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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/pubkey.h>
#include <botan/dh.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)
{
include_length = true;
if(state->server_kex)
{
const std::vector<BigInt>& params = state->server_kex->params();
if(state->suite.kex_algo() == "DH")
{
if(params.size() != 3)
throw Decoding_Error("Bad params size for DH key exchange");
DL_Group group(params[0], params[1]);
if(!group.verify_group(rng, true))
throw Internal_Error("DH group failed validation, possible attack");
DH_PublicKey counterparty_key(group, params[2]);
// 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());
key_material = priv_key.public_value();
}
else
throw Internal_Error("Server key exchange not a known key type");
}
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");
key_material = encryptor.encrypt(pre_master, rng);
if(state->version == Protocol_Version::SSL_V3)
include_length = false;
}
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)
{
include_length = true;
if(using_version == Protocol_Version::SSL_V3 && (suite.kex_algo() == ""))
include_length = false;
if(include_length)
{
TLS_Data_Reader reader(contents);
key_material = reader.get_range<byte>(2, 0, 65535);
}
else
key_material = contents;
}
/*
* Serialize a Client Key Exchange message
*/
MemoryVector<byte> Client_Key_Exchange::serialize() const
{
if(include_length)
{
MemoryVector<byte> buf;
append_tls_length_value(buf, key_material, 2);
return buf;
}
else
return key_material;
}
/*
* 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 DH_PrivateKey* dh_priv = dynamic_cast<const DH_PrivateKey*>(priv_key))
{
try {
PK_Key_Agreement ka(*dh_priv, "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_priv->public_value().size());
}
return pre_master;
}
else if(const RSA_PrivateKey* rsa_priv = dynamic_cast<const RSA_PrivateKey*>(priv_key))
{
PK_Decryptor_EME decryptor(*rsa_priv, "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;
}
else
throw Invalid_Argument("Client_Key_Exchange: Bad key for decrypt");
}
}
}
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