diff --git a/DIRECTORY.md b/DIRECTORY.md
index fd50b2914cff..b621216da7f1 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -27,6 +27,7 @@
* [NonRepeatingNumberFinder](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/NonRepeatingNumberFinder.java)
* [NumbersDifferentSigns](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/NumbersDifferentSigns.java)
* [ReverseBits](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/ReverseBits.java)
+ * [SetKthBit](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/SetKthBit.java)
* [SingleBitOperations](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/bitmanipulation/SingleBitOperations.java)
* ciphers
* a5
@@ -44,6 +45,7 @@
* [ColumnarTranspositionCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ColumnarTranspositionCipher.java)
* [DES](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/DES.java)
* [HillCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/HillCipher.java)
+ * [PlayfairCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java)
* [Polybius](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Polybius.java)
* [ProductCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ProductCipher.java)
* [RSA](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/RSA.java)
@@ -585,6 +587,7 @@
* [NonRepeatingNumberFinderTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/NonRepeatingNumberFinderTest.java)
* [NumbersDifferentSignsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/NumbersDifferentSignsTest.java)
* [ReverseBitsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/ReverseBitsTest.java)
+ * [SetKthBitTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/SetKthBitTest.java)
* [SingleBitOperationsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/bitmanipulation/SingleBitOperationsTest.java)
* ciphers
* a5
@@ -592,6 +595,7 @@
* [BlowfishTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/BlowfishTest.java)
* [CaesarTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/CaesarTest.java)
* [DESTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/DESTest.java)
+ * [PlayfairTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/PlayfairTest.java)
* [PolybiusTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/PolybiusTest.java)
* [RSATest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/RSATest.java)
* [SimpleSubCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/SimpleSubCipherTest.java)
diff --git a/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java b/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java
new file mode 100644
index 000000000000..76ceb6dbce31
--- /dev/null
+++ b/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java
@@ -0,0 +1,128 @@
+package com.thealgorithms.ciphers;
+
+public class PlayfairCipher {
+
+ private char[][] matrix;
+ private String key;
+
+ public PlayfairCipher(String key) {
+ this.key = key;
+ generateMatrix();
+ }
+
+ public String encrypt(String plaintext) {
+ plaintext = prepareText(plaintext.replace("J", "I"));
+ StringBuilder ciphertext = new StringBuilder();
+ for (int i = 0; i < plaintext.length(); i += 2) {
+ char char1 = plaintext.charAt(i);
+ char char2 = plaintext.charAt(i + 1);
+ int[] pos1 = findPosition(char1);
+ int[] pos2 = findPosition(char2);
+ int row1 = pos1[0];
+ int col1 = pos1[1];
+ int row2 = pos2[0];
+ int col2 = pos2[1];
+ if (row1 == row2) {
+ ciphertext.append(matrix[row1][(col1 + 1) % 5]);
+ ciphertext.append(matrix[row2][(col2 + 1) % 5]);
+ } else if (col1 == col2) {
+ ciphertext.append(matrix[(row1 + 1) % 5][col1]);
+ ciphertext.append(matrix[(row2 + 1) % 5][col2]);
+ } else {
+ ciphertext.append(matrix[row1][col2]);
+ ciphertext.append(matrix[row2][col1]);
+ }
+ }
+ return ciphertext.toString();
+ }
+
+ public String decrypt(String ciphertext) {
+ StringBuilder plaintext = new StringBuilder();
+ for (int i = 0; i < ciphertext.length(); i += 2) {
+ char char1 = ciphertext.charAt(i);
+ char char2 = ciphertext.charAt(i + 1);
+ int[] pos1 = findPosition(char1);
+ int[] pos2 = findPosition(char2);
+ int row1 = pos1[0];
+ int col1 = pos1[1];
+ int row2 = pos2[0];
+ int col2 = pos2[1];
+ if (row1 == row2) {
+ plaintext.append(matrix[row1][(col1 + 4) % 5]);
+ plaintext.append(matrix[row2][(col2 + 4) % 5]);
+ } else if (col1 == col2) {
+ plaintext.append(matrix[(row1 + 4) % 5][col1]);
+ plaintext.append(matrix[(row2 + 4) % 5][col2]);
+ } else {
+ plaintext.append(matrix[row1][col2]);
+ plaintext.append(matrix[row2][col1]);
+ }
+ }
+ return plaintext.toString();
+ }
+
+ private void generateMatrix() {
+ String keyWithoutDuplicates = removeDuplicateChars(key + "ABCDEFGHIKLMNOPQRSTUVWXYZ");
+ matrix = new char[5][5];
+ int index = 0;
+ for (int i = 0; i < 5; i++) {
+ for (int j = 0; j < 5; j++) {
+ matrix[i][j] = keyWithoutDuplicates.charAt(index);
+ index++;
+ }
+ }
+ }
+
+ private String removeDuplicateChars(String str) {
+ StringBuilder result = new StringBuilder();
+ for (int i = 0; i < str.length(); i++) {
+ if (result.indexOf(String.valueOf(str.charAt(i))) == -1) {
+ result.append(str.charAt(i));
+ }
+ }
+ return result.toString();
+ }
+
+ private String prepareText(String text) {
+ text = text.toUpperCase().replaceAll("[^A-Z]", "");
+ StringBuilder preparedText = new StringBuilder();
+ char prevChar = '\0';
+ for (char c : text.toCharArray()) {
+ if (c != prevChar) {
+ preparedText.append(c);
+ prevChar = c;
+ } else {
+ preparedText.append('X').append(c);
+ prevChar = '\0';
+ }
+ }
+ if (preparedText.length() % 2 != 0) {
+ preparedText.append('X');
+ }
+ return preparedText.toString();
+ }
+
+ private int[] findPosition(char c) {
+ int[] pos = new int[2];
+ for (int i = 0; i < 5; i++) {
+ for (int j = 0; j < 5; j++) {
+ if (matrix[i][j] == c) {
+ pos[0] = i;
+ pos[1] = j;
+ return pos;
+ }
+ }
+ }
+ return pos;
+ }
+
+ public void printMatrix() {
+ System.out.println("\nPlayfair Cipher Matrix:");
+ for (int i = 0; i < 5; i++) {
+ for (int j = 0; j < 5; j++) {
+ System.out.print(matrix[i][j] + " ");
+ }
+ System.out.println();
+ }
+ }
+}
diff --git a/src/test/java/com/thealgorithms/ciphers/PlayfairTest.java b/src/test/java/com/thealgorithms/ciphers/PlayfairTest.java
new file mode 100644
index 000000000000..5562241b48db
--- /dev/null
+++ b/src/test/java/com/thealgorithms/ciphers/PlayfairTest.java
@@ -0,0 +1,37 @@
+package com.thealgorithms.ciphers;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+public class PlayfairTest {
+
+ @Test
+ public void testEncryption() {
+ PlayfairCipher playfairCipher = new PlayfairCipher("KEYWORD");
+
+ String plaintext = "HELLO";
+ String encryptedText = playfairCipher.encrypt(plaintext);
+ assertEquals("GYIZSC", encryptedText);
+ }
+
+ @Test
+ public void testDecryption() {
+ PlayfairCipher playfairCipher = new PlayfairCipher("KEYWORD");
+
+ String encryptedText = "UDRIYP";
+ String decryptedText = playfairCipher.decrypt(encryptedText);
+ assertEquals("NEBFVH", decryptedText);
+ }
+
+ @Test
+ public void testEncryptionAndDecryption() {
+ PlayfairCipher playfairCipher = new PlayfairCipher("KEYWORD");
+
+ String plaintext = "PLAYFAIR";
+ String encryptedText = playfairCipher.encrypt(plaintext);
+ String decryptedText = playfairCipher.decrypt(encryptedText);
+
+ assertEquals(plaintext, decryptedText);
+ }
+}
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