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/*
* OpenSSL Engine
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/eng_ossl.h>
#include <botan/bn_wrap.h>
#include <openssl/opensslv.h>
#if OPENSSL_VERSION_NUMBER < 0x0090700F
#error Your OpenSSL install is too old, upgrade to 0.9.7 or later
#endif
namespace Botan {
#if defined(BOTAN_HAS_ELGAMAL)
namespace {
/*
* OpenSSL ElGamal Operation
*/
class OpenSSL_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 OpenSSL_ELG_Op(*this); }
OpenSSL_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:
OSSL_BN x, y, g, p;
OSSL_BN_CTX ctx;
};
/*
* OpenSSL ElGamal Encrypt Operation
*/
SecureVector<byte> OpenSSL_ELG_Op::encrypt(const byte in[], u32bit length,
const BigInt& k_bn) const
{
OSSL_BN i(in, length);
if(BN_cmp(i.value, p.value) >= 0)
throw Invalid_Argument("OpenSSL_ELG_Op: Input is too large");
OSSL_BN a, b, k(k_bn);
BN_mod_exp(a.value, g.value, k.value, p.value, ctx.value);
BN_mod_exp(b.value, y.value, k.value, p.value, ctx.value);
BN_mod_mul(b.value, b.value, i.value, p.value, ctx.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;
}
/*
* OpenSSL ElGamal Decrypt Operation
*/
BigInt OpenSSL_ELG_Op::decrypt(const BigInt& a_bn, const BigInt& b_bn) const
{
if(BN_is_zero(x.value))
throw Internal_Error("OpenSSL_ELG_Op::decrypt: No private key");
OSSL_BN a(a_bn), b(b_bn), t;
if(BN_cmp(a.value, p.value) >= 0 || BN_cmp(b.value, p.value) >= 0)
throw Invalid_Argument("OpenSSL_ELG_Op: Invalid message");
BN_mod_exp(t.value, a.value, x.value, p.value, ctx.value);
BN_mod_inverse(a.value, t.value, p.value, ctx.value);
BN_mod_mul(a.value, a.value, b.value, p.value, ctx.value);
return a.to_bigint();
}
}
/*
* Acquire an ElGamal op
*/
ELG_Operation* OpenSSL_Engine::elg_op(const DL_Group& group, const BigInt& y,
const BigInt& x) const
{
return new OpenSSL_ELG_Op(group, y, x);
}
#endif
}
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