BTW, this code would have trouble sending messages between locales. I had a quick look at the encryption code, and found this:

    public static String sign(PrivateKey privateKey, 
         String data, String derivedPassword) {
        return sign(privateKey, data.getBytes(), derivedPassword.getBytes());
    }

... which of course uses the current platform's character set, not a consistent one across platforms. Definitely not what you want in this kind of application (unless Android is UTF-8 in all countries? I don't code for it). That was in this class:

https://github.com/surespot/android/blob/master/src/com/twof...

...but someone making a mistake with getBytes() usually does it everywhere.