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tob1234
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openvpn and AES-256-GCM

Thu Apr 22, 2021 11:02 am

Hello,

According to openvpn the cipher AES-256-GCM is recommended instead of AES-256-CBC. see also here: https://openvpn.net/community-downloads/
My connection gets reset if i use AES-256-GCM when connecting to vpn.

questions:
a) Does mikrotik support ovpn server with the AES-256-GCM cipher ?
b) how to use it in case the answer is "yes"
c) is mikrotik planning to release ovpn with the recommended cipher AES-256-GCM ?

In case the AES-256-CBC is used this gives the following in the vpn logs:
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.

environment:
openvpn community client 2.5.2 on windows 10
mikrotik RouterBOARD 962UiGS-5HacT2HnT, version 6.48.1
 
essides
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 5:34 pm

same problem here.

any solution?
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 5:42 pm

Consider OpenVPN abandoned.
 
essides
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 5:55 pm

it's amazing, mikrotik has a extremily slow evolution, in few year it will be out of market.

any secure solution for VPN with windows clients?
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 5:59 pm

...in few year it will be out of market...
Is the same phrase someoe wroted on 2010, and nowadays all our core business are on MikroTik machines.
OpenVPN is only a toy.
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:04 pm

so what do you suggest to implement an strong and easy VPN system for windows clients?
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:08 pm

 
essides
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:21 pm

With L2tp/Ipsec I have problem when two people over same ip try to connect, one of them is kicked after few time.
I'll read about that. Thanks
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:25 pm

I do not write ultra-obsolete PPTP... I hope you never use it anywhere...
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:25 pm

so what do you suggest to implement an strong and easy VPN system for windows clients?
AES 256-CBC cipher is not considered strong ?
With L2tp/Ipsec I have problem when two people over same ip try to connect, one of them is kicked after few time.
There is an explanation from @sindy as to why this happens...
There it is :viewtopic.php?t=132823

However this seems to be fixed...
*) l2tp - fixed multiple tunnel establishment from the same remote IP address (introduced in v6.47);
https://mikrotik.com/download/changelogs

So, what is your ROS version ?
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:36 pm

AES 256-CBC cipher is not considered strong ?
it's just deprecated for new openvpn client version, I'm not saying that AES 256-CBC is weak
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:38 pm

AES 256-CBC cipher is not considered strong ?
it's just deprecated for new openvpn client version, I'm not saying that AES 256-CBC is weak
It is, but it still works ...
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:43 pm



it's just deprecated for new openvpn client version, I'm not saying that AES 256-CBC is weak
It is, but it still works ...
but does it has sense to implement something that is deprecated? and half-finished ( no compression/no udp/no new ciphers ) etc..
 
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Re: openvpn and AES-256-GCM

Wed Aug 11, 2021 6:44 pm

Maybe yes, maybe no... it depends...
 
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Re: openvpn and AES-256-GCM

Wed Apr 20, 2022 11:29 pm

For anyone wanting some actual technical information on the issue, this article does a good job of explaining the issue with AES-CBC.

"If you really have no choice and need to use CBC, you can still secure it by computing a message authentication code (MAC) from the ciphertext and IV, this can be done using the popular HMAC algorithm."

A pure OpenVPN server has the ability to add an additional layer of protection using HMAC with the tls-auth configuration option. Most other OpenVPN implementations also support this. Unfortunately when Mikrotik wrote their own OpenVPN implementation supposedly, there are a large number of features that they didn't implement (PUSH options being one glaring omission). tls-auth is another, and because of it, using the methods outlined in the article listed above, a VPN tunnel encrypted with AES-CBC and no HMAC protection is susceptible to attack.

I think OpenVPN was right to deprecate AES-CBC as most people seem to do what's easy and not what's right for one reason or another. It will be interesting to see if Mikrotik gives alternate ciphers to use like AES-GCM in their OpenVPN implementation anytime soon, among other OpenVPN fixes (like returning the event AUTH_FAILED instead of NETWORK_EOF_ERROR when an authentication error occurs so the client will know their credentials are wrong...)
 
MrDim
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Re: openvpn and AES-256-GCM

Wed May 25, 2022 8:37 pm

So, still no AES-GCM in RouterOS 7?
 
psztoch
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Re: openvpn and AES-256-GCM

Fri Dec 01, 2023 9:32 pm

No.
Support for AES-256-GCM, AES-128-GCM and CHACHA20-POLY1305 compatible with standard OpenVPN implementation should be added. It is big problem for me.
 
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Re: openvpn and AES-256-GCM

Sat Dec 02, 2023 3:38 am

No.
Support for AES-256-GCM, AES-128-GCM and CHACHA20-POLY1305 compatible with standard OpenVPN implementation should be added. It is big problem for me.
AES-GCM (128/192/256) was added to RouterOS 7.8 in February of 2023 (only after they had added it to just about everything else that uses encryption... :lol:)

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