@hko My understanding is that GCM is a significant point of contention in the OpenPGP standards schism. So it would be relevant here. I have not seen any evidence presented that it would be more efficient than OCB for web applications. My estimation is that it would not be. Even if it was, the sorts of things done as web apps involve short messages (email).
That signalling that you mention (the preferences in the public key) only works for asymmetrical encryption and is not reliable. I have an entire page of examples of where it has failed:
https://articles.59.ca/doku.php?id=pgpfan:noae_shame
... and that is up to now just for a single implementation. Things could get much worse. That page is a reference for this article:
https://articles.59.ca/doku.php?id=pgpfan:interop
Somewhat ironically, it can be legitimately argued that CGM is overall less secure than the existing OCFB-MDC (SEIPD) mode:
https://articles.59.ca/doku.php?id=pgpfan:seip
The relative insecurity of GCM has also come out as a factor in the schism.
#openpgp #pgp