BGN2/bgn2/src/keygen.cpp

#include "keygen.hpp"

extern const scalar_t bn_n;
extern const curvepoint_fp_t bn_curvegen;   
extern const twistpoint_fp2_t bn_twistgen;

void keygen(PublicKey& public_key, PrivateKey& private_key)
{
    Fp i1, j1, k1, l1, i2, j2, k2, l2;
    
    while (true)
    {
        j1.set_random();
        k1.set_random();
        l1.set_random();

        if (!l1.is_zero())
        {
            i1 = (j1 * k1 + Fp(1)) / l1;
            break;
        }
    }

    while (true)
    {
        j2.set_random();
        k2.set_random();
        l2.set_random();

        if (!l2.is_zero())
        {
            i2 = (j2 * k2 + Fp(1)) / l2;
            break;
        }   
    }

    private_key.set(i1, j1, k1, l1, i2, j2, k2, l2);
    
    curvepoint_fp_t c1, c2, c3, c4; 
    
    curvepoint_fp_scalarmult_vartime(c1, bn_curvegen, i1.to_scalar());  
    curvepoint_fp_makeaffine(c1);

    curvepoint_fp_scalarmult_vartime(c2, bn_curvegen, j1.to_scalar());
    curvepoint_fp_makeaffine(c2);

    Bipoint<curvepoint_fp_t> b1(c1, c2);

    twistpoint_fp2_t t1, t2, t3, t4;

    twistpoint_fp2_scalarmult_vartime(t1, bn_twistgen,i2.scalar());
    twistpoint_fp2_makeaffine(t1);

    twistpoint_fp2_scalarmult_vartime(t2, bn_twistgen,j2.scalar());
    twistpoint_fp2_makeaffine(t2);

    Bipoint<twistpoint_fp2_t> b2(t1, t2);
    
    scalar_t s1, s2, s3, s4;
    scalar_setrandom(s1, bn_n);
    scalar_setrandom(s2, bn_n);
    scalar_setrandom(s3, bn_n);
    scalar_setrandom(s4, bn_n);
    
    curvepoint_fp_scalarmult_vartime(c3, bn_curvegen, s1);
    curvepoint_fp_makeaffine(c3);

    curvepoint_fp_scalarmult_vartime(c4, bn_curvegen, s2);
    curvepoint_fp_makeaffine(c4);

    Bipoint<curvepoint_fp_t> b3(c3, c4);    
    
    twistpoint_fp2_scalarmult_vartime(t3, bn_twistgen, s3);
    twistpoint_fp2_makeaffine(t3);
    twistpoint_fp2_scalarmult_vartime(t4, bn_twistgen, s4);
    twistpoint_fp2_makeaffine(t4);
    
    Bipoint<twistpoint_fp2_t> b4(t3, t4);
        
    public_key.set(b1, b2, b3, b4);
}