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opendkim

由 datahunter 在 三, 19/02/2014 - 18:28 發表

最後更新: 2018-12-18

介紹

Run outside the MTA to inspect SMTP events ( All this happens before mail is queued )

目錄

 

Install

 

apt-get install opendkim opendkim-tools # Debian

yum install opendkim                            # Centos 7 (epel)

dnf install opendkim opendkim-tools       # Centos 8

 

Create Key & DNS Setting

 

Create key and dns record

# 建立了 mail.private (opendkim load 它)  mail.txt (在 DNS Server 上設定它)

DOMAIN=datahunter.org

mkdir /etc/opendkim/keys/$DOMAIN -p

cd $_

# 獲得 dkim.private (key) 及 dkim.txt (dns record)

opendkim-genkey -s dkim -d $DOMAIN

# keys referenced by the KeyTable must always be accessible for read by the unprivileged user.

  • chown root.opendkim dkim.private
  • chmod 640 dkim.private

cat dkim.txt                       # dns record

DKIM DNS Record Rormat

SELECTOR._domainkey IN TXT ...

當 "opendkim-genkey -s dkim ..." 時, SELECTOR 就係 dkim

Verify DNS Record

dig -t txt dkim._domainkey.${DOMAIN}

# -d domain ; -s selector ; -k keypath

opendkim-testkey -d $DOMAIN -s dkim -k dkim.private

# 失敗:

opendkim-testkey: 'mail._domainkey.example.com' record not found

# 成功

echo $?                # 成功是 0

 

SigningTable 與 KeyTable

 

grep -e KeyTable -e SigningTable /etc/opendkim

SigningTable

/etc/opendkim/signing.table

# lists the signatures to apply to a message based on the address found in the From: header field

# domain                  short name for the domain
*@datahunter.org          datahunter

KeyTable

/etc/opendkim/key.table

maps key names to signing keys

Format

example     DOMAIN_NAME:SELECTOR:KEY_FILE

i.e.

datahunter    datahunter.org:dkim:/etc/opendkim/keys/datahunter.org/dkim.private

 

Setup opendkim

 

設定(Centos 7)

/etc/opendkim.conf

AutoRestart             Yes
AutoRestartRate         10/1h
UMask                   002

Syslog                  yes
SyslogFacility          mail
SyslogSuccess           Yes
LogWhy                  Yes

SoftwareHeader          Yes

Canonicalization        relaxed/relaxed

# Map domains in From addresses to keys used to sign messages
KeyTable               /etc/opendkim/key.table
SigningTable           refile:/etc/opendkim/signing.table

# Hosts to ignore when verifying signatures
ExternalIgnoreList      /etc/opendkim/TrustedHosts
InternalHosts           /etc/opendkim/TrustedHosts

Mode                    sv
PidFile                 /var/run/opendkim/opendkim.pid
SignatureAlgorithm      rsa-sha256

UserID                  opendkim:opendkim

#設定 Socket, 詳見下一 Part
# 方式1
Socket  inet:8891@localhost
# 方式2
#Socket  local:/var/spool/postfix/opendkim/opendkim.sock
#Umask   000

AutoRestart

Auto restart the filter on failures

AutoRestartRate

Specifies the filter's maximum restart rate, if restarts begin to happen faster than this rate, the filter will terminate;
10/1h - 10 restarts/hour are allowed at most

UMask

gives all access permissions to the user group defined by UserID
and allows other users to read and execute files,

in this case it will allow the creation and modification of a Pid file.

SoftwareHeader

To  add  an "DKIM-Filter" header field indicating the presence of this filter

Canonicalization

Select canonicalizations to use when signing.

Valid values for each are "simple" and "relaxed"

  • simple: allows almost no modification
  • relaxed: one tolerates minor changes such as whitespace replacement;

relaxed/simple - the message header will be processed with the relaxed algorithm and the body with the simple one

refile

regular expression file

Mode

Default 只有 verifier (v)

declares operating modes; in this case the milter acts as a signer (s) and a verifier (v)

TrustedHosts

/etc/opendkim/TrustedHosts

127.0.0.1
localhost
# mx1 IP
# mx2 IP

Enable Service

systemctl start opendkim --now

Checking

[方式 1]

# Socket  inet:8891@localhost

netstat -tnlp | grep 8891

                 OR

# Socket  local:/var/spool/postfix/opendkim/opendkim.sock

ls /var/spool/postfix/opendkim/opendkim.sock

[方式 2] 在有 "Syslog yes" 及 "SyslogFacility mail" 設定時可以到 /var/log/mail.log 查看

grep opendkim /var/log/maillog

... opendkim[5358]: OpenDKIM Filter: mi_stop=1
... opendkim[5358]: OpenDKIM Filter v2.0.1 terminating with status 0, errno = 0
... opendkim[5380]: OpenDKIM Filter v2.0.1 starting (args: ... )

 

設定 Socket

 

[方案 A] TCP Socket  <-  最簡單的做法, 不用理 postfix 的 chroot 及 permission

/etc/opendkim.conf

Socket  inet:8891@localhost

[方案 B] Unix Socket

mkdir -p /var/spool/postfix/var/run/opendkim

chown opendkim.postfix /var/spool/postfix/var/run/opendkim

chmod 770 /var/spool/postfix/var/run/opendkim

[Centos] /etc/opendkim.conf

SOCKET="local:/var/spool/postfix/var/run/opendkim/opendkim.sock"
Umask   000

* chrooted postfix path

ls -l /var/spool/postfix/opendkim/opendkim.sock

srwxrwxrwx 1 opendkim opendkim 0 Aug 13 10:39 /var/spool/postfix/opendkim/opendkim.sock

 

Postfix 設定

 

[方案 A] 使用 TCP port (最簡單)

/etc/postfix/main.cf

# opendkim setup
smtpd_milters           = inet:localhost:8891
non_smtpd_milters       = $smtpd_milters
milter_default_action   = accept
milter_protocol         = 6

[方案 B] unix socket

grep ^smtp /etc/postfix/master.cf

smtp      inet  n       -       n       -       -       smtpd
smtp      unix  -       -       n       -       -       smtp

 *  沒有 chroot

/etc/postfix/main.cf

# opendkim setup
smtpd_milters         = unix:/var/spool/postfix/opendkim/opendkim.sock
non_smtpd_milters     = $smtpd_milters
milter_default_action = accept
milter_protocol       = 6

service postfix restart

出/收信的 log

出信的 log

# opendkim-2.11.0

tail -f /var/log/maillog | grep opendkim

... opendkim[25507]: 741FA53F63: DKIM-Signature field added (s=dkim, d=datahunter.org)

收信的 log

# opendkim-2.11.0

... opendkim[32548]: 342661533: mail-ot1-f43.google.com [209.85.210.43] not internal
... opendkim[32548]: 342661533: not authenticated                # (1)
... opendkim[32548]: 342661533: DKIM verification successful     # (2)

(1) the OpenDKIM milter thinks the mail was not submitted by an authenticated user

(2) 來信沒有 dkim 時: "no signature data"

Remark

當 remote login 後出信時見到

"... opendkim[32548]: 342661533: not authenticated"

OpenDKIM decides whether a message is authenticated or not based on the presence or absence of the {auth_type} macro

postconf milter_mail_macros

milter_mail_macros = i {auth_type} {auth_authen} {auth_author} {mail_addr} {mail_host} {mail_mailer}
  • "i" (the envelope ID, also known as the job ID or the queue ID), which is used for logging;
  • "auth_type", which is used to determine whether or not the SMTP client authenticated to the MTA

postfix 解釋

smtpd_milters (default: empty)

一共有兩類:

  • SMTP mail filters (arrives via the Postfix smtpd server )( smtpd_milters=... )
  • non-SMTP mail filters ( arrives via the Postfix sendmail(CLI) --> cleanup )( non_smtpd_milters=... )

milter_default_action:

The default action is to respond with a temporary error status

Specify "accept" if you want to receive mail as if the filter does not exist

milter_protocol (default: 6)

2    Use Sendmail 8 mail filter protocol version 2
      (default with Sendmail version 8.11 .. 8.13 and Postfix version 2.3 .. 2.5).

6    Use Sendmail 8 mail filter protocol version 6
      (default with Sendmail version 8.14 and Postfix version 2.6).

 

Doc

 

before-queue Milter: http://www.postfix.org/MILTER_README.html

man opendkim.conf

zcat /usr/share/doc/opendkim/examples/opendkim.conf.sample.gz

 

 

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