Posting this as was wondering if anybody had built such a device yet, given now 17 years ago and the costs of building such a device would now be much cheaper and hence would be surprised if somebody not built one. If not then certainly something for my project list for winter as was looking at optical computing and was pondering howto produce large primes with the use of optics and came across this article about TWINKLE.
If it were feasible to build such a device and break RSA with it, I assume the NSA would be doing it. Snowden's leaks implied that, while the NSA has a huge toolchest of various taps and side-channel attacks for attacking cryptosystems, they still lack the ability to break RSA directly (given a proper key length).
Indeed and for me I often feel a 511bit key better than a 512bit key or a 1023bit key better than a 1024 bit key down to the aspect of rainbow tables alone. Though I'm sure somebody with superior knowledge of crypto systems could prove me wrong, I've not had that pleasure yet and I love being wrong - it is when I learn the most.
A 511bit key is just a 512bit key with the last bit zero.
512 bits is definitely not a proper key length though. I think that's breakable on an ordinary desktop PC in a practical amount of time.