I have absolutely no idea why this blog is called “Superconductor,” but when I hear the name, I’m reminded of an project I worked on several years ago that dealt with superconductors. It turns out that superconductors provide an easy way stop magnetic fields, and I used this property to build a shield that prevented certain side-channel attacks.

To carry out a side-channel attack on a cryptographic system, you make some sort of physical measurements and hope that they’re correlated with some aspect of the cryptography. You might be able to do something like measuring the power that a microprocessor uses and use that information to determine a cryptographic key that it’s processing. Maybe processing a bit that’s a ‘1’ takes more power than a bit that’s a ‘0,’ for example. It’s difficult to eliminate side channel attacks. It might even be impossible.

Electronics radiate an electric field when they operate and it’s possible in some cases to determine what information is being processed by looking at how this field changes. This has been known since at least 1985, when Wim van Eck showed that it was possible to measure the emanations from a computer video display and use them to reconstruct the data being displayed.

It’s fairly easy to stop an electric field. A Faraday cage, an enclosure made of conducting material, stops electric fields very well. On the other hand, a Faraday cage doesn’t do much to magnetic fields. These are much tougher to stop.

But just like electric fields don’t penetrate into a conductor, magnetic fields don’t penetrate into a superconductor. So one way to stop magnetic emanations from electronics is to enclose them in a shield made of a superconductor, and I once built a superconducting shield that did just that.

While this sounds easy enough in principle, don’t forget that materials that we know of today aren’t superconductors at room temperature. I used a shield of YBCO, yttrium barium copper oxide, or YBa2Cu3O7. This doesn’t become a superconductor until it’s 93 K (-180 ºC) or colder. This meant that I had to keep a supply of liquid nitrogen (77 K or -196 ºC) in my lab along with all sorts of other interesting stuff to build this prototype. So while the name of this blog must have meant something to someone at some time, it reminds me of working on the superconducting shield and of the clever engineering tricks that it required.

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