Reverse-Engineering a Game Boy Clone’s Boot ROM

[nitro2k01] got his hands on a Game Fighter, a clone of the original Game Boy. While there’s a ton of information about the boot ROM and operation of the original Game Boy, not much is known about these clones. [nitro2k01] wanted to learn more, so he used a clock-glitching technique to dump the device’s ROM and made some interesting discoveries about its copyright protection and boot process along the way.

Reading the contents of the Game Boy ROM is a bit challenging. The ROM is readable while booting, but afterwards the address space of the ROM is remapped for interrupt vectors and other uses. There are a couple of methods to get around this, but the simplest method involves glitching the crystal by grounding one of its leads. This causes the CPU to jump to random locations in memory. Eventually the CPU will jump to a location where the boot ROM is accessible (if you’re lucky!).

Although [nitro2k01]’s clone can run the same games as the Game Boy, it has a different boot ROM and also has some significant hardware differences. [nitro2k01] managed to use a modified version of the crystal-grounding technique to glitch his clock and dump the clone’s boot ROM. He found that the clone uses an unusual variation on the Game Boy’s copyright-checking technique, along with some other oddities. [nitro2k01] also posted a disassembly of the boot ROM, which he explains in detail.

Thanks for the tip, [Ove].

The ChipWhisperer At Defcon

We’ve seen [Colin]’s entry to The Hackaday Prize before. After seeing his lightning talk at Defcon, we had to get an interview with him going over the intricacies of this very impressive piece of hardware.

The ChipWhisperer is a security and research platform for embedded devices that exploits the fact that all security measures must run on real hardware. If you glitch a clock when a microcontroller is processing an instruction, there’s a good probability something will go wrong. If you’re very good at what you do, you can simply route around the code that makes up the important bits of a security system. Power analysis is another trick up the ChipWhisperer’s sleeve, analyzing the power consumption of a microcontroller when it’s running a bit of code to glean a little information on the keys required to access the system. It’s black magic and dark arts, but it does work, and it’s a real threat to embedded security that hasn’t had an open source toolset before now.

Before our interview, [Colin] did a few short and sweet demos of the ChipWhisperer. They were extraordinarily simple demos; glitching the clock when a microcontroller was iterating through nested loops resulted in what can only be described as ‘counter weirdness’. More advanced applications of the ChipWhisperer can supposedly break perfectly implemented security, something we’re sure [Colin] is saving for a followup video.

You can check out [Colin]’s 2-minute video for his Hackaday Prize entry below.

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THP Entry: Embedded Hardware Security With The ChipWhisperer

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There are thousands upon thousands of papers discussing various aspects of embedded hardware security, and dozens of books covering the same subject. The attacks discussed in the literature are very cool – things like side-channel power analysis and clock glitching used to extract keys from a system. The experimental setups in these papers are extraordinarily expensive – you can buy a new car for less. [coflynn] was disheartened with the price of these tools, and thought building his own would make for a great entry to The Hackaday Prize.

The hardware part of the ChipWhisperer includes a breakout board with an FPGA, ADC, and connectors for a lot of different probes, adapters, breakout boards, and a target board, With all these tools, it’s not unreasonable to say that [coflynn] could carry out a power analysis attack on a lot of embedded hardware.

Open source hardware is just one part of this entry. The biggest focus of this project is the open source software for analyzing whatever the probes and target boards record. With this software, anyone can monitor the power used when a chip runs a cryptographic function, or glitch a clock for some unintended functionality in a device. In keeping with the academic pedigree of all the literature on these attacks, there are a ton of tutorials for the ChipWhisperer for all those budding security researchers out there. Very cool stuff, and arguably one of the most technical entries to The Hackaday Prize.

Video below.


SpaceWrencherThe project featured in this post is an entry in The Hackaday Prize. Build something awesome and win a trip to space or hundreds of other prizes.

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