BGN2/bgn2/src/homomorphic_operations.cpp

#include "homomorphic_operations.hpp"

extern const scalar_t bn_n;

Bipoint<curvepoint_fp_t> bgn_homomorphic_addition(const Bipoint<curvepoint_fp_t>& a, const Bipoint<curvepoint_fp_t>& b, const PublicKey& public_key)
{
	Bipoint<curvepoint_fp_t> retval, random_mask;

	scalar_t lambda;
	scalar_setrandom(lambda, bn_n);

	random_mask = public_key.get_bipoint_curve_groupelt().scalarmult_vartime(lambda);
	random_mask.makeaffine();

	retval = a + b + random_mask;
	retval.makeaffine();

	return retval;
}

Bipoint<twistpoint_fp2_t> bgn_homomorphic_addition(const Bipoint<twistpoint_fp2_t>& a, const Bipoint<twistpoint_fp2_t>& b, const PublicKey& public_key)
{
	Bipoint<curvepoint_fp_t> retval, random_mask;

	scalar_t lambda;
	scalar_setrandom(lambda, bn_n);

	random_mask = public_key.get_bipoint_twist_groupelt().scalarmult_vartime(lambda);
	random_mask.makeaffine();

	retval = a + b + random_mask;
	retval.makeaffine();

	return retval;
}

Quadripoint bgn_homomorphic_addition(const Quadripoint& a, const Quadripoint& b, const PublicKey& public_key)
{
	Quadripoint retval, random_mask;
	Bipoint<curvepoint_fp_t> random_mask_curve;
	Bipoint<twistpoint_fp2_t> random_mask_twist;
	
	scalar_t lambda1, lambda2;
	scalar_setrandom(lambda1, bn_n);
	scalar_setrandom(lambda2, bn_n);

	random_mask_curve = public_key.get_bipoint_curve_groupelt().scalarmult_vartime(lambda1);
	random_mask_curve.makeaffine();

	random_mask_twist = public_key.get_bipoint_twist_groupelt().scalarmult_vartime(lambda2);
	random_mask_twist.makeaffine();

	random_mask = pairing(public_key.get_bipoint_curvegen(), random_mask_twist) * pairing(random_mask_curve, public_key.get_bipoint_twistgen());
	retval = a * b * random_mask;

	return retval;
}

Quadripoint bgn_homomorphic_multiplication(const Bipoint<curvepoint_fp_t>& a, const Bipoint<twistpoint_fp2_t>& b, const PublicKey& public_key)
{
	Quadripoint retval, random_mask;
	Bipoint<curvepoint_fp_t> random_mask_curve;
	Bipoint<twistpoint_fp2_t> random_mask_twist;
	
	scalar_t lambda1, lambda2;
	scalar_setrandom(lambda1, bn_n);
	scalar_setrandom(lambda2, bn_n);

	random_mask_curve = public_key.get_bipoint_curve_groupelt().scalarmult_vartime(lambda1);
	random_mask_curve.makeaffine();

	random_mask_twist = public_key.get_bipoint_twist_groupelt().scalarmult_vartime(lambda2);
	random_mask_twist.makeaffine();

	random_mask = pairing(public_key.get_bipoint_curvegen(), random_mask_twist) * pairing(random_mask_curve, public_key.get_bipoint_twistgen());
	retval = pairing(a, b) * random_mask;

	return retval;
}