Preferred method for AES Encryption and Decryption in Java

Question

I have written the following two methods that encrypt and decrypt a given token:

private static final String ALGORITHM_TYPE = "AES";
private static final String CIPHER_TRANSFORMATION = "AES/CBC/PKCS5Padding";
private static byte[] INITIALIZATION_VECTOR = new byte[] {
 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
};
public String encrypt(String token) {
 Cipher cipher = null;
 SecretKey key = null;
 String tokenAsHex = null;
 byte[] encryptedToken = null;
 byte[] sksKey = getKeyAsByteArray(KEY); // SecretKeySpec key.
 try {
 key = new SecretKeySpec(sksKey, ALGORITHM_TYPE);
 AlgorithmParameterSpec paramSpec = new IvParameterSpec(INITIALIZATION_VECTOR);
 cipher = Cipher.getInstance(CIPHER_TRANSFORMATION);
 cipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
 encryptedToken = cipher.doFinal(Base64.encodeBase64(token.getBytes("UTF-8")));
 } catch (Exception e) {
 throw new EncryptionException(e);
 }
 return Base64.encodeBase64String(encryptedToken).toLowerCase();
}
public String decrypt(String token) throws EncryptionException {
 Cipher cipher = null;
 SecretKey key = null;
 byte[] decryptedToken = null;
 byte[] sksKey = getKeyAsByteArray(KEY); // SecretKeySpec key.
 try {
 key = new SecretKeySpec(sksKey, ALGORITHM_TYPE); 
 AlgorithmParameterSpec paramSpec = new IvParameterSpec(INITIALIZATION_VECTOR);
 cipher = Cipher.getInstance(CIPHER_TRANSFORMATION);
 cipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
 decryptedToken = cipher.doFinal(Base64.decodeBase64(token));
 } catch(Exception e){
 throw new EncryptionException(e); 
 }
 if (decryptedToken == null) {
 throw new EncryptionException("Unable to decrypt the following token: " + token);
 }
 return Base64.encodeBase64String(decryptedToken);
}

However, I am unable to successfully decrypt any string encrypted with with the encrypt method. I searched for similar issues and the closest found is here: Encrypt and decrypt with AES and Base64 encoding. Even after using a similar strategy, I am still unable to decrypt the encrypted string. Any help is appreciated diagnosing what the issue maybe.

Also, I am encoding the encrypted/decrypted byte array using Base64 instead of creating a new String as the latter results in a unsafe URL string.

Answer 1

You're encrypting a base64-encoding, and then re-base64-encoding it, and decrypting a base64-decoding, and then for some reason base64-encoding that. It doesn't make sense. You should be:

1. base64-encoding the encryption, i.e. essentially return Base64.encode(cipher.doFinal(...))
2. Decrypting the base64-decoding of (1), i.e. essentially return cipher.doFinal(Base64.decode(...))

• stavarotti: I updated my code accordingly however, I am still getting the same error as before: Given final block not properly padded
• stavarotti: I had an oversight on my part however, the steps you provided resolved my issue. Thanks.