Re: Status update on openvpn work

[Adolf Belka <adolf.belka@ipfire.org>]

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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.
>>>

-- 
Sent from my laptop