Re: [Openvpn-devel] [ovpn-dco] AES-CCM available for testing

[Jan J. K. <ja...@ni...>]

Hi Antonio,

On 06/12/20 17:09, Antonio Quartulli wrote:
> Hi all,
>
> Some people have expressed interest in ovpn-dco supporting AES-CBC.
>
> However, since ovpn-dco is currently using the AEAD kernel crypto API
> only, introducing support for CBC mode would require quite some
> refactoring and we do not really want to do that (the community believes
> that as of now AEAD ciphers should always be preferred moving forward).
>
> In a previous discussion on this mailing list, it was highlighted that
> AES-CCM is nothing else than AES-CBC in disguise as AEAD cipher.
>
> (for the curious: it is AES "Counter with CBC-MAC", known as CCM and
> described in RFC3610).
>
> For this reason I decided to give AES-CCM a try and I implemented in it
> the "aes-ccm" branch of the ovpn-dco repo.
>
> I am not sure if we're going to merge it to master yet, but for now it
> would be interesting to gather feedback from those interested in this
> cipher.
>
> Please note that OpenVPN3 does not yet support this cipher, therefore
> the only way to test AES-CCM in ovpn-dco is to use the ovpn-cli tool
> provided in the tests/ folder.
>
>
> To do so, just specify "aes-ccm" as algorithm when setting a new key.
>
>
>
excellent news!
Thank you very much for adding this so quickly; it won't help Tony He 
though, as he is stuck using a rather old AL314 + R9000 chip which does 
not support CCM or GCM. I just checked the driver code and indeed there 
is no HW support for GCM.  They *do* support some AEAD algorithms:

   authenc-hmac-sha256-cbc-aes
authenc-hmac-sha384-cbc-aes

which are listed as the (true) AEAD equivalent of AES+SHA ; the question 
is : how hard would it be to add support for this (and would it be worth 
it?)

cheers,

JJK