/** Signs a byte[] with a Private Key
     *
     * @param unsigned the unsigned byte array
     * @param privateKey the PrivateKey to sign with
     *
     * @returns a concatenated byte array of the signature and data that was signed
     */
    static byte[] sign(byte[] unsigned, PrivateKey privateKey) {
        //System.out.println("Signing " + unsigned.length + " bytes");
        try {
            Signature signer = Signature.getInstance("SHA1withRSA");
            signer.initSign(privateKey);
            signer.update(unsigned);
            byte[] signature = signer.sign();
            // System.out.println("Size of signature is " + signature.length);
            // Size of signature is 256
            byte[]sigAndData    = Functions.append(signature, unsigned);
            return sigAndData;
        } catch (InvalidKeyException ex) {
            ex.printStackTrace();
        } catch (NoSuchAlgorithmException ex) {
            ex.printStackTrace();
        } catch (SignatureException ex) {
            ex.printStackTrace();
        }
       return null;
    }