A few weeks ago, a great paper was published on side-channel attacks for RSA using the Pentium 4’s branch prediction logic. They were able to get nearly all of the bits of a 512-bit key for a (slightly) reduced-strength RSA implementation. This isn’t an algorithm break per se; it’s a generally applicable technique that can be used by one thread to spy on another thread’s actions, assuming it has the code that the other thread is running.
Hmm, I wonder what would happen if you had an account on a virtual server (e.g. Linode) and wanted to get an RSA key on the host? Hmmm…
If you’re interested in CPUs or security or both, the paper is worth reading.