Cryptology? Cryptography? Crypto?

One of my students claimed that I was being inconsistent because I sometimes wrote cryptology, sometimes cryptography, and sometimes just crypto. What’s going on here? I suppose I could quote Walt Whitman on the subject of contradicting myself, or I could quote Emerson on the subject of foolish consistencies, but the truth is rather more mundane.

When I first started studying cryptology, it was pretty straightforward:

  • The branch of applied mathematics that dealt with constructing codes and ciphers, enciphering plaintexts, and deciphering ciphertexts (when the cipher was known) was called cryptography. This used a combination of algebraic functions and number theory, thus fitting well into an Algebra II course that already included both of those topics.
  • The branch of applied mathematics that dealt with breaking codes and ciphers was called cryptanalysis. This mostly used puzzle solving and statistics, heavily augmented by a combination of algebra and number theory. When an Algebra II course included a statistics unit, this was a good fit there as well.
  • The discipline that included both cryptography and cryptanalysis was called cryptology (a bit like parallelograms including both rectangles and rhombi). It was possible to offer, say, a one-semester elective in cryptology — or a cryptology unit in the kind of Algebra II class mentioned in the previous bullet point.

So where does crypto fit in? Well, it turned out that cryptology became more and more popular, and more and more people started calling it cryptography, even though it showed some semantic drift from the earlier meaning of that word. How do we deal with the cryptography/cryptology confusion? The answer adopted by the crypto community was to abbreviate both disciplines as crypto, thereby neatly side-stepping the whole issue. I usually say crypto, but when I say cryptography or cryptology I mean the original meanings of those terms.

And that’s the complete explanation. Aren’t you sorry you asked?

Categories: Linguistics, Math, Teaching & Learning