I’m posting this little snippet up because I spent ages trying to work out how to do this, and thought that other googlers might benefit from this. I’ve got an Android application that stores some of its information on the SDCard which has some commercial value, and we don’t want our competitors simply walking away with the information. The security doesn’t need to be too tight, so I’m happy to have a password based encryption scheme which has the password in the code of the application.

I have been playing around with the ideas of mobile processing agents lately, and to do this I need to execute code that has been uploaded to my processing environment, rather than the traditional “deployed” code. Java has this ability built in, via ClassLoaders. At any point, a java application can create classes from byte arrays. I wanted to do this on Google App Engine, but GAE does not support the traditional methods of loading classes would work.