PRUI, or Pre-Rendered User Interface, is a design technique intended to reduce the size of the trusted computing base of a software artifact (e.g. VoteBox). By generating most of the user interface ahead of time, we reduce the amount of run-time UI code that needs to be trusted for the system to operate correctly.

In VoteBox, we pre-render ballots using the Ballot Creator (or "ballot prep tool"). The VoteBox booth software uses the pre-rendered ballot, in the form of a ZIP archive containing only PNG graphics and XML files describing how to show those graphics, to present an interface to the user.

An example of a VoteBox screen and its pre-rendered components is shown below:

VoteBox screen	Pre-rendered images and layout

The PRUI technique as applied to voting was pioneered by Ka-Ping Kee in his Pvote voting system project.