Schemes vs. algorithms

I’m often asked why I talk about public-key “schemes” instead of public-key “algorithms” like most people do. I’m one of those people who try to use words correctly. I cringe when I hear marketing people talk about “flushing” things out when they really mean “fleshing” them out. I often feel like sending people a link like this one that describes the difference, but I rarely do.

There’s actually a difference between a pubic-key scheme and a public-key algorithm, but most people don’t really care about it. Even people who understand the difference often use “algorithm” instead of “scheme” unless they’re writing or giving a presentation.

In any event, a public-key scheme is a technique for using public-key cryptography to do something useful like data encryption or digital signatures. More that one algorithm is used to implement a public-key scheme. In the case of DSA digital signatures, one algorithm used to create a signature and a different one used to verify a signature. If you talk about the “DSA algorithm,” which one are you really referring to? That sort of ambiguity is eliminated if you use “scheme” instead of “algorithm,” but it seems like that’s unlikely to ever catch on, and we’ll be talking about things like the RSA algorithm or the Diffie-Hellman algorithm well into the future, even if it's not quite accurate.