CODEWITHSUNDEEP
androidaes
raman
raman

Reputation: 335

AES Decryption not working

In my project i am working on AES encryption and Decryption.i have used this algorithm to encrypt and decryption a string and storing the string in the sq-lite database.Now i get that encrypted key from database and try to decryption it but it shows an Exception (pad Block corrupted).I am converting the Encrypted string into the bytes by using 

 public static byte[] hexStringToByteArray(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                             + Character.digit(s.charAt(i+1), 16));}
    return data;
}

and getting the correct Bytes but while converted into the String it shows 'pad block corrupted'. Thanks in advance.really appreciate if find answer. my code is 

dh=new data_helper(Resy.this);
        mac_db=dh.getData();

//        getdata=mac_db.toString();

        KeyGenerator kgen;
        try {
            kgen = KeyGenerator.getInstance("AES");

             kgen.init(128); // 192 and 256 bits may not be available

  // Generate the secret key specs.
                SecretKey skey = kgen.generateKey();
                byte[] raw = skey.getEncoded();

                SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");


                // Instantiate the cipher

                Cipher cipher = Cipher.getInstance("AES");
                         getdata=mac_db.toString();
//              byte g1[]=getdata.getBytes();
//              System.out.println(g1);

        byte b[]=hexStringToByteArray(getdata);
        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
        byte[] m1=cipher.doFinal(b);   // here pad block corrupt exception came.
                String originalString_mac = new String(original_macadress);
                Toast.makeText(getApplicationContext(),"Original : " +originalString_mac + " " + asHex(original_macadress) , Toast.LENGTH_LONG).show();

Upvotes: 0

Views: 2904

Answers (2)

Nikolay Elenkov
Nikolay Elenkov

Reputation: 52956

First make sure your data is the correct length and there are not errors in your hex conversion. Next you need to use the same key for encryption and decryption. From the code above it looks like you are generating a new key every time. This will not work: even if the decryption succeeds you will get something very different from the original plain text. Then Cipher cipher = Cipher.getInstance("AES"); might produce a cipher using a random IV, which you will need to decrypt. It is better to specify an explicit transformation string like so:

Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding");

In short, find a working sample and start there. Something like this.

Upvotes: 2

Rahul garg
Rahul garg

Reputation: 9362

you have to do Base64 encoding of it to get proper AES encrypt/decrypt to work.

Do it as follows.

For encrytion : Original String --> Aes encryption > base64 encode --->(encrypted string)

For decryption : encrypted string ---> base64 decode > aes decryption ---> Original String

Upvotes: 1

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