Thanks for the link to the OpenSource PKI Book. I've been thinking of bring up a site where instead of passwords, I use certificates. The only problem is that I had issues with getting pyCA to work, and none of the documents out there tell you how to take the public key generated by Netscape (by using keygen) and create the required document for import into Netscape. There's plenty of other documentation, but they seem to think you should already know how to do it, and completely ignore it. Oh well, I haven't made any progress on the site in the months since I decided to start working on it, I'll probably just end up having to use crappy username/password for it.
Also, don't forget that if the decks get too out of order a person will likely compensate with a longer run, so you have to add in a compensation for how many cards are remaining. As an avid card player (and one who hasn't developed a perfect shuffle), I have a decent idea on how it works. Also, don't assume that you'll always have a run of at least one card. Plenty of times a person messes up and skips a card between two runs of the other deck. So, I'd add a modifier to p depending upon the difference between the two remaining decks. Just my thoughts.