The idea behind twoauth is to suppliment user logins with a two-phase challenge
using a second authentication class in addition to their regular credentials.
Here is an example of a normal ssh session using twoauth authentication:
host1 ~ $ ssh host2
Last login: Sat Oct 15 15:47:09 2011 from host1
OpenBSD 4.9 (GENERIC) #477: Wed Mar 2 06:50:31 MST 2011
Welcome to OpenBSD: The proactively secure Unix-like operating system.
ENTERING TWOAUTH AUTHENTICATION PHASE
host2 ~ $
This utility was designed for OpenBSD. For more information, view the README
file which is included in the source distributions.