Add XOR Cipher (#5490)

src/main/java/com/thealgorithms/ciphers/XORCipher.java

@@ -0,0 +1,41 @@
+package com.thealgorithms.ciphers;
+
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
+import java.util.HexFormat;
+
+/**
+ * A simple implementation of XOR cipher that, given a key, allows to encrypt and decrypt a plaintext.
+ *
+ * @author <a href="https://github.com/lcsjunior">lcsjunior</a>
+ *
+ */
+public final class XORCipher {
+
+    private static final Charset CS_DEFAULT = StandardCharsets.UTF_8;
+
+    private XORCipher() {
+    }
+
+    public static byte[] xor(final byte[] inputBytes, final byte[] keyBytes) {
+        byte[] outputBytes = new byte[inputBytes.length];
+        for (int i = 0; i < inputBytes.length; ++i) {
+            outputBytes[i] = (byte) (inputBytes[i] ^ keyBytes[i % keyBytes.length]);
+        }
+        return outputBytes;
+    }
+
+    public static String encrypt(final String plainText, final String key) {
+        byte[] plainTextBytes = plainText.getBytes(CS_DEFAULT);
+        byte[] keyBytes = key.getBytes(CS_DEFAULT);
+        byte[] xorResult = xor(plainTextBytes, keyBytes);
+        return HexFormat.of().formatHex(xorResult);
+    }
+
+    public static String decrypt(final String cipherText, final String key) {
+        byte[] cipherBytes = HexFormat.of().parseHex(cipherText);
+        byte[] keyBytes = key.getBytes(CS_DEFAULT);
+        byte[] xorResult = xor(cipherBytes, keyBytes);
+        return new String(xorResult, CS_DEFAULT);
+    }
+}