Automatic Construction of Hardware Traffic Validators

This paper describes a fully automated process that creates a custom hardware traffic validator directly from a formal grammar and deploys it within a specialized network security appliance. The appliance appears as a hidden, all-hardware “bump-in-the-wire” that can be inserted within any network segment; it stores and validates messages on-the-fly, and either forwards or drops individual packets in real-time. Consequently, it serves to disrupt and mitigate stealthy remote attacks that leverage zero-day exploits and persistent implants. Allowed traffic, files, and mission payload formats are specified formally using a standard Look-Ahead, Left-to-Right (LALR) grammar that operates on ASCII and/or binary data. The grammars can be expressed either in Backus-Naur Form (BNF), used by industry standard tools such as Bison, or through state-of-the-art combinators, such as Hammer, under development within the DARPA SafeDocs program. Bison and Hammer compiler tools are used to generate standard shift/reduce parsing tables. These tables are post-processed to improve their compactness and practical viability. The optimized tables are then combined with a generic push-down automaton to form a complete parser. The parser is then automatically transformed into a hardware circuit using High-Level Synthesis (HLS). The result is a composable block of circuitry that can be directly inserted into a generic communications harness embedded within a Field Programmable Gate Array (FPGA) on the network appliance.