dh.cpp

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/*
* Diffie-Hellman
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
 
#include <botan/dh.h>
#include <botan/numthry.h>
#include <botan/libstate.h>
#include <botan/internal/workfactor.h>
 
namespace Botan {
 
/*
* DH_PublicKey Constructor
*/
DH_PublicKey::DH_PublicKey(const DL_Group& grp, const BigInt& y1)
   {
   group = grp;
   y = y1;
   }
 
/*
* Return the public value for key agreement
*/
MemoryVector<byte> DH_PublicKey::public_value() const
   {
   return BigInt::encode_1363(y, group_p().bytes());
   }
 
/*
* Create a DH private key
*/
DH_PrivateKey::DH_PrivateKey(RandomNumberGenerator& rng,
                             const DL_Group& grp,
                             const BigInt& x_arg)
   {
   group = grp;
   x = x_arg;
 
   if(x == 0)
      {
      const BigInt& p = group_p();
      x.randomize(rng, 2 * dl_work_factor(p.bits()));
      }
 
   if(y == 0)
      y = power_mod(group_g(), x, group_p());
 
   if(x == 0)
      gen_check(rng);
   else
      load_check(rng);
   }
 
/*
* Load a DH private key
*/
DH_PrivateKey::DH_PrivateKey(const AlgorithmIdentifier& alg_id,
                             const MemoryRegion<byte>& key_bits,
                             RandomNumberGenerator& rng) :
   DL_Scheme_PrivateKey(alg_id, key_bits, DL_Group::ANSI_X9_42)
   {
   if(y == 0)
      y = power_mod(group_g(), x, group_p());
 
   load_check(rng);
   }
 
/*
* Return the public value for key agreement
*/
MemoryVector<byte> DH_PrivateKey::public_value() const
   {
   return DH_PublicKey::public_value();
   }
 
DH_KA_Operation::DH_KA_Operation(const DH_PrivateKey& dh) :
   p(dh.group_p()), powermod_x_p(dh.get_x(), p)
   {
   BigInt k(global_state().global_rng(), p.bits() - 1);
   blinder = Blinder(k, powermod_x_p(inverse_mod(k, p)), p);
   }
 
SecureVector<byte> DH_KA_Operation::agree(const byte w[], size_t w_len)
   {
   BigInt input = BigInt::decode(w, w_len);
 
   if(input <= 1 || input >= p - 1)
      throw Invalid_Argument("DH agreement - invalid key provided");
 
   BigInt r = blinder.unblind(powermod_x_p(blinder.blind(input)));
 
   return BigInt::encode_1363(r, p.bytes());
   }
 
}