/*
* Default ElGamal Decrypt Operation
*/
BigInt Default_ELG_Op::decrypt(const BigInt& a, const BigInt& b) const
{
if(a >= p || b >= p)
throw Invalid_Argument("Default_ELG_Op: Invalid message");
return mod_p.multiply(b, inverse_mod(powermod_x_p(a), 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());
}
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);
}