javax.crypto.IllegalBlockSizeException when trying to use AESCrypt

Question

I'm using this library to save an username and password encrypted to SharedPreferences (pretty sure no app can access my SharedPreferences, but anyway this is a requirement).

I did this code, because I also need to use my own IV and key:

public class EncryptionHandler {
    private final static String PREFS_FILE_NAME = "SAVED_CREDENTIALS";
    private final static String MSG_FORMAT = "%s;%s";

    public static void saveCredentials(Context context, String username, String password) {
        try {
            String formattedMsg = String.format(MSG_FORMAT, username, password);

            String encryptedMsg = new String(AESCrypt.encrypt(getKeySpec(), getIV(), stringToBytes(formattedMsg)));

            //save encryptedMsg to SharedPreferences
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static byte[] stringToBytes(String msg) {
        return msg.getBytes(Charset.forName("UTF-8"));
    }

    public static LoginCredentials getSavedCredentials(Context context) {
        try {
            String encryptedMsg = getSharedPreferences(context).getString(PREFS_FILE_NAME, "");
            String messageAfterDecrypt = new String(AESCrypt.decrypt(getKeySpec(), getIV(), stringToBytes(encryptedMsg)));

            String[] split = messageAfterDecrypt.split(";");

            //irrelevant code

            return credentials;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    private static byte[] ivBytes = {0x00, 0x12, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x23, 0x52, 0x00, 0x00, 0x00, 0x00};

    private static SecretKeySpec secretKeySpec = new SecretKeySpec(ivBytes, "AES");

    private static SecretKeySpec getKeySpec() throws Exception {
        return secretKeySpec;
    }

    private static byte[] getIV() {
        return ivBytes;
    }
}

Related questions suggest to use Base64, but I really need to use AESCrypt (it's already working on the iOS app so I have to make the same).

The exception I get is:

javax.crypto.IllegalBlockSizeException: error:1e06b07b:Cipher functions:EVP_DecryptFinal_ex:WRONG_FINAL_BLOCK_LENGTH
    at com.android.org.conscrypt.NativeCrypto.EVP_CipherFinal_ex(Native Method)
    at com.android.org.conscrypt.OpenSSLCipher$EVP_CIPHER.doFinalInternal(OpenSSLCipher.java:568)
    at com.android.org.conscrypt.OpenSSLCipher.engineDoFinal(OpenSSLCipher.java:350)
    at javax.crypto.Cipher.doFinal(Cipher.java:1502)
    at com.scottyab.aescrypt.AESCrypt.decrypt(AESCrypt.java:158)
    at com.mypackage.encryption.EncryptionHandler.getSavedCredentials(EncryptionHandler.java:48)

The exception happens in this line, when I'm trying to read and decrypt:

String messageAfterDecrypt = new String(AESCrypt.decrypt(getKeySpec(), getIV(), stringToBytes(encryptedMsg)));

Edit:

I understood that doing new String(someBytes) doesn't make sense, so I also tried converting the bytes to Base64:

public static void saveCredentials(Context context, String username, String password) {
    try {
        String formattedMsg = String.format(MSG_FORMAT, username, password);
        byte[] bytes = stringToBytes(formattedMsg);
        byte[] encryptedBytes = AESCrypt.encrypt(getKeySpec(), getIV(), bytes);
        String encryptedMsg = Base64.encodeToString(encryptedBytes, Base64.NO_WRAP);

        //save to sharedpreferences
    } catch (Exception e) {
        e.printStackTrace();
    }
}

private static byte[] stringToBytes(String msg) {
    byte[] bytes = msg.getBytes(Charset.forName("UTF-8"));

    return bytes;
}

public static LoginCredentials getSavedCredentials(Context context) {
    try {
        String base64Msg = getSharedPreferences(context).getString(PREFS_FILE_NAME, "");
        byte[] bytes = Base64.decode(base64Msg, Base64.NO_WRAP);
        byte[] decryptedBytes = AESCrypt.decrypt(getKeySpec(), getIV(), bytes);

        String messageAfterDecrypt = ????;

        //...
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

I don't get errors but I don't know how to get the final, decrypted message (line String messageAfterDecrypt = ????;)

Could you let us know which line `EncryptionHandler.java:48` is? — Matt Clark, Nov 24 '16 at 04:24
This line is your real problem: `String encryptedMsg = new String(AESCrypt.encrypt(getKeySpec(), getIV(), stringToBytes(formattedMsg)));` String is not a container for arbitrary byte sequences. If you must have a String result then you need to base64 encode the `byte[]` returned from AESCrypt.encrypt() — President James K. Polk, Nov 24 '16 at 04:43
@JamesKPolk I'm trying that approach now. I edited the question, in case you can help me in that final step that would be great, thanks! — RominaV, Nov 24 '16 at 05:20
@JamesKPolk I used `new String(decryptedBytes, "UTF-8");` , and it works. But is it the right way to do it? — RominaV, Nov 24 '16 at 06:25
You can perform *character-encoding/decoding on the plaintext (i.e. the decrypted bytes) without any problems. The problem occurred when you presumed a certain character-encoding on the *ciphertext*, the encrypted byte array. You need to use (binary to text) encoding such as base 64 for that if you need a string. — Maarten Bodewes, Nov 28 '16 at 20:01
@AmitVaghela my last comment is what I ended up using (from what I can remember) `new String(decryptedBytes, "UTF-8");` — RominaV, Aug 09 '18 at 23:42
but @RominaV it sometimes gives same error. i have used that. — Amit Vaghela, Aug 10 '18 at 04:59

javax.crypto.IllegalBlockSizeException when trying to use AESCrypt

0 Answers0