trunk/Mix2.0/mixmaster.1

.TH MIXMASTER 1 "Mixmaster Version 2.0.4"
.\" $Id: mixmaster.1,v 1.1 2002/08/28 20:06:49 rabbi Exp $
.SH NAME
mixmaster
\- anonymizing remailer
.SH SYNOPSIS
.B mixmaster
[
.B \-c
] [
.I filename
] [
.B \-f
] [
.B \-m
] [
.B \-d
] [
.B \-s
.I "subject"
] [
.B \-v
.I "'Header: text'"
[
.B \-v
\ ... ] ] [
.B \-n
.I numcopies
] [ 
.B \-o
.I outfile
|
.B \-O
.I outfile
] [
.B \-to
.I who@where
] [
.B \-l
.I 1 2 3
\ ... ]
.PP
.B mixmaster
[
.B \-P
] [
.B \-T
]
.PP
.B mixmaster
[
.B \-G
] [
.B \-K
] [
.B \-R
] [
.B \-S
] [
.B \-L
] [
.B \-Q
] [
.B \-D
] [
.B \-X
]
.SH DESCRIPTION
The purpose of anonymous remailers (hereafter simply remailers) is to
provide protection against traffic analysis. Traffic analysis is the study
of who you are communicating with, when, and how often. This reveals more
than you might expect about your activities. It will indicate who your
friends and colleagues are (and they can be told apart by looking at the
times you contact them). What your interests are, from which catalog
companies you contact, and which ftp and WWW sites you visit. Traffic
analysis can even reveal business secrets, e.g. your frequent contact with
a rival could give hints of an impending merger.
.PP
Remailers protect your e-mail from traffic analysis. The original remailers
did this by removing all headers, except the subject line, from any message
you sent to them and then forwarding them a destination of your choice. The
recipient of such a message would not know who had sent it.
.PP
The addition of encryption to this scheme gave significant protection from
attackers who simply look at passing messages for to and from fields.
Passing a message through several remailers in a row is much better, but
still vulnerable to an attacker who can watch messages go into and out of
each remailer.
.PP
Two more elements are required: messages must be reordered within the
remailer before being forwarded (this is being done by a few of the old
style remailers), and all messages must be indistinguishable. This last is
the primary improvement with the type 2 remailer,
.IR Mixmaster .
.SS "Remailer RSA keys with Mixmaster:"
.I Mixmaster
has its own rudimentary key management, and unique key file format.
To get the latest key from a remailer, send mail to the remailer with
the subject
.BR remailer-key .
It will send you a file containing the key and a
line for your
.I type2.list
file. The line after the
.B =\-=\-=\-=\-=
line is the one
you should put in your
.I type2.list
file. If there is already a line with the
same remailer name, the new line should replace it.
.PP
The remailer key is every thing between the 
.B "Begin Mix Key"
and
.BR "End Mix Key" ,
including those lines. You should add that text to your
.I pubring.mix
file. You may also include any text outside of the begin
and end lines to identify the key.
.PP
When you chain through a remailer,
.I Mixmaster
finds which key to use by looking at
.IR type2.list ,
and then finds the corresponding key in
.IR pubring.mix .
.SS "Using type 2 remailers:"
The trend towards ever more complicated remailer message formats has been
clear for some time. Several programs have been written to automatically
build messages which will be remailed by several remailers. This process is
called chaining.
.PP
With type 2 remailers it is no longer possible to create these messages by
hand.
.I Mixmaster
takes a message you wish to send, a list of remailers to
chain it through, and a final destination, and builds the packet which the
remailers will use.
.\"For simplicity I will first describe the interactive
.\"use of Mixmaster, then I will discuss how it can be controlled through
.\"command line arguments.
.SS "Interactive use of Mixmaster:"
If you run
.I Mixmaster
with no arguments, you will be prompted for all the
required information.
.PP
First you will be asked to specify the final destination of the message.
This is the full e-mail address where you want your message delivered.
Remember that the message is being sent by the last remailer in the chain,
so you must specify the full internet address (e.g.
.IR name@machine.place.com ),
you may not use local mail aliases. You may enter multiple recipients on
separate lines. Hit return on a blank line to stop entering destinations.
You must have at least one.
.PP
.I Mixmaster
recognizes these special keywords ending with a colon:
.br
.B "null:"
for cover traffic.
.br
.B "post:"
posts to the following newsgroup.
.PP
Next you will be asked to enter any headers you want to have inserted
before the message. These are those lines at the beginning of e-mail
messages, like
.IR "From: fred@bedrock.univ.edu" ,
or
.IR "Subject: Party invitation" .
If you want your message to have a subject when it is delivered, you must
enter a line like this:
.PP
.B Subject:
.IR "your subject here" .
.PP
Note that 
.B Subject
must be capitalized, with the
.B :
and space as shown. (A subject header can also be added by using the
.B \-s
command line argument.) When you are done entering headers, hit
return. It is OK to have zero headers.
.PP
You will now be presented with a list of remailers through which you can
chain your messages. The order in which you choose them is the order in
which they will be traversed by your message. The remailers that can
be used at the end of a chain are marked with an asterisk; a 
.B U
means that according to the list of reliable remailers, the remailer
is unreliable at the moment. See the file
.B mix.list
for information about the reliability history printed in square
brackets.

You may choose up to 20 remailers, but remember that the reliability
and speed of the chain diminish as the number of remailers in the
chain increases. Four is a reasonable number of remailers to use. It
is fine to use a given remailer more than once in your chain. Press
return on a blank line to stop entering remailers.
.PP
You may enter
.B 0
for the remailer and
.I Mixmaster
will choose a random
remailer for you. This is particularly useful for routing multipacket
messages over different remailer chains. If specified in the
configuration file,
.I Mixmaster
can automatically select a remailer chain.
.PP
Finally you will be asked what file you want to send. This must be an ASCII
file. You may either enter the name of an existing file, or you may choose
to enter the message directly by typing
.B \-
or
.B stdin
as the file name. This is
intended for use by scripts. There are no editing capabilities when using
stdin. Enter the end of file character (EOF is ^D) when you are done
entering the file.
.PP
.I Mixmaster
will now build the type 2 remailer packet, and send it to the
first remailer in the chain.
.PP
List of statistics on remailer usage can be requested by sending
the remailers mail with subject
.BR remailer-stats .
.TP
.B \-X
Seed the random number generator.
This should be done once, before sending messages and creating remailer
keys.
.SH MIXMASTER AS A REMAILER
The
.I Mixmaster
remailer accepts packets in the Mixmaster message format, and re-sends
them to other Mixmaster remailers and \- unless it is configured as a
"middle only" remailer \- to users.
.PP
The same source and binary is used for the remailer program and the
client program. The remailer can be installed on any Unix mail
account.
.PP
To install
.IR Mixmaster ,
run
.BR ./Install .
The Install script will ask a few questions and set up the remailer.
.PP
All remailer functions (as opposed to chaining
functions) are invoked with capital letters on the command line.
.SS Support for "cypherpunk remailer" (type 1) messages:
If you want to be able to handle type 1 messages as well as type 2,
you can do so using the Mixmaster mail address.
.PP
Set up the type 1 remailer just as though it were going to be used on its
own, but do not set up mail forwarding to the remailer. That should
go to
.IR Mixmaster .
.PP
Edit
.I mix.help
to include the help file that comes with your type 1
remailer. Add your type 1 key to
.IR keyinfo.txt .
Edit
.IR mixmaster.conf ,
and define
.I TYPE1
to be the command line needed to
run the type 1 remailer.
.PP
.I Mixmaster
will recognize incoming type 1 messages, and open a pipe to the
program you specified. It will send the message to stdin of that
process.
.PP
You can set the type 1 remailer's
.I sendmail
to be
.B mixmaster
.BR \-Q ,
so the messages will be added to the reordering pool. Mixmaster will
add its disclaimer to all messages sent. If your type 1 remailer has
its own disclaimer, add that line to
.BR headers.del ,
so Mixmaster will filter it out, making type 1 and type 2 messages
indiscernible.
.B \-Q
may optionally be followed by a Mixmaster destination.
.SH OPTIONS
.SS Client mode options:
.TP
.B \-c
Indicates that chaining rather than remailer functions are desired.
It is a NOP since chaining is the default operation.
.TP
.I "input.file"
If a filename is given, then this will be used as the input
file. As in the interactive mode, you may choose
.B \-
or
.BR stdin .
No filename will be prompted for.
.TP
.B \-f
Filter mode. All prompts suppressed, but input still accepted as
described in the interactive section. The remailer list must be
specified on the command line.
.TP
.B \-m
Like
.BR \-f ,
but the input is a message in Internet mail format. Be careful not to
send any mail headers that leak information about your identity.
.TP
.B \-d
Generate a dummy message, which will be sent through 5..15 random remailers
unless specified otherwise in
.I CHAIN
or using
.BR \-l .
You should generate cover messages to foil traffic analysis.
.TP
.I "\fB\-s\fP subject"
Add a subject line to the message. The user should
.I not
include
.B Subject:
in this string.
.I Mixmaster
will not prompt for other headers if
.B \-s
is used.
.TP
.I "\fB\-v\fP 'Header: text'"
Add an arbitrary header line to the message.
.B \-v
can be used repeatedly.
.TP
.I "\fB\-n\fP numcopies"
Create multiple copies of the same message, to increase reliability of
randomly selected chains. Only one copy will be delivered to the
recipient.
.TP
.I "\fB\-o\fP output.file"
Specifies an output file rather than sending the message to the
first remailer automatically. If
.I "output.file"
is
.B \-
or
.BR stdout ,
then the remailer packet will be written to standard output.
.TP
.I "\fB\-O\fP output.file"
As
.B \-o
above, but it includes a "To: " line so the output file can be
sent directly to sendmail.
.TP
.I "\fB\-to\fP foo@bar.org"
Specifies the final destination of the message.
.I Mixmaster
will not prompt for other destinations if
.B \-to
is used.
.TP
.I "\fB\-l\fP 4 3 12 5 ..."
Specifies the list of remailers to chain through. This must be
the last argument on the command line. A maximum of 20 remailers may
be specified.
.I Mixmaster
will not prompt for other remailers if
.B \-l
is used. As in the interactive mode, you may enter
.B 0
for a random
remailer. Remailers may also be specified by their name or address.
.SS "Special command line arguments for scripts:"
Many scripts and other programs which will drive
.I Mixmaster
may need to
know where
.I Mixmaster
keeps its files, and what remailers it knows about.
There are two special commands to help with this. Both are executed before
any other command line options (\fB\-P\fP
then
.BR \-T ).
.TP
.B \-P
Write the 
.I Mixmaster
directory, the name of the remailer list and the mixmaster version
to stdout, each followed by a newline.
The result is something like:
.PP
                /home/joe/Mix
                type2.list
                2.0.5
.TP
.B \-T
Write the list of remailers (usually
.IR type2.list )
to stdout.
.SS Remailer functions:
.TP
.B \-G
Generate a new key pair. The private key is prepended to
.IR secring.mix ,
the public key is prepended to
.IR pubring.mix ,
and a new
.IR mix.key
is created. The
.I mix.key
file has one line (after the 
.BR =\-=\-=\-=\-= )
which goes in
.IR type2.list .
The rest is the new public key, which can be appended to the
public key file by a user who requests the key.

The
.I mix.key
file is mailed to anyone who send mail to the remailer with the
subject
.BR "remailer-key" .

When you generate a new key (if you keep the same passphrase), the old
key will still work. You must remove the key from the ring when you want
to retire it permanently. This allows you to keep supporting the old key
while the new key is propagated.
.TP
.B \-K
Update
.IR mix.key .
.TP
.B \-R
Process incoming mail, reading from stdin.
.I Mixmaster
.B \-R
should be invoked from
.I /etc/aliases
or the
.I .forward
mechanism.
A safer way to invoke
.I Mixmaster
is with the
.B reorder
package.

Output can be redirected to a log file, but this is not required.
If you do, make sure that it is sufficiently writeable. The only
things that go in this log file are failed messages, and error messages.
If
.I Mixmaster
is installed on a personal account, the output should be appended to
the mail folder, to ensure that regular e-mail is delivered. All
non-remailer messages will be sent to stdout.
.TP
.B \-S
Randomly select and send all but
.I POOLSIZE
messages.
.TP
.B \-L
Check all latent messages and converts them to regular 
messages if their time has passed.
Since there is no type 2 latent,
.B \-L
has no effect.
.PP
The functions
.B \-L
and
.B \-S
are typically performed periodically using
.BR crond (8).

If you are unable to run
.BR crontab (1)
or
.BR at (1),
you can process the pooled and latent messages each time a new message
arrives, using
.B mixmaster \-R \-S \-L
in the 
.I .forward
or
.I /etc/aliases
files.
.TP
.B \-Q
Read a message from
.B stdin
and add it to the reordering pool.
.TP
.B \-D
Will be used to run
.I Mixmaster
as a demon waiting for socket
connections in a future version.
.SH CONFIGURATION
The configuration both for the client and the remailer is set in
.IR mixmaster.conf .
Unless otherwise noted, the entries cannot contain whitespace.
.TP
.I SENDMAIL
Name and path of the
.BR sendmail (8)
program. The
.B \-t
flag is required (the destination is in the
.B "To:"
header). Can contain whitespace.

If
.I SENDMAIL
is set to
.B outfile
(this is the default under MSDOS), Mixmaster will write its output to
files named
.I "\fBoutfile.\fPnnn"
instead of mailing it.
.SS Client configuration:
.TP
.I CHAIN
A chain for remailer messages, if you don't want to chose them
manually.
.B 0
means a random remailer. This chain can be overridden by the command
line option
.BR \-l .
Can contain whitespace.
.TP
.I NUMCOPIES
Number of copies (see option
.BR \-n ).
This entry can be useful if you use a long
.I CHAIN
of random remailers. Default: 1.
.TP
.I MINREL
The minimum reliablity
.I Mixmaster
will require for a remailer to be chosen randomly, in % (will be
ignored if no reliability information is available). Default: 98.
.TP
.I RELFINAL
The minimum reliability for a remailer to be randomly chosen as the
final hop, in %.
.I Mixmaster
will chose the most reliable remailer if no remailer reaches the
minimum. Default: 99.
.TP
.I MAXLAT
The maximum latency
.I Mixmaster
will accept for a remailer to be chosen randomly, in hours. Default: 24.
.TP
.I DISTANCE
The distance after which a remailer can be selected again in a chain.
0 is a purely random selection, 20 means previously-used remailers
will not be selected again. Default: 2.
.TP
.I REQUIRE
A list of ability flags the final remailer must have. For example,
set this entry to
.B C
if you want to send all messages compressed. Other remailers will not
be selected randomly. If they are selected by the user,
.I Mixmaster
will print a warning.
.TP
.I REJECT
A list of ability flags the final remailer in the chain must not have.
Default:
.B M
(do not use "middle only" remailers as the last hop).
.TP
.I VERBOSE
Mixmaster prints information about the selected chain if
.I VERBOSE
is set to
.BR 1 .
.SS Remailer configuration:
.TP
.I REMAILERADDR
The remailer's e-mail address. This entry has no default value.
.TP
.I ANONADDR
An e-mail address to appear in the 
.B From:
header of remailed messages. Defaults to the value of
.IR REMAILERADDR .
.TP
.I COMPLAINTS
The address to which you want complaints about the remailer sent (this
is put in the comments block in the outgoing message header). Defaults
to the value of
.IR REMAILERADDR .
.TP
.I REMAILERNAME
The name of your remailer to be put in the message header on remailer
responses. Can contain whitespace.
.TP
.I ANONNAME
A name to appear in remailed messages. Defaults to the value of
.IR REMAILERNAME .
Can contain whitespace.
.TP
.I SHORTNAME
A short name to identify the remailer.
.TP
.I POOLSIZE
The number of messages to be kept in the reordering pool at all
times. Zero means to remail immediately. Five means there will always
be at least five messages in the pool at any time. If you support a
type1 remailer with reordering, its pool size should be the same as
.IR Mixmaster 's
or the
.B remailer-stats
report will be misleading.
.TP
.I RATE
The fraction of messages to send each time the pool is processed, in
%. A reduced rate can be useful to reduce system load when lots
of messages arrive at the same time and to avoid `flooding attacks'.
Default: 100.
.TP
.I NEWS
News posting software. Set to
.B mail-to-news
if you want to use a gateway, or leave empty if you do not want to
allow posting. Can contain whitespace. Default: No posting.
.TP
.I ORGANIZATION
A string to be used in the Organization: line of locally posted articles.
.TP
.I MAILtoNEWS
Address of a mail to news gateway to use to deliver news messages.
.TP
.I TYPE1
Command line to execute for old style type 1 messages.
Define this only if you wish to run a type 1 remailer under
the
.I Mixmaster
remailer. Can contain whitespace.
.TP
.I T1PGPONLY
Set to
.B 1
if you want the type 1 remailer to accept encrypted messages only.
.TP
.I MIDDLEMAN
If set to
.BR 1 ,
the key and statistics messages will not be sent directly. This flag
can be used in combination with the
.B destination.allow
file to hide the location of the remailer from users. (Note that the
address remains visible to the next-hop remailer.)
.TP
.I FORWARDTO
Where to forward messages that do not match
.IR destination.allow .
.B 0
means random remailer. Can contain whitespace. Default: one random
remailer.
.TP
.I IDEXP
Time (in hours) that packet ID numbers will be kept. Messages
containing a timestamp older than
.B IDEXP
hours are discarded. The default is one week, minimum four days to
allow clients to date their messages back. If set to
.BR 0 ,
IDs will be kept forever.
.TP
.I PACKETEXP
Time (in hours) that partially reconstructed multi-part 
messages will be kept. Default: one week.
.PP
The following definitions can be set in
.IR mix.h :
.TP
.I DISCLAIMER
A comment to be inserted into the anonymized messages.
.TP
.I SPOOL
The default directory where
.I Mixmaster
will look for its files if
.I MIXPATH
is not set.
.TP
.I PASSPHRASE
If no passphrase is given at compile time, this one is used. If you
are compiling a remailer, you must do this at compile time by calling
make with
.B make
.I system
.IR "\fBPASS=\fP'your pass phrase'" .
.SH FILES
.TP
.I mixmaster.conf
Configuration file for
.IR Mixmaster .
.TP
.I README
Instructions.
.TP
.I type2.list
List of known type 2 remailers and their abilities.
The first column is the nickname, the second is the address of
your remailer, the third is a unique string from the remailer's key,
the fourth column is the version string, and the fifth column
contains information about the capabilities of the remailer (\fBC\fP
= compression,
.B N
= posting to news,
.B M
= middle only remailer).
.TP
.I pubring.mix
The remailers' public keys.
.TP
.I mix.list
List of reliable Mixmaster remailers.
.SS Remailer files:
.TP
.I id.log
List of used packet ID numbers. They are used to prevent messages from
being sent twice (replay attacks). If this file does not exist,
.I Mixmaster
will assume that you do not want packet ID logging.
.TP
.I destination.block
A list of blocked destination addresses. The message is dropped if the
address matches a regular expression in a line of this file (or a
substring of the address is equal to a line of this file). The search
is case independent.

In a regular expression, a
.B .
represents any one character;
.B .*
stands for any sequence of characters. The dot itself is represented
by
.B \e.
.B ^
means to start the comparison at the leftmost character of the address;
.B $
means to end it at the rightmost character.
For example
.B whitehouse
matches any address containing the string "whitehouse".
.B ^president@.*whitehouse\e.gov
matches the addresses
.B president
may have at any computer in the
.B whitehouse.gov
domain, but not
.BR vice-president@whitehouse.gov .
.B \e.gov$
matches all addresses in the
.B .gov
toplevel domain, but not in
.BR .gov.au .
.TP
.I source.block
A list of blocked source addresses. The message is dropped if the
address matches a regular expression in a line of this file.
.TP
.I destination.allow
If this file exists, messages are delivered only if the address
matches a regular expression in a line of this file. All other
messages are forwarded to another remailer.
.TP
.I headers.del
A list of unwanted message header fields. A message header is filtered
out if it matches a regular expression in a line of this file.
.TP
.I mix.help
Help file sent in response to
.IR remailer-help .
.TP
.I mix.key
File with the key and a line for
.IR type2.list ,
sent in response to
.IR remailer-key .
To change this file, modify
.I keyinfo.txt
or
.IR mixmaster.conf ,
then run
.BR "mixmaster -K" .
.TP
.I keyinfo.txt
Information about the remailer key.
May contain type 1 PGP remailer keys.
.I keyinfo.txt
is prepended to 
.IR mix.key .
.TP
.I coerce
.B sendmail
replacement, to prevent abuse and traffic analysis of type-I messages.
.TP
.I Makefile
Edit
.B CFLAGS
if you want debugging information in the object code.
Remove
.B USE_RX
if you want to block addresses by case-independant substring search
instead of regular expressions. Remove
.B USE_ZLIB
if you don't want to support compression.
.TP
.I "\fBmail\fPXXXXXX"
Pool of processed remailer messages.
.TP
.I "\fBlat\fPXXXXXX"
Latent messages.
.TP
.I "\fBpac\fPXXXXXX"
Packets of partially processed multi-part messages.
.SH ENVIRONMENT
.TP
.I MIXPATH
Full path to the directory with
.IR Mixmaster 's
files.
.SH SEE ALSO
.BR premail (1),
.BR pgp (1),
.BR sendmail (8),
.BR procmail (1),
.BR crontab (1).
.SH AUTHOR
Lance Cottrell
<loki@obscura.com>