c_kex.cpp

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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 {
 
/**
* Create a new Client Key Exchange message
*/
Client_Key_Exchange::Client_Key_Exchange(RandomNumberGenerator& rng,
                                         Record_Writer& writer,
                                         HandshakeHash& hash,
                                         const Public_Key* pub_key,
                                         Version_Code using_version,
                                         Version_Code pref_version)
   {
   include_length = true;
 
   if(const DH_PublicKey* dh_pub = dynamic_cast<const DH_PublicKey*>(pub_key))
      {
      DH_PrivateKey priv_key(rng, dh_pub->get_domain());
 
      PK_Key_Agreement ka(priv_key, "Raw");
 
      pre_master = ka.derive_key(0, dh_pub->public_value()).bits_of();
 
      key_material = priv_key.public_value();
      }
   else if(const RSA_PublicKey* rsa_pub = dynamic_cast<const RSA_PublicKey*>(pub_key))
      {
      pre_master = rng.random_vec(48);
      pre_master[0] = (pref_version >> 8) & 0xFF;
      pre_master[1] = (pref_version     ) & 0xFF;
 
      PK_Encryptor_EME encryptor(*rsa_pub, "PKCS1v15");
 
      key_material = encryptor.encrypt(pre_master, rng);
 
      if(using_version == SSL_V3)
         include_length = false;
      }
   else
      throw Invalid_Argument("Client_Key_Exchange: Key not RSA or DH");
 
   send(writer, hash);
   }
 
/**
* Read a Client Key Exchange message
*/
Client_Key_Exchange::Client_Key_Exchange(const MemoryRegion<byte>& contents,
                                         const CipherSuite& suite,
                                         Version_Code using_version)
   {
   include_length = true;
 
   if(using_version == SSL_V3 && (suite.kex_type() == TLS_ALGO_KEYEXCH_RSA))
      include_length = false;
 
   deserialize(contents);
   }
 
/**
* Serialize a Client Key Exchange message
*/
SecureVector<byte> Client_Key_Exchange::serialize() const
   {
   if(include_length)
      {
      SecureVector<byte> buf;
      append_tls_length_value(buf, key_material, 2);
      return buf;
      }
   else
      return key_material;
   }
 
/**
* Deserialize a Client Key Exchange message
*/
void Client_Key_Exchange::deserialize(const MemoryRegion<byte>& buf)
   {
   if(include_length)
      {
      TLS_Data_Reader reader(buf);
      key_material = reader.get_range<byte>(2, 0, 65535);
      }
   else
      key_material = buf;
   }
 
/**
* Return the pre_master_secret
*/
SecureVector<byte>
Client_Key_Exchange::pre_master_secret(RandomNumberGenerator& rng,
                                       const Private_Key* priv_key,
                                       Version_Code version)
   {
 
   if(const DH_PrivateKey* dh_priv = dynamic_cast<const DH_PrivateKey*>(priv_key))
      {
      try {
         PK_Key_Agreement ka(*dh_priv, "Raw");
 
         pre_master = 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 ||
            make_u16bit(pre_master[0], pre_master[1]) != version)
            throw Decoding_Error("Client_Key_Exchange: Secret corrupted");
      }
      catch(...)
         {
         pre_master = rng.random_vec(48);
         pre_master[0] = (version >> 8) & 0xFF;
         pre_master[1] = (version     ) & 0xFF;
         }
 
      return pre_master;
      }
   else
      throw Invalid_Argument("Client_Key_Exchange: Bad key for decrypt");
   }
 
/**
* Return the pre_master_secret
*/
SecureVector<byte> Client_Key_Exchange::pre_master_secret() const
   {
   return pre_master;
   }
 
}