OpenVPN 2.5

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rseiler
Posts: 208
Joined: Sun Dec 15, 2013 12:31 am

OpenVPN 2.5

Post by rseiler »

The new client is out:
https://openvpn.net/community-downloads

It does work against Gargoyle but with two warnings (the second one is new for sure, not sure of the first):
WARNING: Compression for receiving enabled. Compression has been used in the past to break encryption. Sent packets are not compressed unless "allow-compression yes" is also set.

DEPRECATED OPTION: --cipher set to 'AES-256-CBC' but missing in --data-ciphers (AES-256-GCM:AES-128-GCM). Future OpenVPN version will ignore --cipher for cipher negotiations. Add 'AES-256-CBC' to --data-ciphers or change --cipher 'AES-256-CBC' to --data-ciphers-fallback 'AES-256-CBC' to silence this warning.
This adds further context. We have 2.4 (server), I think, so given that what might be best?
BF-CBC CIPHER IS NO LONGER THE DEFAULT

Cipher handling for the data channel cipher has been significantly changed between OpenVPN 2.3/2.4 and v2.5, most notably there are no “default cipher BF-CBC” anymore because it is no longer considered a reasonable default. BF-CBC is still available, but it needs to be explicitly configured now.

For connections between OpenVPN 2.4 and v2.5 clients and servers, both ends will be able to negotiate a better cipher than BF-CBC. By default they will select one of the AES-GCM ciphers, but this can be influenced using the –data-ciphers setting.

Connections between OpenVPN 2.3 and v2.5 that have no –cipher setting in the config (= defaulting to BF-CBC and not being negotiation-capable) must be updated. Unless BF-CBC is included in –data-ciphers or there is a “–cipher BF-CBC” in the OpenVPN 2.5 config, a v2.5 client or server will refuse to talk to a v2.3 server or client, because it has no common data channel cipher and negotiating a cipher is not possible.

Generally, we recommend upgrading such setups to OpenVPN 2.4 or v2.5. If upgrading is not possible we recommend adding data-ciphers AES-256-GCM:AES-128-GCM:AES-128-CBC (for v2.5+) or cipher AES-128-CBC (v2.4.x and older) to the configuration of all clients and servers.

Lantis
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Joined: Mon Jan 05, 2015 5:33 am
Location: Australia

Re: OpenVPN 2.5

Post by Lantis »

Thanks for the heads up.
This sounds like it will cause a bit of grief for backwards compatibility when we move to 2.5.

It looks like no breaking change (yet) for 2.4 server with newer clients, only warnings.

They haven't updated their reference document yet (still only 2.4 available) so i'll look deeper when they comes out.
http://lantisproject.com/downloads/gargoyle_ispyisail.php for the latest releases
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