Anonymous Remailers - Disappearing Cryptography - page 195

Another program developed just for chaining together the nec-
essary information for remailers is Premail written by Raph Levien.
The software is designed as a replacement for Sendmail, the UNIX
software that handles much of the low-level SMTP. Premail can take
all of the same parameters that modify its behavior including an ad-
ditional set of commands that will invoke chains of remailers. So you
can drop it in place of Sendmail any place you choose.
Premail has several major options. If you just include the line
key: user id in the header with the recipient's user id, then Pre-
mail will look up the key in the PGP files and encrypt the file using
this public key on the way out the door. If you include the header line
Chain: Bob; Ray; Lorraine , then Premail will arrange it so that
the mail will head out through Bob, Ray, and Lorraine's anonymous
remailers before it goes to the final destination. You can also specify
an anonymous return address if you like by adding the Anon-From:
field to the header. Premail is very flexible because it will randomly
select a chain of remailers from the list of currently operating re-
mailers. Just specify the number of hops in a header field like this:
Chain:3 . Premail will find the best remailers from Raph Levien's list
of remailers.
10.3.2 Splitting Paths
The current collection of remailers is fairly simple. A message is sent
out one path. At each step along the line, the remailers strip off the
incoming sender's name and add a new anonymous name. Return
mail can follow this path back because the anonymous remailer will
replace the anonymous name with the name of the original sender.
This approach still leaves a path—albeit one that is as strong as its
strongest link. But someone can certainly find a way to discover the
original sender if they're able to compromise every remailer along
the chain. All you need to know is the last name in the chain, which
is the first one in the return chain.
A better solution is to use two paths. The outgoing mail can be
delivered along one path that doesn't keep track of the mail moving
along its path. The return mail comes back along a path specified
by the original sender. For instance, the original message might go
through the remailer [e-mail] which keeps no records
of who sends information through it. The recipient could send re-
turn mail by using the return address in the encrypted letter. This
might be [e-mail] . Only someone who could
decode the message could know to attack [e-mail]-
er.com to follow the chain back to the sender.