Provided by: opendkim_2.5.2+dfsg-1ubuntu3_amd64 bug

NAME

       opendkim - DKIM signing and verifying filter for MTAs

SYNOPSIS

       opendkim  -p  socketspec [-A] [-b modes] [-c canon] [-d domain[,...]]  [-D] [-e name] [-f]
       [-F time] [-k keyfile] [-l] [-L min] [-n] [-o hdrlist] [-P pidfile]  [-q]  [-Q]  [-r]  [-s
       selector]  [-S  signalg]  [-t  testfiles] [-T secs] [-u userid[:group]] [-v] [-V] [-W] [-x
       configfile]

DESCRIPTION

       opendkim implements the DKIM standard for signing and verifying e-mail messages on a  per-
       domain basis.

       opendkim  uses  the  milter  interface,  originally distributed as part of version 8.11 of
       sendmail(8), to provide DKIM signing  and/or  verifying  service  for  mail  transiting  a
       milter-aware MTA.

       Most,  if  not  all,  of  the  command  line  options listed below can also be set using a
       configuration file.  See the -x option for details.

DATA SETS

       Many of the command line and configuration file parameters will refer to  a  "dataset"  as
       their  values.  This refers to a string that either contains the list of desirable values,
       or to a file that contains them, or (if enabled at compile time) a database containing the
       data.

       Some  data  sets  require  that  the  value contain more than one entry.  How this is done
       depends on which data set type is used.

       Which type is used depends on the format of the specification string.  In particular:

       a)     If the string begins with "file:", then the remainder of the string is presumed  to
              refer  to  a  flat file that contains elements of the data set, one per line.  If a
              line contains whitespace-separated values, then the line is preusmed  to  define  a
              key  and  its  corresponding  value.   Blank  lines are ignored, and the hash ("#")
              character denotes the start of a comment.  If a value  contains  multiple  entries,
              the entries should be separated by colons.

       b)     If  the  string begins with "refile:", then the remainder of the string is presumed
              to specify a file that contains  a  set  of  patterns,  one  per  line,  and  their
              associated  values.   The  pattern  is  taken as the start of the line to the first
              whitespace, and the portion after that whitespace is taken as the value to be  used
              when  that pattern is matched.  Patterns are simple wildcard patterns, matching all
              text except that the asterisk ("*") character is considered a wildcard.  If a value
              contains multiple entries, the entries should be separated by colons.

       c)     If  the  string  begins  with  "db:" and the program was compiled with Sleepycat DB
              support, then the remainder of the string  is  presumed  to  identify  a  Sleepycat
              database  containing keys and corresponding values.  These may be used only to test
              for membership in the data set, or for storing keys and corresponding values.  If a
              value contains multiple entries, the entries should be separated by colons.

       d)     If  the  string begins with "dsn:" and the OpenDKIM library was compiled to support
              that database type, then  the  remainder  of  the  string  is  a  Data  Store  Name
              describing  the type, location parameters and access credentials for an ODBC or SQL
              database.  The DSN is of the form:

              backend://[user[:pwd]@][port+]host/dbase[/key=value[?...]]

              where backend is the name of a supported backend database mechanism (e.g. "mysql"),
              user  and  password  are optional login credentials for the database, port and host
              describe the destination of a TCP connection to connect to that database, dbase  is
              the  name  of  the database to be accessed, and the key=value pairs must specify at
              least "table", "keycol" and "datacol" values specifying the name of the table,  the
              name  of  the column to consider as the key, and the name(s) of the column(s) to be
              considered as the values (separated by commas).  For example (all in one line):

              mysql:://dbuser:dbpass@3306+dbhost/odkim/table=macros
                       ?keycol=host?datacol=v1,v2

              defines a MySQL database listening at  port  3306  on  host  "dbhost";  the  userid
              "dbuser"  and password "dbpass" should be used to access the database; the database
              name is "odkim", and the data are in columns "host" (the keys) and  "v1"  and  "v2"
              (the values) inside table "macros".  This example would thus return two values when
              a match is found.

              No value within the DSN may contain any of the  six  punctuation  characters  (":",
              "/", "@", "+", "?" and "=") used to separate portions of the DSN from each other.

       e)     If  the  string  begins  with "ldap:", "ldaps:" or "ldapi:", it is presumed to be a
              space-separated set of one or more LDAP URLs that identify a set of servers  to  be
              queried.   The  first  one  should  be a full RFC4516 LDAP URL indicating a base DN
              template and optional scope, filter and attribute names to use  in  queries.   When
              constructing a DN template or filter, the special tokens "$d" and "$D" are replaced
              with the key being queried and they key broken into components,  separated  at  "."
              characters,  each component preceded by "dc=" and followed by "," (so "example.com"
              would become "dc=example,dc=com").  If a data set requires multiple  values  to  be
              returned,  the  appropriate attribute names should be given in the correct order to
              satisfy such requests.

       f)     If the string begins with "lua:", it is presumed to refer to a file that contains a
              Lua  script to be executed whenever a query is performed.  The key for the query is
              placed in a global variable called  "query",  which  the  called  script  can  then
              access.   The  script  may  return any number of values as required for the type of
              query being performed.

       g)     If the string begins with "memcache:", it is presumed to refer to  a  memory  cache
              database  provided  by memcached.  The remainder of the string is a comma-separated
              list of hosts to which query attempts should be made, each optionally  followed  by
              ":"  and a port number; that list must be followed by a slash ("/") character and a
              string that will be used to prefix queries send to the cache.  For example:

              memcache:localhost,otherhost/keyname

              This would use either "localhost"  or  "otherhost"  to  conduct  queries,  and  all
              strings sent to the dataset will be prefixed with "keyname:".

       h)     If  the  string contains none of these prefixes but ends with ".db", it is presumed
              to be a Sleepycat DB as described above (if support for same is compiled in).

       i)     If the string contains none of  these  prefixes  but  starts  with  a  slash  ("/")
              character, it is presumed to be a flat file as described above.

       j)     If  the  string begins with "csl:", the string is treated as a comma-separated list
              as described in k) below.

       k)     In any other case, the string is presumed to be a comma-separated  list.   Elements
              in  the  list  are  either simple data elements that are part of the set or, in the
              case of an entry of the form "x=y", are stored  as  key-value  pairs  as  described
              above.

OPTIONS

       -A     Automatically  re-start  on  failures.   Use  with  caution;  if  the  filter fails
              instantly after it starts, this can cause  a  tight  fork(2)  loop.   This  can  be
              mitigated  using  some  values  in the configuration file to limit restarting.  See
              opendkim.conf(5).

       -b modes
              Selects operating modes.  modes is a  concatenation  of  characters  that  indicate
              which  mode(s)  of  operation  are  desired.   Valid  modes  are  s  (signer) and v
              (verifier).  The default is sv except in test mode (see -t below) in which case the
              default is v.

       -c canon
              Selects  the  canonicalization  method(s)  to  be used when signing messages.  When
              verifying, the message's  DKIM-Signature:  header  specifies  the  canonicalization
              method.   The  recognized  values  are  relaxed  and  simple as defined by the DKIM
              specification.  The default  is  simple.   The  value  may  include  two  different
              canonicalizations  separated  by  a  slash ("/") character, in which case the first
              will be applied to the headers and the second to the body.

       -d dataset
              A set of domains whose mail should be signed  by  this  filter.   Mail  from  other
              domains will be verified rather than being signed.

       -D     Sign subdomains of those listed by the -d option as well as the actual domains.

       -e name
              Extracts the value of name from the configuration file (if any).

       -f     Normally  opendkim  forks and exits immediately, leaving the service running in the
              background.  This flag suppresses that behaviour so that it runs in the foreground.

       -F time
              Specifies a fixed time to use when generating signatures.  Ignored unless also used
              in  conjunction  with -t (see below).  The time must be expressed in the usual UNIX
              time_t (seconds since epoch) format.

       -k keyfile
              Gives the location of a PEM-formatted private  key  to  be  used  for  signing  all
              messages.  Ignored if a configuration file is referenced that defines a KeyTable.

       -l     Log via calls to syslog(3) any interesting activity.

       -L min[%+]
              Instructs  the verification code to fail messages for which a partial signature was
              received.  There are three possible formats: min indicating at least min  bytes  of
              the  message  must  be signed (or if the message is smaller than min then all of it
              must be signed); min% requiring that at least min percent of the  received  message
              must  be  signed;  and min+ meaning there may be no more than min bytes of unsigned
              data appended to the message for it to be considered valid.

       -n     Parse the configuration file and  command  line  arguments,  reporting  any  errors
              found,  and  then  exit.   The  exit  value  will be 0 if the filter would start up
              without complaint, or non-zero otherwise.

       -o dataset
              Specifies a list of headers that should be omitted when generating signatures.   If
              an  entry in the list names any header which is mandated by the DKIM specification,
              the entry is ignored.  A set of headers is listed  in  the  DKIM  specification  as
              "SHOULD  NOT" be signed; the default list for this parameter contains those headers
              (Return-Path, Received, Comments, Keywords, Bcc,  Resent-Bcc  and  DKIM-Signature).
              To  omit  no  headers,  simply use the string "-" (or any string that will match no
              headers).

       -p socketspec
              Specifies  the  socket  that  should  be  established  by  the  filter  to  receive
              connections  from sendmail(8) in order to provide service.  socketspec is in one of
              two forms: local:path which creates a UNIX domain socket at the specified path,  or
              inet:port[@host]  which creates a TCP socket on the specified port.  If the host is
              not given as either a hostname or an IP address, the socket will  be  listening  on
              all interfaces.  If neither socket type is specified, local is assumed, meaning the
              parameter is interpreted as a path at which the socket  should  be  created.   This
              parameter is mandatory.

       -P pidfile
              Specifies a file into which the filter should write its process ID at startup.

       -q     Requests  that  messages  which  fail  verification  be  quarantined  by  the  MTA.
              (Requires a sufficiently recent version of the milter library.)

       -Q     Query test mode.   The  filter  will  read  two  lines  from  standard  input,  one
              containing  a  database description to be opened and one containing a string of the
              form "q/n" where "q" is the query to be performed and "n" is the number  of  fields
              to be retrieved.

       -r     Checks  all  messages  for compliance with RFC5322 header count requirements.  Non-
              compliant messages are rejected.

       -s selector
              Defines the name of the selector to be used when signing messages.   See  the  DKIM
              specification for details.

       -S signalg
              Selects the signing algorithm to use when generating signatures.  Use 'opendkim -V'
              to see the list of supported algorithms.   The  default  is  rsa-sha256  if  it  is
              available, otherwise it will be rsa-sha1.

       -t testfiles
              Evaluates  (verifies)  one or more RFC5322-formatted message found in testfiles and
              exits.  The value of testfiles should be a comma-separated  list  of  one  or  more
              filenames,  one  of  which  may  be "-" if the message should be read from standard
              input.

       -T secs
              Sets the DNS timeout in seconds.  A value  of  0  causes  an  infinite  wait.   The
              default is 5.  Ignored if not using an asynchronous resolver package.  See also the
              NOTES section below.

       -u userid[:group]
              Attempts to be come the specified userid before starting operations.   The  process
              will  be assigned all of the groups and primary group ID of the named userid unless
              an alternate group is  specified.   See  the  FILE  PERMISSIONS  section  for  more
              information.

       -v     Increase  verbose  output  during  test mode (see -t above).  May be specified more
              than once to request increasing amounts of output.

       -V     Print the version number and supported canonicalization and  signature  algorithms,
              and then exit without doing anything else.

       -W     If  logging is enabled (see -l above), issues very detailed logging about the logic
              behind the filter's decision to either sign a message or verify it.  The "W" stands
              for  "Why?!"   since  the  logic  behind  the  decision  is  non-trivial and can be
              confusing to administrators not familiar with its operation.  A description of  how
              the  decision is made can be found in the OPERATION section of this document.  This
              causes a large increase in the amount of log data generated for each message, so it
              should be limited to debugging use and not enabled for general operation.

       -x configfile
              Read  the named configuration file.  See the opendkim.conf(5) man page for details.
              Values in the configuration file are overridden when their equivalents are provided
              on  the  command  line  until a configuration reload occurs.  The OPERATION section
              describes how reloads are triggered.  The default is to read a  configuration  file
              from  /etc/opendkim.conf  if  one  exists,  or  otherwise  to apply defaults to all
              values.

OPERATION

       A message will be verified unless it conforms to the signing criteria, which are: (1)  the
       domain  on  the  From:  address  or  Sender: address (if present) must be listed by the -d
       command line switch or the Domain configuration file  setting,  and  (2)  (a)  the  client
       connecting  to  the  MTA  must have authenticated, or (b) the client connecting to the MTA
       must be listed in the file referenced by the InternalHosts configuration file setting  (or
       be  in  the default list for that option), or (c) the client must be connected to a daemon
       port named by the MTAs configuration file setting, or (d) the MTA must  have  set  one  or
       more macros matching the criteria set by the MacroList configuration file setting.

       For  (a) above, the test is whether or not the MTA macro "{auth_type}" is set and contains
       any non-empty value.  This means the MTA must pass the value of that macro to  the  filter
       before or during the end-of-header (EOH) phase in order for its value to be tested.  Check
       your MTA's configuration documentation for details.

       When signing a message, a DKIM-Signature: header will be prepended to  the  message.   The
       signature  is  computed  using the private key provided.  You must be running a version of
       sendmail(8) recent enough to be able to do header prepend operations (8.13.0 or later).

       When verifying a message, an Authentication-Results: header will be prepended to  indicate
       the  presence  of a signature and whether or not it could be validated against the body of
       the message using the public key advertised by the sender's nameserver.  The value of this
       header can be used by mail user agents to sort or discard messages that were not signed or
       could not be verified.

       Upon receiving SIGUSR1, if the filter was started with a configuration file,  it  will  be
       re-read and the new values used.  Note that any command line overrides provided at startup
       time will be lost when this is done.  Also, the following configuration file  values  (and
       their  corresponding  command  line  items, if any) are not reloaded through this process:
       AutoRestart (-A),  AutoRestartCount,  AutoRestartRate,  Background,  MilterDebug,  PidFile
       (-P), POPDBFile, Quarantine (-q), QueryCache, Socket (-p), StrictTestMode, TestPublicKeys,
       UMask, UserID (-u).  The filter does not automatically check the  configuration  file  for
       changes and reload.

MTA MACROS

       opendkim  makes use of three MTA-provided macros, plus any demanded by configuration.  The
       basic three are: "i" (the envelope ID, also known as the job ID or the queue ID), which is
       used for logging; "daemon_name" (the symbolic name given to the MTA instance that accepted
       the connection), which is used when performing tests against any "MTAs" setting used;  and
       "auth_type",  which  is  used to determine whether or not the SMTP client authenticated to
       the MTA.  If the MTA does not provide them to opendkim then it is not able to apply  their
       corresponding tests or do useful logging.  Consult your MTA documentation to determine how
       to adjust your its configuration if some or all of these are not available.

FILE PERMISSIONS

       When the filter is started as the superuser and the  UserID  (-u)  setting  is  used,  the
       filter  gives up its root privileges by changing to the specified user after the following
       steps are taken: (1) the configuration file (if any) is loaded; (2) if  the  KeyFile  (-k)
       setting  is  used,  that key is loaded into memory; (3) all data sets in the configuration
       file are opened, and those that are based on flat files are also read into memory; and (4)
       if  ChangeRootDirectory is set, the process root is changed to that directory.  This means
       on configuration reload, the filter will not be accessing these files or the configuration
       file  as  the superuser (and possibly from a different root), and any key files referenced
       by the KeyTable will also be accessed by the new user.

       Thus, keys referenced  by  the  KeyTable  must  always  be  accessible  for  read  by  the
       unprivileged user.  Also, run-time reloads are not possible if any of the other files will
       not be readable by the unprivileged user.

ENVIRONMENT

       The following environment variable(s) can be used to adjust the behaviour of this filter:

       DKIM_TMPDIR
              The directory to use when creating temporary files.  The default is /var/tmp.

NOTES

       When using DNS timeouts (see the -T option above), be sure not to use a  timeout  that  is
       larger  than  the  timeout  being  used  for  interaction between sendmail and the filter.
       Otherwise, the MTA could abort a message while waiting for a reply from the filter,  which
       in turn is still waiting for a DNS reply.

       The POP authentication database is expected to be a Sleepycat DB file (formerly known as a
       Berkeley DB) in hash format with keys containing the IP address in  text  form  without  a
       terminating NULL.  The values of these records are not checked; only the existence of such
       records is of interest.  The filter will  attempt  to  establish  a  shared  lock  on  the
       database  before  reading from it, so any programs which write to the database should keep
       their lock use to a minimum or else this filter will appear to hang while waiting for  the
       lock operation to complete.

       Features  that  involve  specification  of  IPv4  addresses  or  CIDR  blocks will use the
       inet_addr(3) function to parse that information.  Users should be familiar  with  the  way
       that  function handles the non-trivial cases (for example, "192.0.2/24" and "192.0.2.0/24"
       are not the same thing).

HISTORY

       DKIM is an amalgam of Yahoo!'s DomainKeys proposal, and Cisco's Internet  Identified  Mail
       (IIM) proposal.

VERSION

       This man page covers version 2.5.2 of opendkim.

COPYRIGHT

       Copyright (c) 2005-2008, Sendmail, Inc. and its suppliers.  All rights reserved.

       Copyright (c) 2009-2011, The OpenDKIM Project.  All rights reserved.

SEE ALSO

       opendkim.conf(5), sendmail(8)

       Sendmail Operations Guide

       RFC5321 - Simple Mail Transfer Protocol

       RFC5322 - Internet Messages

       RFC5451 - Message Header Field for Indicating Message Authentication Status

       RFC6008  -  Authentication-Results  Registration  for  Differentiating among Cryptographic
       Results

       RFC6376 - DomainKeys Identified Mail

                                       The OpenDKIM Project                           opendkim(8)