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/*
* ECDH implemenation
* (C) 2007 Manuel Hartl, FlexSecure GmbH
* 2007 Falko Strenzke, FlexSecure GmbH
* 2008-2010 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/pk_utils.h>
#include <botan/ecdh.h>
namespace Botan {
namespace {
/**
* ECDH operation
*/
class ECDH_KA_Operation : public PK_Ops::Key_Agreement_with_KDF
{
public:
typedef ECDH_PrivateKey Key_Type;
ECDH_KA_Operation(const ECDH_PrivateKey& key, const std::string& kdf) :
PK_Ops::Key_Agreement_with_KDF(kdf),
curve(key.domain().get_curve()),
cofactor(key.domain().get_cofactor())
{
l_times_priv = inverse_mod(cofactor, key.domain().get_order()) * key.private_value();
}
secure_vector<byte> raw_agree(const byte w[], size_t w_len) override
{
PointGFp point = OS2ECP(w, w_len, curve);
PointGFp S = (cofactor * point) * l_times_priv;
BOTAN_ASSERT(S.on_the_curve(), "ECDH agreed value was on the curve");
return BigInt::encode_1363(S.get_affine_x(), curve.get_p().bytes());
}
private:
const CurveGFp& curve;
const BigInt& cofactor;
BigInt l_times_priv;
};
}
BOTAN_REGISTER_PK_KEY_AGREE_OP("ECDH", ECDH_KA_Operation);
}
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