postfix + tls + sasl2 + courier-imap ( 建立加密及安全認證之郵件伺服器 )_qmail:站长天空

Description :

TLS - Transport Layer Security ( 為網路 OSI 七層中的第四層加密技術，SSL - Secure Socket Layer 協定為之前身 )
SASL - Simple Authentication and Security Layer ( 簡易的安全認證，SASL 同時也提供 SMTP 認證，定義在 RFC-2554 http://www.ietf.org/rfc/rfc2554.txt )
Key - 安全連線金鑰 ( key-pair ) CA - 授權憑證 ( Certification Authority )

網路上有些獨立公正單位例如 VeriSign 及 GlobalSign 等等、、、它們就是專門販賣安全金鑰 Key 以及授權憑證 CA 的單位，我們這邊採用自行製作安全金鑰以及授權憑證，自行製作的安全金鑰與授權憑證，在功能上與買來的相同，只是向獨立公正單位購買來的 Key 跟 CA，會讓 Client 使用者心理上覺得比較有保障，因為我們不做生意所以也不需要花錢買Key 跟 CA ，這邊 Postfix + TLS 主要目的是保障我的連線加密防止帳號密碼外洩。

Environment :

硬體：i386 PC Intel Pentium III 500
記憶體：256M RAM
作業系統：FreeBSD 6.0 Release

Setp 1. 伺服器的 SMTP 安全強化

#cd /usr/ports/mail/postfix # 安裝 Postfix MTA 郵件伺服器軟體
#make install clean

※ 出現的第一個選單只選擇 SASL 跟 TLS

[X] SASL2 Cyrus SASLv2 (Simple Authentication and Security Layer)
[X] TLS SSL and TLS
[X] DB41 Berkeley DB4.1 (required if SASL also built with DB4.1)

You need user "postfix" added to group "mail".
Would you like me to add it [y]? y

Would you like to activate Postfix in /etc/mail/mailer.conf [n]? y

# cd /usr/ports/security/cyrus-sasl2-saslauthd # 安裝 cyrus-sasl2-saslauthd
#make install clean

#vi /etc/rc.conf # 關閉 sendmail , 在 FreeBSD 中 Sendmail 預設是開機會自動啟動 127.0.0.1 本機的 MTA 功能，同時也加入開機自動啟動 postfix 及 saslauthd

sendmail_enable="NONE"
postfix_enable="YES"
saslauthd_enable="YES"

#ls -l /usr/local/etc/sasldb* # 查看 sasdb 檔權限因為 postfix 要使用 SASL 認證必須要對 sasldb 有讀取的權限

-rw-r----- 1 cyrus mail 16384 6 13 02:52 sasldb2.db

# vi /etc/group # 把 postfix 代理使用者加入 cyrus 群組 postfix 便可讀取 sasldb 檔

cyrus:*:60:postfix

#vi /usr/local/etc/postfix/main.cf # 修改 postfix 設定檔 main.cf

myhostname = ms1.ntut.idv.tw
mydomain = nttu.idv.tw
alias_maps = hash:/usr/local/etc/postfix/aliases
smtpd_banner = $myhostname ESMTP
myorigin = $myhostname
mynetworks = $myhostname, 127.0.0.1
home_mailbox = Maildir/

broken_sasl_auth_clients = yes
smtpd_sasl_auth_enable= yes
smtpd_sasl_security_options= noanonymous
smtpd_sasl_local_domain =
smtpd_recipient_restrictions = permit_sasl_authenticated, check_relay_domains

#vi master.conf # 修改 master.conf 中的 smtp 及 smtps，smtps 是開 465 port 提供 outlook express 做加密傳輸使用

smtp inet n n n - - smtpd
smtps inet n - n - - smtpd
-o smtpd_tls_wrappermode=yes -o smtpd_sasl_auth_enable=yes

#postalias /usr/local/etc/postfix/aliases # 製做 aliases.db 檔

#vi /usr/local/lib/sasl2/smtpd.conf # 編寫 SASL smtpd 的認證方式採用 plain login

pwcheck_method: saslauthd
mechlist: plain login crammd5 digestmd5

#vi /usr/local/etc/rc.d/saslauthd.sh # 修改 saslauthd.sh

原本 >> saslauthd_flags=${saslauthd_flags:-"-a pam"}
改為 >> saslauthd_flags=${saslauthd_flags:-"-a getpwent"}

#reboot # 重新開機自動啟動 saslauthd 及 postfix

#ps -aux | grep saslauthd # 再次確認 saslauthd 有無啟動

584 ?? Is 0:00.01 /usr/local/sbin/saslauthd -a getpwent
585 ?? I 0:00.00 /usr/local/sbin/saslauthd -a getpwent
586 ?? I 0:00.00 /usr/local/sbin/saslauthd -a getpwent
587 ?? I 0:00.00 /usr/local/sbin/saslauthd -a getpwent
588 ?? I 0:00.00 /usr/local/sbin/saslauthd -a getpwent

#telnet localhost 25 # 測試 25 port 看是否多了兩行 250-AUTH
Trying ::1...
telnet: connect to address ::1: Connection refused
Trying 127.0.0.1...
Connected to localhost.ntut.idv.tw.
Escape character is ^].
220 ms1.ntut.idv.tw ESMTP
ehlo locahost
250-ms1.ntut.idv.tw
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-AUTH NTLM LOGIN PLAIN GSSAPI DIGEST-MD5 CRAM-MD5
250-AUTH=NTLM LOGIN PLAIN GSSAPI DIGEST-MD5 CRAM-MD5
250 8BITMIME
quit
221 Bye
Connection closed by foreign host.

Setp 2. 伺服器的 SMTP 憑證製作

#cd /usr/ports/security/openssl # 安裝 openssl 的目的為產生 CA.pl 這支 perl 程式，好讓我們可以輕鬆產生金鑰
#make install clean

#mkdir /usr/local/etc/postfix/CA # 建立 CA 存放的資料夾
#cd /usr/local/etc/postfix/CA
#cp /usr/local/openssl/misc/CA.pl ./ # 將 CA.pl 這支 perl 程式 copy 到剛剛建立的 CA 目錄

# perl CA.pl -newca
CA certificate filename (or enter to create)

Making CA certificate ...
Generating a 1024 bit RSA private key
.++++++
.......................++++++
writing new private key to ./demoCA/private/cakey.pem
Enter PEM pass phrase: ( 輸入密碼 )
Verifying - Enter PEM pass phrase: ( 輸入密碼 )
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter ., the field will be left blank.
-----
Country Name (2 letter code) [AU]:TW
State or Province Name (full name) [Some-State]:Taiwan
Locality Name (eg, city) []:Taichung
Organization Name (eg, company) [Internet Widgits Pty Ltd]:ERA
Organizational Unit Name (eg, section) []:ISP
Common Name (eg, YOUR name) []:ms1.ntut.idv.tw
Email Address []:xxxxx@gmail.com

#openssl req -nodes -config /usr/local/openssl/openssl.cnf -new -days 3650 -newkey rsa:1024 -keyout serverkey.pem -out serverreq.pem
Generating a 1024 bit RSA private key
......++++++
...............++++++
writing new private key to serverkey.pem
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter ., the field will be left blank.
-----
Country Name (2 letter code) [AU]:TW
State or Province Name (full name) [Some-State]:Taiwan
Locality Name (eg, city) []:Taichung
Organization Name (eg, company) [Internet Widgits Pty Ltd]:ERA
Organizational Unit Name (eg, section) []:ISP
Common Name (eg, YOUR name) []:ms1.ntut.idv.tw
Email Address []:xxxxxx@gmail.com

Please enter the following extra attributes
to be sent with your certificate request
A challenge password []: ( 輸入密碼 )
An optional company name []:ERA

#openssl ca -config /usr/local/openssl/openssl.cnf -policy policy_anything -out servercert.pem -infiles serverreq.pem
Using configuration from /usr/local/openssl/openssl.cnf
Enter pass phrase for ./demoCA/private/cakey.pem:
Check that the request matches the signature
Signature ok
Certificate Details:
Serial Number:
96:a5:d5:76:64:ad:3f:31
Validity
Not Before: Apr 13 01:52:30 2006 GMT
Not After : Apr 13 01:52:30 2007 GMT
Subject:
countryName = TW
stateOrProvinceName = Taiwan
localityName = Taichung
organizationName = ERA
organizationalUnitName = ISP
commonName = ms1.ntut.idv.tw
emailAddress = xxxxx@gmail.com
X509v3 extensions:
X509v3 Basic Constraints:
CA:FALSE
Netscape Comment:
OpenSSL Generated Certificate
X509v3 Subject Key Identifier:
32:98:18:2A:98:B9:03:EC:A2:A9:E5:1A:C9:09:82:6B:95:5D:D2:D3
X509v3 Authority Key Identifier:
keyid:66:9D:78:67:61:75:95:B0:60:72:59:F5:77:4B:83:0D:D1:E4:B7:E8
DirName:/C=TW/ST=Taiwan/L=Taichung/O=ERA/OU=ISP/CN=ms1.ntut.idv.tw/emailAddress=xxxxx@gmail.com
serial:96:A5:D5:76:64:AD:3F:30

Certificate is to be certified until Apr 13 01:52:30 2007 GMT (365 days)
Sign the certificate? [y/n]:y

1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated

#cat serverkey.pem servercert.pem > post.pem

#vi /usr/local/etc/postfix/main.cf # 將 Postfix 的 smtpd 加入 TLS 設定

smtp_use_tls = yes
smtpd_use_tls = yes
smtp_tls_note_starttls_offer = yes
smtpd_tls_key_file = /usr/local/etc/postfix/CA/post.pem
smtpd_tls_cert_file = /usr/local/etc/postfix/CA/post.pem
smtpd_tls_CAfile = /usr/local/etc/postfix/CA/post.pem
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
mtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom

#postfix reload # 重新啟動 postfix

#telnet loadlhost 25 # 測試是否啟動 TLS 加密，手動輸入 STARTTLS 如果成功會回應下面那行紅字

Trying ::1...
telnet: connect to address ::1: Connection refused
Trying 127.0.0.1...
Connected to localhost.ntut.idv.tw.
Escape character is ^].
220 ms1.ntut.idv.tw ESMTP
ehlo localhost
250-ms1.ntut.idv.tw
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH NTLM LOGIN PLAIN GSSAPI DIGEST-MD5 CRAM-MD5
250-AUTH=NTLM LOGIN PLAIN GSSAPI DIGEST-MD5 CRAM-MD5
250 8BITMIME
STARTTLS
220 Ready to start TLS
quit
quit
221 Bye
Connection closed by foreign host.

※ SMTP 在 Client 端設定方式若以 Outlook Express 的設定方式如下：

圖 (一)、讓 Outlook Express 支援驗證 ( 可預防 Mail Relay )

在 Outlook Express 《工具》《帳戶》《郵件》《內容》《伺服器》中
把『外寄郵件伺服器』、『我的外寄伺服器需要驗證』打勾，就可以使用身分認證機制。

圖 (二)、讓 Outlook Express 支援 SSL/TLS 加密的郵件伺服器 ( 加密後可預防帳號密碼資料被竊取，就算資料被從中竊取也是加密的資料很難破解 )。

必須向使用 Outlook Express 的使者宣導改用 SSL/TLS 來做寄信的動作，客戶端只要在 Outlook Express 《工具》《帳戶》《郵件》《內容》《進階》中
將『伺機器連接戶號碼』、『外寄伺服器 - SMTP 』的 port 號從 25 port 改到 465 port 以及『這個伺服器需要安全連線 - SSL 』打勾，就可以採用 TLS 加密連線了。

圖 (一)

圖 (二)

Setp 3. 設定 POP3 及 IMAP 加密

#cd /usr/ports/mail/courier-imap # 光讓發信 SMTP 加密還不夠，POP3 收信也得加密，這邊因為我們的 Postfix 採用 Maildir 格式所以我們安裝 Courier-imap
#make install

Options for courier-imap 4.0.6_1,1

[X] OPENSSL Build with OpenSSL support # 因為採用 FreeBSD 本機上的帳號及密碼認證所以只選 openssl 不選其他種類的 AUTH

#cd /usr/local/etc/courier-imap
#cp pop3d.cnf.dist pop3d.cnf # 設定 POP3s 995 port 金鑰產生設定檔

RANDFILE = /usr/local/share/courier-imap/pop3d.rand

[ req ]
default_bits = 1024
encrypt_key = yes
distinguished_name = req_dn
x509_extensions = cert_type
prompt = no

[ req_dn ]
C=TW
ST=Taiwan
L=Taichung
O=ERA
OU=ISP
CN=localhost
emailAddress=xxxxx@gmail.com

[ cert_type ]
nsCertType = server

#cp imapd.cnf.dist imapd.cnf # 設定 IMAPs 993 port 金鑰產生設定檔

RANDFILE = /usr/local/share/courier-imap/imapd.rand

[ req ]
default_bits = 1024
encrypt_key = yes
distinguished_name = req_dn
x509_extensions = cert_type
prompt = no

[ req_dn ]
C=TW
ST=Taiwan
L=Taichung
O=ERA
OU=ISP
CN=localhost
emailAddress=xxxxx@gmail.com

[ cert_type ]
nsCertType = server

#/usr/local/sbin/mkimapdcert # 開始產生安全登入認證的金鑰 imapd.pem 及 pop3d.pem 檔，放置於 /usr/local/share/courier-iamp 下
#/usr/local/sbin/mkpop3dcert

#vi /etc/rc.conf # 設定預設開機啟動程式

courier_authdaemond_enable="YES"
courier_imap_imapd_ssl_enable="YES"
courier_imap_pop3d_ssl_enable="YES"

#/usr/local/etc/rc.d/courier-authdaemond.sh start
#/usr/local/etc/rc.d/courier-imap-pop3d-ssl.sh start # 啟動 pop3s
#/usr/local/etc/rc.d/courier-imap-imapd-ssl.sh start # 啟動 imaps

# sockstat -l4 # 確定開啟的服務 port

USER COMMAND PID FD PROTO LOCAL ADDRESS FOREIGN ADDRESS
root couriertcp 59481 3 tcp4 *:993 *:*
root couriertcp 59470 3 tcp4 *:995 *:*
root master 15580 11 tcp4 *:25 *:*
root master 15580 14 tcp4 *:465 *:*
root sshd 441 4 tcp4 *:22 *:*

※ POP3 在 Client 端設定方式若以 Outlook Express 的設定方式如下：

必須向使用 Outlook Express 的使者宣導改用 SSL/TLS 來收信，同時我們也關掉 110 port 讓這個不安全的協定 port 不再運行，客戶端只要在 Outlook Express 《工具》《帳戶》《郵件》《內容》《進階》中
將『伺機器連接戶號碼』、『外寄伺服器 - POP3 』的 port 號從 110 port 改到 995 port 以及將『這個伺服器需要安全連線 - SSL 』打勾，就可以採用加密連線了。

圖 (三)

參考資料：

http://www.hacker.org.tw/?c=articles_show%26amp;articleid=1225
http://www.ascc.sinica.edu.tw/nl/90/1713/02.txt

最後修改日期： 2006/04/14
最後修改:http://freebsd.ntut.idv.tw/document/postfix_tls_sasl2_courier-imap.html

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