"Dh key too small" appears when connecting to https on Ubuntu

Overview

When I try to connect to https with Ubuntu installed on docker, I get a "dh key too small" error and cannot connect.

Cause

Since the security version of the server is old, increase the security level on the server side or decrease it on the client side.

Solution

Since it only touches the client side, fix the following (lower the security level).

/usr/lib/ssl/openssl.cnf

#Added to the first line
openssl_conf = default_conf

...
...
...

#Add to last line
[ default_conf ]
ssl_conf = ssl_sect

[ssl_sect]
system_default = system_default_sect

[system_default_sect]
MinProtocol = TLSv1.2
CipherString = DEFAULT:@SECLEVEL=1

It can be used without reloading.