import java.math.*;
import java.util.*;
import java.io.*;

public class rsatest
{ 
  private static BigInteger one=new BigInteger("1");

  public static String BigIntegerToString(BigInteger n)
  { return new String(n.toByteArray()); }

  public static BigInteger StringToBigInteger(String s)
  { return new BigInteger(s.getBytes()); }

  public static void main(String[] args)
  { BigInteger p, q, n, phi, phiminusone, d, e, msg, code, decode;
    Random r=new Random(System.currentTimeMillis());
    InputStreamReader ISRin=new InputStreamReader(System.in);
    BufferedReader in=new BufferedReader(ISRin);
    String s, inp;
    p=new BigInteger(20,40,r);
    System.out.println("     p = "+p);
    q=new BigInteger(20,40,r);
    System.out.println("     q = "+q);
    n=p.multiply(q);
    System.out.println("     n = "+n);
    phi=p.subtract(one).multiply(q.subtract(one));
    System.out.println("   phi = "+phi);
    phiminusone=phi.subtract(one);
    System.out.println(" phi-1 = "+phiminusone);
    d=new BigInteger(18,40,r);
    System.out.println("     d = "+d);
    e=d.modInverse(phi);
    System.out.println("     e = "+e);
    System.out.println("");
    System.out.println("   Private key is ("+n+","+d+")");
    System.out.println("    Public key is ("+n+","+e+")");
    System.out.println("");
    while (true)
    { System.out.print("Message: ");
      try { inp=in.readLine(); } catch (Exception ee) { break; }
      if (inp.equals("")) break;
      while (!inp.equals(""))
      { if (inp.length()>4)
        { s=inp.substring(0,4);
          inp=inp.substring(4); }
        else
        { s=inp;
          inp=""; }
        msg=StringToBigInteger(s);
        System.out.println("  message \""+s+"\"="+msg);
        code=msg.modPow(d,n);
        System.out.print("                         ");
        System.out.println("encrypted: "+code);
        decode=code.modPow(e,n);
        s=BigIntegerToString(decode);
        System.out.println("decrypted \""+s+"\"="+decode);
        System.out.println(""); } } } }