Change project structure to a Maven Java project + Refactor (#2816)

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

@@ -0,0 +1,97 @@
+package com.thealgorithms.ciphers;
+
+import javax.crypto.*;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+
+/**
+ * This example program shows how AES encryption and decryption can be done in
+ * Java. Please note that secret key and encrypted text is unreadable binary and
+ * hence in the following program we display it in hexadecimal format of the
+ * underlying bytes.
+ */
+public class AESEncryption {
+
+    private static final char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
+
+    /**
+     * 1. Generate a plain text for encryption 2. Get a secret key (printed in
+     * hexadecimal form). In actual use this must by encrypted and kept safe.
+     * The same key is required for decryption.
+     */
+    public static void main(String[] args) throws Exception {
+        String plainText = "Hello World";
+        SecretKey secKey = getSecretEncryptionKey();
+        byte[] cipherText = encryptText(plainText, secKey);
+        String decryptedText = decryptText(cipherText, secKey);
+
+        System.out.println("Original Text:" + plainText);
+        System.out.println("AES Key (Hex Form):" + bytesToHex(secKey.getEncoded()));
+        System.out.println("Encrypted Text (Hex Form):" + bytesToHex(cipherText));
+        System.out.println("Descrypted Text:" + decryptedText);
+    }
+
+    /**
+     * gets the AES encryption key. In your actual programs, this should be
+     * safely stored.
+     *
+     * @return secKey (Secret key that we encrypt using it)
+     * @throws NoSuchAlgorithmException (from KeyGenrator)
+     */
+    public static SecretKey getSecretEncryptionKey() throws NoSuchAlgorithmException {
+        KeyGenerator aesKeyGenerator = KeyGenerator.getInstance("AES");
+        aesKeyGenerator.init(128); // The AES key size in number of bits
+        return aesKeyGenerator.generateKey();
+    }
+
+    /**
+     * Encrypts plainText in AES using the secret key
+     *
+     * @return byteCipherText (The encrypted text)
+     * @throws NoSuchPaddingException (from Cipher)
+     * @throws NoSuchAlgorithmException (from Cipher)
+     * @throws InvalidKeyException (from Cipher)
+     * @throws BadPaddingException (from Cipher)
+     * @throws IllegalBlockSizeException (from Cipher)
+     */
+    public static byte[] encryptText(String plainText, SecretKey secKey)
+            throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException,
+            IllegalBlockSizeException, BadPaddingException {
+        // AES defaults to AES/ECB/PKCS5Padding in Java 7
+        Cipher aesCipher = Cipher.getInstance("AES");
+        aesCipher.init(Cipher.ENCRYPT_MODE, secKey);
+        return aesCipher.doFinal(plainText.getBytes());
+    }
+
+    /**
+     * Decrypts encrypted byte array using the key used for encryption.
+     *
+     * @return plainText
+     */
+    public static String decryptText(byte[] byteCipherText, SecretKey secKey)
+            throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException,
+            IllegalBlockSizeException, BadPaddingException {
+        // AES defaults to AES/ECB/PKCS5Padding in Java 7
+        Cipher aesCipher = Cipher.getInstance("AES");
+        aesCipher.init(Cipher.DECRYPT_MODE, secKey);
+        byte[] bytePlainText = aesCipher.doFinal(byteCipherText);
+        return new String(bytePlainText);
+    }
+
+    /**
+     * Convert a binary byte array into readable hex form Old library is
+     * deprecated on OpenJdk 11 and this is faster regarding other solution is
+     * using StringBuilder
+     *
+     * @return hexHash
+     */
+    public static String bytesToHex(byte[] bytes) {
+        char[] hexChars = new char[bytes.length * 2];
+        for (int j = 0; j < bytes.length; j++) {
+            int v = bytes[j] & 0xFF;
+            hexChars[j * 2] = HEX_ARRAY[v >>> 4];
+            hexChars[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
+        }
+        return new String(hexChars);
+    }
+}