One of my latest projects is the Baochip-1x, a mostly-open, full-custom silicon chip fabricated in TSMC 22nm, targeted at high assurance applications. It’s a security chip, but far more open than any other security chip; it’s also a general purpose microcontroller that fills a gap in between the Raspberry Pi RP2350 (found on the Pi Pico2) and the NXP iMXRT1062 (found on the Teensy 4.1).
It’s the latest step in the Betrusted initiative, spurred by work I did with Ed Snowden 8 years ago trying to answer the question of “can we trust hardware to not betray us?” in the context of mass surveillance by state-level adversaries. The Baochip-1x’s CPU core is descended directly from the FPGA SoC used inside Precursor, a device I made to keep secrets; designed explicitly to run Xous, a pure-Rust rethink of the embedded OS I helped write; and made deliberately compatible with IRIS inspection, a method I pioneered for non-destructively inspecting silicon for correct construction.
In a nutshell, the Baochip-1x is a SoC featuring a 350MHz Vexriscv CPU + MMU, combined with a I/O processor (“BIO”) featuring quad 700MHz PicoRV32s, 4MiB of nonvolatile memory (in the form of RRAM), and 2MiB of SRAM. Also packed into the chip are features typically found exclusively in secure elements, such as a TRNG, a variety of cryptographic accelerators, secure mesh, glitch sensors, ECC-protected RAM, hardware protected key slots and one-way counters.
The chip is fabricated using a fully-production qualified TSMC process using a dedicated mask set. In other words, this isn’t a limited-run MPW curiosity: Baochip’s supply chain is capable of pumping out millions of chips should such demand appear.
Hardware Built to Run High-Assurance Software
The Baochip-1x’s key differentiating feature is the inclusion of a Memory Management Unit (MMU). No other microcontroller in this performance/integration class has this feature, to the best of my knowledge. For those not versed in OS-nerd speak, the MMU is what sets the software that runs on your phone or desktop apart from the software that runs in your toaster oven. It facilitates secure, loadable apps by sticking every application in its own virtual memory space.
The MMU is a venerable piece of technology, dating back to the 1960’s. Its page-based memory protection scheme is well-understood and has passed the test of time; I’ve taught its principles to hundreds of undergraduates, and it continues to be a cornerstone of modern OSes.
Above: Diagram illustrating an early virtual memory scheme from Kilburn, et al, “One-level storage system”, IRE Transactions, EC-11(2):223-235, 1962
When it comes to evaluating security-oriented features, older is not always worse; in fact, withstanding the test of time is a positive signal. For example, the AES cipher is about 26 years old. This seems ancient for computer technology, yet many cryptographers recommend it over newer ciphers explicitly because AES has withstood the test of hundreds of cryptographers trying to break it, with representation from every nation state, over years and years.
I’m aware of newer memory protection technologies, such as CHERI, PMPs, MPUs… and as a nerd, I love thinking about these sorts of things. In fact, in my dissertation, I even advocated for the use of CHERI-style hardware capabilities and tagged pointers in new CPU architectures.
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