From: wcs@anchor.ho.att.com (bill.stewart@pleasantonca.ncr.com +1-510-484-6204)
Date: Thu, 14 Apr 94 22:47:41 PDT
To: cypherpunks@toad.com
Subject: Re: New anon mailer idea?
Message-ID: <9404150546.AA12667@anchor.ho.att.com>
MIME-Version: 1.0
Content-Type: text/plain


Hal writes:
>  - You'd want this feature to be optional.  Some people might not want
>    their anonymity limited by having their return address recorded, even
>    in encrypted form.

The obvious implementation is to add a Generate-Return-Address: header 
so you can use it if you want it, but won't get one otherwise.
The encryption definitely needs some sort of random padding,
though CBC with a random IV plus length-padding at the end
should probably suffice.

>  - The use of a symmetric cypher is a very nice way of getting the use-once
>    capability, along with the "burn after reading" effect of a remailer
>    chain which destroys itself as it goes.  But it could be a considerable
>    burden on the remailer operator to maintain the database.  One possibility
>    would be to fix a maximum time limit on how long the return addresses are
>    kept "alive" and require some real money to keep them longer.

Public key has the advantage that the operator doesn't *need* a database.
If you want to implement use-once addresses (or use-N-times),
you could include a tag with the address (such as the IV),
and reject future messages using that tag (e.g. save a hash of the tag).
You could also implement time-limits by including an expiration date.

Perhaps something S-Key like might be applicable, if you want to stick
to private-key methods?

>  - What we would really like is for the recipient to hit the "reply" button
>    and be able to send his mail back.  

Matt Ghio's remailer+62647629379278@wherever.com syntax does this fine.
If desired, you could implement anonymous bit-bucket addresses
this way as well, though they're somewhat more useful if your remailer
generates encrypted outgoing messages.  Alternatively, you can *always*
generate either a real or a bit-bucket return address, and leave it up to
the sender to inform the recipient that there's a probably-working return path.

		Bill