The Cross Domain Desktop Compositor: Using Hardware-based Video Compositing for a Multi-level Secure User Interface

We have developed the Cross Domain Desktop Compositor, a hardware-based multi-level secure user interface, suitable for deployment in high-assurance environments. Through composition of digital display data from multiple physically-isolated single-level secure domains, and judicious switching of keyboard and mouse input, we provide an integrated multi-domain desktop solution. The system developed enforces a strict information flow policy and requires no trusted software. To fulfil high-assurance requirements and achieve a low cost of accreditation, the architecture favours simplicity, using mainly commercial-off-the-shelf components complemented by small trustworthy hardware elements. The resulting user interface is intuitive and responsive and we show how it can be further leveraged to create integrated multi-level applications and support managed information flows for secure cross domain solutions. This is a new approach to the construction of multi-level secure user interfaces and multi-level applications which minimises the required trusted computing base, whilst maintaining much of the desired functionality.