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/*
* Client Key Exchange Message
* (C) 2004-2010,2016 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/rng.h>
#include <botan/tls_extensions.h>
#include <botan/credentials_manager.h>
#include <botan/internal/ct_utils.h>
#include <botan/internal/stl_util.h>
#include <botan/internal/tls_handshake_hash.h>
#include <botan/internal/tls_handshake_io.h>
#include <botan/internal/tls_handshake_state.h>
#include <botan/internal/tls_reader.h>
#include <botan/ecdh.h>
#include <botan/rsa.h>
namespace Botan::TLS {
/*
* Create a new Client Key Exchange message
*/
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) {
const Kex_Algo kex_algo = state.ciphersuite().kex_method();
if(kex_algo == Kex_Algo::PSK) {
std::string identity_hint;
if(state.server_kex()) {
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, to_byte_vector(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()) {
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, to_byte_vector(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()) {
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 = state.callbacks().tls_generate_ephemeral_key(curve_id, rng);
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);
}
if(curve_id.is_ecdh_named_curve()) {
auto ecdh_key = dynamic_cast<ECDH_PublicKey*>(private_key.get());
if(!ecdh_key) {
throw TLS_Exception(Alert::InternalError, "Application did not provide a ECDH_PublicKey");
}
append_tls_length_value(m_key_material,
ecdh_key->public_value(state.server_hello()->prefers_compressed_ec_points()
? EC_Point_Format::Compressed
: EC_Point_Format::Uncompressed),
1);
} else {
append_tls_length_value(m_key_material, private_key->public_value(), 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) {
throw Internal_Error("No server public key for RSA exchange");
}
if(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));
}
/*
* Read a Client Key Exchange message
*/
Client_Key_Exchange::Client_Key_Exchange(const std::vector<uint8_t>& contents,
const Handshake_State& state,
const Private_Key* server_rsa_kex_key,
Credentials_Manager& creds,
const Policy& policy,
RandomNumberGenerator& rng) {
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) {
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");
}
}
}
} // namespace Botan::TLS