List of one-shot passwords

[Perry E. Metzger]

Matthew J Ghio says:
>  "Alan (Gesture Man) Wexelblat" <wex at media.mit.edu> wrote:
> 
> > It seems to me that a simpler solution than challenge-response would
> > be to emultate the tear-sheet crypto systems and just have a series of
> > one-shot passwords generated.  Each time you log in, it requires the
> > next password from the sheet, so capturing the old one does no good
> > (just as breaking the one-time codes from tear sheets doesn't help).
> >
> > Now if I could just figure out a simple way to do this on UNIX...
> 
> You can use a sequential PRNG to do this, and then add a scrambling
> system to the output (to confuse anyone trying to break the pattern).  I
> once wrote a program to do this (just for experimentation, and not in
> UNIX...).

You want to use a cryptographically strong one, however, because most
PRNGs are easily guessed. This in practice means using MD5 or DES or
IDEA or something as an RNG.

Perry