And, of course, he did write about polyamorous bisexual vegans in Imperial Earth. Though not cryptographers. Although the characters had some sort of mobile devices which probably resembled Psions more than anything, will have to check if they did phoney or webby stuff.
[Edit... looking for a description of the minisec - it certainly can receive messages and there is a mention of cyphers and decoding if not actual crypography]
