> > consider generating random challenges( i think here they have a
> > weakness where the passphrase need to be in clear text).
>
> OPIE cannot use random challenges, because one of the requirements is
> that it should be possible to print a list of pre-generated responses.
>
> The advantage of OPIE over traditional passwords is that OPIE is not
> vulnerable to replay attacks, but this is not as relevant these days as
> it was back when S/Key (on which OPIE is based) was designed. Replay
> attacks aren't very effective against encrypted protocols such as SSH.
>
> > My problem is to determine the best challenge/response implementation
> > for authenticating the clients.
>
> Systems like OPIE, where the challenge is actually issued to the user
> and not just to the user's software, require the user to have access to
> a response calculator, or to carry a sheet of precalculated responses.
> The former is difficult unless the users always log in from their own
> desktop or laptop computer, and the latter is usually a bad idea since
> someone might steel the sheet. On the bright side, it should be fairly
> easy to write an OTP calculator that run on a cell phone, such as an
> S60-based Nokia phones or an iPhone.
>
> I'd say that the only advantage of OPIE today is that it's free.
>
> DES
> --
> Dag-Erling Smørgrav -
des@des.no
>
