diff --git a/src/protocol-detail/crypto-helper.hpp b/src/protocol-detail/crypto-helper.hpp
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+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2017-2020, Regents of the University of California.
+ *
+ * This file is part of ndncert, a certificate management system based on NDN.
+ *
+ * ndncert is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation, either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * ndncert 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 copies of the GNU General Public License along with
+ * ndncert, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndncert authors and contributors.
+ */
+
+#ifndef NDNCERT_PROTOCOL_DETAIL_CRYPTO_HELPER_HPP
+#define NDNCERT_PROTOCOL_DETAIL_CRYPTO_HELPER_HPP
+
+#include "ndncert-common.hpp"
+
+namespace ndn {
+namespace ndncert {
+
+static const int INFO_LEN = 10;
+static const uint8_t INFO[] = {0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9};
+static const int AES_128_KEY_LEN = 16;
+
+class ECDHState
+{
+public:
+  ECDHState();
+  ~ECDHState();
+
+  std::string
+  getBase64PubKey();
+
+  uint8_t*
+  deriveSecret(const std::string& peerKeyStr);
+
+  uint8_t m_publicKey[256];
+  size_t m_publicKeyLen;
+  uint8_t m_sharedSecret[256];
+  size_t m_sharedSecretLen;
+
+PUBLIC_WITH_TESTS_ELSE_PRIVATE:
+  uint8_t*
+  deriveSecret(const uint8_t* peerkey, int peerKeySize);
+
+  uint8_t*
+  getRawSelfPubKey();
+
+private:
+  struct ECDH_CTX;
+  unique_ptr<ECDH_CTX> context;
+};
+
+/**
+ * HMAC based key derivation function (HKDF)
+ * @p secret, intput, the input to the HKDF
+ * @p secretLen, intput, the length of the secret
+ * @p salt, intput, the salt used in HKDF
+ * @p saltLen, intput, the length of the salt
+ * @p output, output, the output of the HKDF
+ * @p output_len, intput, the length of expected output
+ * @p info, intput, the additional information used in HKDF
+ * @p info_len, intput, the additional information used in HKDF
+ * @return the length of the derived key if successful, -1 if failed
+ */
+int
+hkdf(const uint8_t* secret, int secret_len,
+     const uint8_t* salt, int salt_len,
+     uint8_t* output, int output_len,
+     const uint8_t* info = INFO, int info_len = INFO_LEN);
+
+/**
+ * HMAC based on SHA-256
+ * @p data, intput, the array to hmac
+ * @p data_length, intput, the length of the array
+ * @p key, intput, the key for the function
+ * @p key_len, intput, the length of the key
+ * @p result, output, result of the HMAC. Enough memory (32 Bytes) must be allocated beforehands
+ * @return 0 if successful, -1 if failed
+ */
+int
+hmac_sha256(const uint8_t* data, const unsigned data_length,
+            const uint8_t* key, const unsigned key_length,
+            uint8_t* result);
+
+/**
+ * Authenticated GCM 128 Encryption with associated data
+ * @p plaintext, input, plaintext
+ * @p plaintext_len, input, size of plaintext
+ * @p associated, input, associated authentication data
+ * @p associated_len, input, size of associated authentication data
+ * @p key, input, 16 bytes AES key
+ * @p iv, input, 12 bytes IV
+ * @p ciphertext, output, enough memory must be allocated beforehands
+ * @p tag, output, 16 bytes tag
+ * @return the size of ciphertext
+ * @throw runtime_error when there is an error in the process of encryption
+ */
+int
+aes_gcm_128_encrypt(const uint8_t* plaintext, size_t plaintext_len, const uint8_t* associated, size_t associated_len,
+                    const uint8_t* key, const uint8_t* iv, uint8_t* ciphertext, uint8_t* tag);
+
+/**
+ * Authenticated GCM 128 Decryption with associated data
+ * @p ciphertext, input, ciphertext
+ * @p ciphertext_len, input, size of ciphertext
+ * @p associated, input, associated authentication data
+ * @p associated_len, input, size of associated authentication data
+ * @p tag, input, 16 bytes tag
+ * @p key, input, 16 bytes AES key
+ * @p iv, input, 12 bytes IV
+ * @p plaintext, output, enough memory must be allocated beforehands
+ * @return the size of plaintext or -1 if the verification fails
+ * @throw runtime_error when there is an error in the process of encryption
+ */
+int
+aes_gcm_128_decrypt(const uint8_t* ciphertext, size_t ciphertext_len, const uint8_t* associated, size_t associated_len,
+                    const uint8_t* tag, const uint8_t* key, const uint8_t* iv, uint8_t* plaintext);
+
+/**
+ * Encode the payload into TLV block with Authenticated GCM 128 Encryption
+ * @p tlv::type, intput, the TLV TYPE of the encoded block, either ApplicationParameters or Content
+ * @p key, intput, 16 Bytes, the AES key used for encryption
+ * @p payload, input, the plaintext payload
+ * @p payloadSize, input, the size of the plaintext payload
+ * @p associatedData, input, associated data used for authentication
+ * @p associatedDataSize, input, the size of associated data
+ * @return the TLV block with @p tlv::type TLV TYPE
+ */
+Block
+encodeBlockWithAesGcm128(uint32_t tlv_type, const uint8_t* key, const uint8_t* payload, size_t payloadSize,
+                         const uint8_t* associatedData, size_t associatedDataSize);
+
+/**
+ * Decode the payload from TLV block with Authenticated GCM 128 Encryption
+ * @p block, intput, the TLV block in the format of NDNCERT protocol
+ * @p key, intput, 16 Bytes, the AES key used for encryption
+ * @p associatedData, input, associated data used for authentication
+ * @p associatedDataSize, input, the size of associated data
+ * @return the plaintext buffer
+ */
+Buffer
+decodeBlockWithAesGcm128(const Block& block, const uint8_t* key,
+                         const uint8_t* associatedData, size_t associatedDataSize);
+
+} // namespace ndncert
+} // namespace ndn
+
+#endif // NDNCERT_PROTOCOL_DETAIL_CRYPTO_HELPER_HPP