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/*
* Client Key Exchange Message
* (C) 2004-2010 Jack Lloyd
*
* Released under the terms of the Botan license
*/
#include <botan/internal/tls_messages.h>
#include <botan/internal/tls_reader.h>
#include <botan/internal/tls_extensions.h>
#include <botan/pubkey.h>
#include <botan/dh.h>
#include <botan/ecdh.h>
#include <botan/rsa.h>
#include <botan/rng.h>
#include <botan/loadstor.h>
#include <memory>
namespace Botan {
namespace TLS {
namespace {
SecureVector<byte> strip_leading_zeros(const MemoryRegion<byte>& input)
{
size_t leading_zeros = 0;
for(size_t i = 0; i != input.size(); ++i)
{
if(input[i] != 0)
break;
++leading_zeros;
}
SecureVector<byte> output(&input[leading_zeros],
input.size() - leading_zeros);
return output;
}
}
/*
* Create a new Client Key Exchange message
*/
Client_Key_Exchange::Client_Key_Exchange(Record_Writer& writer,
Handshake_State* state,
const std::vector<X509_Certificate>& peer_certs,
RandomNumberGenerator& rng)
{
if(state->server_kex)
{
TLS_Data_Reader reader(state->server_kex->params());
if(state->suite.kex_algo() == "DH")
{
BigInt p = BigInt::decode(reader.get_range<byte>(2, 1, 65535));
BigInt g = BigInt::decode(reader.get_range<byte>(2, 1, 65535));
BigInt Y = BigInt::decode(reader.get_range<byte>(2, 1, 65535));
if(reader.remaining_bytes())
throw Decoding_Error("Bad params size for DH key exchange");
DL_Group group(p, g);
if(!group.verify_group(rng, true))
throw Internal_Error("DH group failed validation, possible attack");
DH_PublicKey counterparty_key(group, Y);
// FIXME Check that public key is residue?
DH_PrivateKey priv_key(rng, group);
PK_Key_Agreement ka(priv_key, "Raw");
pre_master = strip_leading_zeros(
ka.derive_key(0, counterparty_key.public_value()).bits_of());
append_tls_length_value(key_material, priv_key.public_value(), 2);
}
else if(state->suite.kex_algo() == "ECDH")
{
const byte curve_type = reader.get_byte();
if(curve_type != 3)
throw Decoding_Error("Server sent non-named ECC curve");
const u16bit curve_id = reader.get_u16bit();
const std::string name = Supported_Elliptic_Curves::curve_id_to_name(curve_id);
if(name == "")
throw Decoding_Error("Server sent unknown named curve " + to_string(curve_id));
EC_Group group(name);
MemoryVector<byte> ecdh_key = reader.get_range<byte>(1, 1, 255);
ECDH_PublicKey counterparty_key(group, OS2ECP(ecdh_key, group.get_curve()));
ECDH_PrivateKey priv_key(rng, group);
PK_Key_Agreement ka(priv_key, "Raw");
pre_master = strip_leading_zeros(
ka.derive_key(0, counterparty_key.public_value()).bits_of());
append_tls_length_value(key_material, priv_key.public_value(), 1);
}
else
throw Internal_Error("Server key exchange type " + state->suite.kex_algo() +
" not known");
}
else
{
// No server key exchange msg better mean a RSA key in the cert
std::auto_ptr<Public_Key> pub_key(peer_certs[0].subject_public_key());
if(peer_certs.empty())
throw Internal_Error("No certificate and no server key exchange");
if(const RSA_PublicKey* rsa_pub = dynamic_cast<const RSA_PublicKey*>(pub_key.get()))
{
const Protocol_Version pref_version = state->client_hello->version();
pre_master = rng.random_vec(48);
pre_master[0] = pref_version.major_version();
pre_master[1] = pref_version.minor_version();
PK_Encryptor_EME encryptor(*rsa_pub, "PKCS1v15");
MemoryVector<byte> encrypted_key = encryptor.encrypt(pre_master, rng);
if(state->version == Protocol_Version::SSL_V3)
key_material = encrypted_key; // no length field
else
append_tls_length_value(key_material, encrypted_key, 2);
}
else
throw TLS_Exception(HANDSHAKE_FAILURE,
"Expected a RSA key in server cert but got " +
pub_key->algo_name());
}
send(writer, state->hash);
}
/*
* Read a Client Key Exchange message
*/
Client_Key_Exchange::Client_Key_Exchange(const MemoryRegion<byte>& contents,
const Ciphersuite& suite,
Protocol_Version using_version)
{
if(suite.kex_algo() == "" && using_version == Protocol_Version::SSL_V3)
key_material = contents;
else
{
TLS_Data_Reader reader(contents);
if(suite.kex_algo() == "" || suite.kex_algo() == "DH")
key_material = reader.get_range<byte>(2, 0, 65535);
else if(suite.kex_algo() == "ECDH")
key_material = reader.get_range<byte>(1, 1, 255);
else
throw Internal_Error("Unknown client key exch type " + suite.kex_algo());
}
}
/*
* Return the pre_master_secret
*/
SecureVector<byte>
Client_Key_Exchange::pre_master_secret(RandomNumberGenerator& rng,
const Private_Key* priv_key,
Protocol_Version client_version)
{
if(const RSA_PrivateKey* rsa = dynamic_cast<const RSA_PrivateKey*>(priv_key))
{
PK_Decryptor_EME decryptor(*rsa, "PKCS1v15");
try {
pre_master = decryptor.decrypt(key_material);
if(pre_master.size() != 48 ||
client_version.major_version() != pre_master[0] ||
client_version.minor_version() != pre_master[1])
{
throw Decoding_Error("Client_Key_Exchange: Secret corrupted");
}
}
catch(...)
{
pre_master = rng.random_vec(48);
pre_master[0] = client_version.major_version();
pre_master[1] = client_version.minor_version();
}
return pre_master;
}
// DH or ECDH
if(const PK_Key_Agreement_Key* dh = dynamic_cast<const PK_Key_Agreement_Key*>(priv_key))
{
try {
PK_Key_Agreement ka(*dh, "Raw");
pre_master = strip_leading_zeros(ka.derive_key(0, key_material).bits_of());
}
catch(...)
{
/*
* Something failed in the DH computation. To avoid possible
* timing attacks, randomize the pre-master output and carry
* on, allowing the protocol to fail later in the finished
* checks.
*/
pre_master = rng.random_vec(dh->public_value().size());
}
return pre_master;
}
throw Invalid_Argument("Client_Key_Exchange: Unknown key type " + priv_key->algo_name());
}
}
}
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