Javax.crypto.BadPaddingException: Data must start with zero

Question

Actually, I didn't write the entire codes, most of it was written by someone here, and I only tried to add a method. Here:
public class RSAEncrypt {
    private KeyPair keys;
    private Cipher rsaCipher;
    public RSAEncrypt() throws GeneralSecurityException {
        KeyPairGenerator keygen = KeyPairGenerator.getInstance("RSA");
        keygen.initialize(512);
        keys = keygen.generateKeyPair();
        rsaCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
    public byte[] encrypt(byte[] message) throws GeneralSecurityException {
        rsaCipher.init(Cipher.ENCRYPT_MODE, keys.getPublic());
        return rsaCipher.doFinal(message);
    public byte[] decrypt(byte[] encryptedMessage) throws GeneralSecurityException {
         rsaCipher.init(Cipher.DECRYPT_MODE, keys.getPrivate());
         return rsaCipher.doFinal(encryptedMessage);
     * @param args
    public static void main(String[] args) throws Exception {
         String message = "The quick brown fox ran away";
         System.out.println("Message: " + message);
         byte[] encrypted = new RSAEncrypt().encrypt(message.getBytes());
        System.out.println("Cipher Text: " + HexBin.encode(encrypted));
        byte[] decrypted = new RSAEncrypt().decrypt(encrypted);
        System.out.println("Decrypted Text: " + decrypted);
}The idea is that the program should encrypt the String, "The quick brown fox ran away," which it does. But when it gets to this line:
byte[] decrypted = new RSAEncrypt().decrypt(encrypted);i get the error: javax.crypto.BadPaddingException: Data must start with zero.
But here's the funny thing: If I edit the codes so that the encryption and decryption are done in the constructor, it works! Here:
public class RSAEncrypt {
    private KeyPair keys;
    private Cipher rsaCipher;
    public RSAEncrypt() throws GeneralSecurityException {
        KeyPairGenerator keygen = KeyPairGenerator.getInstance("RSA");
        keygen.initialize(512);
        keys = keygen.generateKeyPair();
        rsaCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        rsaCipher.init(Cipher.ENCRYPT_MODE, keys.getPublic());
        String message = "The quick brown fox ran away";
        byte[] cipherText = rsaCipher.doFinal(message.getBytes());
        System.out.println(new BASE64Encoder().encode(cipherText));
        rsaCipher.init(Cipher.DECRYPT_MODE, keys.getPrivate());
        byte[] decryptedText = rsaCipher.doFinal(cipherText);
        String dText = new String(decryptedText);
        System.out.println(dText);
     * @param args
    public static void main(String[] args) throws Exception {
         new RSAEncrypt();
}So, I'm confused. The Data must start with zero error is coming up when I pass encrypted data to a method for decryption, but it doesn't come out when I run everything in one method or in the constructor. Why???
Also, when performing RSA encryption (or decryption) on a plaintext stored in a file (not a big file, just a file with probably one or two lines), this is what I do (and it works):
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pubKey);
CipherInputStream cis = new CipherInputStream(new FileInputStream(new File("message.txt")),cipher);My question is, I do see some people doing this as well:
cipher.doFinal(byteArray);The fact that I don't have this in my code when encrypting data from a file, that's ok, right? I don't need to do a ".doFinal()" method, do I?
Edited by: glenak on Aug 19, 2010 4:26 AM

Answer 1

glenak wrote:
I don't quite understand, but if you mean this:
String message = "The quick brown fox ran away";
System.out.println("Message: " + message);
RSAEncrypt rsaEncrypt = new RSAEncrypt();
Creates and instance of RSAEncrypt with a new random RSA key pair.
byte[] encrypted = rsaEncrypt.encrypt(message.getBytes());Encrypts with the random public key created in the first instance.
System.out.println("Cipher Text: " + HexBin.encode(encrypted));
RSAEncrypt rsaDecrypt = new RSAEncrypt();Creates and second instance of RSAEncrypt with a new random RSA key pair nothing to do with the first instance.
byte[] decrypted = rsaDecrypt.decrypt(encrypted);Attempts to decrypt the ciphertext created with the public key of the first instance using the private key of the second, and totally unrelated, instance.
System.out.println("Decrypted Text: " + decrypted);I still get the "Data must start with zero" error.
If you could show me an example of what you mean, it would help very muchNo example is required. You cannot encrypt with the public key of one key pair and expect to decrypt with the private key of a totally independent key pair.