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/*************************************************
* GMP ElGamal Engine Source File *
* (C) 1999-2007 Jack Lloyd *
*************************************************/
#include <botan/eng_gmp.h>
#include <botan/gmp_wrap.h>
#include <gmp.h>
namespace Botan {
#if defined(BOTAN_HAS_ELGAMAL)
namespace {
/*************************************************
* GMP ElGamal Operation *
*************************************************/
class GMP_ELG_Op : public ELG_Operation
{
public:
SecureVector<byte> encrypt(const byte[], u32bit, const BigInt&) const;
BigInt decrypt(const BigInt&, const BigInt&) const;
ELG_Operation* clone() const { return new GMP_ELG_Op(*this); }
GMP_ELG_Op(const DL_Group& group, const BigInt& y1, const BigInt& x1) :
x(x1), y(y1), g(group.get_g()), p(group.get_p()) {}
private:
GMP_MPZ x, y, g, p;
};
/*************************************************
* GMP ElGamal Encrypt Operation *
*************************************************/
SecureVector<byte> GMP_ELG_Op::encrypt(const byte in[], u32bit length,
const BigInt& k_bn) const
{
GMP_MPZ i(in, length);
if(mpz_cmp(i.value, p.value) >= 0)
throw Invalid_Argument("GMP_ELG_Op: Input is too large");
GMP_MPZ a, b, k(k_bn);
mpz_powm(a.value, g.value, k.value, p.value);
mpz_powm(b.value, y.value, k.value, p.value);
mpz_mul(b.value, b.value, i.value);
mpz_mod(b.value, b.value, p.value);
const u32bit p_bytes = p.bytes();
SecureVector<byte> output(2*p_bytes);
a.encode(output, p_bytes);
b.encode(output + p_bytes, p_bytes);
return output;
}
/*************************************************
* GMP ElGamal Decrypt Operation *
*************************************************/
BigInt GMP_ELG_Op::decrypt(const BigInt& a_bn, const BigInt& b_bn) const
{
if(mpz_cmp_ui(x.value, 0) == 0)
throw Internal_Error("GMP_ELG_Op::decrypt: No private key");
GMP_MPZ a(a_bn), b(b_bn);
if(mpz_cmp(a.value, p.value) >= 0 || mpz_cmp(b.value, p.value) >= 0)
throw Invalid_Argument("GMP_ELG_Op: Invalid message");
mpz_powm(a.value, a.value, x.value, p.value);
mpz_invert(a.value, a.value, p.value);
mpz_mul(a.value, a.value, b.value);
mpz_mod(a.value, a.value, p.value);
return a.to_bigint();
}
}
/*************************************************
* Acquire an ElGamal op *
*************************************************/
ELG_Operation* GMP_Engine::elg_op(const DL_Group& group, const BigInt& y,
const BigInt& x) const
{
return new GMP_ELG_Op(group, y, x);
}
#endif
}
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