tls_session_key.cpp

/*

* TLS Session Key

* (C) 2004-2006,2011,2016,2019 Jack Lloyd

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/internal/tls_session_key.h>

#include <botan/kdf.h>

#include <botan/mem_ops.h>

#include <botan/tls_messages.h>

#include <botan/internal/tls_handshake_state.h>

namespace Botan::TLS {

/**

* Session_Keys Constructor

*/

Session_Keys::Session_Keys(const Handshake_State* state,

                           const secure_vector<uint8_t>& pre_master_secret,

                           bool resuming) {

   const size_t cipher_keylen = state->ciphersuite().cipher_keylen();

   const size_t mac_keylen = state->ciphersuite().mac_keylen();

   const size_t cipher_nonce_bytes = state->ciphersuite().nonce_bytes_from_handshake();

   const bool extended_master_secret = state->server_hello()->supports_extended_master_secret();

   const size_t prf_gen = 2 * (mac_keylen + cipher_keylen + cipher_nonce_bytes);

   const uint8_t MASTER_SECRET_MAGIC[] = {0x6D, 0x61, 0x73, 0x74, 0x65, 0x72, 0x20, 0x73, 0x65, 0x63, 0x72, 0x65, 0x74};

   const uint8_t EXT_MASTER_SECRET_MAGIC[] = {0x65, 0x78, 0x74, 0x65, 0x6E, 0x64, 0x65, 0x64, 0x20, 0x6D, 0x61,

                                              0x73, 0x74, 0x65, 0x72, 0x20, 0x73, 0x65, 0x63, 0x72, 0x65, 0x74};

   const uint8_t KEY_GEN_MAGIC[] = {0x6B, 0x65, 0x79, 0x20, 0x65, 0x78, 0x70, 0x61, 0x6E, 0x73, 0x69, 0x6F, 0x6E};

   auto prf = state->protocol_specific_prf();

   if(resuming) {

      // This is actually the master secret saved as part of the session

      m_master_sec = pre_master_secret;

   } else {

      std::vector<uint8_t> salt;

      std::vector<uint8_t> label;

      if(extended_master_secret) {

         label.assign(EXT_MASTER_SECRET_MAGIC, EXT_MASTER_SECRET_MAGIC + sizeof(EXT_MASTER_SECRET_MAGIC));

         salt += state->hash().final(state->ciphersuite().prf_algo());

      } else {

         label.assign(MASTER_SECRET_MAGIC, MASTER_SECRET_MAGIC + sizeof(MASTER_SECRET_MAGIC));

         salt += state->client_hello()->random();

         salt += state->server_hello()->random();

      m_master_sec = prf->derive_key(48, pre_master_secret, salt, label);

   std::vector<uint8_t> salt;

   std::vector<uint8_t> label;

   label.assign(KEY_GEN_MAGIC, KEY_GEN_MAGIC + sizeof(KEY_GEN_MAGIC));

   salt += state->server_hello()->random();

   salt += state->client_hello()->random();

   const secure_vector<uint8_t> prf_output = prf->derive_key(

      prf_gen, m_master_sec.data(), m_master_sec.size(), salt.data(), salt.size(), label.data(), label.size());

   const uint8_t* key_data = prf_output.data();

   m_c_aead.resize(mac_keylen + cipher_keylen);

   m_s_aead.resize(mac_keylen + cipher_keylen);

   copy_mem(&m_c_aead[0], key_data, mac_keylen);

   copy_mem(&m_s_aead[0], key_data + mac_keylen, mac_keylen);

   copy_mem(&m_c_aead[mac_keylen], key_data + 2 * mac_keylen, cipher_keylen);

   copy_mem(&m_s_aead[mac_keylen], key_data + 2 * mac_keylen + cipher_keylen, cipher_keylen);

   m_c_nonce.resize(cipher_nonce_bytes);

   m_s_nonce.resize(cipher_nonce_bytes);

   copy_mem(&m_c_nonce[0], key_data + 2 * (mac_keylen + cipher_keylen), cipher_nonce_bytes);

   copy_mem(&m_s_nonce[0], key_data + 2 * (mac_keylen + cipher_keylen) + cipher_nonce_bytes, cipher_nonce_bytes);

}  // namespace Botan::TLS