Hello,
we (Sequoia PGP) would love to see OCB being implemented in Nettle. The OpenPGP working group is working on a revision of RFC4880, which will mostly be a cryptographic refresh, and will bring AEAD to OpenPGP.
The previous -now abandoned- draft called for EAX being mandatory, and OCB being optional [0]. This was motivated by OCB being encumbered by patents. However, said patents were waived by the holder [1].
0: https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-rfc4880bis-10#secti... 1: https://mailarchive.ietf.org/arch/msg/cfrg/qLTveWOdTJcLn4HP3ev-vrj05Vg/
With OCB being no longer patent-encumbered, it seems preferable over the two-pass EAX construction. Therefore, it seems plausible that the WG makes OCB mandatory to implement. To support that in Sequoia, we'd need support for that in Nettle (Nettle is our main cryptographic backend).
Unfortunately, we don't have the expertise in our team to contribute a patch, and we currently aren't in a position to offer funding for the implementation.
Thanks, Justus