire = wire;
+  m_wire.parse();
+
+  if (m_wire.type() != tlv::AdditionalDescription)
+    throw Error("Unexpected TLV type when decoding AdditionalDescription");
+
+  Block::element_const_iterator it = m_wire.elements_begin();
+  while (it != m_wire.elements_end()) {
+    const Block& entry = *it;
+    entry.parse();
+
+    if (entry.type() != tlv::DescriptionEntry)
+      throw Error("Unexpected TLV type when decoding DescriptionEntry");
+
+    if (entry.elements_size() != 2)
+      throw Error("DescriptionEntry does not have two sub-TLVs");
+
+    if (entry.elements()[KEY_OFFSET].type() != tlv::DescriptionKey ||
+        entry.elements()[VALUE_OFFSET].type() != tlv::DescriptionValue)
+      throw Error("Invalid DescriptionKey or DescriptionValue field");
+
+    m_info[readString(entry.elements()[KEY_OFFSET])] = readString(entry.elements()[VALUE_OFFSET]);
+    it++;
+  }
+}
+
+bool
+AdditionalDescription::operator==(const AdditionalDescription& other) const
+{
+  return (m_info == other.m_info);
+}
+
+bool
+AdditionalDescription::operator!=(const AdditionalDescription& other) const
+{
+  return !(*this == other);
+}
+
+std::ostream&
+operator<<(std::ostream& os, const AdditionalDescription& other)
+{
+  size_t count = 0;
+  os << "(";
+  for (const auto& entry : other) {
+    if (count > 0)
+      os << ", ";
+    os << "(" << entry.first << ":" << entry.second << ")";
+    count++;
+  }
+  os << ")";
+
+  return os;
+}
+
+} // namespace security
+} // namespace ndn
diff --git a/src/security/additional-description.hpp b/src/security/additional-description.hpp
new file mode 100644
index 0000000..b34cb74
--- /dev/null
+++ b/src/security/additional-description.hpp
@@ -0,0 +1,131 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2015 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_ADDITIONAL_DESCRIPTION_HPP
+#define NDN_SECURITY_ADDITIONAL_DESCRIPTION_HPP
+
+#include "../common.hpp"
+#include "../encoding/tlv.hpp"
+#include "../encoding/block.hpp"
+#include <map>
+
+namespace ndn {
+namespace security {
+
+/**
+ * @brief Abstraction of AdditionalDescription
+ * @sa docs/tutorials/certificate-format.rst
+ */
+class AdditionalDescription
+{
+public:
+  class Error : public tlv::Error
+  {
+  public:
+    explicit
+    Error(const std::string& what)
+      : tlv::Error(what)
+    {
+    }
+  };
+
+  typedef std::map<std::string, std::string>::iterator iterator;
+  typedef std::map<std::string, std::string>::const_iterator const_iterator;
+
+public:
+
+  /**
+   * @brief Create an empty AdditionalDescription
+   */
+  AdditionalDescription() = default;
+
+  /**
+   * @brief Create AdditionalDescription from @p block
+   */
+  explicit
+  AdditionalDescription(const Block& block);
+
+  const std::string&
+  get(const std::string& key) const;
+
+  void
+  set(const std::string& key, const std::string& value);
+
+  bool
+  has(const std::string& key) const;
+
+  size_t
+  size() const
+  {
+    return m_info.size();
+  }
+
+  iterator
+  begin();
+
+  iterator
+  end();
+
+  const_iterator
+  begin() const;
+
+  const_iterator
+  end() const;
+
+  /** @brief Fast encoding or block size estimation
+   */
+  template<encoding::Tag TAG>
+  size_t
+  wireEncode(EncodingImpl<TAG>& encoder) const;
+
+  /** @brief Encode ValidityPeriod into TLV block
+   */
+  const Block&
+  wireEncode() const;
+
+  /** @brief Decode ValidityPeriod from TLV block
+   *  @throw Error when an invalid TLV block supplied
+   */
+  void
+  wireDecode(const Block& wire);
+
+public: // EqualityComparable concept
+
+  bool
+  operator==(const AdditionalDescription& other) const;
+
+  bool
+  operator!=(const AdditionalDescription& other) const;
+
+private:
+
+  std::map<std::string, std::string> m_info;
+
+  mutable Block m_wire;
+};
+
+std::ostream&
+operator<<(std::ostream& os, const AdditionalDescription& period);
+
+} // namespace security
+} // namespace ndn
+
+#endif // NDN_SECURITY_ADDITIONAL_DESCRIPTION_HPP
diff --git a/tests/unit-tests/security/additional-info.t.cpp b/tests/unit-tests/security/additional-info.t.cpp
new file mode 100644
index 0000000..63320f7
--- /dev/null
+++ b/tests/unit-tests/security/additional-info.t.cpp
@@ -0,0 +1,101 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2015 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 "security/additional-description.hpp"
+
+#include "boost-test.hpp"
+
+namespace ndn {
+namespace security {
+namespace tests {
+
+BOOST_AUTO_TEST_SUITE(SecurityAdditionalDescription)
+
+static const uint8_t description[] = {
+  0xfd, 0x01, 0x02, 0x28,
+    0xfd, 0x02, 0x00, 0x10, // DescriptionEntry
+      0xfd, 0x02, 0x01, 0x04, // DescriptionKey
+        0x6b, 0x65, 0x79, 0x31, // "key1"
+      0xfd, 0x02, 0x02, 0x04, // DescriptionValue
+        0x76, 0x61, 0x6c, 0x31, // "val1"
+    0xfd, 0x02, 0x00, 0x10, // DescriptionEntry
+      0xfd, 0x02, 0x01, 0x04, // DescriptionKey
+        0x6b, 0x65, 0x79, 0x32, // "key2"
+      0xfd, 0x02, 0x02, 0x04, // DescriptionValue
+        0x76, 0x61, 0x6c, 0x32, // "val2"
+};
+
+static const std::string text = "((key1:val1), (key2:val2))";
+
+BOOST_AUTO_TEST_CASE(Basic)
+{
+  AdditionalDescription aDescription;
+
+  aDescription.set("key2", "val2");
+  aDescription.set("key1", "val1");
+
+  BOOST_REQUIRE_NO_THROW(aDescription.get("key1"));
+  BOOST_REQUIRE_NO_THROW(aDescription.get("key2"));
+  BOOST_REQUIRE_THROW(aDescription.get("key3"), AdditionalDescription::Error);
+
+  BOOST_CHECK_EQUAL(aDescription.has("key1"), true);
+  BOOST_CHECK_EQUAL(aDescription.has("key2"), true);
+  BOOST_CHECK_EQUAL(aDescription.has("key3"), false);
+
+  auto val1 = aDescription.get("key1");
+  auto val2 = aDescription.get("key2");
+
+  BOOST_CHECK_EQUAL(val1, "val1");
+  BOOST_CHECK_EQUAL(val2, "val2");
+
+  auto it = aDescription.begin();
+  BOOST_CHECK_EQUAL(it->second, "val1");
+  it++;
+  BOOST_CHECK_EQUAL(it->second, "val2");
+  it++;
+  BOOST_CHECK(it == aDescription.end());
+
+  BOOST_CHECK_EQUAL_COLLECTIONS(aDescription.wireEncode().wire(),
+                                aDescription.wireEncode().wire() + aDescription.wireEncode().size(),
+                                description,
+                                description + sizeof(description));
+
+  BOOST_REQUIRE_NO_THROW(AdditionalDescription(Block(description, sizeof(description))));
+  AdditionalDescription aDescription2(Block(description, sizeof(description)));
+
+  BOOST_CHECK(aDescription2 == aDescription);
+
+  AdditionalDescription aDescription3;
+  aDescription3.set("key3", "val3");
+  aDescription3.set("key2", "val2");
+
+  BOOST_CHECK(aDescription2 != aDescription3);
+
+  std::ostringstream os;
+  os << aDescription;
+  BOOST_CHECK_EQUAL(os.str(), text);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+
+} // namespace tests
+} // namespace security
+} // namespace ndn