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

Ard Biesheuvel ardb at kernel.org
Tue Nov 17 10:52:36 CET 2020

On Tue, 17 Nov 2020 at 10:47, Antonio Quartulli <a at unstable.cc> wrote:
> Hi,
> On 17/11/2020 09:31, Ard Biesheuvel wrote:
> > 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.
> > 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)

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