How to force a own set of ciphers in Postfix 2.11?
I would like to force a own set of TLS cipher suites rather than use the Postfix built in ones.
My desired set of ciphers is (taken from nginx configuration):
ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:-DES:!RC4:!MD5:!PSK:!aECDH:EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA
Unfortunately I cannot find a reference to override the cipher suites. I found notices that it is possible but not how.
How would look like the equivalent Postfix configuration for smtp and smtpd?
Using Debian/7, Postfix/2.11.2, OpenSSL/1.0.1e
From Applied Crypto Hardening by bettercrypto.org:
smtpd_tls_security_level = may
smtp_tls_security_level = may
smtp_tls_loglevel = 1
# if you have authentication enabled, only offer it after STARTTLS
smtpd_tls_auth_only = yes
tls_ssl_options = NO_COMPRESSION
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
smtpd_tls_mandatory_ciphers=high
tls_high_cipherlist=EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-SHA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA
[UPDATE: As the bettercrypto project, where I have the cipher-string from, is no longer active, make sure to chose your cipher-string from a current source.]
For master.cf you may want to configure the submission port to TLS only:
submission inet n - - - - smtpd
-o smtpd_tls_security_level=encrypt
-o tls_preempt_cipherlist=yes
However, this does not disallow usage of outdated ciphers for security level may, according to pull request #97, you can do this with:
smtpd_tls_protocols=!SSLv2,!SSLv3
smtp_tls_protocols=!SSLv2,!SSLv3
But this has not been merged with the following reason:
I am going to close this, SSLv3 makes sense here since it's better than good ol' plaintext.
man postconf says "You are strongly encouraged to not change this setting."
Nevertheless, you can, like this:
smtp_tls_security_level = encrypt
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
smtp_tls_mandatory_ciphers=high
smtpd_tls_security_level = encrypt
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
smtpd_tls_mandatory_ciphers=high
tls_high_cipherlist=ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:-DES:!RC4:!MD5:!PSK:!aECDH:EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA
I assume this is experimental and you're not worried about mail flow from most MTAs. Check for "handshake failure" in the postfix logs. I'd suggest testing with smtp_ outgoing first so you can see what's in the queue and any local nginx-generated SMTP sessions shouldn't fail.