RE: Remailer ideas

[John Douceur <johndo@microsoft.com>]

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>From: Eric Hughes  <hughes@ah.com>
>Date: Saturday, August 06, 1994 4:02PM

>Hal's random-send spool has an expected value of latency which is
>approximately the size of the spool but has no deterministic upper
>bound for that latency.  Fine.  Great.  No problem.  There should be
>zero hesitation here, because the expected value -- the probabilistic
>average -- is what you want.

There is an important distinction between systems for which the only
observable behavior is the probabilistic average and those for which
the observable behavior is that of the individual actions.  An example
of the former system is a hash table with open addressing:  The
absolute worst case for a lookup is as bad as that in an unsorted
list; however, this is not usually a problem, because programs
generally perform large numbers of lookups, and the performance that
the user observes is therefore equal to the probabilistic average.
An example of the latter system is the case in point, a remailer:
If a message is delayed unduly, the sender is unlikely to be
contented by the fact that many other users' messages were serviced
with considerably greater promptness.

Therefore, the probabilistic distribution of service times is as
important a metric of a remailer's performance as the probabilistic
average service time.  It may thus be quite reasonable to build in a
hard cutoff in service time, such that any message that has been
delayed by more than a set amount will be guaranteed to be sent on
the next transmission.  For some user of the remailer, this will make
an observable improvement in performance; and since the extreme delay
which triggers the expedited transmission is an unpredictable and
infrequent event, it will not make cryptanalysis of the remailer any
easier.

JD


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