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Microsemi rebuts silicon backdoor claim

Researchers aren’t talking so verification is hard

Microsemi, manufacturer of the ProASIC3 field-programmable gate array (FPGA) that researchers Sergei Skorobogatov and Christopher Woods claim has a highly hackable backdoor, has issued a statement (PDF) about the attack.

The statement also casts doubt on the experimental method used to detect the backdoor, as it says the company “has not been able to confirm or deny the researchers’ claims since they have not contacted Microsemi with the necessary technical details of the set-up nor given Microsemi access to their custom-designed equipment for independent verification.”

The statement also says “there is no designed feature that would enable the circumvention of the user security.”

The document goes on to say that the internal test facility the researchers cracked, by obtaining a key after secretive electronic snooping, does indeed exist but is “disabled in all shipped devices” and “can only be entered in a customer-programmed device when the customer supplies their passcode, thus preventing unauthorized access by Microsemi or anyone else.” The FPGA can also, the statement says, be configured so the internal test facility is disabled and access is not possible, with or without a passcode.

On our reading, the statement says the “backdoor” is a feature in the form of an internal test facility, not a bug. While the researchers may have been able to extract a key, their work does not therefore constitute a revelation because it accesses a known set of functions that aren't hidden from customers.

Here in El Reg’s antipodean eyrie, we’re therefore keen to know if Skorobogatov and Woods worked with a brand new FPGA, because if we take Microsemi’s word for it there’s no reason a virgin ProASIC3 would have a passkey lurking within. But we can imagine a used ProASIC3’s passkey being extracted using the researchers’ cunning methods.

How did the key get there? It’s tempting to suppose that spies got wind of the research, intercepted the FPGA before it reached the lab and inserted a key for the team to find. The resulting explosive finding of a “backdoor” means we all now worry more about China. That makes somebody happy.

We’ve no idea who’s spies would have bothered, but feel justified in floating the idea because this will almost certainly be far from the oddest theory concocted to explain the affair. ®

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