Hi Erik,
On 11/10/2023 16:20, ummeegge wrote:
Hi Adolf,
Am Montag, dem 09.10.2023 um 19:26 +0200 schrieb Adolf Belka:
Hi All,
I thought it was too good to be true.
Before creating a client connection with something like BlowFish I thought I would just test the server settings with selecting BF in the data-ciphers-fallback selection box.
Have disabled all the 64 bit block cipher in my previouse patches since the cipher negotiaton managed the whole thing. I think AEAD ciphers are since OpenSSL-1.0.1 available so if AES-GCM is available in --data- ciphers, the clients will use them even BF-CBC is set in client.ovpn . We have had a conversation about this also with some tests which you can find in here --> https://community.ipfire.org/t/openvpn-2-6-development-version/8603/3
Thanks for the feedback and the link to our conversation at the beginning of this year.
So even if the user has BF-CBC set in the client.ovpn, with the server having server negotiation in this update then the client will end up getting connected with an available cipher from the data-ciphers list. I will do a test of that then on my system
If my understanding is correct, then why do we need to still leave the weak ciphers in the data-fallback list. Those could also be removed, they are blocked anyway.
OpenVPN plan to remove those weak ciphers completely in version 2.7 If a user at that time still had a client with say BF-CBC would the negotiation still work then or would it fail because OpenVPN no longer recognises the old weak cipher?
Regards,
Adolf.
Then pressed Start OpenVPN Server and nothing happened. Checked the logs and there is the openssl error
OpenSSL: error:0308010C:digital envelope routines::unsupported
which occurs because Openssl-3.x doesn't support the older ciphers like BF unless legacy is selected. In this case I think it is the OpenVPN server conf file that requires the
providers legacy default
to be included, rather than the client conf file.
Still it does feel like two steps forward and one backwards so overall still making progress.
Regards,
Adolf.
Best,
Erik
On 09/10/2023 14:05, Adolf Belka wrote:
Hi All,
Over the last week I have been working on the openvpn update using Erik's previous patches as my starting point.
My first attempt to try and be able to understand the changes from each patch to figure out what I needed to do proved difficult for me to work with.
What I then did was take the current ovpnmain.cgi and apply all of Erik's patches to it.
Then I have gone through that new version of ovpnmain.cgi and made the changes based on previous discussions with Michael.
So I have removed the b2sum options that were present for the Data and Channel Authentication.
I also moved all the cryptographic options from an additional advanced cryptographic options button into the Advanced Server options button.
I was successful in doing all the above and then tested the ovpnmain.cgi out with a vm using the existing openvpn-2.5.9 version for openvpn.
My old profile for my laptop which had a ciphers entry worked without any problem. My laptop was working withy openvpn-2.6.6
I then created a new profile using the new ovpnmain.cgi using the negotiation option which ended up with a data-ciphers line. That also worked in making a successful openvpn tunnel with my laptop without any issues.
I then downgraded my laptop to openvpn-2.4.8 and had to install openvpn-1.1.1 to make that work.
With that client version on my laptop both the old and new profiles connected with a tunnel with no problems.
I then tried downgrading my laptop to openvpn-2.3.14 but to make this work I would have had to downgrade the laptop to openssl-1.0.0 which I was not willing to do as that is very old and very insecure.
The oldest openvpn version working with openssl-1.1.1 is 2.4.0 which is nearly 7 years old.
That version also worked with both the old and new laptop profiles.
I then tested out the openvpn server on my IPFire vm with a 2.6.0 and 2.6.6 version of openvpn.
Both these openvpn versions worked with both the old and new laptop connection profiles with my laptop on version 2.4.0 and on 2.6.6
All the above was using network manager with its openvpn plugin option on the laptop for making the openvpn tunnel connections.
As far as I can tell everything is working fine when negotiation is specified on the server. Old profiles that just use the cipher option also work fine. Therefore my plan is to only use the negotiation option and not make it selectable for older clients. The data-ciphers-fallback option in the server seems to be doing its job.
The negotiation option on the server was able to connect to a 2.4.0 client on my laptop.
According to the OpenVPN wiki on cipher negotiation the data- ciphers-fallback option will work with 2.4.x and 2.3.x clients. As the 2.3.x clients need to be using openssl-1.0.0 then I think if those clients work then fine but nothing further back.
Overall, I am very happy with what I have succeeded in doing so far. I achieved things much quicker than I had expected.
I will now try and see about creating a profile on a CU 179 based system that uses one of the old insecure ciphers such as Blow Fish and restore that into my evaluation vm and see how that works with my laptop when I have it downgraded to openvpn-2.4.0
I already know that if the laptop is at openvpn-2.6.6 then it will not accept a blowfish cipher (or another weak cipher such as DES) as that is something I tested in the past.
If that also works then my plan will be to take the updated ovpnmain.cgi and split the changes into a new range of patches and then submit them for consideration.
That will probably end up later in November as I will be busy with personal things at the end of October / beginning of November.
Regards,
Adolf.