Deprecated Options in OpenVPN

[ispyisail]

Maybe it's Blowfish that's deprecated.

agree

On your last message, is that /etc/openvpn/server.conf that you're showing? I don't have the "ns-cert-type" line at all, but maybe that's the default even if absent.

Don't know

Mine was a fresh re-flash and just used the default settings where possible via GUI only.

[rseiler]

Looks like. From this:
https://community.openvpn.net/openvpn/w ... n24ManPage

The default is BF-CBC, an abbreviation for Blowfish in Cipher Block Chaining mode. When cipher negotiation (NCP) is allowed, OpenVPN 2.4 and newer on both client and server side will automatically upgrade to AES-256-GCM. See --ncp-ciphers and --ncp-disable for more details on NCP.

Using BF-CBC is no longer recommended, because of its 64-bit block size. This small block size allows attacks based on collisions, as demonstrated by SWEET32. See https://community.openvpn.net/openvpn/wiki/SWEET32 for details. Due to this, support for BF-CBC, DES, CAST5, IDEA and RC2 ciphers will be removed in OpenVPN 2.6.

BTW, so people coming along to this thread don't get tripped up, one of the commands you mentioned is just this:

Code: Select all

--auth-nocache

Though in the context of server.conf, we don't use "--" at all.

[ispyisail]

The other question is what version of OpenVPN are we using and does it need upgrading?

or just a reconfigure?

[rseiler]

If snooping in /usr/sbin/openvpn is valid, then it's 2.3.6, which even in the context of 2.3.x releases is very old (Dec 2014).

[rseiler]

Back to the two remaining warnings, starting with the relatively unimportant one (auth-nocache), the only way that I could get it to take effect was to put it in the .ovpn. YMMV.

On "remote-cert-tls server," I can't connect when it's in server.conf. It requires that "peer certificate was signed with an explicit key usage and extended key usage based on RFC3280 TLS rules," which I'm guessing isn't the case.

I later found that "To use this feature, you will need to generate your server certificates with the nsCertType field set to "server". The build-key-server script in the easy-rsa folder will do this."

And there's more about it here:
https://openvpn.net/index.php/open-sour ... .html#mitm

My guess is that whatever script is used in Gargoyle to generate the certificates might need to be tweaked.

[rseiler]

OK, so in the beta released today:

"...default cipher to AES-CBC-256 and replacing ns-cert-type with remote-cert-tls."

I'll try to test that ASAP. @ispyisail, have you had a chance to test "remote-cert-tls server" with any version yet? I didn't pursue getting it to work, but it does seem like it needs more than just that line to work. Perhaps that takes place now in the new version, I don't know, but I think the script change was just about combing the config files.

Also, it might be worth looking into the effect of 256 bits (which isn't needed to avoid the error--that was Blowfish's fault, which is now gone) vs 128 in the context of an average router.

[ispyisail]

No testing, I just pushed it out as fast as I could

[rseiler]

Current Server Config

You mean client.

No wonder your "server.conf" has seemed so different than mine. It's never been the server.conf.

Yes, "ns-cert-type" has appeared on the client ovpn this whole time, but I wasn't looking for it there so didn't notice it.

So, just like adding auth-nocache there worked to eliminate the cache warning, adding remote-cert-tls server there eliminates the other.

Apparently there is no server analogue for these, and trying to add the latter there will break it.

[ispyisail]

yes, sorry

[ispyisail]

Are you not happy with Eric's changes?

Do they not fix the problem?