removing ssh access in an emergency

[Ian Malone]

This occurred to me this morning:

I log into my home machine remotely using an ssh
authorised key which I keep on a USB stick.  In the
event it was lost or stolen it's pretty unlikely anyone
would use it to try to break into my machine, but
ideally you would want a remote way to disable the key.
Has anyone thought about this?

My first thought was a user account with password
authentication that instead of a login shell would run a
program which deleted the authorized_keys file in
question.  Is this open to exploitation? (other than
running the risk that someone cracks the password
and prevents me logging in)

-- 
imalone