🚀 go-pugleaf

In comp.security.misc, dsiebert@icaen.uiowa.edu (Doug Siebert) writes:

[good stuff about promiscuous LAN-listeners blowing a hole in plain-traffic
LANs deleted, and then:]

> I'm not so sure about the timed read method, but it sure sounds unduly
> difficult and unrealiable.  Does anyone know if this method would even be
> possible?

Maybe yes, maybe not; but I'm reminded of a classic password attack I heard
about on (oneof (multics tops20)) a while back...

The nice authenticate-passwd routine on this system was internally coded
to do a letter-by-letter compare of the submitted password against the
hidden registered password; it returned with failure on detecting the
first mismatch.  Thus-and-therefore, by repeated probes with your submitted
password guess broken across a page boundary, arranging for the "far" page to
be swapped out, and timing the return (remember, page faults cost *lots* of
time in them thar days) you could reduce the number of probes from
[alphabet_size ** passwd_length] to [alphabet_size * passwd_length].

(For the numberically impaired: with an 8-character password drawn from a
64-letter alphabet, that's the difference between 281,474,976,710,656 and
512).

Unsurprisingly, the internal routine was changed to access all chars of the
probe password before returning.

A nice example of "covert channels"!

Corrections expected --- Cheers, Stefek