Building and Hacking USB with FPGAs

The talk revisits the USB hardware work of Great Scott Gadgets, tracing how the earlier Daisho project, a super speed USB board, led to the smaller Cynthion analyzer. The speaker explains that Cynthion pairs an FPGA with open-source gateware, and that the Luna library, written in Amaranth HDL, provides the USB logic. Python scripts drive the build flow, so a new bitstream can be generated and loaded onto the board in seconds.

A large part of the talk covers Packetry, a Rust-based USB analyzer. Using live demos, the speaker compares it with Wireshark while capturing from a HackRF. The comparison shows that Linux usbmon exposes host controller requests rather than the traffic on the wire, and that Wireshark slows badly once a capture reaches millions of packets. An upcoming interleaved hierarchical view is previewed as a way to keep both protocol hierarchy and chronological order.

The later sections cover Facedancer, which lets a host Python script act as a USB device for a target computer, so the target sees a real device. A live example reverse engineers the board ID and version requests of a HackRF using the suggest feature. The closing part lists ways to build USB devices in software, gateware, or added hardware, and points listeners to the open-source projects and documentation behind them.