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package ecckrypt;
import java.math.BigInteger;


class  PECC
{
    BigInteger x,y,a,b,q;
    PECC(BigInteger x, BigInteger y, BigInteger a, BigInteger b, BigInteger q)
    {
        this.a = a;
        this.b = b;
        this.x = x;
        this.y = y;
        this.q = q;
    }
}
public class ECCKRYPT {

    public static BigInteger ODW(BigInteger m, BigInteger n)
    {
        BigInteger a, ap, s, sp, t, tp, r, q;
        BigInteger L1 = new BigInteger("1"), L0=new BigInteger("0");
        a = m;
        ap = n;
        s = L1;
        sp=L0;
        t=L0;
        tp = L1;

        while(ap.compareTo(L0) !=0)
        {
          q = a.divide(ap);
          r = a; a=ap; ap=r.subtract(q.multiply(ap));
          r = s; s=sp; sp=r.subtract(q.multiply(sp));
          r = t; t=tp; tp=r.subtract(q.multiply(tp));
        }
        if (t.compareTo(L0)>0) r=t;
        else  r=t.add(n);
        return r;
    }

  public static   PECC DOD(PECC P1, PECC P2)
    {
        BigInteger x1, x2, x3, y1, y2, y3, lam, q, dwa, trzy;
        x1 = P1.x;
        x2 = P2.x;
        x3 = new BigInteger("0");

        y1 = P1.y;
        y2 = P2.y;
        y3 = new BigInteger("0");

        dwa = new BigInteger("2");
        trzy = new BigInteger("3");
        q = P1.q;


        if (x1.compareTo(x2)!=0)
        {
            lam = x2.subtract(x1);
            lam = ODW(lam, P1.q);
            lam = lam.multiply(y2.subtract(y1));
            lam = lam.mod(q);
            x3 = lam.multiply(lam);
            x3 = (x3.subtract(x1)).subtract(x2);
            x3 = x3.mod(q);
            y3 = (x1.subtract(x3)).multiply(lam);
            y3 = y3.subtract(y1);
            y3 = y3.mod(q);

        }

        else
        {
            if (y1.compareTo(y2)==0)
            {
             lam = ODW(dwa.multiply(y1), q);
             BigInteger r;
             r = trzy.multiply(x1.multiply(x1));

             r = r.add(P1.a);
             lam = lam.multiply(r);
             x3 = lam.multiply(lam);
             x3 = x3.subtract(dwa.multiply(x1));
             x3 = x3.mod(q);
             y3 = (x1.subtract(x3)).multiply(lam);
             y3 = y3.subtract(y1);
             y3 = y3.mod(q);

            }

        }
        return new PECC (x3, y3, P1.a, P1.b, q);

    }
  public static  PECC MNOZENIE(int  k, PECC P)
    {


        PECC R = P;
        for (int j=0; j<k; j++)

        {
            R = DOD(R, P);

        }
        return R;
    }
    public static BigInteger SLegendrea(BigInteger a, BigInteger p) {
        BigInteger jeden = new BigInteger("1");
        BigInteger dwa = new BigInteger("2");

        return (a.modPow((p.subtract(jeden)).divide(dwa),p));
    }

    public static BigInteger pierw(BigInteger r, BigInteger q)
    {
        BigInteger L1 = new BigInteger("1");
        BigInteger L2 = new BigInteger("2");
        BigInteger r1 = L1;

        while((r1.multiply(r1)).compareTo(r)!=0)
        r1.add(L1);
        return r1;
    }

   public static  void Wyswietlanie (PECC P)
    {
        System.out.print("( "+P.x+" , "+P.y+" )");
    }

    public static void main(String[] args) {


        BigInteger p, q, a, b, L1, L2, L10, r1, r2, x, y;
        int n = 5;


        p = new BigInteger("3");
        p = p.nextProbablePrime();

        L2 = new BigInteger("2");
        L1 = new BigInteger("1");
        L10 = new BigInteger("10");
        q = p.pow(n);
        q = q.add(L1);
        a = L1;
        b = L2.pow(n);
        b = b.nextProbablePrime();
        while (b.compareTo(q)>0)
        {
            b = b.divide(L2);
            b = b.nextProbablePrime();
        }
        System.out.println("Równanie krzywej eliptycznej:\n" + "(y^2=x^3+x+"+b+") mod " + q);
            /*Znalezienie pktu krzywej ECC
                ustalenie mnoznika ka
                znalezienie P do przeslania*/

        x = L1;
        do
        {
            r1 = ((x.pow(3)).add(x)).add(b);
            r1 = r1.mod(q);
            r2 = SLegendrea(r1,q);
            //System.out.println("SL="+r2+" x="+x);
            x=x.add(L1);
        } while(r2.compareTo(L1)!=0);
        System.out.println("SL=" + r2+" x="+x);
        y=pierw(r1,q);
        x.subtract(L1);

        System.out.println("x = " + x +" y="+y);

        int  k=123466;
        k = (int)Math.round(k*Math.random());
        BigInteger kk=new BigInteger (Long.toString(k));
        PECC P=new PECC(x,y,a,b,q);
        P= MNOZENIE(k,P);
        System.out.println("Klucz do szyfrowania ECC :");
                Wyswietlanie(P);
    }

}