BigInt PointGFp::get_affine_y() const
{
if(is_zero())
throw Illegal_Transformation("Cannot convert zero point to affine");
BigInt z3 = curve_mult(m_coord_z, curve_sqr(m_coord_z));
z3 = inverse_mod(z3, m_curve.get_p());
m_curve.to_rep(z3, m_monty_ws);
return curve_mult(z3, m_coord_y);
}
BigInt PointGFp::get_affine_x() const
{
if(is_zero())
throw Illegal_Transformation("Cannot convert zero point to affine");
BigInt z2 = curve_sqr(m_coord_z);
m_curve.from_rep(z2, m_monty_ws);
z2 = inverse_mod(z2, m_curve.get_p());
return curve_mult(z2, m_coord_x);
}
BigInt PointGFp::get_affine_y() const
{
if(is_zero())
throw Illegal_Transformation("Cannot convert zero point to affine");
secure_vector<word> monty_ws;
BigInt z3 = m_curve.mul_to_tmp(m_coord_z, m_curve.sqr_to_tmp(m_coord_z, monty_ws), monty_ws);
z3 = inverse_mod(z3, m_curve.get_p());
m_curve.to_rep(z3, monty_ws);
return m_curve.mul_to_tmp(z3, m_coord_y, monty_ws);
}
BigInt PointGFp::get_affine_y() const
{
if(is_zero())
throw Illegal_Transformation("Cannot convert zero point to affine");
const BigInt& r2 = curve.get_r2();
BigInt z3 = monty_mult(coord_z, monty_sqr(coord_z));
z3 = inverse_mod(z3, curve.get_p());
z3 = monty_mult(z3, r2);
return monty_mult(coord_y, z3);
}
