trunk/Mix/mixmaster.1

.TH MIX 1 "Mixmaster Version 3.0 beta"
.\" $Id: mix.1,v 1.15 2002/09/06 00:46:26 rabbi Exp $
.SH NAME
mix \- anonymous remailer software
.SH SYNOPSIS
.B mix
[\fB\-hpmdSvT\fR]
[\fB\-t \fIuser@host\fR]
[\fB\-g \fInewsgroup\fR]
[\fB\-s \fIsubject\fR]
[\fB\-a \fIfilename\fR]
[\fB\-n \fInym\fR]
[\fB\-l \fImix1,mix2,mix3,...\fR]
[\fB\-c \fInum\fR]
[\fIuser@host\fR]
[\fIfilename\fR]
.PP
.B mix
[\fB\-f\fR[\fBrfg\fR] \fIfilename\fR]
.PP
.B mix \-\-nym\-config=\fIyournym \fR[\fBname=\fIPseudonym\fR]
[\fBopt=\fInymserver options\fR] [\fB\-\-latency=\fIhours\fR]
[\fB\-\-reply\-chain=\fIrem1,rem2,...\fR]
.PP
.B mix \fR[\fB\-RGKSP\fR]
.SH DESCRIPTION
Mixmaster is an anonymous remailer. Remailers provide protection
against traffic analysis and allow sending mail anonymously or
pseudonymously.
.PP
In the non-interactive mode, Mixmaster reads a message from its
standard input or from a file.  Destination address and input file can
be specified in the command line.  If no address is given in the
command line, the input file is expected to contain a message complete
with mail headers.  Messages to be send under a pseudonym must contain
a
.I Nym:
header rather than
.IR From: .
.SH OPTIONS
.TP
.B "\-h, \-\-help"
Print a summary of command line options.
.TP
.B "\-t, \-\-to=\fIuser@host"
Add the destination address(es) to the message header. The input file
contains the message body without headers.
.TP
.B "\-g, \-\-post-to=\fInewsgroup"
Add the newsgroup(s) to the message header. The input file
contains the message body without headers.
.TP
.B
\-p, \-\-post
Post the message to Usenet.
.TP
.B
\-m, \-\-mail
Send the message as electronic mail. (This is the default.)
.TP
.B "\-s, \-\-subject=\fIsubject"
Add the
.I subject
to the message header.
.TP
.B "\-\-header=\fI'Header: text'
Add the header line to the message header.
.TP
.B "\-a, \-\-attachment=\fIfilename"
Attach
.I file
to the message.
.TP
.B "\-n, \-\-nym=\fIyournym"
Use the given pseudonym to send the message.
.TP
.B \-\-encrypt
Encrypt the message using the OpenPGP format.
.TP
.B \-\-sign
Sign the message using the OpenPGP format.
.TP
.B "\-l, \-\-chain=\fImix1,mix2,mix3,..."
Use this remailer chain to send the message. Alternatively, the input
message may contain a pseudo-header
.BR Chain: .
If no chain is specified, Mixmaster will use a chain of four random
remailers.
.TP
.B "\-T, \-\-type\-list"
Display the contents of the
.BR type2.list
file.
.TP
.B "\-c, \-\-copies=\fInum"
Send
.I num
copies of the message to increase reliability.
.TP
.B \-d, \-\-dummy
Generate a dummy message as protection against traffic analysis.
.TP
.B \-S, \-\-send
Send the message(s) from the pool.
.TP
.B \-v, \-\-verbose
Output informational messages.
.TP
.B "\-f\fR [\fIfile\fR]"
Read a mail folder. This function requires ncurses support.
.TP
.B "\-fr\fR [\fIfile\fR]"
Reply to a message.
.TP
.B "\-ff\fR [\fIfile\fR]"
Post a follow-up to a message.
.TP
.B "\-fg\fR [\fIfile\fR]"
Send a group reply to a message.
.TP
.B "\-\-nym\-config=\fInym \fR[\fBname=\fIPseudonym\fR] [\fBopt=\fInymserver options\fR]"
Generate a pseudonym.

For example, to set up a pseudonym with two mail reply blocks and nym
server acknowledgment for successfully remailed messages:
.PP
mix --nym-config=yournym@nym.alias.net opt=+acksend --to=user@domain
--reply-chain=privacy,hr13,hyper --to=user@domain
--reply-chain=replay,squirrel,mix

To use a message pool:
.PP
mix --nym-config=yournym@nym.alias.net
--post-to=alt.anonymous.messages
--subject="secret message" --reply-chain=base
.TP
.B "\-\-latency=\fIhours"
Reply chain latency.
.TP
.B "\-\-reply\-chain=\fIrem1,rem2,..."
Reply chain for the pseudonym.
.SS Remailer options:
.TP
.B \-R, \-\-read\-mail
Read a remailer message from standard input and store it in the pool.
.TP
.B \-I, \-\-store\-mail
Read a remailer message from standard input and store it in the pool
without decrypting it immediately. It will be processed the next time
Mixmaster processes the queue (called with \fP-M\fP or in daemon mode).
.TP
.B \-P, \-\-pop-mail
Read mail from the POP3 servers listed in
.BR pop3.cfg .
.TP
.B \-M, \-\-remailer
Check if it is time to perform the regular remailer actions:
Send messages from the pool, get mail from POP3 servers and keep the
internal files up\-to\-date.
.TP
.B \-D, \-\-daemon
Detach from the console and process the pool, get mail and update the
internal files in regular intervals.
.TP
.B \-\-no-detach
Run as daemon but do not detach from the terminal (This option is
only useful together with \fB--daemon\fP).
.TP
.B -G, \-\-generate\-key
Generate a new remailer key.
.TP
.B \-K, \-\-update\-keys
Generate remailer keys if necessary.
.TP
.B \-S, \-\-send
Force sending the message(s) from the pool.
.TP
.B \-\-install\-svc
Install the Mixmaster Service on Win32.
.TP
.B \-\-remove\-svc
Remove the Mixmaster Service on Win32.
.TP
.B \-\-run\-svc
Run the Mixmaster Service on Win32.
.SH CONFIGURATION
Mixmaster reads its configuration from the file
.B mix.cfg
in its working directory.  The configuration file consists of lines of
the type
.PP
.I VARIABLE       values
.PP
and of comments, which begin with a
.B #
character.  The variables have reasonable default values, but it is
useful to create a configuration file using the
.B Install
script when setting up a remailer.
.PP
All configuration variables can be overridden from the command line,
e.g.
.B mix -S --POOLSIZE=0 --RATE=100
will send all messages currently in the message pool.
.SS Client configuration:
.TP
.B ADDRESS
Your address for sending non-anonymous messages.
.TP
.B NAME
Your real name (used for sending non-anonymous messages).
.TP
.B MAILtoNEWS
Address of a mail-to-news gateway. Default:
.BR mail2news@nym.alias.net .
.TP
.B CHAIN
Default chain for anonymous messages to be sent.
.B CHAIN
is a comma-separated list of remailer names or addresses.
A
.B *
represents a random reliable remailer. Default:
.BR *,*,*,* .
.TP
.B NUMCOPIES
Number of redundant copies of an anonymous message to be
sent, unless specified otherwise on the command line.
Default:
.BR 1 .
.TP
.B DISTANCE
When selecting random remailers, the chain will contain
.I DISTANCE
other remailers between two occurences of the
same remailer in the chain. Default:
.BR 2 .
.TP
.B MINREL
Only select remailers with a reliability of at least
.IR MINREL %.
Default:
.BR 98 .
.TP
.B RELFINAL
Only select a remailer with a reliability of at least
.IR RELFINAL %
as the final remailer. Default:
.BR 99 .
.TP
.B MAXLAT
Only select remailers with a latency of maximally
.IR MAXLAT .
Default:
.BR 36h .
.TP
.B PGPPUBRING
Path to your public PGP key ring. Default:
.BR ~/.pgp/pubring.pkr .
(Windows default: PGP registry value.)
.TP
.B PGPSECRING
Path to your secret PGP key ring. Default:
.BR ~/.pgp/secring.skr .
(Windows default: PGP registry value.)
.SS Remailer configuration:
.TP
.B SENDMAIL
Path to the
.BR sendmail (1)
program. If set to
.BR outfile ,
Mixmaster will create text files named
.BI out * .txt
in the
.B pool
directory instead of sending mail.
Default:
.BR "/usr/lib/sendmail -t" .
.TP
.B SMTPRELAY
Name of SMTP relay. If set, mail will be delivered to the relay
rather than by
.BR sendmail (1).
.TP
.B HELONAME
Name used in the SMTP dialogue.
Default: The
.I ENVFROM
host name or the current network name associated with the socket.
.TP
.B ENVFROM
Envelope from address used in the SMTP dialogue. (When the client is
used to send non-anonymous messages,
.I ADDRESSS
is used instead.)
Default:
.IR ANONADDR .
.TP
.B NEWS
Path to the news posting program, or address of a
mail-to-news gateway. Default: no news posting.
(When using a news posting program,
.I ORGANIZATION
contains
an Organization line for anonymous messages. Default:
.BR "Anonymous Posting Service" .)
.TP
.B SENDANONMAIL
Path to a program for sending anonymous mail. Default:
.IR SENDMAIL .
.B SENDANONMAIL
can be used to invoke an external mail filter for anonymized messages.
.TP
.B SHORTNAME
A short name for the remailer to be used in lists. Defaults to the host name.
.TP
.B REMAILERADDR
The remailer mail address.
.TP
.B ANONADDR
An address to be inserted in the
.B From:
line of anonymous messages. Default:
.IR REMAILERADDR .
.TP
.B REMAILERNAME
A name to be inserted in the
.B From:
line of remailer status
messages. Default:
.BR "Anonymous Remailer" .
.TP
.B ANONNAME
A name to be inserted in the
.B From:
line of anonymous messages.
Default:
.BR "Anonymous" .
.TP
.B COMPLAINTS
An address for complaints to be sent to. Default:
.IR REMAILERADDR .
.TP
.B ERRLOG
Name of a file to log error messages, or
.B stdout
or
.BR stderr .
Default:
.BR stderr .
(When run from a tty, Mixmaster will always print a copy of error
messages to
.BR stderr .)
.TP
.B MAILBOX
A generic mail folder for non-remailer messages that are not stored in
any of the following folders.
If
.B MAILBOX
begins with a
.BR | ,
it specifies the path to a program. If it contains an
.B @
sign, the message is forwarded to the given address (with an
.B X-Loop:
header to prevent mail loops). If it ends with a
.B /
it is threated as a Maildir, otherwise the message is appended
to the given file name or written to standard output if
.B MAILBOX
is
.BR stdout .
Default:
.BR mbox .
.TP
.B MAILIN
If defined an additional mail folder where Mixmaster should read messages from
when processing its pool. If it ends with a
.B /
it is threated as a Maildir, otherwise a standard mbox format file
is expected. All messages are removed from the folder after reading.
.B MAILIN
is not set by default.
It is an incredible bad idea to set this the same as \fBMAILBOX\fP.
.TP
.B MAILABUSE
Mail folder for messages sent to the
.I COMPLAINTS
address.
Default:
.IR MAILBOX .
.TP
.B MAILBLOCK
Mail folder for messages sent to the remailer address with a
.B DESTINATION-BLOCK
line.
Default:
.IR MAILBOX .
.TP
.B MAILUSAGE
Mail folder for messages sent to the remailer address that do not
contain any valid remailer commands. Default:
.BR /dev/null .
.TP
.B MAILANON
Mail folder for replies sent to the
.I ANONADDR
address.
Default:
.BR /dev/null .
.TP
.B MAILERROR
Mail folder for messages that cannot be decrypted or contain other
errors. Default:
.BR /dev/null .
.TP
.B MAILBOUNCE
Mail folder for bounce messages. Default:
.IR MAILBOX .
.TP
.B VERBOSE
If
.B VERBOSE
is set to
.BR 0 ,
Mixmaster will log error
messages only. If it is set to
.BR 1 ,
error message and warnings are logged. If
.B VERBOSE
is set to
.BR 2 ,
successful operation is logged as well.
If set to
.BR 3 ,
a log file entry is created whenever a message
enters or leaves the pool.  Default:
.BR 2 .
.TP
.B PASSPHRASE
A passphrase used to protect the remailer secret keys from
casual attackers. This setting overrides the compile-time
defined
.B COMPILEDPASS
which is now deprecated.
This should
.I not
be the same as the client passphrase.
.PP
The following variables can be set to
.B y
or
.BR n :
.TP
.B REMAIL
Enable remailer functionality. Default:
.BR y .
.TP
.B MIDDLEMAN
Act as an intermediate hop only, forward anonymized
messages to an other remailer. This mode can be used
where complaints about anonymous messages must be
avoided. (The variable
.B FORWARDTO
specifies the remailer
chain to be used; default: 
.BR * .)
Default:
.BR n .
.TP
.B AUTOREPLY
Send help files in response to non-remailer messages. Explicit
.B remailer-help
requests are always served.
Default:
.BR n .
.TP
.B MIX
Accept Mixmaster messages. Default:
.BR y .
.TP
.B PGP
Accept OpenPGP-encrypted Cypherpunk remailer messages.
Default:
.BR y .
.TP
.B UNENCRYPTED
Accept unencrypted Cypherpunk remailer messages.
Default:
.BR n .
.TP
.B REMIX
Re-encrypt Type I messages to other remailers in the Mixmaster format
.RB ( x
= only when requested by user explicitly).
Default:
.BR y .
.TP
.B BINFILTER
Filter out binary attachments. Default:
.BR n .
.TP
.B LISTSUPPORTED
List known remailers and their keys in remailer-conf reply. Default:
.BR y .
.TP
.B MID
Use a hash of the message body as Message-ID, to avoid
Usenet spam. Default:
.BR y .
If
.B MID
is set to a string
beginning with
.BR @ ,
that string is used as the domain part of the message ID.
.TP
.B AUTOBLOCK
Allow users to add their address to the
.B dest.blk
file by sending the remailer a message containing the line
.BR destination-block .
Default:
.BR y .
.PP
The following variables have numeric values:
.TP
.B POOLSIZE
The size of the Mixmaster reordering pool. Larger sizes
imply higher security and longer delays. Default:
.BR 0 .
.TP
.B RATE
Percentage of messages from the pool to be sent. Default:
.BR 100 .
Lower values cause the pool to increase in size when
many messages are recieved at a time, reducing the effect
of flooding attacks.
.TP
.B SIZELIMIT
Maximal size for anonymous messages in kB.
.B 0
means no limit.
Default:
.BR 0 .
.TP
.B POP3SIZELIMIT
Maximal size for incoming messages in kB when using POP3.
.B 0
means no limit.
Default:
.BR 0 .
Larger messages are deleted unread if
.B POP3DEL
is set to
.BR y ,
and left on the server otherwise.
.TP
.B INFLATEMAX
Maximal size for
.B Inflate:
padding in kB.
.B 0
means padding is not allowed.
Default:
.B 50
.BR kB .
.TP
.B MAXRANDHOPS
Maximal chain length for message forwarding requested by
.B Rand-Hop
directives.
Default:
.BR 20 .
.PP
The following are time variables. They can be given as days, hours, or
minutes.
.TP
.B SENDPOOLTIME
How often Mixmaster should check the pool for messages
to be sent. Default:
.BR 1h .
.TP
.B POP3TIME
How often Mixmaster should check the POP3 accounts
listed in
.B pop3.cfg
for new mail.
Default:
.BR 1h .
.TP
.B MAILINTIME
How often Mixmaster should read mail from
.BR MAILIN
and process mails fetched via POP3. Processing here means to 
answer remailer-xxx requests and decrypt messages to the Mixmaster
and place them in the pool. No other processing of the pool is
done. This action is always performed sending out messages from the pool (at
.BR SENDPOOLTIME
intervals) or receiving mail via POP3 (at
.BR POP3TIME
invervals). Default:
.BR 5m .
.TP
.B PACKETEXP
How long to store parts of incomplete multipart messages and other 
temporary pool files.
Default:
.BR 7d .
.TP
.B IDEXP
Mixmaster keeps a log of packet IDs to prevent replay
attacks.
.B IDEXP
specifies after which period of time old
IDs are expired. Default:
.BR 7d ,
minimum:
.BR 5d .
If set to
.BR 0 ,
no log is kept.
.PP
The following strings must be specified at compile-time in
.BR config.h .
Usually it is not necessary to modify any of these:
.TP
.B
DISCLAIMER
A default string to be inserted in the header of all anonymous
messages if no
.B disclaim.txt
file is available. If
.B DISCLAIMER
contains the substring
.BR "%s" ,
it will be substituted with the
.I COMPLAINTS
address.
.TP
.B FROMDISCLAIMER
A default string to be inserted at the top of the message body
if an anonymous message contains a user-supplied
.B From:
line and no
.B fromdscl.txt
file is available.
.TP
.B MSGFOOTER
A default string to be inserted at the bottom of the message body
of all anonymous messages and no
.B footer.txt
file is available.
.TP
.B BINDISCLAIMER
A string to replace the body of a binary attachment when
the remailer is configured to filter out binaries.
.TP
.B CHARSET
The character set used for MIME-encoded header lines.
.TP
.B DESTBLOCK
A quoted list of files that contain blocked addresses. 
Files must be separated by one space. Mixmaster will choose 
the first file for writing 
.B AUTOBLOCK
is enabled.
.PP
The following variables can be set in the
.B Makefile
or in
.BR config.h :
.TP
.B COMPILEDPASS
A passphrase used to protect the remailer secret keys from
casual attackers. You can use
.B `make PASS="\fIyour passphrase\fB"'
to set a passphrase. This should
.I not
be the same as the client passphrase. This option is now deprecated in 
favor of the configuration file option
.BR PASSPHRASE .
.TP
.B SPOOL
Set
.B SPOOL
if you want to use a default directory other than
.B ~/Mix
or if Mixmaster is run in an environment where
.B $HOME
is not set, e.g. when invoked via
.BR .forward .
This value can be overridden by use of the environment variable
.BR $MIXPATH .
.TP
.B USE_SSLEAY
Use the SSLeay/OpenSSL cryptographic library. Currently this is the
only cryptographic library supported by Mixmaster.
.TP
.B USE_IDEA
Use the IDEA encryption algorithm. A license is required to use IDEA
for commercial purposes. See file
.B idea.txt
for details.
.TP
.B USE_PGP
Support the OpenPGP encryption format. Mixmaster does not call any
external encryption program.
.TP
.B USE_PCRE
Use the regular expression library.
.TP
.B USE_ZLIB
Use the
.B zlib
compression library.
.TP
.B USE_NCURSES
Use the
.B ncurses
library.
.TP
.B USE_SOCK
Use sockets to transfer mail by POP3 and SMTP.
.TP
.B USE_WINGUI
Use the
.B Win32
GUI.
.TP
.B HAVE_GETDOMAINNAME
The
.BR getdomainname (2)
function is available.
.SH FILES
These filenames can be overriden by setting the corresponding configuration
option (given in parentheses).
.TP
.B mix.cfg
Mixmaster configuration file.
.TP
.B pubring.asc
Type 1 remailer keys (\fBPGPREMPUBASC\fP).
.TP
.B pubring.mix
Type 2 remailer keys (\fBPUBRING\fP).
.TP
.B rlist.txt
List of reliable type 1 remailers (\fBTYPE1LIST\fP).
.TP
.B mlist.txt 
List of reliable type 2 remailers (\fBTYPE2REL\fP).
.TP
.B type2.list
List of known type 2 remailers (optional) (\fBTYPE2LIST\fP).
.SS Remailer files:
.TP
.B disclaim.txt
A string to be inserted in the header of all anonymous
messages (\fBDISCLAIMFILE\fP).
.TP
.B fromdscl.txt
A string to be inserted at the top of the message body
if an anonymous message contains a user-supplied
.B From:
line (\fBFROMDSCLFILE\fP).
.TP
.TP
.B footer.txt
A string to be inserted at the bottom of the message body
of all anonymous messages (\fBMSGFOOTERFILE\fP).
.TP
.B help.txt
Help file sent in response to
.B remailer-help
requests (\fBHELPFILE\fP).
.TP
.B adminkey.txt
The PGP key of the remailer operator sent in response to
.B remailer-adminkey
requests (\fBADMKEYFILE\fP).
.TP
.B abuse.txt
File sent in response to mail to the
.I COMPLAINTS
address if
.B AUTOREPLY
is set (\fBABUSEFILE\fP).
.TP
.B reply.txt
Help file sent in response to replies to anonymous messages if
.B AUTOREPLY
is set (\fBREPLYFILE\fP).
.TP
.B usage.txt
Help file sent in response to non-remailer message sent to
.I REMAILERADDR
if
.B AUTOREPLY
is set. If
.B usage.log
exists, recipients are logged and a reply is sent only once to avoid
mail loops (\fBUSAGEFILE\fP).
.TP
.B blocked.txt
Information sent in response to automatically processed blocking requests if
.B AUTOREPLY
is set (\fBBLOCKFILE\fP).
.TP
.B pop3.cfg
List of POP3 accounts with lines of the form
.I account@host.domain password
to get remailer messages from. The lines may optionally contain the
keyword "apop" or "pass" to select an authentication method (\fBPOP3CONF\fP).
.TP
.B dest.alw
List of addresses to which Mixmaster will deliver, even in middleman mode (\fBDESTALLOW\fP).
.TP
.B dest.blk
List of blocked destination addresses.
Mixmaster does not send mail to the blocked addresses listed in this file (\fBDESTBLOCK\fP).
.TP
.B rab.blk
Identical to
.BR dest.blk ,
except that Mixmaster will not write to this file.
For use with external remailer abuse blocklists.
.TP
.B source.blk
List of blocked source addresses.  If an incoming message originates
from an address or IP in this in this list, it will be ignored. This
feature can be used to avoid spam and other abusive mail (\fBSOURCEBLOCK\fP).
.TP
.B header.blk
List of unwanted header fields. The file is used to delete unwanted
header lines (e.g. lines that indicate a false identity, or Usenet
control messages), and do other header filtering (\fBHDRFILTER\fP).
.PP
A destination address or header line is left out if it contains a
search string or matches a regular expression specified in the block
file. Lines in the block file that begin and end with a slash
.RB ( /\fIregexp\fB/ )
are interpreted as regular expressions. Lines without
slashes are used for case-independent substring search.

If a message contains a header line that matches a
.B /\fIregexp\fB/q
entry in
.BR header.blk ,
the entire message is deleted.

In addition, regular expressions can be substituted. Backreferences
are supported. For example

 /^From: *([^@]*) <.*>/From: $1/
 /^From:.* \\(([^@]*)\)/From: $1/
 /^From: *([^@]*).*$/From: $1 <\fInobody@remailer.domain\fR>/

would allow user-defined names in the
.B From:
line, while replacing any given address with the remailer address.
.SS
Mixmaster uses the following files internally:
.TP
.B mixrand.bin
Random seed file (\fBMIXRAND\fP).
.TP
.B secrets.mix
List of your nyms with configuration data (encrypted) (\fBNYMDB\fP).
.TP
.B nymsec.pgp
Your nyms' secret PGP keys (encrypted) (\fBNYMSECRING\fP).
.TP
.B secring.pgp
Remailer type 1 secret keys (\fBPGPREMSECRING\fP).
.TP
.B secring.mix
Remailer type 2 secret keys (\fBSECRING\fP).
.TP
.B pgpkey.txt
The public type 1 remailer key (\fBPGPKEY\fP).
.TP
.B key.txt
The public type 2 remailer key (\fB\fP).
.TP
.B id.log
Log file of messages already processed (\fBKEYFILE\fP).
.TP
.B stats.log
Log file for remailer statistics (\fBSTATS\fP).
.TP
.B time.log
Time for periodic remailer actions (\fBREGULAR\fP).
.TP
.B dhparam.mix
Public Diffie-Hellman parameters used for El-Gamal key generation (\fBDHPARAMS\fP).
.TP
.B dsaparam.mix
Public DSA parameters used for DSA key generation (\fBDSAPARAMS\fP).
.TP
.BI pool/m *
Message pool.
.TP
.BI pool/p *
Partial messages.
.TP
.BI pool/l *
Latent messages.
.TP
.BI pool/s *
Messages to be sent.
.TP
.BI pool/t *
Temporary files.
.SH ENVIRONMENT
.TP
.I MIXPATH
The path to the Mixmaster directory. The default is
.BR ~/Mix .
.TP
.I MIXPASS
The passphrase used to protect your nyms and PGP keys.
(The remailer uses a different passphrase.) If
.I MIXPASS
is not set, the client will ask for a passphrase.
.SH SEE ALSO
.BR pgp (1),
.BR procmail (1),
.BR sendmail (8).
.SH COPYRIGHT
(C) 1999 Anonymizer Inc.
Mixmaster may be redistributed and modified under certain conditions.
This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF
ANY KIND, either express or implied. See the file COPYRIGHT for
details.