[Thomas Roche] of NinjaLab is out with EUCLEAK, (pdf) a physical attack against Infineon security microcontrollers, and the security tokens that contain them. The name is a portmanteau of Euclidean and leak. And no surprise, it’s a data leak in some implementations of the Extended Euclidean Algorithm (EEA), a component of an Elliptical Curve Digital Signature Algorithm (ECDSA).

OK, time to step back. Infineon microcontrollers are the digital smart parts inside popular security tokens like the Yubikey 5, some Java smart cards, and even the Infineon TPMs. These devices all serve a similar purpose. They store one or more secret keys, and are guaranteed to never disclose those keys. Instead, they use their secret keys to do cryptographic functions, like ECDSA signatures, and output the result. There’s even a special set of tests, the Common Criteria, that are intended to backstop these guarantees. What’s interesting is that an otherwise excellent product like the Yubikey 5, that passes all these auditing and certification processes, is still vulnerable.

The actual attack is to perform ECDSA signatures while monitoring the physical chip with an electromagnetic probe. This tiny directional antenna can pick up on EM noise generated by the microprocessor. That EM noise leaks timing information about the internal state of the cryptography, and the secret key can be derived as a result.

This process does require physical access to the token for several minutes. To get useful readings, the plastic case around the security token does need to be disassembled to get the probe close enough to pick up signals. From there it’s at least an hour of post-processing to actually get the key. And most of these security tokens intentionally make the disassembly process rather difficult. The point isn’t that it’s impossible to open up, but that it’s impossible not to notice that your token has been tampered with. Continue reading “This Week In Security: EUCLEAK, Revival Hijack, And More” →