The referenced paper is discussing passwords typed within an ssh session; I think it, and Richard's comments, are worth keeping around, but no longer believe in the answer itself. (I still do prefer public keys.)

<strike>[Song, Wagner, and Tian](http://www.ece.cmu.edu/~dawnsong/papers/ssh-timing.pdf) have shown that it is possible to speed up brute-force password searches roughly 50 times by using _timing information from `ssh` sessions_. [Noack revisited their study](nds.hgi.rub.de/lehre/seminar/WS06/noack_seminar.pdf) and found SSH2 vulnerable to timing analysis as well.

The attack makes two assumptions:

- The password hash is available for brute-force cracking.
- An attacker can get accurate timestamps on packets sent between hosts, or otherwise acquiring timing information.

Public keys are not only more convenient, but more secure against certain threats.</strike>