From: Matthew J Ghio <mg5n+@andrew.cmu.edu>
Date: Thu, 3 Feb 94 09:09:43 PST
To: cypherpunks@toad.com
Subject: Re: contemplating remailer postage
In-Reply-To: <9402022200.AA01456@uu4.psi.com>
Message-ID: <IhIGwnW00awQA2M2Ep@andrew.cmu.edu>
MIME-Version: 1.0
Content-Type: text/plain


Jim_Miller@suite.com wrote:

> Seems simple enough.  The major sticking point (to me) is the remailer's
> "used stamp" archive.  This could grow to be very large.  Something needs
> to be done to keep the archive from getting too large.
>
> One idea is to have the remailer periodically change the key it uses to
> sign stamps.  Changing the "stamp validation key" effectively invalidates
> all unused stamps signed by that key.  If you haven't used the stamp by
> that time, you're out of luck.  The remailer can purge its "used stamp"
> archive whenever it changes its "stamp validation key".
>
> Of course, invalidating peoples' unused stamps out from under them is
> not a nice thing for a remailer to do.  The remailer could provide a
> mechanism whereby people could get new stamps from old, unused
> stamps.  To make this work, the remailer would have to retain the
> previous "used stamp" archive for a while to give people a chance to get
> new stamps.  However, there still needs to be a limit on how long the
> remailer retains the "used stamp" archives for old validation keys.  If
> you wait too long, you would lose any chance to get new stamps from old.
>
> Comments welcome.

How about this: 

Issue numbered stamps sequentially.  Encrypt them and add a
cryptographic checksum to each stamp.  You then create a database such
that one bit of data corresponds to one stamp.  With a mere 64K
database, you could issue and keep track of 524288 postage stamps.  That
ought to last you a few years.  (At 100 letters a day, it would last
over 14 years.  Most cypherpunk remailers get considerably less than 100
emails a day.)