解密返回空字符串

Question

I am trying to encrypt a message from android then decrypt it in web.

Firstly, I generate a key using Javascript and store it in my database

var text = "";
var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

for( var i=0; i <10; i++ )
    text += possible.charAt(Math.floor(Math.random() * possible.length));
secondaryDatabase.ref().update({
    [displayName]:text
})

Secondly, I encrypt the message in Java by retrieving the message in the input field and the key from the database.

message.setText(message);
String key = String.valueOf(dataSnapshot);
encryptedI = AESCrypt.encrypt(key,message);

For simplicity purpose, lets just take it that message is "hello world " and the key is password

String message = "hello world";
String key = "password";
encryptedI = AESCrypt.encrypt(key,message);

Thirdly, i stored the encrypted message in the database.

mRef.child(uid).child("encryptedmessage").setValue(encryptedI);

Lastly, I decrypted the message using the key both retrieved from database with Cryto-js on javascript but it returns a empty string

var decrypted = CryptoJS.AES.decrypt(message,key);
var decryptedvalue=decrypted.toString(CryptoJS.enc.Utf8)

I have checked that the key and encrypted message used is the same, I even decrypted in Java to make sure that the encryption is done correctly. I used https://github.com/scottyab/AESCrypt-Android for encryption in Android while cryto-js for decryption in javascript

The question is why does it returns a empty string and how can i solve it.

Answer 1

You cannot just get two different libraries together and hope they will be compatible. Although AES in itself has been standardized, it has only has been standardized as a block cipher with three possible key sizes: AES-128, AES-192 and AES-256. To actually encrypt something you need a mode of operation and possibly padding. If you want to use a password instead of a key you need to derive a key from the password, for instance using PBKDF2.

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As the two libraries you've mentioned are both weak and badly specified I strongly urge you to find two compatible password based encryption libraries for Java and JavaScript.

It should be possible to perform PBKDF2 using both Crypto-JS and Android. I would not use a standalone crypto library though, just use the functionality already available through Android. Don't forget to implement a high iteration count and make sure that the passwords used are up to par. If you want any kind of security you want to use authenticated encryption or implement that yourself using HMAC-SHA256 or similar.

As I don't know your use cases or threat model (and I'm not planning to) just see this as general hints in the right direction, not as solid security advice.