Cryptography using the Transposition Technique can be done by using Transposition ciphers which uses the letters of the plaintext message and after that, they permute the order of the letters. The Columnar Transposition Cipher is a form of transposition cipher just like Rail Fence Cipher. Columnar Transposition involves writing the plaintext out in rows, and then reading the ciphertext off in columns one by one.
It should be easy to spot a transposition cipher because the letter frequencies should mimic the usual frequencies for English – high frequencies for a,e, i, n, o r, s, t. But, cryptanalysis of a transposition cipher might be difficult. The essential technique is anagramming which is rearranging the ciphertext letters to “make sense. The key to the cipher is the pattern of rearrangement. In mathematically terms it can simply be assumed that a bijective function is used on the characters’ positions to encrypt and an inverse function to decrypt.
Illustration:
Example 1
Input : Plaintext : how are you Output : Ciphertext : a e oowu hyrExample 2
Input : Plaintext : you are a champion Output : Ciphertext : h aa ep o nuc i yaorm
Implementation: Given a plain-text message and a numeric key, cipher/de-cipher the given text using Columnar Transposition Cipher. ‘Hello Geek’ is custom input taken as plain text!
Example
Java
// Java Program to Perform Cryptography// using Transposition Technique // Importing all classes from// java.util package// Importing input output classesimport java.io.*;import java.util.*; // Class// For transposition cipherpublic class GFG { // Member variables of this class public static String selectedKey; public static char sortedKey[]; public static int sortedKeyPos[]; // Constructor 1 of this class // Default constructor defining the default key public GFG() { selectedKey = "megabuck"; sortedKeyPos = new int[selectedKey.length()]; sortedKey = selectedKey.toCharArray(); } // Constructor 2 of this class // Parameterized constructor defining the custom key public GFG(String GeeksForGeeks) { selectedKey = GeeksForGeeks; sortedKeyPos = new int[selectedKey.length()]; sortedKey = selectedKey.toCharArray(); } // Method 1 - doProcessOnKey() // To reorder data do the sorting on selected key public static void doProcessOnKey() { // Find position of each character in selected key // and arranging it in alphabetical order int min, i, j; char orginalKey[] = selectedKey.toCharArray(); char temp; // Step 1: Sorting the array of selected key // using nested for loops for (i = 0; i < selectedKey.length(); i++) { min = i; for (j = i; j < selectedKey.length(); j++) { if (sortedKey[min] > sortedKey[j]) { min = j; } } if (min != i) { temp = sortedKey[i]; sortedKey[i] = sortedKey[min]; sortedKey[min] = temp; } } // Step 2: Filling the position of array // according to alphabetical order // using nested for loops for (i = 0; i < selectedKey.length(); i++) { for (j = 0; j < selectedKey.length(); j++) { if (orginalKey[i] == sortedKey[j]) sortedKeyPos[i] = j; } } } // Method 2 - doEncryption() // To encrypt the targeted string public static String doEncryption(String plainText) { int min, i, j; char orginalKey[] = selectedKey.toCharArray(); char temp; doProcessOnKey(); // Step 3: Generating the encrypted message by // doing encryption using Transpotion Cipher int row = plainText.length() / selectedKey.length(); int extrabit = plainText.length() % selectedKey.length(); int exrow = (extrabit == 0) ? 0 : 1; int rowtemp = -1, coltemp = -1; int totallen = (row + exrow) * selectedKey.length(); char pmat[][] = new char[(row + exrow)] [(selectedKey.length())]; char encry[] = new char[totallen]; int tempcnt = -1; row = 0; for (i = 0; i < totallen; i++) { coltemp++; if (i < plainText.length()) { if (coltemp == (selectedKey.length())) { row++; coltemp = 0; } pmat[row][coltemp] = plainText.charAt(i); } else { // Padding can be added between two // consecutive alphabets or a group of // alphabets of the resultant cipher text pmat[row][coltemp] = '-'; } } int len = -1, k; for (i = 0; i < selectedKey.length(); i++) { for (k = 0; k < selectedKey.length(); k++) { if (i == sortedKeyPos[k]) { break; } } for (j = 0; j <= row; j++) { len++; encry[len] = pmat[j][k]; } } String p1 = new String(encry); return (new String(p1)); } // Method 3 - doEncryption() // To decrypt the targeted string public static String doDecryption(String s) { int min, i, j, k; char key[] = selectedKey.toCharArray(); char encry[] = s.toCharArray(); char temp; doProcessOnKey(); // Step 4: Generating a plain message int row = s.length(); selectedKey.length(); char pmat[][] = new char[row][(selectedKey.length())]; int tempcnt = -1; for (i = 0; i < selectedKey.length(); i++) { for (k = 0; k < selectedKey.length(); k++) { if (i == sortedKeyPos[k]) { break; } } for (j = 0; j < row; j++) { tempcnt++; pmat[j][k] = encry[tempcnt]; } } // Step 5: Storing matrix character in // to a single string char p1[] = new char[row * selectedKey.length()]; k = 0; for (i = 0; i < row; i++) { for (j = 0; j < selectedKey.length(); j++) { if (pmat[i][j] != '*') { p1[k++] = pmat[i][j]; } } } p1[k++] = '\0'; return (new String(p1)); } @SuppressWarnings("static-access") // Method 4 - main() // Main driver method public static void main(String[] args) { // Creating object of class in main method GFG tc = new GFG(); // Printing the ciphere text // Custom input - Hello Geek System.out.println("Cipher Text : " + tc.doEncryption("Hello Geek")); }} |
Cipher Text : l-o-G-ekl-e-He -
