postfix - ssl & setting

由 datahunter 在五, 23/11/2012 - 16:08 發表

最後更新: 2018-05-04

介紹

SMTP Port

TLS (Port 587)
Secure SMTP (SSMTP) - port 465

postfix - TLS (Port 587)

main.cf

# STARTTLS support to remote SMTP clients
# By default, TLS is disabled in the Postfix SMTP server
# Postfix >= 2.3 use smtpd_tls_security_level instead
smtpd_use_tls       = yes
smtpd_tls_cert_file = /etc/postfix/ssl/server.cert
smtpd_tls_key_file  = /etc/postfix/ssl/server.key

Cert. file permission

-rw-r----- 1 root root 1675 Jun 21 16:46 server.key
-rw-r--r-- 1 root root 1663 Jun 21 16:46 server.cert

# Postfix SMTP server announces STARTTLS support to remote SMTP clients. Not force to use

smtpd_tls_security_level = may

opts

none # TLS will not be used
may # announce STARTTLS support to remote SMTP clients (Opportunistic)
encrypt # Mandatory TLS encryption

Checking & Log:

main.cf

smtpd_tls_loglevel = 1

log:

... setting up TLS connection from unknown[x.x.x.x]
... Anonymous TLS connection established from unknown[x.x.x.x]: 
    TLSv1 with cipher AES128-SHA (128/128 bits)

建立 SSL/TLS 的 Cert

mkdir /etc/postfix/ssl; cd /etc/postfix/ssl

openssl req -new -x509 -days 3650 -keyout server.x -out server.crt

touch server.key; chmod 600 server.key

openssl rsa -in server.x > server.key

rm server.x

Disable SSLv2, SSLv3

smtpd_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1

分別

smtpd_tls_mandatory_protocols = mandatory TLS encryption

Secure SMTP (SSMTP) (Port 465)

TLS is sometimes used in the non-standard "wrapper" mode where a server always uses TLS

修改 /etc/postfix/master.conf

-o smtpd_tls_wrappermode=yes

... mail postfix/smtpd[30891]: connect from CLIENT_IP[CLIENT_IP]
... mail postfix/smtpd[30891]: setting up TLS connection from CLIENT_IP[CLIENT_IP]
... mail postfix/smtpd[30891]: Anonymous TLS connection established from CLIENT_IP[CLIENT_IP]:
    TLSv1 with cipher RC4-MD5 (128/128 bits)

Telnet 亂打字:

... case2square postfix/smtpd[7370]: warning: TLS library problem: 
    7370:error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unnown protocol:s23_srvr.c:578:

warning: unknown[115.160.172.18]: SASL LOGIN authentication failed: UGFzc3dvcmQ6

Open relay 測試:

... case2square postfix/smtpd[7520]: NOQUEUE: reject: RCPT from unknown[x.x.x.x]: 554 5.7.1 <to_mail>: 
    Relay access denied; from=<test_mail> to=<to_mail> proto=ESMTP helo=<lwyPC>

Outlook SSL 設定

次次都問

未答是/否時的 Server log

... SERVER dovecot: imap-login: Disconnected (no auth attempts): rip=R.R.R.R, lip=L.L.L.L,
    TLS: SSL_read() syscall failed: Connection reset by peer

Check Postfix Support TLS

ldd /usr/libexec/postfix/smtp | grep libssl

libsasl2.so.2 => /usr/lib/libsasl2.so.2 (0x00322000)
libssl.so.10 => /usr/lib/libssl.so.10 (0x00cd0000)
libcrypto.so.10 => /usr/lib/libcrypto.so.10 (0x0033d000)

smtpd (incoming) TLS

/etc/postfix/main.cf

# must be in "PEM" format (RSA, DSA, ECDSA)
# This file may also contain the Postfix SMTP server private RSA key.
# intermediate CAs: cat server_cert.pem intermediate_CA.pem > server.pem
smtpd_tls_cert_file = /etc/postfix/ssl/server.pem

# chmod 440 server.key
smtpd_tls_key_file = /etc/postfix/ssl/server.key

# yes: announce STARTTLS support, but do not require. 
# Default: no
# 在 postfix 2.3 後, 用 smtpd_tls_security_level 去 control
smtpd_use_tls = yes

# Default: no
# require that clients use TLS encryption (Mandatory TLS)
# "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".
smtpd_enforce_tls = no

# default: empty
# none: TLS will not be used.
# may: Opportunistic TLS
# encrypt => require that clients use TLS encryption (implies "smtpd_tls_auth_only = yes")
# 當 "smtpd_tls_security_level=none" 系統就唔會 announce "STARTTLE"
smtpd_tls_security_level = may        

# do not announce or accept SASL authentication over unencrypted connections. 
# plantext login "must issue a starttls command first"
# default: no

smtpd_tls_auth_only = no

# Log
# (default: 0) 0 = Log only a summary message on TLS handshake completion

smtpd_tls_loglevel = 0

smtp (Outgoing) TLS

/etc/postfix/main.cf

# Mandatory TLS encryption setting
smtp_tls_security_level = may

none - No TLS. TLS will not be used unless enabled for specific destinations via smtp_tls_policy_maps.

may - Opportunistic TLS. Use TLS if this is supported by the remote SMTP server, otherwise use plaintext.

TLS Policy Table

/etc/postfix/main.cf

# Default: NULL
smtp_tls_policy_maps = hash:/etc/postfix/outgoing_tls_policy

# 1     Log only a summary message on TLS handshake completion
# 2     Also log levels during TLS negotiation.
smtp_tls_loglevel = 0

TLS policy table

The TLS policy table is indexed by the full next-hop destination

* which is either the recipient domain, or the verbatim next-hop specified in the transport table

/etc/postfix/outgoing_tls_policy

example.edu             none
example.com             verify
example.gov             encrypt

* parent domain starting with a leading "." is matched recursively (".example.com encrypt")

opts

none No TLS

may Opportunistic TLS

encrypt TLS encryption is always used, mail delivery continues even if the server certificate is untrusted

verify Mandatory server certificate verification

Mail is delivered only if the TLS handshake succeeds

(not expired or revoked, and signed by a trusted Certification Authority)

# 指定用其他 Domain

.example.net            secure match=.example.net:example.net

fingerprint

there are no trusted Certification Authorities.

[thumb.example.org]         fingerprint
        match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
        match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1

建立 map

postmap hash:/etc/postfix/outgoing_tls_policy

log

... certificate verification failed for w.y.z[x.x.x.x]:25:
untrusted issuer /C=SE/O=AddTrust AB/OU=AddTrust External TTP Network/CN=AddTrust External CA Root

保護 TLS Connection

# Fix 'The Logjam Attack'.

smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH,
 EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CDC3-SHA, KRB5-DE5, CBC3-SHA

dh 檔 (forward secrecy)

# Postfix ≥ 2.2 support 1024-bit-prime EDH out of the box, with no additional configuration

smtpd_tls_X_param_file => To use a non-default prime (此設定係有關 EDH 方式)

( for improved security against pre-computation attacks )

建立 dh 檔

# mkdir /etc/postfix/tls; cd /etc/postfix/tls

openssl dhparam -out dh512.pem 512

openssl dhparam -out dh2048.pem 2048

# smtpd_tls_dh1024_param_file 可用 1024 bit / 2048 bit 檔(建議用 2048 bit 的)

smtpd_tls_dh512_param_file  = /etc/postfix/tls/dh512.pem
smtpd_tls_dh1024_param_file = /etc/postfix/tls/dh2048.pem

Checking

smtp_tls_loglevel = 1
smtpd_tls_loglevel = 1

smtpd_tls_received_header = yes

參考

https://datahunter.org/dh

Troubleshoot

Error1:

TLS not available due to local problem

Solution1:

mkdir /etc/postfix/tls

cd /etc/postfix/tls

openssl req -new -x509 -nodes -out smtpd.crt -keyout smtpd.key -days 3650

openssl dhparam -out dh1024.pem 1024

chmod 440 smtpd.key dh1024.pem

smtpd_tls_dh1024_param_file = /etc/postfix/tls/dh1024.pem
smtpd_tls_CAfile            = /etc/postfix/tls/smtpd.crt
smtpd_tls_cert_file         = /etc/postfix/tls/smtpd.crt
smtpd_tls_key_file          = /etc/postfix/tls/smtpd.key

Doc

http://www.postfix.org/TLS_README.html

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夢想家

postfix - ssl & setting

目錄

介紹

postfix - TLS (Port 587)

建立 SSL/TLS 的 Cert

Disable SSLv2, SSLv3

Secure SMTP (SSMTP) (Port 465)

Outlook SSL 設定

Check Postfix Support TLS

smtpd (incoming) TLS

smtp (Outgoing) TLS

TLS Policy Table

保護 TLS Connection

Troubleshoot

Doc