The Rail Fence Cipher and how to decrypt

The Rail Fence Cipher is a type of transposition cipher. A transposition cipher involves the rearranging of the letters in the plaintext to encrypt the message. This is in contrast to a substitution cipher, in which the plaintext letters are replaced by letters from another alphabet (or by different letters from the same alphabet).

note: The rail fence cipher is not very strong; the number of practical keys (the number of rails) is small enough that a crypt analyst can try them all by hand.

In the rail fence cipher, the plaintext is written downwards and diagonally on successive "rails" of an imaginary fence, then moving up when we reach the bottom rail. When we reach the top rail, the message is written downwards again until the whole plaintext is written out. The message is then read off in rows. For example, if we have 4 "rails" and a message of 'REPEAT ATTACK TONIGHT', the cipherer writes out:

3 rails

R . . . A . . . T . . . K . . . N . . . T
. E . E . T . A . T . C . X . O . I . H .
. . P . . . X . . . A . . . T . . . G . .

Encrypted :RATKNTEETATCXOIHPXATG

4 rails

R . . . . . X . . . . . K . . . . . G . .
. E . . . T . A . . . C . X . . . I . H .
. . P . A . . . T . A . . . T . N . . . T
. . . E . . . . . T . . . . . O . . . . .

Encrypted :RXKGETACXIHPATATNTETO

Note: Space in text are replaced with any suitable random alphabet. in this case iam using 'X' as replace of white space

Download code :- RFcipher

oopss.. i miss how to decrypt without key

2. Decrypt without key

In railfence cipher, the maximun level we can make is the length of text. If the ciphertext length is 100, so the maximum level is 100. To decrypt that ciphertext, the possibility of correct message will get is 100.  Below is example of decrypt without key..

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/* authors by hafiq Rail Fence cipher and decrypt with key and no key any expert can advise me to improve this code...tq.. */ import java.util.*; public class RFCipher { public static void main(String[] args) { Scanner scan = new Scanner(System.in); String line = System.getProperty("line.separator"); scan.useDelimiter(line); System.out.print("1. Encrypt 2. Decrypt :"); int option = scan.nextInt(); switch (option) { case 1: System.out.print("Enter Plain Text: "); String text = scan.next(); System.out.print("Enter Key Level [more than 1] :"); int key = scan.nextInt(); if (key > 1) { String enc = RFEncryptionWork(key, text); System.out.println("Encrypted :" + enc); } else System.out.println("invalid level"); break; case 2: System.out.print("Enter Cipher text: "); String enc = scan.next(); System.out.print("1. No key 2. With Key: "); int k = scan.nextInt(); if(k==1){ String[] dec = RFDecryptionWork(enc); for (String a: dec) { System.out.println(a); } } else{ System.out.print("Enter Key Level [more than 1] :"); key = scan.nextInt(); String dec = RFDecryptionWork(enc,key); System.out.println("Decrypted :"+dec); } break; default: break; } } static String RFEncryptionWork(int key, String text) { int move = 1; int count = 0; String[][] rfp = new String[key][text.length()]; // arrange dot fence for (int x = 0; x < rfp.length; x++) { for (int y = 0; y < rfp[x].length; y++) { rfp[x][y] = "."; } } // formatting according fence rails for (int i = 0; i < text.length(); i++) { if ((move % 2) != 0) { rfp[count][i] = "" + text.charAt(i); if (count == (key - 1)) { move = 2; count = (key - 2); } else count++; } else if ((move % 2) == 0) { rfp[count][i] = "" + text.charAt(i); if (count == 0) { move = 1; count = 1; } else count--; } } //replace any white space with X or random for (int x = 0; x < rfp.length; x++) { for (int y = 0; y < rfp[x].length; y++) { if (rfp[x][y].equals(" ")) rfp[x][y] = "X"; } } // display System.out.println(); for (int i = 0; i < rfp.length; i++) { for (int u = 0; u < rfp[i].length; u++) { System.out.print(rfp[i][u] + " "); } System.out.println(); } System.out.println(); StringBuilder cb = new StringBuilder(); //encode string from fence for (int i = 0; i < rfp.length; i++) { for (int u = 0; u < rfp[i].length; u++) { if (!".".equals(rfp[i][u])) { cb.append(rfp[i][u]); } } } return "" + cb; } static String[] RFDecryptionWork(String text) { String[] ans = new String[text.length() - 2]; for (int z = 2; z < text.length(); z++) { int key = z; String[][] rfp = new String[key][text.length()]; for (int x = 0; x < rfp.length; x++) { for (int y = 0; y < rfp[x].length; y++) { rfp[x][y] = "."; } } // arrange accroding to fence rail int count = 0; int c = 1; int a = 0, b = 0; int init = (2 * key) - 2; a = init - 2; b = 2; for (int i = 0; i < rfp.length; i++) { c = 0; for (int u = i; u < rfp[i].length;) { if (count != text.length()) { if (i == 0 || i == key - 1) { rfp[i][u] = "" + text.charAt(count); u = u + init; } else { rfp[i][u] = "" + text.charAt(count); if (c % 2 == 0) u = u + a; else if (c % 2 == 1) u = u + b; c++; } count++; } else break; } if (i != 0 && i != key - 1) { a = a - 2; b = b + 2; } } int move = 1; count = 0; String sb = ""; for (int i = 0; i < text.length(); i++) { if ((move % 2) != 0) { sb = sb + rfp[count][i]; if (count == (key - 1)) { move = 2; count = (key - 2); } else count++; } else if ((move % 2) == 0) { sb = sb + rfp[count][i]; if (count == 0) { move = 1; count = 1; } else count--; } } ans[z - 2] = sb; } return ans; } static String RFDecryptionWork(String text, int key) { String[][] rfp = new String[key][text.length()]; for (int x = 0; x < rfp.length; x++) { for (int y = 0; y < rfp[x].length; y++) { rfp[x][y] = "."; } } // arrange accroding to fence rail int count = 0; int c = 1; int a = 0, b = 0; int init = (2 * key) - 2; a = init - 2; b = 2; for (int i = 0; i < rfp.length; i++) { c = 0; for (int u = i; u < rfp[i].length;) { if (count != text.length()) { if (i == 0 || i == key - 1) { rfp[i][u] = "" + text.charAt(count); u = u + init; } else { rfp[i][u] = "" + text.charAt(count); if (c % 2 == 0) u = u + a; else if (c % 2 == 1) u = u + b; c++; } count++; } else break; } if (i != 0 && i != key - 1) { a = a - 2; b = b + 2; } } //display System.out.println("\n\nDecrypting..list into table"); for (int i = 0; i < rfp.length; i++) { for (int u = 0; u < rfp[i].length; u++) { System.out.print(rfp[i][u] + " "); } System.out.println(); } int move = 1; count = 0; String sb = ""; for (int i = 0; i < text.length(); i++) { if ((move % 2) != 0) { sb = sb + rfp[count][i]; if (count == (key - 1)) { move = 2; count = (key - 2); } else count++; } else if ((move % 2) == 0) { sb = sb + rfp[count][i]; if (count == 0) { move = 1; count = 1; } else count--; } } return sb; } }