Today I encoutered the
dh key too small issue when running curl and wget commands.
And most of the reasons is that server is passing a weak DH key to client. This is the most pages say in the Internet. However today I found the issue only happens on Kali Linux. This should be the hint that there is some wrong in client side instead of server side.
/etc/ssl/openssl.cnf. No surprise there is an extra configuration for SSL security level:
[system_default_sect] MinProtocol = TLSv1.2 CipherString = DEFAULT@SECLEVEL=2
The default security level is 1 for OpenSSL. So setting it up to 2, some of the websites may not meet level 2 security requirement and caused the "dh key to small" issue.
Recorded in this page, https://www.openssl.org/docs/man1.1.0/man3/SSL_CTX_get_security_level.html:
DSA and DH keys shorter than 2048 bits and ECC keys shorter than 224 bits are prohibited.
--cipher 'DEFAULT:!DH'as command line parameter