From: rjc@gnu.ai.mit.edu (Ray)
Date: Mon, 6 Sep 93 03:26:14 PDT
To: cypherpunks@toad.com
Subject: Anonymous Forwarding
Message-ID: <9309061019.AA29877@geech.gnu.ai.mit.edu>
MIME-Version: 1.0
Content-Type: text/plain



  Do you have spare email accounts laying around? 

  Would you like to have them forward mail to your main account anonymously?

  These are the questions which led me to hack up an anonymous .forward
technique. I figured that I'd use a spare account to receive mail which I 
normally wouldn't want connected to my main address. Furthermore, mail
forwarded to my main email address would be automatically encrypted to
prevent the prying eyes of the sysadmin from snooping.

Anonymous Forwarding
--------------------

  My software works like this. The destination address is prepared
as a standard remailer header and pgp encrypted for one or more remailers, 
e.g.

====================================
::
Request-Remailing-To: my_real_address

====================================

  becomes

===================================
::
Encrypted: PGP

-----BEGIN PGP MESSAGE-----
Version: 2.3a

hIwCPhjICRQCw4kBBACnRARz+qDK21BXcSUba3WjT4NEjoMtq+PZoJujGN2A/Ati
O31UHYpULTP7j8OKBC+4Zuuan2e8CLTG9f3/XgYSuv8YRU5DtKr6bEuDDuojjgfr
/ZudUWTej646ZJTqhrXRQldg/x/Wuu3kx8tby0zf+PcqqOssw7S2rgT6yrrdG6YA
AABFct7lohDMViS01vOxzWr3RYernaqB9bkQmWlGd32TFrbe9bGf6BFBMvlDT8v+
C6xf1qI24mDslNiGoabjd/nCsE6d4EFT
=7jt6
-----END PGP MESSAGE-----
===================================

  These "anonymous return addresses" are stored in the home directory
(e.g. lib/shell.addr, lib/rosebud.addr, etc) on the spare account.

  When an incoming message is processed through .forward, the body
of the message is stored and optionally encrypted with the public key
of the main email account. The software then picks a remailer return address
at random (e.g. lib/rosebud.addr), and appends it on the front of the
encrypted body. This file is then re-encrypted with the public key of the
destination anonymous remailer (optional). I did this so no one sees the
obvious two-part message (pgp encrypted return address and pgp encrypted
body). It probably doesn't add security, but it's optional.

  There is a configuration variable called "chain". If it is higher than
1, then up to "chain" number of remailers are chosen at random and
chained together. Optionally, each new envelope in the chain will use
the public key of the next remailer for encryption.

  So what happens is an incoming message is encrypted, the forwarding
address (which is already encrypted for specific remailers) is
added to an encrypted body and bounced randomly off a certain number
of remailers to the final destination which is the main email account.
Now you're all set to subscribe to alt.bomb.building with your other
email account without fear of it being connected to your "real" account. ;-)


Anonymous Mailing Lists
-----------------------

  Using my anonymous-forwarding script I have thrown together a kludgy
anonymous mailing list program. Not only are the users on this list totally
anonymous but the list address itself is secret! (Don't ya just love
double-blind mechanisms?)

  To subscribe, users simply pgp encrypt a "Request-Remailing-To:"
block as I detailed above and send it to the list request address. The
list software sends out messages using the exact same script as
anonymous-forward. At no time does the mailing list software see the
real e-mail address. Only by collaborating with the operators of 
anonymous remailers can the list operator find out the real
address of a user.

  The list address itself is also secret. Ihe true address is embedded
in an encrypted "Request-Remailing-To:" block and chained through several
remailers. Users post to the mailing list by adding their response to the
encrypted return block and sending it to the first anonymous remailer in the 
chain. (the list software automatically puts the list's return block
at the start of every message for easy response. [no cut/pasting needed])

Hopes, Dreams, and Bugs
-----------------------

  Obviously, with the small number of remailers on the net, and most of
them running from multiuser machines and student accounts, security is
not high. As the number of remailers increase, the probability of a bunch
of remailer operators all collaborating is small. If remailers ever
reach the level of popularity of gopher/fsp sites, it would be near 
impossible to shut down an anonymous mailing list. (there's no postmaster
to complain to because you don't know the true address!)

  Alas, there is currently no way of returning error messages so if something
bad happens, you aren't notified. Shutting down a single remailer in the
chain would be very harmful. A fault-tolerant mechanism is needed and
a robust way of returning error messages.

-rjc

p.s. If I have reinvented the wheel, ignore this message. I didn't see
any anonymous forward/list software on soda so I figured no one had
written any.