diff --git a/src/detail/crypto-helpers.cpp b/src/detail/crypto-helpers.cpp
new file mode 100644
index 0000000..3142268
--- /dev/null
+++ b/src/detail/crypto-helpers.cpp
@@ -0,0 +1,386 @@
+/* -*- 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.
+ */
+
+#include "detail/crypto-helpers.hpp"
+
+#include <boost/endian/conversion.hpp>
+#include <cstring>
+#include <ndn-cxx/encoding/buffer-stream.hpp>
+#include <ndn-cxx/security/transform/base64-decode.hpp>
+#include <ndn-cxx/security/transform/base64-encode.hpp>
+#include <ndn-cxx/security/transform/buffer-source.hpp>
+#include <ndn-cxx/security/transform/stream-sink.hpp>
+#include <ndn-cxx/util/random.hpp>
+#include <openssl/ec.h>
+#include <openssl/err.h>
+#include <openssl/hmac.h>
+#include <openssl/kdf.h>
+#include <openssl/pem.h>
+
+namespace ndn {
+namespace ndncert {
+
+ECDHState::ECDHState()
+{
+  auto EC_NID = NID_X9_62_prime256v1;
+  // params context
+  EVP_PKEY_CTX* ctx_params = EVP_PKEY_CTX_new_id(EVP_PKEY_EC, nullptr);
+  if (ctx_params == nullptr) {
+    NDN_THROW(std::runtime_error("Could not create context"));
+  }
+  if (EVP_PKEY_paramgen_init(ctx_params) != 1) {
+    EVP_PKEY_CTX_free(ctx_params);
+    NDN_THROW(std::runtime_error("Could not initialize parameter generation"));
+  }
+  if (1 != EVP_PKEY_CTX_set_ec_paramgen_curve_nid(ctx_params, EC_NID)) {
+    EVP_PKEY_CTX_free(ctx_params);
+    NDN_THROW(std::runtime_error("Likely unknown elliptical curve ID specified"));
+  }
+  // generate params
+  EVP_PKEY* params = nullptr;
+  if (!EVP_PKEY_paramgen(ctx_params, &params)) {
+    EVP_PKEY_CTX_free(ctx_params);
+    NDN_THROW(std::runtime_error("Could not create parameter object parameters"));
+  }
+  // key generation context
+  EVP_PKEY_CTX* ctx_keygen = EVP_PKEY_CTX_new(params, nullptr);
+  if (ctx_keygen == nullptr) {
+    EVP_PKEY_free(params);
+    EVP_PKEY_CTX_free(ctx_params);
+    NDN_THROW(std::runtime_error("Could not create the context for the key generation"));
+  }
+  if (1 != EVP_PKEY_keygen_init(ctx_keygen)) {
+    EVP_PKEY_CTX_free(ctx_keygen);
+    EVP_PKEY_free(params);
+    EVP_PKEY_CTX_free(ctx_params);
+    NDN_THROW(std::runtime_error("Could not init context for key generation"));
+  }
+  if (1 != EVP_PKEY_keygen(ctx_keygen, &m_privkey)) {
+    EVP_PKEY_CTX_free(ctx_keygen);
+    EVP_PKEY_free(params);
+    EVP_PKEY_CTX_free(ctx_params);
+    NDN_THROW(std::runtime_error("Could not generate DHE keys in final step"));
+  }
+  EVP_PKEY_CTX_free(ctx_keygen);
+  EVP_PKEY_free(params);
+  EVP_PKEY_CTX_free(ctx_params);
+}
+
+ECDHState::~ECDHState()
+{
+  if (m_privkey != nullptr) {
+    EVP_PKEY_free(m_privkey);
+  }
+}
+
+const std::vector<uint8_t>&
+ECDHState::getSelfPubKey()
+{
+  auto privECKey = EVP_PKEY_get1_EC_KEY(m_privkey);
+  if (privECKey == nullptr) {
+    NDN_THROW(std::runtime_error("Could not get key when calling EVP_PKEY_get1_EC_KEY()"));
+  }
+  auto ecPoint = EC_KEY_get0_public_key(privECKey);
+  auto group = EC_KEY_get0_group(privECKey);
+  auto requiredBufLen = EC_POINT_point2oct(group, ecPoint, POINT_CONVERSION_UNCOMPRESSED, nullptr, 0, nullptr);
+  m_pubKey.resize(requiredBufLen);
+  auto rev = EC_POINT_point2oct(group, ecPoint, POINT_CONVERSION_UNCOMPRESSED,
+                                m_pubKey.data(), requiredBufLen, nullptr);
+  EC_KEY_free(privECKey);
+  if (rev == 0) {
+    NDN_THROW(std::runtime_error("Could not convert EC_POINTS to octet string when calling EC_POINT_point2oct()"));
+  }
+  return m_pubKey;
+}
+
+const std::vector<uint8_t>&
+ECDHState::deriveSecret(const std::vector<uint8_t>& peerKey)
+{
+  // prepare self private key
+  auto privECKey = EVP_PKEY_get1_EC_KEY(m_privkey);
+  if (privECKey == nullptr) {
+    NDN_THROW(std::runtime_error("Cannot not get key when calling EVP_PKEY_get1_EC_KEY()"));
+  }
+  auto group = EC_KEY_get0_group(privECKey);
+  EC_KEY_free(privECKey);
+  // prepare the peer public key
+  auto peerPoint = EC_POINT_new(group);
+  if (peerPoint == nullptr) {
+    NDN_THROW(std::runtime_error("Cannot create the EC_POINT for peer key when calling EC_POINT_new()"));
+  }
+  if (EC_POINT_oct2point(group, peerPoint, peerKey.data(), peerKey.size(), nullptr) == 0) {
+    EC_POINT_free(peerPoint);
+    NDN_THROW(std::runtime_error("Cannot convert peer's key into a EC point when calling EC_POINT_oct2point()"));
+  }
+  EC_KEY* ecPeerkey = EC_KEY_new();
+  if (ecPeerkey == nullptr) {
+    EC_POINT_free(peerPoint);
+    NDN_THROW(std::runtime_error("Cannot create EC_KEY for peer key when calling EC_KEY_new()"));
+  }
+  if (EC_KEY_set_group(ecPeerkey, group) != 1) {
+    EC_POINT_free(peerPoint);
+    NDN_THROW(std::runtime_error("Cannot set group for peer key's EC_KEY when calling EC_KEY_set_group()"));
+  }
+  if (EC_KEY_set_public_key(ecPeerkey, peerPoint) == 0) {
+    EC_KEY_free(ecPeerkey);
+    EC_POINT_free(peerPoint);
+    NDN_THROW(std::runtime_error("Cannot initialize peer EC_KEY with the EC_POINT when calling EC_KEY_set_public_key()"));
+  }
+  EVP_PKEY* evpPeerkey = EVP_PKEY_new();
+  if (EVP_PKEY_set1_EC_KEY(evpPeerkey, ecPeerkey) == 0) {
+    EC_KEY_free(ecPeerkey);
+    EC_POINT_free(peerPoint);
+    NDN_THROW(std::runtime_error("Cannot create EVP_PKEY for peer key when calling EVP_PKEY_new()"));
+  }
+  EC_KEY_free(ecPeerkey);
+  EC_POINT_free(peerPoint);
+  // ECDH context
+  EVP_PKEY_CTX* ctx = EVP_PKEY_CTX_new(m_privkey, nullptr);
+  if (ctx == nullptr) {
+    EVP_PKEY_free(evpPeerkey);
+    NDN_THROW(std::runtime_error("Cannot create context for ECDH when calling EVP_PKEY_CTX_new()"));
+  }
+  // Initialize
+  if (1 != EVP_PKEY_derive_init(ctx)) {
+    EVP_PKEY_CTX_free(ctx);
+    EVP_PKEY_free(evpPeerkey);
+    NDN_THROW(std::runtime_error("Cannot initialize context for ECDH when calling EVP_PKEY_derive_init()"));
+  }
+  // Provide the peer public key
+  if (1 != EVP_PKEY_derive_set_peer(ctx, evpPeerkey)) {
+    EVP_PKEY_CTX_free(ctx);
+    EVP_PKEY_free(evpPeerkey);
+    NDN_THROW(std::runtime_error("Cannot set peer key for ECDH when calling EVP_PKEY_derive_set_peer()"));
+  }
+  // Determine buffer length for shared secret
+  size_t secretLen = 0;
+  if (1 != EVP_PKEY_derive(ctx, nullptr, &secretLen)) {
+    EVP_PKEY_CTX_free(ctx);
+    EVP_PKEY_free(evpPeerkey);
+    NDN_THROW(std::runtime_error("Cannot determine the needed buffer length when calling EVP_PKEY_derive()"));
+  }
+  m_secret.resize(secretLen);
+  // Derive the shared secret
+  if (1 != (EVP_PKEY_derive(ctx, m_secret.data(), &secretLen))) {
+    EVP_PKEY_CTX_free(ctx);
+    EVP_PKEY_free(evpPeerkey);
+    NDN_THROW(std::runtime_error("Cannot derive ECDH secret when calling EVP_PKEY_derive()"));
+  }
+  EVP_PKEY_CTX_free(ctx);
+  EVP_PKEY_free(evpPeerkey);
+  return m_secret;
+}
+
+void
+hmacSha256(const uint8_t* data, size_t dataLen,
+           const uint8_t* key, size_t keyLen,
+           uint8_t* result)
+{
+  auto ret = HMAC(EVP_sha256(), key, keyLen,
+                  data, dataLen, result, nullptr);
+  if (ret == nullptr) {
+    NDN_THROW(std::runtime_error("Error computing HMAC when calling HMAC()"));
+  }
+}
+
+size_t
+hkdf(const uint8_t* secret, size_t secretLen, const uint8_t* salt,
+     size_t saltLen, uint8_t* output, size_t outputLen,
+     const uint8_t* info, size_t infoLen)
+{
+  EVP_PKEY_CTX* pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, nullptr);
+  if (EVP_PKEY_derive_init(pctx) <= 0) {
+    EVP_PKEY_CTX_free(pctx);
+    NDN_THROW(std::runtime_error("HKDF: Cannot init ctx when calling EVP_PKEY_derive_init()"));
+  }
+  if (EVP_PKEY_CTX_set_hkdf_md(pctx, EVP_sha256()) <= 0) {
+    EVP_PKEY_CTX_free(pctx);
+    NDN_THROW(std::runtime_error("HKDF: Cannot set md when calling EVP_PKEY_CTX_set_hkdf_md()"));
+  }
+  if (EVP_PKEY_CTX_set1_hkdf_salt(pctx, salt, saltLen) <= 0) {
+    EVP_PKEY_CTX_free(pctx);
+    NDN_THROW(std::runtime_error("HKDF: Cannot set salt when calling EVP_PKEY_CTX_set1_hkdf_salt()"));
+  }
+  if (EVP_PKEY_CTX_set1_hkdf_key(pctx, secret, secretLen) <= 0) {
+    EVP_PKEY_CTX_free(pctx);
+    NDN_THROW(std::runtime_error("HKDF: Cannot set secret when calling EVP_PKEY_CTX_set1_hkdf_key()"));
+  }
+  if (EVP_PKEY_CTX_add1_hkdf_info(pctx, info, infoLen) <= 0) {
+    EVP_PKEY_CTX_free(pctx);
+    NDN_THROW(std::runtime_error("HKDF: Cannot set info when calling EVP_PKEY_CTX_add1_hkdf_info()"));
+  }
+  size_t outLen = outputLen;
+  if (EVP_PKEY_derive(pctx, output, &outLen) <= 0) {
+    EVP_PKEY_CTX_free(pctx);
+    NDN_THROW(std::runtime_error("HKDF: Cannot derive result when calling EVP_PKEY_derive()"));
+  }
+  EVP_PKEY_CTX_free(pctx);
+  return outLen;
+}
+
+size_t
+aesGcm128Encrypt(const uint8_t* plaintext, size_t plaintextLen, const uint8_t* associated, size_t associatedLen,
+                 const uint8_t* key, const uint8_t* iv, uint8_t* ciphertext, uint8_t* tag)
+{
+  EVP_CIPHER_CTX* ctx;
+  int len;
+  size_t ciphertextLen;
+  if (!(ctx = EVP_CIPHER_CTX_new())) {
+    NDN_THROW(std::runtime_error("Cannot create and initialise the context when calling EVP_CIPHER_CTX_new()"));
+  }
+  if (1 != EVP_EncryptInit_ex(ctx, EVP_aes_128_gcm(), nullptr, nullptr, nullptr)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot initialize the encryption operation when calling EVP_EncryptInit_ex()"));
+  }
+  if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 12, nullptr)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot set IV length when calling EVP_CIPHER_CTX_ctrl()"));
+  }
+  if (1 != EVP_EncryptInit_ex(ctx, nullptr, nullptr, key, iv)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot initialize key and IV when calling EVP_EncryptInit_ex()"));
+  }
+  if (1 != EVP_EncryptUpdate(ctx, nullptr, &len, associated, associatedLen)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot set associated authentication data when calling EVP_EncryptUpdate()"));
+  }
+  if (1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintextLen)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot encrypt when calling EVP_EncryptUpdate()"));
+  }
+  ciphertextLen = len;
+  if (1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot finalise the encryption when calling EVP_EncryptFinal_ex()"));
+  }
+  ciphertextLen += len;
+  if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, tag)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot get tag when calling EVP_CIPHER_CTX_ctrl()"));
+  }
+  EVP_CIPHER_CTX_free(ctx);
+  return ciphertextLen;
+}
+
+size_t
+aesGcm128Decrypt(const uint8_t* ciphertext, size_t ciphertextLen, const uint8_t* associated, size_t associatedLen,
+                 const uint8_t* tag, const uint8_t* key, const uint8_t* iv, uint8_t* plaintext)
+{
+  EVP_CIPHER_CTX* ctx;
+  int len;
+  size_t plaintextLen;
+  if (!(ctx = EVP_CIPHER_CTX_new())) {
+    NDN_THROW(std::runtime_error("Cannot create and initialise the context when calling EVP_CIPHER_CTX_new()"));
+  }
+  if (!EVP_DecryptInit_ex(ctx, EVP_aes_128_gcm(), nullptr, nullptr, nullptr)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot initialise the decryption operation when calling EVP_DecryptInit_ex()"));
+  }
+  if (!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 12, nullptr)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot set IV length when calling EVP_CIPHER_CTX_ctrl"));
+  }
+  if (!EVP_DecryptInit_ex(ctx, nullptr, nullptr, key, iv)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot initialise key and IV when calling EVP_DecryptInit_ex()"));
+  }
+  if (!EVP_DecryptUpdate(ctx, nullptr, &len, associated, associatedLen)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot set associated authentication data when calling EVP_EncryptUpdate()"));
+  }
+  if (!EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertextLen)) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot decrypt when calling EVP_DecryptUpdate()"));
+  }
+  plaintextLen = len;
+  if (!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, 16, const_cast<void*>(reinterpret_cast<const void*>(tag)))) {
+    EVP_CIPHER_CTX_free(ctx);
+    NDN_THROW(std::runtime_error("Cannot set tag value when calling EVP_CIPHER_CTX_ctrl()"));
+  }
+  auto ret = EVP_DecryptFinal_ex(ctx, plaintext + len, &len);
+  EVP_CIPHER_CTX_free(ctx);
+  if (ret > 0) {
+    plaintextLen += len;
+    return plaintextLen;
+  }
+  else {
+    NDN_THROW(std::runtime_error("Cannot finalize the decryption when calling EVP_DecryptFinal_ex()"));
+  }
+}
+
+Block
+encodeBlockWithAesGcm128(uint32_t tlvType, const uint8_t* key, const uint8_t* payload, size_t payloadSize,
+                         const uint8_t* associatedData, size_t associatedDataSize, uint32_t& counter)
+{
+  Buffer iv(12);
+  random::generateSecureBytes(iv.data(), 8);
+  if (tlvType == ndn::tlv::ApplicationParameters) {
+    // requester
+    iv[0] &= ~(1UL << 7);
+  }
+  else {
+    // CA
+    iv[0] |= 1UL << 7;
+  }
+  uint32_t temp = boost::endian::native_to_big(counter);
+  std::memcpy(&iv[8], reinterpret_cast<const uint8_t*>(&temp), 4);
+  uint32_t increment = (payloadSize + 15) / 16;
+  if (std::numeric_limits<uint32_t>::max() - counter < increment) {
+    NDN_THROW(std::runtime_error("Error incrementing the AES block counter: "
+                                 "too many blocks have been encrypted for the same request instance"));
+  }
+  else {
+    counter += increment;
+  }
+
+  // The spec of AES encrypted payload TLV used in NDNCERT:
+  //   https://github.com/named-data/ndncert/wiki/NDNCERT-Protocol-0.3#242-aes-gcm-encryption
+  Buffer encryptedPayload(payloadSize);
+  uint8_t tag[16];
+  size_t encryptedPayloadLen = aesGcm128Encrypt(payload, payloadSize, associatedData, associatedDataSize,
+                                                key, iv.data(), encryptedPayload.data(), tag);
+  auto content = makeEmptyBlock(tlvType);
+  content.push_back(makeBinaryBlock(tlv::InitializationVector, iv.data(), iv.size()));
+  content.push_back(makeBinaryBlock(tlv::AuthenticationTag, tag, 16));
+  content.push_back(makeBinaryBlock(tlv::EncryptedPayload, encryptedPayload.data(), encryptedPayloadLen));
+  content.encode();
+  return content;
+}
+
+Buffer
+decodeBlockWithAesGcm128(const Block& block, const uint8_t* key, const uint8_t* associatedData, size_t associatedDataSize)
+{
+  // The spec of AES encrypted payload TLV used in NDNCERT:
+  //   https://github.com/named-data/ndncert/wiki/NDNCERT-Protocol-0.3#242-aes-gcm-encryption
+  block.parse();
+  const auto& encryptedPayloadBlock = block.get(tlv::EncryptedPayload);
+  Buffer result(encryptedPayloadBlock.value_size());
+  auto resultLen = aesGcm128Decrypt(encryptedPayloadBlock.value(), encryptedPayloadBlock.value_size(),
+                                    associatedData, associatedDataSize, block.get(tlv::AuthenticationTag).value(),
+                                    key, block.get(tlv::InitializationVector).value(), result.data());
+  if (resultLen != encryptedPayloadBlock.value_size()) {
+    NDN_THROW(std::runtime_error("Error when decrypting the AES Encrypted Block: "
+                                 "Decrypted payload is of an unexpected size"));
+  }
+  return result;
+}
+
+} // namespace ndncert
+} // namespace ndn