Resolve build errors & cleanup structure (#2334)

Ciphers/AESEncryption.java

@@ -0,0 +1,97 @@
+package Ciphers;
+
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+import javax.crypto.BadPaddingException;
+import javax.crypto.Cipher;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.KeyGenerator;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.SecretKey;
+
+/**
+ * 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);
+  }
+}