/*

* Server Key Exchange Message

* (C) 2004-2010,2012,2015,2016 Jack Lloyd

*     2017 Harry Reimann, Rohde & Schwarz Cybersecurity

*

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

*/

#include <botan/tls_messages.h>

#include <botan/tls_extensions.h>

#include <botan/internal/tls_reader.h>

#include <botan/internal/tls_handshake_io.h>

#include <botan/internal/tls_handshake_state.h>

#include <botan/credentials_manager.h>

#include <botan/internal/loadstor.h>

#include <botan/pubkey.h>

#include <botan/dh.h>

#include <botan/ecdh.h>

#if defined(BOTAN_HAS_CURVE_25519)

  #include <botan/curve25519.h>

#endif

#if defined(BOTAN_HAS_CECPQ1)

  #include <botan/cecpq1.h>

#endif

namespace Botan::TLS {

/**

* Create a new Server Key Exchange message

*/

Server_Key_Exchange::Server_Key_Exchange(Handshake_IO& io,

                                         Handshake_State& state,

                                         const Policy& policy,

                                         Credentials_Manager& creds,

                                         RandomNumberGenerator& rng,

                                         const Private_Key* signing_key)

   {

   const std::string hostname = state.client_hello()->sni_hostname();

   const Kex_Algo kex_algo = state.ciphersuite().kex_method();

   if(kex_algo == Kex_Algo::PSK || kex_algo == Kex_Algo::ECDHE_PSK)

      {

      std::string identity_hint =

         creds.psk_identity_hint("tls-server", hostname);

      append_tls_length_value(m_params, identity_hint, 2);

      }

   if(kex_algo == Kex_Algo::DH)

      {

      const std::vector<Group_Params> dh_groups = state.client_hello()->supported_dh_groups();

      Group_Params shared_group = Group_Params::NONE;

      /*

      If the client does not send any DH groups in the supported groups

      extension, but does offer DH ciphersuites, we select a group arbitrarily

      */

      if(dh_groups.empty())

         {

         shared_group = policy.default_dh_group();

         }

      else

         {

         shared_group = policy.choose_key_exchange_group(dh_groups);

         }

      if(shared_group == Group_Params::NONE)

         throw TLS_Exception(Alert::HANDSHAKE_FAILURE,

               "Could not agree on a DH group with the client");

      BOTAN_ASSERT(group_param_is_dh(shared_group), "DH groups for the DH ciphersuites god");

      const std::string group_name = state.callbacks().tls_decode_group_param(shared_group);

      auto dh = std::make_unique<DH_PrivateKey>(rng, DL_Group(group_name));

      append_tls_length_value(m_params, BigInt::encode(dh->get_domain().get_p()), 2);

      append_tls_length_value(m_params, BigInt::encode(dh->get_domain().get_g()), 2);

      append_tls_length_value(m_params, dh->public_value(), 2);

      m_kex_key.reset(dh.release());

      }

   else if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK)

      {

      const std::vector<Group_Params> ec_groups = state.client_hello()->supported_ecc_curves();

      if(ec_groups.empty())

         throw Internal_Error("Client sent no ECC extension but we negotiated ECDH");

      Group_Params shared_group = policy.choose_key_exchange_group(ec_groups);

      if(shared_group == Group_Params::NONE)

         throw TLS_Exception(Alert::HANDSHAKE_FAILURE, "No shared ECC group with client");

      std::vector<uint8_t> ecdh_public_val;

      if(shared_group == Group_Params::X25519)

         {

#if defined(BOTAN_HAS_CURVE_25519)

         auto x25519 = std::make_unique<X25519_PrivateKey>(rng);

         ecdh_public_val = x25519->public_value();

         m_kex_key.reset(x25519.release());

#else

         throw Internal_Error("Negotiated X25519 somehow, but it is disabled");

#endif

         }

      else

         {

         Group_Params curve = policy.choose_key_exchange_group(ec_groups);

         const std::string curve_name = state.callbacks().tls_decode_group_param(curve);

         EC_Group ec_group(curve_name);

         auto ecdh = std::make_unique<ECDH_PrivateKey>(rng, ec_group);

         // follow client's preference for point compression

         ecdh_public_val = ecdh->public_value(

            state.client_hello()->prefers_compressed_ec_points() ?

            PointGFp::COMPRESSED : PointGFp::UNCOMPRESSED);

         m_kex_key.reset(ecdh.release());

         }

      const uint16_t named_curve_id = static_cast<uint16_t>(shared_group);

      m_params.push_back(3); // named curve

      m_params.push_back(get_byte<0>(named_curve_id));

      m_params.push_back(get_byte<1>(named_curve_id));

      append_tls_length_value(m_params, ecdh_public_val, 1);

      }

#if defined(BOTAN_HAS_CECPQ1)

   else if(kex_algo == Kex_Algo::CECPQ1)

      {

      std::vector<uint8_t> cecpq1_offer(CECPQ1_OFFER_BYTES);

      m_cecpq1_key.reset(new CECPQ1_key);

      CECPQ1_offer(cecpq1_offer.data(), m_cecpq1_key.get(), rng);

      append_tls_length_value(m_params, cecpq1_offer, 2);

      }

#endif

   else if(kex_algo != Kex_Algo::PSK)

      {

      throw Internal_Error("Server_Key_Exchange: Unknown kex type " +

                           kex_method_to_string(kex_algo));

      }

   if(state.ciphersuite().signature_used())

      {

      BOTAN_ASSERT(signing_key, "Signing key was set");

      std::pair<std::string, Signature_Format> format =

         state.choose_sig_format(*signing_key, m_scheme, false, policy);

      std::vector<uint8_t> buf = state.client_hello()->random();

      buf += state.server_hello()->random();

      buf += params();

      m_signature =

         state.callbacks().tls_sign_message(*signing_key, rng,

                                            format.first, format.second, buf);

      }

   state.hash().update(io.send(*this));

   }

/**

* Deserialize a Server Key Exchange message

*/

Server_Key_Exchange::Server_Key_Exchange(const std::vector<uint8_t>& buf,

                                         const Kex_Algo kex_algo,

                                         const Auth_Method auth_method,

                                         Protocol_Version version)

   {

   BOTAN_UNUSED(version); // remove this

   TLS_Data_Reader reader("ServerKeyExchange", buf);

   /*

   * Here we are deserializing enough to find out what offset the

   * signature is at. All processing is done when the Client Key Exchange

   * is prepared.

   */

   if(kex_algo == Kex_Algo::PSK || kex_algo == Kex_Algo::ECDHE_PSK)

      {

      reader.get_string(2, 0, 65535); // identity hint

      }

   if(kex_algo == Kex_Algo::DH)

      {

      // 3 bigints, DH p, g, Y

      for(size_t i = 0; i != 3; ++i)

         {

         reader.get_range<uint8_t>(2, 1, 65535);

         }

      }

   else if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK)

      {

      reader.get_byte(); // curve type

      reader.get_uint16_t(); // curve id

      reader.get_range<uint8_t>(1, 1, 255); // public key

      }

   else if(kex_algo == Kex_Algo::CECPQ1)

      {

      // u16 blob

      reader.get_range<uint8_t>(2, 1, 65535);

      }

   else if(kex_algo != Kex_Algo::PSK)

      throw Decoding_Error("Server_Key_Exchange: Unsupported kex type " +

                           kex_method_to_string(kex_algo));

   m_params.assign(buf.data(), buf.data() + reader.read_so_far());

   if(auth_method != Auth_Method::IMPLICIT)

      {

      m_scheme = static_cast<Signature_Scheme>(reader.get_uint16_t());

      m_signature = reader.get_range<uint8_t>(2, 0, 65535);

      }

   reader.assert_done();

   }

/**

* Serialize a Server Key Exchange message

*/

std::vector<uint8_t> Server_Key_Exchange::serialize() const

   {

   std::vector<uint8_t> buf = params();

   if(!m_signature.empty())

      {

      if(m_scheme != Signature_Scheme::NONE)

         {

         const uint16_t scheme_code = static_cast<uint16_t>(m_scheme);

         buf.push_back(get_byte<0>(scheme_code));

         buf.push_back(get_byte<1>(scheme_code));

         }

      append_tls_length_value(buf, m_signature, 2);

      }

   return buf;

   }

/**

* Verify a Server Key Exchange message

*/

bool Server_Key_Exchange::verify(const Public_Key& server_key,

                                 const Handshake_State& state,

                                 const Policy& policy) const

   {

   policy.check_peer_key_acceptable(server_key);

   std::pair<std::string, Signature_Format> format =

      state.parse_sig_format(server_key, m_scheme, state.client_hello()->signature_schemes(), false, policy);

   std::vector<uint8_t> buf = state.client_hello()->random();

   buf += state.server_hello()->random();

   buf += params();

   const bool signature_valid =

      state.callbacks().tls_verify_message(server_key, format.first, format.second,

                                           buf, m_signature);

#if defined(BOTAN_UNSAFE_FUZZER_MODE)

   BOTAN_UNUSED(signature_valid);

   return true;

#else

   return signature_valid;

#endif

   }

const Private_Key& Server_Key_Exchange::server_kex_key() const

   {

   BOTAN_ASSERT_NONNULL(m_kex_key);

   return *m_kex_key;

   }

}