Botan::TLS::Client_Key_Exchange Class Reference

#include <tls_messages.h>

Inheritance diagram for Botan::TLS::Client_Key_Exchange:

Public Member Functions
	Client_Key_Exchange (const std::vector< uint8_t > &buf, const Handshake_State &state, const Private_Key *server_rsa_kex_key, Credentials_Manager &creds, const Policy &policy, RandomNumberGenerator &rng)
	Client_Key_Exchange (Handshake_IO &io, Handshake_State &state, const Policy &policy, Credentials_Manager &creds, const Public_Key *server_public_key, std::string_view hostname, RandomNumberGenerator &rng)
const secure_vector< uint8_t > &	pre_master_secret () const
const std::optional< std::string > &	psk_identity () const
Handshake_Type	type () const override
std::string	type_string () const
virtual Handshake_Type	wire_type () const

Detailed Description

Client Key Exchange Message

Definition at line 485 of file tls_messages.h.

Constructor & Destructor Documentation

Client_Key_Exchange() [1/2]

Botan::TLS::Client_Key_Exchange::Client_Key_Exchange	(	Handshake_IO &	io,
		Handshake_State &	state,
		const Policy &	policy,
		Credentials_Manager &	creds,
		const Public_Key *	server_public_key,
		std::string_view	hostname,
		RandomNumberGenerator &	rng )

Definition at line 26 of file msg_client_kex.cpp.

                                                                     {
   const Kex_Algo kex_algo = state.ciphersuite().kex_method();
 
   if(kex_algo == Kex_Algo::PSK) {
      std::string identity_hint;
 
      if(state.server_kex() != nullptr) {
         TLS_Data_Reader reader("ClientKeyExchange", state.server_kex()->params());
         identity_hint = reader.get_string(2, 0, 65535);
      }
 
      m_psk_identity = creds.psk_identity("tls-client", std::string(hostname), identity_hint);
 
      append_tls_length_value(m_key_material, as_span_of_bytes(m_psk_identity.value()), 2);
 
      SymmetricKey psk = creds.psk("tls-client", std::string(hostname), m_psk_identity.value());
 
      std::vector<uint8_t> zeros(psk.length());
 
      append_tls_length_value(m_pre_master, zeros, 2);
      append_tls_length_value(m_pre_master, psk.bits_of(), 2);
   } else if(state.server_kex() != nullptr) {
      TLS_Data_Reader reader("ClientKeyExchange", state.server_kex()->params());
 
      SymmetricKey psk;
 
      if(kex_algo == Kex_Algo::ECDHE_PSK) {
         std::string identity_hint = reader.get_string(2, 0, 65535);
 
         m_psk_identity = creds.psk_identity("tls-client", std::string(hostname), identity_hint);
 
         append_tls_length_value(m_key_material, as_span_of_bytes(m_psk_identity.value()), 2);
 
         psk = creds.psk("tls-client", std::string(hostname), m_psk_identity.value());
      }
 
      if(kex_algo == Kex_Algo::DH) {
         const auto modulus = BigInt::from_bytes(reader.get_range<uint8_t>(2, 1, 65535));
         const auto generator = BigInt::from_bytes(reader.get_range<uint8_t>(2, 1, 65535));
         const std::vector<uint8_t> peer_public_value = reader.get_range<uint8_t>(2, 1, 65535);
 
         if(reader.remaining_bytes() > 0) {
            throw Decoding_Error("Bad params size for DH key exchange");
         }
 
         DL_Group group(modulus, generator);
 
         if(!group.verify_group(rng, false)) {
            throw TLS_Exception(Alert::InsufficientSecurity, "DH group validation failed");
         }
 
         const auto private_key = state.callbacks().tls_generate_ephemeral_key(group, rng);
         m_pre_master = CT::strip_leading_zeros(
            state.callbacks().tls_ephemeral_key_agreement(group, *private_key, peer_public_value, rng, policy));
         append_tls_length_value(m_key_material, private_key->public_value(), 2);
      } else if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
         const uint8_t curve_type = reader.get_byte();
         if(curve_type != 3) {
            throw Decoding_Error("Server sent non-named ECC curve");
         }
 
         const Group_Params curve_id = static_cast<Group_Params>(reader.get_uint16_t());
         const std::vector<uint8_t> peer_public_value = reader.get_range<uint8_t>(1, 1, 255);
 
         if(!curve_id.is_ecdh_named_curve() && !curve_id.is_x25519() && !curve_id.is_x448()) {
            throw TLS_Exception(Alert::IllegalParameter,
                                "Server selected a group that is not compatible with the negotiated ciphersuite");
         }
 
         if(policy.choose_key_exchange_group({curve_id}, {}) != curve_id) {
            throw TLS_Exception(Alert::HandshakeFailure, "Server sent ECC curve prohibited by policy");
         }
 
         const auto private_key = [&] {
            if(curve_id.is_ecdh_named_curve()) {
               const auto pubkey_point_format = state.server_hello()->prefers_compressed_ec_points()
                                                   ? EC_Point_Format::Compressed
                                                   : EC_Point_Format::Uncompressed;
               return state.callbacks().tls12_generate_ephemeral_ecdh_key(curve_id, rng, pubkey_point_format);
            } else {
               return state.callbacks().tls_generate_ephemeral_key(curve_id, rng);
            }
         }();
 
         if(!private_key) {
            throw TLS_Exception(Alert::InternalError, "Application did not provide an EC key");
         }
 
         auto shared_secret =
            state.callbacks().tls_ephemeral_key_agreement(curve_id, *private_key, peer_public_value, rng, policy);
 
         if(kex_algo == Kex_Algo::ECDH) {
            m_pre_master = std::move(shared_secret);
         } else {
            append_tls_length_value(m_pre_master, shared_secret, 2);
            append_tls_length_value(m_pre_master, psk.bits_of(), 2);
         }
 
         // Note: In contrast to public_value(), raw_public_key_bits() takes the
         // point format (compressed vs. uncompressed) into account that was set
         // in its construction within tls_generate_ephemeral_key().
         append_tls_length_value(m_key_material, private_key->raw_public_key_bits(), 1);
      } else {
         throw Internal_Error("Client_Key_Exchange: Unknown key exchange method was negotiated");
      }
 
      reader.assert_done();
   } else {
      // No server key exchange msg better mean RSA kex + RSA key in cert
 
      if(kex_algo != Kex_Algo::STATIC_RSA) {
         throw Unexpected_Message("No server kex message, but negotiated a key exchange that required it");
      }
 
      if(server_public_key == nullptr) {
         throw Internal_Error("No server public key for RSA exchange");
      }
 
      if(const auto* rsa_pub = dynamic_cast<const RSA_PublicKey*>(server_public_key)) {
         const Protocol_Version offered_version = state.client_hello()->legacy_version();
 
         rng.random_vec(m_pre_master, 48);
         m_pre_master[0] = offered_version.major_version();
         m_pre_master[1] = offered_version.minor_version();
 
         PK_Encryptor_EME encryptor(*rsa_pub, rng, "PKCS1v15");
 
         const std::vector<uint8_t> encrypted_key = encryptor.encrypt(m_pre_master, rng);
 
         append_tls_length_value(m_key_material, encrypted_key, 2);
      } else {
         throw TLS_Exception(Alert::HandshakeFailure,
                             "Expected a RSA key in server cert but got " + server_public_key->algo_name());
      }
   }
 
   state.hash().update(io.send(*this));
}

References Botan::Asymmetric_Key::algo_name(), Botan::TLS::append_tls_length_value(), Botan::as_span_of_bytes(), Botan::TLS::TLS_Data_Reader::assert_done(), Botan::OctetString::bits_of(), Botan::TLS::Handshake_State::callbacks(), Botan::TLS::Policy::choose_key_exchange_group(), Botan::TLS::Handshake_State::ciphersuite(), Botan::TLS::Handshake_State::client_hello(), Botan::Compressed, Botan::TLS::DH, Botan::TLS::ECDH, Botan::TLS::ECDHE_PSK, Botan::PK_Encryptor::encrypt(), Botan::BigInt::from_bytes(), Botan::TLS::TLS_Data_Reader::get_byte(), Botan::TLS::TLS_Data_Reader::get_range(), Botan::TLS::TLS_Data_Reader::get_string(), Botan::TLS::TLS_Data_Reader::get_uint16_t(), Botan::TLS::Handshake_State::hash(), Botan::TLS::Group_Params::is_ecdh_named_curve(), Botan::TLS::Group_Params::is_x25519(), Botan::TLS::Group_Params::is_x448(), Botan::TLS::Ciphersuite::kex_method(), Botan::OctetString::length(), Botan::TLS::Protocol_Version::major_version(), Botan::TLS::Protocol_Version::minor_version(), Botan::TLS::PSK, Botan::Credentials_Manager::psk(), Botan::Credentials_Manager::psk_identity(), Botan::RandomNumberGenerator::random_vec(), Botan::TLS::TLS_Data_Reader::remaining_bytes(), Botan::TLS::Handshake_IO::send(), Botan::TLS::Handshake_State::server_hello(), Botan::TLS::Handshake_State::server_kex(), Botan::TLS::STATIC_RSA, Botan::CT::strip_leading_zeros(), Botan::TLS::Callbacks::tls12_generate_ephemeral_ecdh_key(), Botan::TLS::Callbacks::tls_ephemeral_key_agreement(), Botan::TLS::Callbacks::tls_generate_ephemeral_key(), Botan::Uncompressed, Botan::TLS::Handshake_Hash::update(), and Botan::DL_Group::verify_group().

Client_Key_Exchange() [2/2]

Botan::TLS::Client_Key_Exchange::Client_Key_Exchange	(	const std::vector< uint8_t > &	buf,
		const Handshake_State &	state,
		const Private_Key *	server_rsa_kex_key,
		Credentials_Manager &	creds,
		const Policy &	policy,
		RandomNumberGenerator &	rng )

Definition at line 174 of file msg_client_kex.cpp.

                                                                     {
   const Kex_Algo kex_algo = state.ciphersuite().kex_method();
 
   if(kex_algo == Kex_Algo::STATIC_RSA) {
      BOTAN_ASSERT(state.server_certs() && !state.server_certs()->cert_chain().empty(),
                   "RSA key exchange negotiated so server sent a certificate");
 
      if(server_rsa_kex_key == nullptr) {
         throw Internal_Error("Expected RSA kex but no server kex key set");
      }
 
      if(server_rsa_kex_key->algo_name() != "RSA") {
         throw Internal_Error("Expected RSA key but got " + server_rsa_kex_key->algo_name());
      }
 
      TLS_Data_Reader reader("ClientKeyExchange", contents);
      const std::vector<uint8_t> encrypted_pre_master = reader.get_range<uint8_t>(2, 0, 65535);
      reader.assert_done();
 
      PK_Decryptor_EME decryptor(*server_rsa_kex_key, rng, "PKCS1v15");
 
      const uint8_t client_major = state.client_hello()->legacy_version().major_version();
      const uint8_t client_minor = state.client_hello()->legacy_version().minor_version();
 
      /*
      * PK_Decryptor::decrypt_or_random will return a random value if
      * either the length does not match the expected value or if the
      * version number embedded in the PMS does not match the one sent
      * in the client hello.
      */
      const size_t expected_plaintext_size = 48;
      const size_t expected_content_size = 2;
      const uint8_t expected_content_bytes[expected_content_size] = {client_major, client_minor};
      const uint8_t expected_content_pos[expected_content_size] = {0, 1};
 
      m_pre_master = decryptor.decrypt_or_random(encrypted_pre_master.data(),
                                                 encrypted_pre_master.size(),
                                                 expected_plaintext_size,
                                                 rng,
                                                 expected_content_bytes,
                                                 expected_content_pos,
                                                 expected_content_size);
   } else {
      TLS_Data_Reader reader("ClientKeyExchange", contents);
 
      SymmetricKey psk;
 
      if(key_exchange_is_psk(kex_algo)) {
         m_psk_identity = reader.get_string(2, 0, 65535);
 
         psk = creds.psk("tls-server", state.client_hello()->sni_hostname(), m_psk_identity.value());
 
         if(psk.empty()) {
            if(policy.hide_unknown_users()) {
               psk = SymmetricKey(rng, 16);
            } else {
               throw TLS_Exception(Alert::UnknownPSKIdentity, "No PSK for identifier " + m_psk_identity.value());
            }
         }
      }
 
      if(kex_algo == Kex_Algo::PSK) {
         std::vector<uint8_t> zeros(psk.length());
         append_tls_length_value(m_pre_master, zeros, 2);
         append_tls_length_value(m_pre_master, psk.bits_of(), 2);
      } else if(kex_algo == Kex_Algo::DH || kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
         const PK_Key_Agreement_Key& ka_key = state.server_kex()->server_kex_key();
 
         const std::vector<uint8_t> client_pubkey = (ka_key.algo_name() == "DH")
                                                       ? reader.get_range<uint8_t>(2, 0, 65535)
                                                       : reader.get_range<uint8_t>(1, 1, 255);
 
         const auto shared_group = state.server_kex()->shared_group();
         BOTAN_STATE_CHECK(shared_group && shared_group.value() != Group_Params::NONE);
 
         try {
            auto shared_secret =
               state.callbacks().tls_ephemeral_key_agreement(shared_group.value(), ka_key, client_pubkey, rng, policy);
 
            if(ka_key.algo_name() == "DH") {
               shared_secret = CT::strip_leading_zeros(shared_secret);
            }
 
            if(kex_algo == Kex_Algo::ECDHE_PSK) {
               append_tls_length_value(m_pre_master, shared_secret, 2);
               append_tls_length_value(m_pre_master, psk.bits_of(), 2);
            } else {
               m_pre_master = shared_secret;
            }
         } catch(Invalid_Argument& e) {
            throw TLS_Exception(Alert::IllegalParameter, e.what());
         } catch(TLS_Exception& e) {
            // NOLINTNEXTLINE(cert-err60-cpp)
            throw e;
         } catch(std::exception&) {
            /*
            * Something failed in the DH/ECDH computation. To avoid possible
            * attacks which are based on triggering and detecting some edge
            * failure condition, randomize the pre-master output and carry on,
            * allowing the protocol to fail later in the finished checks.
            */
            rng.random_vec(m_pre_master, ka_key.public_value().size());
         }
 
         reader.assert_done();
      } else {
         throw Internal_Error("Client_Key_Exchange: Unknown key exchange negotiated");
      }
   }
}

References Botan::Asymmetric_Key::algo_name(), Botan::TLS::append_tls_length_value(), Botan::TLS::TLS_Data_Reader::assert_done(), Botan::OctetString::bits_of(), BOTAN_ASSERT, BOTAN_STATE_CHECK, Botan::TLS::Handshake_State::callbacks(), Botan::TLS::Handshake_State::ciphersuite(), Botan::TLS::Handshake_State::client_hello(), Botan::PK_Decryptor::decrypt_or_random(), Botan::TLS::DH, Botan::TLS::ECDH, Botan::TLS::ECDHE_PSK, Botan::OctetString::empty(), Botan::TLS::TLS_Data_Reader::get_range(), Botan::TLS::TLS_Data_Reader::get_string(), Botan::TLS::Policy::hide_unknown_users(), Botan::TLS::Ciphersuite::kex_method(), Botan::TLS::key_exchange_is_psk(), Botan::OctetString::length(), Botan::TLS::PSK, Botan::Credentials_Manager::psk(), Botan::PK_Key_Agreement_Key::public_value(), Botan::RandomNumberGenerator::random_vec(), Botan::TLS::Handshake_State::server_certs(), Botan::TLS::Handshake_State::server_kex(), Botan::TLS::STATIC_RSA, Botan::CT::strip_leading_zeros(), Botan::TLS::Callbacks::tls_ephemeral_key_agreement(), and Botan::Exception::what().

Member Function Documentation

pre_master_secret()

const secure_vector< uint8_t > & Botan::TLS::Client_Key_Exchange::pre_master_secret ( ) const

inline

Definition at line 489 of file tls_messages.h.

{ return m_pre_master; }

psk_identity()

const std::optional< std::string > & Botan::TLS::Client_Key_Exchange::psk_identity ( ) const

inline

Returns

the agreed upon PSK identity or std::nullopt if not applicable

Definition at line 494 of file tls_messages.h.

{ return m_psk_identity; }

type()

Handshake_Type Botan::TLS::Client_Key_Exchange::type ( ) const

inlineoverridevirtual

Returns

the message type

Implements Botan::TLS::Handshake_Message.

Definition at line 487 of file tls_messages.h.

{ return Handshake_Type::ClientKeyExchange; }

References Botan::TLS::ClientKeyExchange.

type_string()

std::string Botan::TLS::Handshake_Message::type_string ( ) const

inherited

Returns

string representation of this message type

Definition at line 18 of file tls_handshake_state.cpp.

                                               {
   return handshake_type_to_string(type());
}

References Botan::TLS::handshake_type_to_string(), and type().

wire_type()

virtual Handshake_Type Botan::TLS::Handshake_Message::wire_type ( ) const

inlinevirtualinherited

Returns

the wire representation of the message's type

Reimplemented in Botan::TLS::Hello_Retry_Request.

Definition at line 39 of file tls_handshake_msg.h.

                                               {
         // Usually equal to the Handshake_Type enum value,
         // with the exception of TLS 1.3 Hello Retry Request.
         return type();
      }

References type().

Referenced by Botan::TLS::Stream_Handshake_IO::send().

---

The documentation for this class was generated from the following files:

• src/lib/tls/tls_messages.h
• src/lib/tls/tls12/msg_client_kex.cpp