Re: [PATCH cryptodev] crypto: lib/chacha20poly1305 - allow users to specify 96bit nonce

On Tue, 17 Nov 2020 at 10:47, Antonio Quartulli [off-list ref] wrote:

Hi,


On 17/11/2020 09:31, Ard Biesheuvel wrote:

quoted

If you are going back to the drawing board with in-kernel acceleration
for OpenVPN, I strongly suggest to:
a) either stick to one implementation, and use the library interface,
or use dynamic dispatch using the crypto API AEAD abstraction, which
already implements 96-bit nonces for ChaCha20Poly1305,

What we are implementing is a simple Data Channel Offload, which is
expected to be compatible with the current userspace implementation.
Therefore we don't want to change how encryption is performed.

Using the crypto API AEAD abstraction will be my next move at this point.

Aren't you already using that for gcm(aes) ?

I just find it a bit strange that an API of a well defined crypto schema
is implemented in a way that accommodates only some of its use cases.

You mean the 64-bit nonce used by the library version of
ChaCha20Poly1305? I agree that this is a bit unusual, but a library
interface doesn't seem like the right abstraction for this in the
first place, so I guess it is irrelevant.

But I guess it's accepted that we will have to live with two APIs for a bit.

quoted

b) consider using Aegis128 instead of AES-GCM or ChaChaPoly - it is
one of the winners of the CAESAR competition, and on hardware that
supports AES instructions, it is extremely efficient, and not
encumbered by the same issues that make AES-GCM tricky to use.

We might implement a library interface for Aegis128 if that is preferable.

Thanks for the pointer!
I guess we will consider supporting Aegis128 once it gets standardized
(AFAIK it is not yet).

It is. The CAESAR competition is over, and produced a suite of
recommended algorithms, one of which is Aegis128 for the high
performance use case. (Note that other variants of Aegis did not make
it into the final recommendation)