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/*
* Server Key Exchange Message
* (C) 2004-2010,2012,2015 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/tls_messages.h>
#include <botan/internal/tls_reader.h>
#include <botan/internal/tls_extensions.h>
#include <botan/internal/tls_handshake_io.h>
#include <botan/credentials_manager.h>
#include <botan/loadstor.h>
#include <botan/pubkey.h>
#include <botan/oids.h>
#include <botan/dh.h>
#include <botan/ecdh.h>
#if defined(BOTAN_HAS_SRP6)
#include <botan/srp6.h>
#endif
namespace Botan {
namespace 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 std::string kex_algo = state.ciphersuite().kex_algo();
if(kex_algo == "PSK" || kex_algo == "DHE_PSK" || 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 == "DH" || kex_algo == "DHE_PSK")
{
std::unique_ptr<DH_PrivateKey> dh(new DH_PrivateKey(rng, DL_Group(policy.dh_group())));
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 == "ECDH" || kex_algo == "ECDHE_PSK")
{
const std::vector<std::string>& curves =
state.client_hello()->supported_ecc_curves();
if(curves.empty())
throw Internal_Error("Client sent no ECC extension but we negotiated ECDH");
const std::string curve_name = policy.choose_curve(curves);
if(curve_name == "")
throw TLS_Exception(Alert::HANDSHAKE_FAILURE,
"Could not agree on an ECC curve with the client");
EC_Group ec_group(curve_name);
std::unique_ptr<ECDH_PrivateKey> ecdh(new ECDH_PrivateKey(rng, ec_group));
const std::string ecdh_domain_oid = ecdh->domain().get_oid();
const std::string domain = OIDS::lookup(OID(ecdh_domain_oid));
if(domain == "")
throw Internal_Error("Could not find name of ECDH domain " + ecdh_domain_oid);
const u16bit named_curve_id = Supported_Elliptic_Curves::name_to_curve_id(domain);
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));
// follow client's preference for point compression
if(state.client_hello()->prefers_compressed_ec_points())
{
append_tls_length_value(m_params, ecdh->public_value(PointGFp::COMPRESSED), 1);
}
else
{
append_tls_length_value(m_params, ecdh->public_value(PointGFp::UNCOMPRESSED), 1);
}
m_kex_key.reset(ecdh.release());
}
#if defined(BOTAN_HAS_SRP6)
else if(kex_algo == "SRP_SHA")
{
const std::string srp_identifier = state.client_hello()->srp_identifier();
std::string group_id;
BigInt v;
std::vector<byte> salt;
const bool found = creds.srp_verifier("tls-server", hostname,
srp_identifier,
group_id, v, salt,
policy.hide_unknown_users());
if(!found)
throw TLS_Exception(Alert::UNKNOWN_PSK_IDENTITY,
"Unknown SRP user " + srp_identifier);
m_srp_params.reset(new SRP6_Server_Session);
BigInt B = m_srp_params->step1(v, group_id,
"SHA-1", rng);
DL_Group group(group_id);
append_tls_length_value(m_params, BigInt::encode(group.get_p()), 2);
append_tls_length_value(m_params, BigInt::encode(group.get_g()), 2);
append_tls_length_value(m_params, salt, 1);
append_tls_length_value(m_params, BigInt::encode(B), 2);
}
#endif
else if(kex_algo != "PSK")
throw Internal_Error("Server_Key_Exchange: Unknown kex type " + kex_algo);
if(state.ciphersuite().sig_algo() != "")
{
BOTAN_ASSERT(signing_key, "Signing key was set");
std::pair<std::string, Signature_Format> format =
state.choose_sig_format(*signing_key, m_hash_algo, m_sig_algo, false, policy);
PK_Signer signer(*signing_key, format.first, format.second);
signer.update(state.client_hello()->random());
signer.update(state.server_hello()->random());
signer.update(params());
m_signature = signer.signature(rng);
}
state.hash().update(io.send(*this));
}
/**
* Deserialize a Server Key Exchange message
*/
Server_Key_Exchange::Server_Key_Exchange(const std::vector<byte>& buf,
const std::string& kex_algo,
const std::string& sig_algo,
Protocol_Version version)
{
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 == "PSK" || kex_algo == "DHE_PSK" || kex_algo == "ECDHE_PSK")
{
reader.get_string(2, 0, 65535); // identity hint
}
if(kex_algo == "DH" || kex_algo == "DHE_PSK")
{
// 3 bigints, DH p, g, Y
for(size_t i = 0; i != 3; ++i)
{
reader.get_range<byte>(2, 1, 65535);
}
}
else if(kex_algo == "ECDH" || kex_algo == "ECDHE_PSK")
{
reader.get_byte(); // curve type
reader.get_u16bit(); // curve id
reader.get_range<byte>(1, 1, 255); // public key
}
else if(kex_algo == "SRP_SHA")
{
// 2 bigints (N,g) then salt, then server B
reader.get_range<byte>(2, 1, 65535);
reader.get_range<byte>(2, 1, 65535);
reader.get_range<byte>(1, 1, 255);
reader.get_range<byte>(2, 1, 65535);
}
else if(kex_algo != "PSK")
throw Decoding_Error("Server_Key_Exchange: Unsupported kex type " + kex_algo);
m_params.assign(buf.data(), buf.data() + reader.read_so_far());
if(sig_algo != "")
{
if(version.supports_negotiable_signature_algorithms())
{
m_hash_algo = Signature_Algorithms::hash_algo_name(reader.get_byte());
m_sig_algo = Signature_Algorithms::sig_algo_name(reader.get_byte());
}
m_signature = reader.get_range<byte>(2, 0, 65535);
}
reader.assert_done();
}
Server_Key_Exchange::~Server_Key_Exchange() {}
/**
* Serialize a Server Key Exchange message
*/
std::vector<byte> Server_Key_Exchange::serialize() const
{
std::vector<byte> buf = params();
if(m_signature.size())
{
// This should be an explicit version check
if(m_hash_algo != "" && m_sig_algo != "")
{
buf.push_back(Signature_Algorithms::hash_algo_code(m_hash_algo));
buf.push_back(Signature_Algorithms::sig_algo_code(m_sig_algo));
}
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_hash_algo, m_sig_algo,
false, policy);
PK_Verifier verifier(server_key, format.first, format.second);
verifier.update(state.client_hello()->random());
verifier.update(state.server_hello()->random());
verifier.update(params());
return verifier.check_signature(m_signature);
}
const Private_Key& Server_Key_Exchange::server_kex_key() const
{
BOTAN_ASSERT_NONNULL(m_kex_key);
return *m_kex_key;
}
}
}
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