Ian & Stuart's Australian Mac: Not for Sale/Another.not.for.sale (Australia).iso/fade into you/being there/Issues & Ideas/Anonymous remailers/Remailers/chain Folder/chain.doc

Text File | 1993-06-04 | 11KB | 247 lines

Chain
-----

Chain is a program designed to assist in using the Cypherpunks remailers.
These remailers are simple servers which forward mail according to embedded
requests, erasing information about the sender of the message.  They are
designed to enhance personal privacy by preventing network eavesdroppers
from acquiring information about whom you communicate with by email.

(More information about the Cypherpunks remailers is available by anonymous
ftp to the Cypherpunks archive site, soda.berkeley.edu, in directory
/pub/cypherpunks/remailer.)

For maximum privacy, remailers can be "chained".  Messages are sent
through a series of remailers before arriving at their final destination.
Also, some of the remailers can receive encrypted messages whose contents
are indecypherable to outsiders.  Only when the remailer decrypts the
message are the contents revealed, including instructions for where to
send the message as the next hop in the chain.

Setting up these chains is a multi-step procedure, and the purpose of
the chain program is to make this simpler.  Chain can process an email
message to go through a large number of Cypherpunks remailers very
easily.  It can also work with the encryption program PGP to encrypt
the mail for those remailers which support it.

In its simplest mode, it is run as:

chain destination-address remailer-nickname [...]

Chain runs as a "filter" program, meaning that it reads a message as its
input, processes it according to the command-line arguments, and writes
the resulting message to its output.  The message may be typed directly
into the chain program's input, or it may be put into a file and directed
to chain using redirection.  This method would lead to a command line like:

chain destination-address remailer-nickname [...] < infile > outfile

The first command line argument is the "destination-address", the name
to which the mail should finally be sent.  This typically needs to be an
Internet email address like [e-mail].

This is followed by one or more "remailer nicknames".  The message will
be prepared to be sent through these remailers in the order given on the
command line before being sent to the final destination-address.  A
remailer nickname is an abbreviation of some part of the remailer address.

Chain uses a remailer file called chain.ini.  It looks for it either in the
current directory, or if it is not found there and the environment variable
PGPPATH is set (which it typically is for users of the PGP encryption
program) it looks in that directory.  Chain.ini consists of a list of
Cypherpunks remailer addresses, one per line.  In addition, if the first
character of a line is a star ("*"), that is a flag that that remailer
supports encryption, and chain will attempt to encrypt messages to that
remailer.   Here is a typical chain.ini file:

    [e-mail]
    [e-mail]
*    [e-mail]
*    [e-mail]
*    [e-mail]

This lists five remailers, two of which do not support encryption and
three which do (the ones with the '*' at the front).  The latest version
of the chain.ini file should be available at the Cypherpunks archive
site listed above.  If you don't have the PGP program then remove the
'*' from all the lines so chain won't try to use it.

Chain looks up the remailer nicknames in this file, stopping when it
finds the first match to the nickname anywhere in the file.  In the
file above, for example, "soda" would match on the first line, while
"rosebud" would match on the fourth.  "edu" would not be a very good
nickname because it matches more than one, but chain doesn't check for
that and just takes the first match (the first line, in this case).

A sample command line for the chain program would be:

chain [e-mail] rosebud soda extropia < mail.in > mail.out

This sets up a remailing chain which will go through the rosebud, soda,
and extropia remailers (in that order) before being sent to the final
destination, [e-mail].  It reads the mail from the file
mail.in and produces the processed output in mail.out.

This output file then would need to be sent manually to the first
remailer in the chain.  In this case that would be
[e-mail].

Chain creates two temp files as it runs.  They are put either in the
local directory or, if the environment variable TMP is set, in that
directory.  It normally deletes them when it terminates.


Chain -m
--------

The -m switch is only available on Unix systems which use the
sendmail program to send mail.  It causes chain to pipe the message
into sendmail, directing the message to the first remailer in the
chain, automatically.  A sample command line would be:

chain -m [e-mail] soda portal < mail.in

This would set up a chain for the soda and portal remailer, taking
the mail from the file mail.in, and automatically sending the result
to the first remailer, in this case [e-mail].

Chain -s
--------

Most of the remailers offer the option of changing the "Subject"
line of your message as it is remailed.  (I'm not sure at this point
whether any don't support this.)  This enhances privacy because you
don't have to put a subject lin on your mail as you send it; it can
be added later in the chain.

The -s switch can be used to specify the subject which your message
will be tagged with as it leaves the last remailer in the chain.  This
switch is used as -s, then a blank, then your subject, surrounded by
quotes.  It works on both MS-DOS and Unix systems.  Here is an
example:

chain -s "Questionable mail" [e-mail] portal < mail.in > mail.out

This would create mail to be sent to [e-mail] via the portal
remailer; as it leaves portal, the mail will be given the subject
"Questionable mail".

On Unix systems, this switch can be used in conjunction with -m, to
both automatically mail the message and arrange for it to get tagged
with an appropriate subject on its last leg:

chain -m -s "Questionable mail" [e-mail] portal < mail.in

This will automatically mail the message to the portal remailer,
causing the subject to be set as it leaves that remailer.

Chain -e
--------

The -e switch adds one extra level of encryption.  It encrypts the
outgoing message with the public key of your final message
destination before adding the chaining instructions.  This means that
when your message is received, it will be encrypted in the public key
of the recipient.

Chain looks up the public key in your regular PGP key ring, using the
full destination address you specified for the lookup.  Chain will
abort if no match is found when you specify -e.  An example:

chain -e [e-mail] nowhere portal < mail.in > mail.out

This will encrypt the message with the public key of [e-mail],
then process it for sending via the nowhere and portal remailers.

The -e switch can be used with -s and -m.

Chain -r
--------

Chain -r is used to create anonymous return addresses (ARA's).  An ARA is a
block of text which others can use to direct messages to you via a chain of
Cypherpunks remailers without knowing who you are.  To be useful, ARA's
should use encryption for at least the first step in the chain so that your
true address is not revealed.

Chain creates anonymous return addresses with a command line similar to
those described above, except that the -r switch is used.  (The -r
switch may not be used at the same time as the other switches
described above.)

chain -r destination-address remailer-nickname [...]

This creates an anonymous return address which is an alias for the
specified "destination-address" and which passes through the remailers
listed by the "remailer nicknames".  Chain does not read any input in
this mode (other than the chain.ini remailer file) and writes the ARA
on its output.  Typically this will be directed to a file with "> file.out"
or something similar.

The format of chain's anonymous return address output is as follows.

    Copy the material between the "cut here" lines below and put it
    at the top of your reply message, then send the message to:
    [e-mail]

    vvvvvvvvvvvvvvvvvvvvvvv cut here vvvvvvvvvvvvvvvvvvvvvvv
    ::
    Encrypted: PGP

    -----BEGIN PGP MESSAGE-----
    Version: 2.2

    pfQ648MrsmsLOFO5BanPl1P8g1SnGr1S0R7um0yHYhxxXIjKx2/CwFQcCXEcsexd
    KBYZjocNGAe/tVqvSVaaZcr4X/wiEK9Y22yx6fPymhlCH5fbKIyQrZR4xqHvr/ED
    2BKmw2redmLcs0f9ZlttdwDb0cPahnZgXvuz6HkPDX/LGVj4Zz14K0z+uaCrchBR
    aVKMa4pT49lf6StSf5wUdxHgnsNfxGbAYAwqswahdLNdniD7Ue8HTRZYF23ubd98
    Rzv2PYG7G2j/hvtyCrcwKMI/wQP6wDNY0bgj9Q+F
    =P2Q+
    -----END PGP MESSAGE-----
    ^^^^^^^^^^^^^^^^^^^^^^^ cut here ^^^^^^^^^^^^^^^^^^^^^^^

This block of text is intended to be placed somewhere in a message which
you have mailed or posted anonymously.  It includes instructions to those
who wish to reply to you.  They are supposed to take the material between
the "cut here" lines and put it at the top of the message they want to
send to you.  They then send the resulting message to the first remailer
in the chain you chose for your ARA, in this case [e-mail].

For example, if they wanted to send you the message, "Tell me more about
your ideas", they would create a message which looked like:

    ::
    Encrypted: PGP

    -----BEGIN PGP MESSAGE-----
    Version: 2.2

    pfQ648MrsmsLOFO5BanPl1P8g1SnGr1S0R7um0yHYhxxXIjKx2/CwFQcCXEcsexd
    KBYZjocNGAe/tVqvSVaaZcr4X/wiEK9Y22yx6fPymhlCH5fbKIyQrZR4xqHvr/ED
    2BKmw2redmLcs0f9ZlttdwDb0cPahnZgXvuz6HkPDX/LGVj4Zz14K0z+uaCrchBR
    aVKMa4pT49lf6StSf5wUdxHgnsNfxGbAYAwqswahdLNdniD7Ue8HTRZYF23ubd98
    Rzv2PYG7G2j/hvtyCrcwKMI/wQP6wDNY0bgj9Q+F
    =P2Q+
    -----END PGP MESSAGE-----
    Tell me more about
    your ideas.

They would then send this to [e-mail].  The ARA at
the front of the message would be decrypted and the resulting data would
allow the message to be passed on to the next remailer in the chain,
until it is finally sent directly to you by the last chained remailer.

This procedure is a little complicated, granted, but the chain -r program
makes it easy to create ARA's, and it should not be overwhelmingly difficult
for those who wish to reply to you to cut a block of text from your
message and put it at the front of their own reply.

(NOTE: for technical reasons, the "extropia" remailer cannot be used for
anonymous return addresses at present.)


Chain is written by Hal Finney, [e-mail].
This is the initial release.  Please report problems to the author.
Chain is placed in the public domain; its source code may be freely
used.