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/*
* ElGamal Core
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/elg_core.h>
#include <botan/numthry.h>
#include <botan/pk_engine.h>
#include <botan/parsing.h>
#include <algorithm>
namespace Botan {
namespace {
const u32bit BLINDING_BITS = BOTAN_PRIVATE_KEY_OP_BLINDING_BITS;
}
/*
* ELG_Core Constructor
*/
ELG_Core::ELG_Core(const DL_Group& group, const BigInt& y)
{
op = Engine_Core::elg_op(group, y, 0);
p_bytes = 0;
}
/*
* ELG_Core Constructor
*/
ELG_Core::ELG_Core(RandomNumberGenerator& rng,
const DL_Group& group, const BigInt& y, const BigInt& x)
{
op = Engine_Core::elg_op(group, y, x);
const BigInt& p = group.get_p();
p_bytes = p.bytes();
if(BLINDING_BITS)
{
BigInt k(rng, std::min(p.bits()-1, BLINDING_BITS));
blinder = Blinder(k, power_mod(k, x, p), p);
}
}
/*
* ELG_Core Copy Constructor
*/
ELG_Core::ELG_Core(const ELG_Core& core)
{
op = 0;
if(core.op)
op = core.op->clone();
blinder = core.blinder;
p_bytes = core.p_bytes;
}
/*
* ELG_Core Assignment Operator
*/
ELG_Core& ELG_Core::operator=(const ELG_Core& core)
{
delete op;
if(core.op)
op = core.op->clone();
blinder = core.blinder;
p_bytes = core.p_bytes;
return (*this);
}
/*
* ElGamal Encrypt Operation
*/
SecureVector<byte> ELG_Core::encrypt(const byte in[], u32bit length,
const BigInt& k) const
{
return op->encrypt(in, length, k);
}
/*
* ElGamal Decrypt Operation
*/
SecureVector<byte> ELG_Core::decrypt(const byte in[], u32bit length) const
{
if(length != 2*p_bytes)
throw Invalid_Argument("ELG_Core::decrypt: Invalid message");
BigInt a(in, p_bytes);
BigInt b(in + p_bytes, p_bytes);
return BigInt::encode(blinder.unblind(op->decrypt(blinder.blind(a), b)));
}
}
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