Re: [PATCH RFC 4/4] fscrypt: Add new encryption policy for btrfs.

[David Sterba]

On Mon, Jul 25, 2022 at 10:16:07PM -0400, Sweet Tea Dorminy wrote:
> On 7/25/22 19:32, Eric Biggers wrote:
> > On Sat, Jul 23, 2022 at 08:52:28PM -0400, Sweet Tea Dorminy wrote:

> > Given that this new proposal uses per-block metadata, has
> > support for authenticated encryption been considered? Has space been reserved
> > in the per-block metadata for authentication tags so that authenticated
> > encryption support could be added later even if it's not in the initial version?
> 
> I don't know sufficiently much about authenticated encryption to have 
> considered it. As currently drafted, btrfs encrypts before checksumming 
> if checksums are enabled, and checks against checksums before 
> decrypting. Although at present we haven't discussed authentication 
> tags, btrfs could store them in a separate itemtype which could be added 
> at any time, much as we currently store fsverity data. We do have 
> sufficient room saved for adding other encryption types, if necessary; 
> we could use some of that to indicate the existence of authentication 
> tags for the extents' data.

The AEAD tag can be used in place of checksum (also stored in the
checksum item).