Digital signature problem

Question

Here is my code . in this d value of 'v' shouls come equal to 'r' but its nt coming.please tell me what is the problem in this??
import java.io.*;
import java.nio.charset .*;
import java.util.Random;
import java.math.*;
//import java.acm.util.RandomGenerator;
class key
public static void main(String args[])
               String sm="I AM A SUDENT OF COMPUTER SCIENCE";
     //this is the starting of first module i.e. key generation
               try
                    String s11="13";
                    int a1=Integer.parseInt(s11);
                    double a=(double)a1;
                    byte[] q = new byte[20];
                    q=s11.getBytes("UTF8" );
                    System.out.println("Prime number q="+a1);
                    String s1="4";
                    int b=Integer.parseInt(s1);
                    double b1=(double)b;
                    System.out.println(b);
                    byte[]z= new byte[20];
                    z=s1.getBytes("UTF8" );
                    System.out.println("Random number z="+z);
                    byte[] p=new byte [256];     
     int c=((a1*b)+1);
                    double c1=(double)c;
                    String s2=Double.toString(c);
                    p=s2.getBytes("UTF8");
     System.out.println("Prime number p="+c);
                    //java.util.Random generator = new java.util.Random(System.currentTimeMillis());
                    //public class RandomGenerator extends Random
                    //RandomGenerator rgen = RandomGenerator.getInstance();
                    //double h=rgen.nextDouble(0.0,c-1);
                    Random ra=new Random();
                    //double h=((c-1)*(ra.nextDouble()));
                    double h=35;
                    //double h=(Math.random()*(c-1));
                    //double h=ra.nextDouble(0.0,c-1);
                    //double h=(generator.nextDouble()*(c-1)); // 0.0 <= d < 1.0
                    System.out.println("The value of h="+h);
                    double g1=(Math.pow(h,b));
                    double d=(g1%c);
                    //String s3=Double.toString(d);
                    //byte[]g=new byte[20];
                    //g=s3.getBytes("UTF8");
                    System.out.println("The value of g="+d);
                    //public class RandomGenerator extends Random
                    //RandomGenerator rgen = RandomGenerator.getInstance();
                    // double x=rgen.nextDouble(0.0,a);
                    //double x=(Math.random()*(a));
                    //double x = (generator.nextDouble()*a); // 0.0 <= d < 1.0
                    //double x=ra.nextDouble(0.0,a);
                    //int x=(ra.nextInt(a1));
int x=2;
double x1=(double)x;
                    //double x1=(double)x;
                    //double x=8;
                    System.out.println("The value of x="+x);
                    String s4=Double.toString(x);
                    byte[]rno1=new byte[20];
                    rno1=s4.getBytes("UTF8");
                    System.out.println(rno1);
                    double y1=((Math.pow(d,x1))%c1);
                    System.out.println("The value of y="+y1);
                    String s5=Double.toString(y1);
                    byte[]y=new byte[20];
                    y=s5.getBytes("UTF8");
                    System.out.println(y);
                    System.out.println("THE VALUE OF PUBLIC KEY="+c+","+a+","+d+","+y1);
                    System.out.println("THE VALUE OF PRIVATE KEY="+x);
                    //This ends the process of key generation
                    //Now starts the next module of signing
                    //public class RandomGenerator extends Random
                    //RandomGenerator rgen = RandomGenerator.getInstance();
                    //double k= rgen.nextDouble(0.0, a);
                    //double k=(ra.nextDouble()*a);
                    //double k=(Math.random()*(a));
                    //double k =(generator.nextDouble()*a); // 0.0 <= d < 1.0
                    //double k=ra.nextDouble(0.0,c-1);//                    int k=(ra.nextInt(a1));
                    //double k1=(double)k;
int k=4;                         
double k1=(double)k;
                    //double k=11;
                    System.out.println("The value of k="+k);
                    String s6=Double.toString(k1);
                    byte[]n=new byte[20];
                    n=s6.getBytes("UTF8");
                    System.out.println("The value of nonce="+n);
                    double r1=(((Math.pow(d,k1))%c1)%a1);
                    System.out.println("The value of r="+r1);
                    String s7=Double.toString(r1);
                    byte[]r=new byte[20];
                    r=s7.getBytes("UTF8");
                    System.out.println("The value of r="+r1);
                    int h1 =10;
/* for (int i = 0; i < sm.length(); i++) {
h1= 31*h1 + sm.charAt(i);
                    System.out.println(h1);*/
                    double hash=(double)h1;
                    System.out.println("The value of hash code="+hash);
                    //double s12=(((hash/k1)+(x1*r1))%a1);
                    double a11=(hash+(x1*r1));
                    double s12=((a11/k1)%a1);
                    System.out.println("The value of s="+s12);
                    String s8=Double.toString(s12);
                    byte[]s=new byte[20];
                    s=s8.getBytes("UTF8");
                    System.out.println("The value of s="+s);
                    System.out.println("THE VALUE OF SIGNATURE= ("+r1+","+s12+" )");
                    //The process of signing is complete
                    //Now starts the process of verifying
                    double m=1/s12;
                    double w=(m%a1);
                    System.out.println("The value of w="+w);
                    double u1=((hash*w)%a1);
                    System.out.println("The value of u1="+u1);
                    double u2=((r1*w)%a1);
                    System.out.println("The value of u2="+u2);
                    double m1=(Math.pow(d,u1));
                    System.out.println(m1);
                    double m2=(Math.pow(y1,u2));
                    System.out.println(m2);
                    double v=(((m1*m2)%c1)%a1);
                    //double v=((((Math.pow(d,u1))*(Math.pow(y1,u2)))%a)%b);
                    System.out.println("The value of v="+v);
               catch(Exception e)
}

Answer 1

Do not use doubles or floats for arithmetic mod n, ever! Even for small examples, the BigInteger class is very easy to use. You'll be using the add, subtract, etc. methods, but also the mod, modPow, and modInverse methods. So, your code might start out looking like this:
java.math.BigInteger;
class Key
    public static void main (String [] args)
        String sm="I AM A SUDENT OF COMPUTER SCIENCE";
        BigInteger q = BigInteger.valueOf(13);
        System.out.println("Prime number q=" + q);
        // ...and so on...
}