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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>
namespace Botan {
/**
* Derive a key
*/
SecureVector<byte> ECDH_PrivateKey::derive_key(const byte key[],
u32bit key_len) const
{
PointGFp point = OS2ECP(key, key_len, public_point().get_curve());
return derive_key(point);
}
/**
* Derive a key
*/
SecureVector<byte> ECDH_PrivateKey::derive_key(const ECDH_PublicKey& key) const
{
return derive_key(key.public_point());
}
/**
* Derive a key
*/
SecureVector<byte> ECDH_PrivateKey::derive_key(const PointGFp& point) const
{
const BigInt& cofactor = domain().get_cofactor();
const BigInt& n = domain().get_order();
BigInt l = inverse_mod(cofactor, n); // can precompute this
PointGFp S = (cofactor * point) * (private_value() * l);
S.check_invariants();
return BigInt::encode_1363(S.get_affine_x(),
point.get_curve().get_p().bytes());
}
}
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