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/*
* ECDH implemenation
* (C) 2007 Manuel Hartl, FlexSecure GmbH
* 2007 Falko Strenzke, FlexSecure GmbH
* 2008-2010 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/ecdh.h>
#include <botan/internal/assert.h>
namespace Botan {
ECDH_KA_Operation::ECDH_KA_Operation(const ECDH_PrivateKey& key) :
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> ECDH_KA_Operation::agree(const byte w[], size_t w_len)
{
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());
}
}
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