[onion2k]

I was pointing out that they didn't, not that they couldn't. But I don't believe they could anyway. Deciphering a OTP is absolutely trivial if you have the key. You're just doing modular addition, and that's something computers do a great deal of during the course of running stuff. Even assuming a reasonably long ciphertext of 500 characters, that'd take only 1000 operations (an add and a mod 10) - any modern CPU could do that in fractions of a millisecond. The deciphering operation wouldn't even register above idling.

Additionally, there's the problem that there isn't a 'industry standard' OTP app, so there'd be no reference fingerprint to look for.

I would love to be proved wrong though. That'd be very cool.