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/*
* ECKAEG Operation
* (C) 2007 FlexSecure GmbH
* 2008 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/eckaeg_op.h>
#include <botan/numthry.h>
namespace Botan {
Default_ECKAEG_Op::Default_ECKAEG_Op(const EC_Domain_Params& dom_pars,
const BigInt& priv_key,
const PointGFp& pub_key)
: m_dom_pars(dom_pars),
m_pub_key(pub_key),
m_priv_key(priv_key)
{
}
SecureVector<byte> Default_ECKAEG_Op::agree(const PointGFp& i) const
{
BigInt cofactor(m_dom_pars.get_cofactor());
BigInt n = m_dom_pars.get_order();
BigInt l(inverse_mod(cofactor,n)); // l=h^-1 mod n
PointGFp Q(cofactor*i); // q = h*Pb
PointGFp S(Q);
BigInt group_order = m_dom_pars.get_cofactor() * n;
S.mult_this_secure((m_priv_key*l)%n, group_order, n-1);
S.check_invariants();
return FE2OSP(S.get_affine_x()); // fe2os(xs)
}
}
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