| Type: | string |
| Default: | HIGH:MEDIUM:+3DES:!aNULL |
| Context: | sighup |
| Restart: | false |
Specifies a list of SSL cipher suites that are allowed to be used by SSL connections. See the ciphers manual page in the OpenSSL package for the syntax of this setting and a list of supported values. Only connections using TLS version 1.2 and lower are affected. There is currently no setting that controls the cipher choices used by TLS version 1.3 connections. The default value is HIGH:MEDIUM:+3DES:!aNULL. The default is usually a reasonable choice unless you have specific security requirements.
This parameter can only be set in the postgresql.conf file or on the server command line.
Explanation of the default value: HIGH
Cipher suites that use ciphers from HIGH group (e.g., AES, Camellia, 3DES)
MEDIUM
Cipher suites that use ciphers from MEDIUM group (e.g., RC4, SEED)
+3DES
The OpenSSL default order for HIGH is problematic because it orders 3DES higher than AES128. This is wrong because 3DES offers less security than AES128, and it is also much slower. +3DES reorders it after all other HIGH and MEDIUM ciphers.
!aNULL
Disables anonymous cipher suites that do no authentication. Such cipher suites are vulnerable to MITM attacks and therefore should not be used.
Available cipher suite details will vary across OpenSSL versions. Use the command openssl ciphers -v 'HIGH:MEDIUM:+3DES:!aNULL' to see actual details for the currently installed OpenSSL version. Note that this list is filtered at run time based on the server key type.