Hello,
I setup my postfix mailserver a while ago with tls settings from:
http://www.postfix.org/TLS_README.html
http://www.postfix.org/FORWARD_SECRECY_README.html
I don't know much about TLS settings so I used the settings which seemed
be important in the documentation.
When scanning my server with: https://www.hardenize.com I got some
results that need improvement:
- Server doesn't enforce cipher suite preferences: Servers that don't
enforce cipher suite preferences select the first cipher suite they
support from the list provided by clients. This approach doesn't
guarantee that best-possible cipher suite is negotiated.
- Weak key exchange detected: his server uses key exchange parameters
that are weak. When using the ephemeral Diffie-Hellman key exchange
(DHE), parameters below 2048 bits are considered insecure. For
sufficient security, use 2048-bit parameters. It is generally not
advisable to use stronger key exchange because there is a measurable
performance penalty and there is no meaningful increase in security. A
well-configured TLS server should generally prefer the faster ECDHE key
exchange anyway.
- Reconfigure server to use forward secrecy and authenticated
encryption: Even though this server supports TLS 1.2, the cipher suite
configuration is suboptimal. We recommend that you reconfigure the
server so that the cipher suites providing forward secrecy (ECDHE or DHE
in the name, in this order of preference) and authenticated encryption
(GCM or CHACHA20 in the name) are at the top. The server must also be
configured to select the best-available suite.
So I was wondering what are the recommended TLS settings for a postfix
mailserver now days? And what settings do I need to improve these points
pointed out by this scan?
