Silicon backdoor: not an international crisis

Researcher’s second lesson: how to troll the entire Internet

Is it something to do with Slavic names? The Register is quite accustomed to Eugene Kaspersky’s astonishing ability to escalate every threat into a “cybergeddon”; now Cambridge researcher Sergei Skorobogatov seems to have taken his lessons to heart.

Let’s pick up the high points of Skorobogatov’s story again: (1) a ‘military grade’ FPGA that is (2) manufactured in China (3) has a backdoor. With a combination like that, the headlines are guaranteed – even if the threat is nebulous.

First, as Errata Security points out, “military grade” does not have the “wow, spook stuff!” meaning that it’s been given in too many outlets. Here is Actel’s outline of specifications for the ProASIC3 series of chips, including the mil-spec device. The first table shows the difference between different devices in the series; the A3P1000 is the “military” version – which means that it has been tested to military temperature requirements.

“Military” doesn’t mean “this is a chip designed to protect military secrets.” It means “if you put this chip into a product it can stand temperatures from -55°c to 125°C.”

Errata Security also points out that “manufactured in China” does not mean “the Chinese tampered with the design to insert the backdoor”. Following the old rule that a stuff-up is more likely than a conspiracy, Errata suggests that the backdoor was probably an intentional feature that the designers forgot to disable when they committed the FPGA’s design to manufacture.

It’s also important to remember that even if the backdoor exists, and even if it’s malicious, it’s not a very useful backdoor. For example, it’s not likely to enable a remote attack allowing Boeing 787 Dreamliners to drop out of the sky.

FPGAs are attacked not by sending a packet over the Internet with the evil bit set. To interfere with the FPGA, you need physical access to the device, and the appropriate equipment and software to program it.

That puts into context another observation made by Errata Security: the purpose of the encryption that Skorobogatov has cracked. The encryption exists not to protect communication between the device and the Big Bad Internet (more on this in a second) – it exists to protect the design placed on the chip. In other words, the threat is not that “military secrets will be stolen”, it’s that your design (and therefore your intellectual property) will be copied. At worst, if that particular chip was in something like a military drone, and if it were captured by an enemy, and if they were able to reproduce the attack – then the design might yield useful information about the drone’s design.

There is, of course, a scenario in which the FPGA might communicate with the Internet: the design implemented on the chip might be a communications stack. Even in that case, the purely internal encryption, designed to protect the gate designs on the chip, has nothing to do with its relationship to the outside world.

Should sensitive users of the chip be worried? Certainly. They want their designs protected. There’s even a discernable risk to someone like Boeing, since it’s feasible that someone with legitimate access to FPGAs might be persuaded or forced to reprogram them with malicious code, or steal Boeing’s code.

For the rest of us, our time would be better spent defending ourselves against the thousands of threats that affect our security. ®

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