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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/tls_extensions.h>
#include <botan/rng.h>
#include <botan/internal/tls_reader.h>
#include <botan/internal/tls_handshake_io.h>
#include <botan/internal/tls_handshake_state.h>
#include <botan/internal/tls_handshake_hash.h>
#include <botan/credentials_manager.h>
#include <botan/internal/ct_utils.h>
#include <botan/rsa.h>
#if defined(BOTAN_HAS_CECPQ1)
#include <botan/cecpq1.h>
#endif
#if defined(BOTAN_HAS_SRP6)
#include <botan/srp6.h>
#endif
namespace Botan {
namespace 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,
const std::string& 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);
}
const std::string psk_identity =
creds.psk_identity("tls-client", hostname, identity_hint);
append_tls_length_value(m_key_material, psk_identity, 2);
SymmetricKey psk = creds.psk("tls-client", hostname, psk_identity);
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::DHE_PSK ||
kex_algo == Kex_Algo::ECDHE_PSK)
{
std::string identity_hint = reader.get_string(2, 0, 65535);
const std::string psk_identity =
creds.psk_identity("tls-client", hostname, identity_hint);
append_tls_length_value(m_key_material, psk_identity, 2);
psk = creds.psk("tls-client", hostname, psk_identity);
}
if(kex_algo == Kex_Algo::DH ||
kex_algo == Kex_Algo::DHE_PSK)
{
const std::vector<uint8_t> modulus = reader.get_range<uint8_t>(2, 1, 65535);
const std::vector<uint8_t> generator = 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");
const std::pair<secure_vector<uint8_t>, std::vector<uint8_t>> dh_result =
state.callbacks().tls_dh_agree(modulus, generator, peer_public_value, policy, rng);
if(kex_algo == Kex_Algo::DH)
m_pre_master = dh_result.first;
else
{
append_tls_length_value(m_pre_master, dh_result.first, 2);
append_tls_length_value(m_pre_master, psk.bits_of(), 2);
}
append_tls_length_value(m_key_material, dh_result.second, 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(policy.choose_key_exchange_group({curve_id}) != curve_id)
{
throw TLS_Exception(Alert::HANDSHAKE_FAILURE,
"Server sent ECC curve prohibited by policy");
}
const std::string curve_name = state.callbacks().tls_decode_group_param(curve_id);
if(curve_name == "")
throw Decoding_Error("Server sent unknown named curve " +
std::to_string(static_cast<uint16_t>(curve_id)));
const std::pair<secure_vector<uint8_t>, std::vector<uint8_t>> ecdh_result =
state.callbacks().tls_ecdh_agree(curve_name, peer_public_value, policy, rng,
state.server_hello()->prefers_compressed_ec_points());
if(kex_algo == Kex_Algo::ECDH)
{
m_pre_master = ecdh_result.first;
}
else
{
append_tls_length_value(m_pre_master, ecdh_result.first, 2);
append_tls_length_value(m_pre_master, psk.bits_of(), 2);
}
append_tls_length_value(m_key_material, ecdh_result.second, 1);
}
#if defined(BOTAN_HAS_SRP6)
else if(kex_algo == Kex_Algo::SRP_SHA)
{
const BigInt N = BigInt::decode(reader.get_range<uint8_t>(2, 1, 65535));
const BigInt g = BigInt::decode(reader.get_range<uint8_t>(2, 1, 65535));
std::vector<uint8_t> salt = reader.get_range<uint8_t>(1, 1, 255);
const BigInt B = BigInt::decode(reader.get_range<uint8_t>(2, 1, 65535));
const std::string srp_group = srp6_group_identifier(N, g);
const std::string srp_identifier =
creds.srp_identifier("tls-client", hostname);
const std::string srp_password =
creds.srp_password("tls-client", hostname, srp_identifier);
std::pair<BigInt, SymmetricKey> srp_vals =
srp6_client_agree(srp_identifier,
srp_password,
srp_group,
"SHA-1",
salt,
B,
rng);
append_tls_length_value(m_key_material, BigInt::encode(srp_vals.first), 2);
m_pre_master = srp_vals.second.bits_of();
}
#endif
#if defined(BOTAN_HAS_CECPQ1)
else if(kex_algo == Kex_Algo::CECPQ1)
{
const std::vector<uint8_t> cecpq1_offer = reader.get_range<uint8_t>(2, 1, 65535);
if(cecpq1_offer.size() != CECPQ1_OFFER_BYTES)
throw TLS_Exception(Alert::HANDSHAKE_FAILURE, "Invalid CECPQ1 key size");
std::vector<uint8_t> newhope_accept(CECPQ1_ACCEPT_BYTES);
secure_vector<uint8_t> shared_secret(CECPQ1_SHARED_KEY_BYTES);
CECPQ1_accept(shared_secret.data(), newhope_accept.data(), cecpq1_offer.data(), rng);
append_tls_length_value(m_key_material, newhope_accept, 2);
m_pre_master = shared_secret;
}
#endif
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()->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::HANDSHAKE_FAILURE,
"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(!dynamic_cast<const RSA_PrivateKey*>(server_rsa_kex_key))
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()->version().major_version();
const uint8_t client_minor = state.client_hello()->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))
{
const std::string psk_identity = reader.get_string(2, 0, 65535);
psk = creds.psk("tls-server",
state.client_hello()->sni_hostname(),
psk_identity);
if(psk.length() == 0)
{
if(policy.hide_unknown_users())
psk = SymmetricKey(rng, 16);
else
throw TLS_Exception(Alert::UNKNOWN_PSK_IDENTITY,
"No PSK for identifier " + psk_identity);
}
}
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);
}
#if defined(BOTAN_HAS_SRP6)
else if(kex_algo == Kex_Algo::SRP_SHA)
{
SRP6_Server_Session& srp = state.server_kex()->server_srp_params();
m_pre_master = srp.step2(BigInt::decode(reader.get_range<uint8_t>(2, 0, 65535))).bits_of();
}
#endif
#if defined(BOTAN_HAS_CECPQ1)
else if(kex_algo == Kex_Algo::CECPQ1)
{
const CECPQ1_key& cecpq1_offer = state.server_kex()->cecpq1_key();
const std::vector<uint8_t> cecpq1_accept = reader.get_range<uint8_t>(2, 0, 65535);
if(cecpq1_accept.size() != CECPQ1_ACCEPT_BYTES)
throw Decoding_Error("Invalid size for CECPQ1 accept message");
m_pre_master.resize(CECPQ1_SHARED_KEY_BYTES);
CECPQ1_finish(m_pre_master.data(), cecpq1_offer, cecpq1_accept.data());
}
#endif
else if(kex_algo == Kex_Algo::DH ||
kex_algo == Kex_Algo::DHE_PSK ||
kex_algo == Kex_Algo::ECDH ||
kex_algo == Kex_Algo::ECDHE_PSK)
{
const Private_Key& private_key = state.server_kex()->server_kex_key();
const PK_Key_Agreement_Key* ka_key =
dynamic_cast<const PK_Key_Agreement_Key*>(&private_key);
if(!ka_key)
throw Internal_Error("Expected key agreement key type but got " +
private_key.algo_name());
std::vector<uint8_t> client_pubkey;
if(ka_key->algo_name() == "DH")
{
client_pubkey = reader.get_range<uint8_t>(2, 0, 65535);
}
else
{
client_pubkey = reader.get_range<uint8_t>(1, 1, 255);
}
try
{
PK_Key_Agreement ka(*ka_key, rng, "Raw");
secure_vector<uint8_t> shared_secret = ka.derive_key(0, client_pubkey).bits_of();
if(ka_key->algo_name() == "DH")
shared_secret = CT::strip_leading_zeros(shared_secret);
if(kex_algo == Kex_Algo::DHE_PSK ||
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::ILLEGAL_PARAMETER, e.what());
}
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");
}
}
}
}