App.java

App.java

contents ::

  App.java
  plaintext_1
  plaintext_2
  plaintext_3
  plaintext_4
  plaintext_5
  RSA_test_script

/* J. A. Little 18/5/01
   ok, this one is definately going to be the last.. hmm.. maybee not :)
*/

package jlittle_ex10;
import java.io.*;

public class App {

    private static BufferedReader in;
    private static BufferedOutputStream out;

    public static void main(String [] args) throws IOException {
         in = new BufferedReader(new InputStreamReader(System.in));
         out = new BufferedOutputStream(System.out);
         reading();
         in.close();
         out.close();

    }

    // encrypt: C = P(M) = M^P mod N
    // decrypt: M = S(C) = C^S mod N

    public static void reading(){
             String method =null;
             int k=-1;
             int N=-1;
             int M=-1;
             try{
                  method = in.readLine();
                  k = Integer.parseInt(in.readLine());
                  N = Integer.parseInt(in.readLine());
             } catch (IOException e) {
                  System.out.println("This went badly 1 "+e);
             } catch (NumberFormatException e) {
                  System.out.println("This went badly 2 "+e);
             }
             //  System.out.println(method);
             // System.out.println(k);
             // System.out.println(N);

             try{
                  // start reading input
                  int c1 =01;
                  while((c1=in.read())!=-1) {
                      int c2;
                      int cryptic;

                      c1=c1*256;

                      if((c2=in.read())!=-1){

                           cryptic =c1+c2;
                      }
                      else
                           cryptic =c1+128;


                      int cypher = 1;

                      for(int i = 1; i<=k; i++){
                           cypher =(int)(((long)cypher * cryptic) % N);
                      }

                      out.write((cypher/256));

                      if(method.equals("encrypt")||(cypher%256 != 128)){
                           out.write((cypher%256));
                      }

                  }
             } catch (IOException e) {
                  System.out.println("This went badly 1 "+e);
             }
    }


}

James Little