Tuesday, October 6, 2015

Columnar Transposition Cipher Without Key

From previous topic about columnar transposition cipher with key. This topic show how  columnar transposition cipher without key and how to decrypt..

note: anyone who exactly how its work can correct me. this is how i understand.








Download code -> With key
Download code -> No key



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/*
   authors by hafiq
   
   Colummnar Transposition without key and possible decrytion
   
   any expert can advise me to improve this code...tq..
*/
import java.util.*;
import java.lang.*;

public class CLCipher {
    public static void main(String[] args) {
        String str = "REPEAT ATTACK TONIGHT";
        System.out.println("Encryption Text: " + encrypt(str));
        String get[] = decrypt(encrypt(str));

        System.out.println("Possible Decyrption Text:");
        for (int x = 0; x < get.length; x++)
            System.out.println((x + 1) + ". " + get[x]);

    }

    public static String encrypt(String str) {

        String[] get = str.split(" ");

        int maxlen = 0;
        String init = "";
        for (String a: get) {
            if (a.length() >= init.length())
                init = a;
        }

        //if maxlen == 7, so the column must be 7
        //get.length will be the row number;
        maxlen = init.length();
        char[][] grid = new char[get.length][maxlen];

        for (int x = 0; x < get.length; x++) {
            String gt = get[x];
            for (int y = 0; y < maxlen; y++) {
                if (y != gt.length())
                    grid[x][y] = gt.charAt(y);
                else
                // can be replace with random alphabet also
                    grid[x][y] = 'X';
            }
        }

        StringBuilder cb = new StringBuilder();
        for (int x = 0; x < maxlen; x++) {
            for (int y = 0; y < get.length; y++) {
                cb.append(grid[y][x]);
            }
        }

        return cb.toString();
    }

    public static String[] decrypt(String str) {

        int getnum = str.length();

        //get possible division number
        List < Integer > val = new ArrayList < Integer > ();
        for (int x = 1; x < getnum; x++) {
            if (getnum % x == 0)
                val.add(x);
        }

        String[] dec = new String[val.size()];
        for (int x = 0; x < val.size(); x++) {
            int now = (int) val.get(x);
            String regex = "(?<=\\G.{" + now + "})";
            String[] get = str.split(regex);

            //tranpose
            char grid[][] = new char[now][get.length];
            for (int y = 0; y < get.length; y++) {
                String nw = get[y];
                for (int z = 0; z < nw.length(); z++) {
                    grid[z][y] = nw.charAt(z);
                }
            }

            //combine
            dec[x] = "";
            for (int y = 0; y < now; y++) {
                for (int z = 0; z < get.length; z++) {
                    dec[x] = dec[x] + grid[y][z];
                }
                dec[x] = dec[x] + " ";
            }

        }


        return dec;
    }

}
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