upgrade 2.2 to 2.3, diffie-hellman, ssl_min_protocol

[Joseph Tam]

On Fri, 22 Jun 2018, Aki Tuomi wrote:

>> Do I need to make a fresh dh.pem? The upgrade doc tells how to convert 
>> ssl-parameters.dat but how to make a new one?
>
> ... or you can make a fresh one using openssl
> gendh 4096 > dh.pem

This also works

 	openssl dhparam -out dh.pem 4096

> Note that this will require quite a lot of entropy, so you should
> probably ensure that you run it on a laptop or with virtual machine
> that has some entropy source/helper.

It can take an extraordinary amount of time for long keys.  Most of
the time/entropy is taken up to produce a "safe" prime (p) such that
(p-1)/2 is also prime to resist some factoring algorithms.

However, recent advances make this condition obsolete [*] and not
really safer, so a much faster way to generate a DH key is

 	openssl dhparam -dsaparam -out dh.pem 4096

DH generation is a one time operation, so if you're paranoid and you've
got time to burn, go ahead and generate the "safe" DH key.

[*] https://security.stackexchange.com/questions/42415/openvpn-dhparam)

Joseph Tam <jtam.home at gmail.com>