The study of hidden, obscure, very rare, and/or often high toposophic tech. Some Cryptotechnology is actually nothing but rumor or memetic ploy (this is sometimes known as rumorware), but others are genuine devices, sometimes rare and one-off, sometimes dangerous, sometimes just inscrutable to lower toposophics. Because of the difficulty of procuring cryptotech, cryptotechologists themselves disagree over what is authentic and what is mere folklore.
Cryptography - Text by Anders Sandberg The art of creating and using cryptosystems. A cryptosystem (or cipher system) is a method of disguising messages so that only certain people can see through the disguise, e.g, encryption. Cryptanalysis is the art of breaking cryptosystems - seeing through the disguise even when you're not supposed to be able to. Cryptology is the study of both cryptography and cryptanalysis. Very popular in the Cyberian worlds, where there is an obsession with personal privacy.
Cryptomemetic Index - Text by M. Alan Kazlev The degree to which an engineered meme cannot be detected, even by conventional memetic analysis. It is based on a complex of factors, most of which are incomprehensible to subsingularitan sophonts.