It seems the basic encryption/decryption functions are unreliable,

Question

I am having trouble with the following code. I am just using the resources provided in the latest SDK.
My code compiles and appears to run without generating any errors. The problem is that I have yet to get back the same string as I entered.
I am following an example in a J2EE security text, but the example seems to be incomplete.
I suspect the problem is not so much with the encryption and decryption functions per se, but rather a problem, not discussed in any of the references I have read, with managing and storing the cipher text. Can anyone confirm or refute my suspicions, and/or show me how to modify my code so that it invariably results in the decrypted string being identical to the original plain text string?
It looks like the cipher text I will get will invariably be binary data, and not just sequences of alphanumeric characters. Can anyone tell me where I can find a function that will generate a unique integer for an arbitrary length byte array, or how one might be constructed? Or, if there is one, perhaps someone can tell me if there is a good encryption algorithm that will create cipher text that consists only of a sequence of alphanumeric characters.
Here are the two relevant functions, along with the relevant declarations of class data members:
    private void encryptBTNMouseClicked(java.awt.event.MouseEvent evt) {
        if ( !OK2run ) return;
        String tmp = PlainTextArea.getText();
        int length = tmp.length();
        if (length < 20) {
            tmp = new String("We need a longer string. we are trying to understand encryption and decryption.");
            PlainTextArea.setText(tmp);
        try {
            myCypher.init(Cipher.ENCRYPT_MODE,sk);
        } catch (java.security.InvalidKeyException ivke) {
            PlainTextArea.setText("Problem with key!");
        byte[] pBytes = tmp.getBytes();
        byte[] cBytes = null;
        try {
            cBytes = myCypher.doFinal(pBytes);
        } catch (javax.crypto.BadPaddingException nspe) {
            CypherTextArea.setText("Problem with padding!");
        } catch (javax.crypto.IllegalBlockSizeException ibse) {
            CypherTextArea.setText("Problem with block size!");
        tmp = new String(cBytes);
        CypherTextArea.setText(tmp);
        tmp = PlainTextArea.getText() + "\n\nWrapped Key = " + wrappedKey;
        PlainTextArea.setText(tmp);
        decryptBTN.enable();
    private void decryptBTNMouseClicked(java.awt.event.MouseEvent evt) {
        String tmp = CypherTextArea.getText();
        byte[] cBytes = tmp.getBytes();
        try {
            myCypher.init(Cipher.DECRYPT_MODE,sk);
        } catch (java.security.InvalidKeyException ivke) {
            DecypheredTextArea.setText("Problem with key!");
        byte[] dBytes = null;
        try {
            dBytes = myCypher.doFinal(cBytes);
        } catch (javax.crypto.BadPaddingException nspe) {
            CypherTextArea.setText("Problem with padding!");
        } catch (javax.crypto.IllegalBlockSizeException ibse) {
            DecypheredTextArea.setText("Problem with block size!");
        tmp = new String(dBytes);
        DecypheredTextArea.setText(tmp);
    private javax.crypto.KeyGenerator kg;
    private boolean OK2run = false;
    private javax.crypto.SecretKey sk = null;
    private javax.crypto.Cipher myCypher = null;
    private byte[] theBytes = null;
    private String wrappedKey = null;Thanks,
Ted

Answer 1

One should not try to create a String object from the encrypted bytes using
tmp = new String(cBytes);
because it is not guaranteed to be reversible.
If you need a String then use Base64 or Hex encoding. Google for Jakarta Commons Codec.