MURI - HTTP Proxy Server Demo

Proxy Server Demo

Class Substitution

We are using a proxy to modify Java class files(in Java bytecode format) sent by a web server, in an attempt to put restrictions on applets. The basic approach is to substitute reference to one class with reference to a more restrictive class.

Restrictions on Window

    Class Window can be replaced with a subclass of Window (which will
be called Safe$Window in this demo) that performs more security and
sanity checks. For example, Safe$Window's setSize() method can
limit the size of a window so that the window should be fully shown up.
Since Safe$Window is a subclass of Window, the applet should not
notice the change, unless it attempts to create a very large window.
The proxy server can restrict applets without requiring any changes in
either web server or the Jave Virtual Machine in the web browser.

With Safe$Window, we put some restrictions on applets such as the following:

Window size
- an applet can't create a window whose size is bigger than 700*500 in pixels

Window position
- every window is poped up at (0, 0) so that the status line should be shown up

Number of windows
- an applet can't open more than 2 windows at the same time

Possible Other Restrictions on Applets

Number of threads

High thread priorities

Access to network resources

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