It's not possible to allow non-OPIE logins only from trusted networks

[Peter Jeremy]

On 2011-Mar-10 23:09:07 +0000, Miguel Lopes Santos Ramos <mbox at miguel.ramos.name> wrote:
>- The objection on S/KEY on that wiki page, that it's possible to
>compute all previous passwords, is a bit odd, since past passwords won't
>be used anymore.

One weakness of S/KEY and OPIE is that if an attacker finds the
password (response) for sequence N then they can trivially determine
the response for any sequence > N.  This could occur if (eg) you have
a printout of OPIE keys and are just crossing them off (which was a
common recommendation prior to smart phones etc) - an attacker just
needs to memorise the lowest N and response.

-- 
Peter Jeremy
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