如何检查字符串是否在Java中加密？

Question

I am using the following code for encrypting my data:

public static String encrypt(String clearData, String password)
            throws UnsupportedEncodingException {
        byte[] bytes = encrypt(clearData.getBytes("UTF-8"), password);
        return Base64.encodeBytes(bytes);
    }


public static byte[] encrypt(byte[] clearData, String password)
            throws UnsupportedEncodingException {
        byte[] passwordKey = encodeDigest(password);
        try {
            aesCipher = Cipher.getInstance(CIPHER_TRANSFORMATION);
        } catch (NoSuchAlgorithmException e) {
            Log.e(TAG, "No such algorithm " + CIPHER_ALGORITHM, e);
        } catch (NoSuchPaddingException e) {
            Log.e(TAG, "No such padding PKCS5", e);
        }
        secretKey = new SecretKeySpec(passwordKey, CIPHER_ALGORITHM);

        try {
            aesCipher.init(Cipher.ENCRYPT_MODE, secretKey, ivParameterSpec);
        } catch (InvalidKeyException e) {
            Log.e(TAG, "Invalid key", e);
            return null;
        } catch (InvalidAlgorithmParameterException e) {
            Log.e(TAG, "Invalid algorithm " + CIPHER_ALGORITHM, e);
            return null;
        }

        byte[] encryptedData;
        try {
            encryptedData = aesCipher.doFinal(clearData);
        } catch (IllegalBlockSizeException e) {
            Log.e(TAG, "Illegal block size", e);
            return null;
        } catch (BadPaddingException e) {
            Log.e(TAG, "Bad padding", e);
            return null;
        }
        return encryptedData;
    }

How can I check that an input string data is encrypted or not without using try-catch ?

Update:

for example the user gives me a string. If it is encrypted I store it in database if not I encrypt it then store.

Answer 1

Well, with the code you've written, you could be fairly confident that you've got an encrypted string by simply checking if it's a valid Base64 encoding .

Broadly speaking however, if you could tell for sure a string was encrypted simply by looking at it, that would mean the encryption was very weak. Properly encrypted data is indiscernible from random noise.

If the user can send you arbitrary encrypted or clear-text data they'll need to tell you which it is.

Answer 2

You Can't; you can just play the odds(which are in your favor due to the complexity of padding algorithms which make cipher texts very non random (data-authenticity-checking-wise)).

The reason why is that you are inputting data with infinite number of combinations which indeed include the combinations that would produce valid results after decryption(but are never really encrypted);

No matter how rare certain combinations are infinity has it.

and also containing only base64 characters means it contains only base64 characters; nothing more. (it definitely doesn't mean it's encrypted data!)

Answer 3

This can be done in two ways.

1. Anyway you might have written some logic for encryption and decryption. Now you can try with your decryption and see weather it was decrypted properly or not.

2. You can try to decode with base64 and see weather you can able to do it without exception. Code will be like following.

   enter code here

 private boolean isBase64(String input) { try { new String(Base64.getDecoder().decode(input)); return true; } catch (Exception e) { return false; } }