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PlayfairCipher.java
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PlayfairCipher.java
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// Path: Java\Cryptography\PlayfairCipher.java
// Java program to implement playfair cipher algorithm.
// The Playfair cipher algorithm is a symmetric encryption technique that uses a 5x5 grid of letters to encrypt plaintext.
// It employs the rules of letter substitution and rearrangement based on pairs of letters to generate ciphertext.
// Rules for Encryption using playfair cipher Algorithm
// 1). 5 X 5 matrix -> Table
// 2). Digraphs (3 conditions):
// i). same row
// ii). same column
// iii). different row and column
import java.util.Scanner;
public class PlayfairCipher {
private static final int SIZE = 5;
// Function to prepare the input string
private static String prepareString(String line) {
StringBuilder preparedString = new StringBuilder();
int len = line.length();
for (int i = 0; i < len; i++) {
char ch = line.charAt(i);
ch = Character.toUpperCase(ch);
if (ch == 'J')
ch = 'I';
else if (ch == ' ')
continue;
preparedString.append(ch);
}
return preparedString.toString();
}
// Function to construct the table based on the key
private static void constructTable(String key, char[][] table) {
int[] visited = new int[26];
int row = 0, col = 0;
int len = key.length();
// First, fill the key in the table
for (int i = 0; i < len; i++) {
char ch = key.charAt(i);
if (visited[ch - 'A'] == 0) {
table[row][col] = ch;
visited[ch - 'A'] = 1;
if (col == SIZE - 1) {
row++;
col = 0;
} else
col++;
}
}
// Then, fill the remaining characters from A to Z
for (int i = 0; i < 26; i++) {
if (visited[i] == 0) {
char ch = (char) (i + 'A');
if (ch == 'J')
continue;
table[row][col] = ch;
visited[i] = 1;
if (col == SIZE - 1) {
row++;
col = 0;
} else
col++;
}
}
}
// Function to split the plain text into digraphs
private static String[] digraphPlainText(String plainText) {
int len = plainText.length();
StringBuilder preparedString = new StringBuilder();
for (int i = 0; i < len; i++) {
char ch = plainText.charAt(i);
preparedString.append(ch);
if (i == len - 1 || ch == plainText.charAt(i + 1)) {
preparedString.append('X');
} else {
preparedString.append(plainText.charAt(i + 1));
i++;
}
}
String digraphPlainText = preparedString.toString();
// Split the digraphs into an array
int digraphCount = digraphPlainText.length() / 2;
String[] digraphs = new String[digraphCount];
for (int i = 0, j = 0; i < digraphCount; i++, j += 2) {
digraphs[i] = digraphPlainText.substring(j, j + 2);
}
return digraphs;
}
// Function to get the coordinates of a character in the table
private static void getCoordinates(char[][] table, char ch, int[] coordinates) {
for (int i = 0; i < SIZE; i++) {
for (int j = 0; j < SIZE; j++) {
if (table[i][j] == ch) {
coordinates[0] = i;
coordinates[1] = j;
return;
}
}
}
coordinates[0] = -1;
coordinates[1] = -1;
}
// Function to encrypt the plain text
private static String encrypt(String[] digraphs, char[][] table) {
StringBuilder cipherText = new StringBuilder();
for (String digraph : digraphs) {
int row1, col1, row2, col2;
char ch1 = digraph.charAt(0);
char ch2 = digraph.charAt(1);
int[] coordinates1 = new int[2];
int[] coordinates2 = new int[2];
getCoordinates(table, ch1, coordinates1);
getCoordinates(table, ch2, coordinates2);
row1 = coordinates1[0];
col1 = coordinates1[1];
row2 = coordinates2[0];
col2 = coordinates2[1];
// Case 1: Same row
if (row1 == row2) {
col1 = (col1 + 1) % SIZE;
col2 = (col2 + 1) % SIZE;
}
// Case 2: Same column
else if (col1 == col2) {
row1 = (row1 + 1) % SIZE;
row2 = (row2 + 1) % SIZE;
}
// Case 3: Rectangle
else {
int temp = col1;
col1 = col2;
col2 = temp;
}
cipherText.append(table[row1][col1]);
cipherText.append(table[row2][col2]);
}
return cipherText.toString();
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter Key: ");
String key = scanner.nextLine().toUpperCase();
System.out.print("Enter Plain Text: ");
String plainText = scanner.nextLine().toUpperCase();
String preparedKey = prepareString(key);
String preparedPlainText = prepareString(plainText);
char[][] table = new char[SIZE][SIZE];
constructTable(preparedKey, table);
String[] digraphs = digraphPlainText(preparedPlainText);
String cipherText = encrypt(digraphs, table);
System.out.println("\nCipher Text: " + cipherText);
System.out.print("\nDeciphered text: ");
for (String d : digraphs) {
System.out.print(d);
}
System.out.println();
scanner.close();
}
}