From: Sameer <sameer@soda.berkeley.edu>
Date: Sun, 13 Mar 94 14:38:39 PST
To: cypherpunks@toad.com
Subject: The blind anon-server
Message-ID: <199403132238.OAA18638@soda.berkeley.edu>
MIME-Version: 1.0
Content-Type: text


file://soda.berkeley.edu/pub/cypherpunks/remailer/blind-server.docs

	This server is running in testing mode.
	Please contact Sameer if you'd like to help test it.


---------- The Blind Anon-Server ----------

by Sameer Parekh <sameer@soda.berkeley.edu> Copyright 1994


Introduction

	I hatched up the Blind Anon Server because of Eric Hughes's
comments about the safety in ignorance. I wanted to run an anon
server, maybe similar to Julf's remailer, but I did *not* want to know
the connection between anon-ids and real IDs. I still wanted it to be
easy to use so that someone who wanted to send mail to an anonymous
person need only send it to a standard mail address, instead of using
Hal's remailer return address block, which is an incredible pain to
use.
	The system I have hatched up is relatively secure. If you take
the proper steps to secure your identity from me, even if I were
keeping complete logs, I would still know nothing of your true
identity and if my records were subpoenaed, I could freely hand over
the contents of my records without any worry that the privacy of my
users will be violated.
	The system requires all commands to be pgp signed. Thus you
will create a public/private keypair for your anonymous identity, and
all administrative commands to the list regarding this identity must
be signed by that key. You can send list commands from *any* address--
an anon remailer, a friend's address, Julf's remailer, whatever.. and
as long as it is signed by your identity's key, all will be well.

Setup
	First you have to create your alias on the anonymous
server. Creating the alias is easy, but setting it up to work right
takes a bit of effort and bookkeeping on your part. (Maybe I'll write
a client which can take care of all the bookkeeping.)
	Create a pgp keypair with a User ID of the form "Psuedonym
<alias@sitename>". Send your public key to
admin@sitename with the subject line, "addkey". This
will create for you an anonymous id which can be accessed via
"alias@sitename". You should only send one key to the
server in any single addkey request.
	You have to choose an account name which hasn't been used
before. In order to get the list of all account names which have been
used and are not available, send a message with the subject "sendused
address" to admin@sitename and the list of
unavailable names will be sent to address, with the body of your request
tacked on to the top, so you can use a remailer for the "address"
and the body can be an encrypted mailing block-- you need not
reveal your identity to me in any case.

	Starting an account gives you 100 credits.
	Now if you would like to send a message to someone from 
your newly formed alias, you can send a signed message to the 
administration address (admin@sitename) with the "mailmessage" 
command. For example:

::mailmessage recipient
Subject:  here's the plans to the stealth bomber
Keywords: bomber

	Here's the plans...
--END OF MESSAGE--

	The message will be sent out from sitename just as if you
had sent it out using a standard mail program from sitename.

	Then comes the more complex part. You have to tell my
anonserver how mail to your alias will actually get to you. There are
various levels of security which you can use. Because the remailernet
is not very reliable, the idea is that you setup a number of paths
which mail can get to you through, so that if one path goes down you
can still use the other paths to get mail. You can either configure it
so that mail to you goes through every path (for reliability with less
security) or one path chosen at random (more secure but less
reliable).
	To add a path to your list of paths, you must send a signed
message to the list, with the lines

::addpath firsthop
PATH INFORMATION GOES HERE
--END OF PATH--

	The firsthop is the first hop along the path between my anon
server and you. It *can* be your address, in which case there is a
good deal of reliability, but you get absolutely no good security. The
"path information" is what gets tacked onto the top of the body before
the message gets sent to the first hop. Suppose your firsthop was
Hal's remailer, hfinney@shell.portal.com.. You would have something like:

::addpath hfinney@shell.portal.com
::
Encrypted: PGP

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

hEwCKlkQ745WINUBAfwPrO+z9LMBz7boyyC7gUqX/QCEZkXmJCeZYoskgtH5qqbi
y4mYUL5a0ApbzrhPs8ULkPnW2c4Pfr1AfYSSgvrzpgAAAEvJtPOuQsW8IVQfl+iW
CAr2gd5jax+t75qbux5U/RRxlbsq4cOeGrO/i/6Km6m71Vsdj0rquEQBvREnXxdj
81YsBM9QlFNxQAB8rrQ=
=Ylli
-----END PGP MESSAGE-----
--END OF PATH--

	That pgp message is encrypted for Hal's remailer. When Hal's remailer gets the message, it will have this block on the front of the body. Hal's remailer can then decrypt it.. Maybe on the inside of this block you can put:

::
Anon-Send-To: <yourrealaddress>

	So then there's only one remailer on the chain between
myserver and your real address. For more security you can embed
*another* hop to another remailer with another encrypted address
block. This can continue for as long as you want. The longer the path,
the more secure, but the less reliable.

	Once the path has been added, you will be sent mail (through
the anon server) encrypted with your key (all mail to your alias will
be sent out encrypted with your key) with the pathnumber that your
command created. Store this path number in a safe place, because you
will need to use it when you test all your paths for reliability.
	You can create multiple paths in this fashion. The remailer
defaults to "spray" mode-- this means that mail to your alias will be
sent through *each* of your paths. This adds reliability at the
expense of security. (It makes traffic analysis easier.)
	If you would like to turn off spray mode, send a command to
admin@sitename:

::randmode

	To turn spray mode on:

::spraymode


	You can actually use this spray mode for more than just an
anon-server. If you'd like to create a mailing list, you can generate
a keypair, distribute to everyone on the mailing list the secret key,
and everyone can send into the anon server a path to themselves. Using
spray mode, mail to the address will go out to every path. This of
course means that anyone can subscribe or unsubscribe (Removing paths
is described below) people to/from the list.

The Credit Scheme

	When you startup an account, you get 100 credits. When
mail is sent out along one of the paths, credit is deducted from the
account-- 1 credit per 512 bytes of traffic. Note that if you are in
spray mode credits are deducted for *every* path which is active for
your alias.
	If your account does not have enough credit, when a message
comes in you will get mail detailing the size of the message that was
lost and the amount of credits you have in your account. (Size is
listed in 512 byte blocks)

Removing paths

	If a certain path which you have active flakes out and becomes
ineffective, you need some way of turning that path off so you're not
paying for it in spray mode, and so you don't lose mail in random
mode. That's what the disablepath command is for. To run the
disablepath command you simply send the command (signed, as always) to
admin@sitename:

::disablepath pathnumber

	Pathnumber, here, is the number of the path which was assigned
when you created that path. Hence it is useful for you to keep good
records of your active and disabled paths.
	It is possible to reenable a path once it has been
disabled. In order to do this you need to remember the path number
*and* the remailer that it's associated with. To recover a path you
just send:

::recoverpath firsthop pathnum

	And the path with the number pathnum is reactivated, with the
firsthop that you give it in the recover command.


Path Verification

	You will likely want to keep tabs such that you know when a
given path flakes out on you. For this reaon the "regping" option is
available. This command lets you tell the system how often you want
the anon-server to send a message through every path of yours, with
the pathnumber in the message (encrypted, of course) so that you can
keep tabs on which paths are flaking out on you.
	To set your ping frequency, use the regping command:

::regping frequency

	Where frequency can be none, hourly, daily, or
weekly. Remember that you are still being charged for these
testpings. The system defaults to weekly.
	To get a list of all your active paths, use the command
"showpaths".  This command will send out a listing of the 
pathnumber and first hop of each of your active paths:

::showpaths


Defeating Traffic Analysis

	The system works in concert with remail@sitename, which does
the work to defeat traffic analysis. All mail to each path is first
sent through remail@sitename for added difficulty in traffic analysis.

	remail@sitename is a standard cypherpunks remailer with PGP
with a few added features. All outgoing mail is not delivered immediately
upon receipt. Outgoing messages are stored in a pool until five minutes
after each hour, when all messages in the pool are delivered in a random
order, ignoring the order in which they came in.
	Every minute there is also a chance that a random uuencoded 
message is injected into the remailernet. Each message injected into
the remailer net is sent through a random path of the remailers in
the remailernet, usually between five and 20 hops.