Encryption/Decryption in Android

Question

I have done encryption in android with a static password i.e. "encrypt". The encryption works fine and encrypts the data. But when i try to decrypt the encrypted text it does not show. The code to decrypt is as follow.

public String decrypt(String msg, String inputPassword) throws Exception{
    SecretKeySpec key= generateKey(inputPassword);
    Cipher c = Cipher.getInstance(AES);
    c.init(Cipher.DECRYPT_MODE, key);
    byte[] decodedValue= Base64.decode(msg, Base64.DEFAULT);

    /*If this line is present the encrypted message is not seen*/
    byte[] decValue = c.doFinal(Base64.decode(decodedValue, 
Base64.DEFAULT));
    String decryptedValue = new String(decodedValue);
    String decryptedValue = new String(decValue, StandardCharsets.UTF_8);
    return decryptedValue;
}

When the code (below the comment) is enabled. The message is not displayed. But when the line is commented. This is shown in the message box

After the code is commented.

This is the encrypt and key generate methods.

public String encrypt(String message, String inputPassword) throws Exception{
    SecretKeySpec key = generateKey(inputPassword);
    Cipher c = Cipher.getInstance(AES);
    c.init(c.ENCRYPT_MODE, key);
    byte[] encVal = c.doFinal(message.getBytes());
    String encryptedValue = Base64.encodeToString(encVal, Base64.DEFAULT);
    return encryptedValue;
}

//For generating key for encryption
public SecretKeySpec generateKey(String inputPassword) throws  Exception{
    final MessageDigest digest = MessageDigest.getInstance("SHA-256");
    byte[] bytes = inputPassword.getBytes("UTF-8");
    digest.update(bytes, 0, bytes.length);
    byte[] key = digest.digest();
    SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
    return secretKeySpec;
}

The log is follow enter image description here

Also the API level is not maintained... I don't know where to setup this as well. enter image description here

The exception handler shows the error in this line byte[] decValue = c.doFinal(decodedValue); — newbie dev, Feb 07 '19 at 08:26
are you using the same password while encrypting and decryption? if not you are not going to get the desired output. Test the code by creating a normal java class. — Durgesh Kumar, Feb 07 '19 at 08:33
Why do you base64-decode your message twice in your decrypt method? I don't see you encode twice in the encrypt method after all... — Maarten Bodewes, Feb 07 '19 at 14:42
@MaartenBodewes. Even when i use that one time. The error and the problem is same. — newbie dev, Feb 07 '19 at 15:00
Well, if I use `"AES/ECB/PKCS5Padding"` this works perfectly. Of course, since you've forgot to specify the `AES` constant but do not use an IV, I presume you are using ECB mode or just `"AES"` as cipher. — Maarten Bodewes, Feb 07 '19 at 15:09

Bach Vu · Answer 1 · 2019-02-07T08:51:03.640

1

Could you try changing this

String decryptedValue = new String(decodedValue)

to this

String decryptedValue = new String(decodedValue, StandardCharsets.UTF_8)

And for your error, try changing to this

c.doFinal(Base64.decode(decodedValue, Base64.DEFAULT))

edited Feb 07 '19 at 08:51

answered Feb 07 '19 at 08:19

Bach Vu

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The message is not displayed when the is not commented. After this line nothing executes byte[] decValue = c.doFinal(decodedValue); – newbie dev Feb 07 '19 at 08:26
still the same error. There seems to have problem in decrypt method . It says that it doesnot take API less than 24 or so – newbie dev Feb 07 '19 at 13:25
Maybe this can be useful for you https://stackoverflow.com/questions/13433529/android-4-2-broke-my-encrypt-decrypt-code-and-the-provided-solutions-dont-work – Bach Vu Feb 08 '19 at 03:09

Encryption/Decryption in Android

1 Answers1