Cracking a SAM7XC cryptographic coprocessor


[Adam Laurie] spent time tearing into the security of the SAM7XC chip produced by Atmel. Even if he hadn’t found some glaring security holes just reading about his methodology is worth it.

The chip is used in a secure RFID system. The chip is added to the mix to do the heavy lifting required when using encryption. [Adam] grabbed a couple of open source libraries to put it to the test. The firmware is locked down pretty tight, but his explorations into the content of the RAM yield a treasure trove of bits. After investigating the sample code for the chip he’s shocked to learn that it uses RAM to store the keys at one point. The rest of his journey has him dumping the data and sifting through it until he gets to the “Master Diversification Key”. That’s the big daddy which will let him decrypt any of the tags used.

He reported his findings to Atmel in September of 2011. Their response is that they have no way of protecting RAM from exploit. [Adam] asserts that the problem is that the sample software wasn’t designed with the vulnerability of RAM in mind. The keys should never be stored there specifically because it is vulnerable to being dumped from a running system.


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