REMAIL: Ray's improved anonymous remailer

[Hal <hfinney@shell.portal.com>]

I meant to reply to this several weeks ago, but was too busy then, so here
are some comments now.

From: rjc@gnu.ai.mit.edu (Ray)
>     Seeing as how everyone else is announcing their anonymous remailers,
> I may as well announce mine which is nearing completion.  The remailer
> is written in Knuth's WEB using Perl so there is nice documentation.

This sounds like an interesting approach.  WEB is Knuth's methodology
for creating self-documenting programming projects.  You run them through
a filter to create the executable code, Perl in this case.  This should
help portability and ease of support.

> The remailer includes among other things, virtual addresses (handles),
> padding/packetizing messages (splitting them up and sending pieces through
> multiple remailer chains), chaining, mixing, a key-server, a list of
> remailers server, a socket-server to bypass the sendmail queue and
> get immediate error return, a stealth mode (delivery via direct SMTP or
> socket instead of through the local sendmail), secure remailer network
> (remailers sign and encrypt chained messages between each other), 
> fake remailer traffic, and other small features. The virtual handles are 
> fairly secure. They can be stored in the database as either plaintext real 
> email addresses, virtual addresses located elsewhere on the remailer network, 
> or SAEE cypherpunk remailer blocks (self-addressed encrypted envelope)

These mostly sound like great features.  The virtual addresses are something
we have needed for a long time.  The idea of keeping records of which remailers
are responding should help with the use of the network, too.  The one problem
with this is that it might be tempting for the users to just trust the
remailers to choose their chain paths.  It would be much better for the user's
own software to hook up, find out which remailers are operating, then choose
a chain.  Ray's software will allow this, but this function could be split
off from the remailers to a specialized server, perhaps.

I'm not sure about the advantages of remailers signing and encrypting messages
between themselves.  It seems to me that the network should work even without
this.  Ideally we don't want the remailer network to be too centralized and
close-knit.  It's better for them to be strangers to each other since if they
coordinate their efforts they can defeat anonymity.

> p.p.s. e-mail commands are of the same form as the extropian's mailing
> list, backwards compatibility with the cypherpunks pasting token is not
> supported. Why? All headers in the message are ignored (and in socket-mode,
> there is no header anyway) and the prefered mode of operation is to encrypt 
> the body and the commands so no outside eyes can see the remail request
> destination nor the message subject.

This was one reason I suggested supporting both old-style CP and the
extropians-style syntax ("::Anon-To").  As Ray suggests, in some cases we
might not have message headers in the RFC822 sense.  I think it is simpler
to think about a message which has remailer commands at the top.

>   Socket mode provides a more secure form of operation by bypassing the
> standard sendmail delivery mechanism allowing a message to be
> piped directly to the remailer. In addition, the socket mode remailer
> functions as an information server allowing clients to request
> a publically networked list of public keys and up-to-date list of
> \rem servers. The port number can be anything but I'm suggesting we all 
> agree to use port 2258.

The number of sites which allow users to run socket servers is far smaller
than the number which allow mail filters, so not many people will be able
to use this feature.  OTOH the mail-only sites are generally of low security
and an owned-and-operated system should be able to use this feature.  So it
is definately a plus for those who can use it.

>   Upon connection to the remailer port, a greeting message will be sent to you
> of the following form. On the first line is a general greeting message
> which can be any string. On the next line is status information separated
> by ``/''. The status information in order is: \verb|remailer_name|,
> version, administrator e-mail address, and finally a list of flags.
> The flags are single character upper case letters specifying
> the following options. {\bf P} to specify that the machine is 
> privately owned and single-user, {\bf M} for mixing enabled, {\bf C} for 
> chaining, {\bf K} if the keyserver is turned on, {\bf E} if this remailer
> only accepts encrypted messages, and {\bf S} if stealth mode is on.

This is a good feature, but it should also be available from non-socket
remailers.  There should probably also be a "Help" command to tell how to
use the remailer.  (A lot of people already have these features.)

>    Virtual Addresses consist of a {\bf user handle} and an optional 
> {\bf remailer name} separated by `{\bf \#}' I used `\#' because I wanted
> to differentiate virtual addresses from internet style addresses.
> An example of a virtual address is ``darkmodem\#deepanon'' which
> means that the message should be sent to the user connected with the
> handle ``darkmodem'' through the remailer named ``deepanon'' You can
> chain your own remailers by simply adding multiple remailer names to the
> virtual address. For example, ``user\#remailer1\#remailer2\#remailer3''
> which will send the message first through remailer1, then remailer2,
> then remailer 3, and finally to whoever happens to be connected with
> ``user''. A special remailer name ``*'' is provided. Each instance of
> ``*'' in a remailer chain will be replaced by a random remailer.
> For example, ``darkmodem\#*#*#deepanon'' will first chain the message
> through two random remailers and then finally to deepanon. The random
> remailers chosen are not guaranteed to be unique.

Ray had mentioned above that these user handles can also map to encrypted
remailer strings.  This way users don't have to trust any one remailer op-
erator to keep their identity secret.  This need for trust is one reason
I am not enthusiastic about user#remailer1#remailer2#remailer3 as an
address, although it is admirably concise and easy to use.  The problem is
that it exposes the path to the first remailer in the chain.  I really feel
that paths must use nested encryption to be of much value.  Similarly, the
darkmodem#*#*#deepanon requires the user to really trust the first remailer
in the chain.  Perhaps it deserves such trust, but I feel that a system which
does not require such trust would be superior.  (Again, Ray's proposal is
broad enough that it will allow non-trust modes of operation, as I understand
it; my main concern is that these other options are so easy that they will
tempt people to be lazy and slip into modes where they are vulnerable to
unscrupulous remailer operators.)

I am really looking forward to seeing Ray's software.  It sounds like a
good package of functions.

Hal