Bug 24457 - AES-KW can only wrap a JWK key if its serialization happens to be 8*n bytes long

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24457

Alexey re-opened this bug with:

"A WebCrypto implementation can pad JWK with spaces for AES-KW, but
the same padding can destroy the ability to wrap with RSA-OAEP,
because you can run out of size limit. So, any padding should be
conditional on which algorithm will be used for encryption in a later
step of wrapping algorithm.

I think that it would be appropriate to have normative text. But even
if it's simply a note, it should be:
1. Substantially more elaborate than suggested above.
2. Added as part of this bug (so it seems like the bug should remain
open until the note is added)."

I would suggest that any such note be non-normative:

- There has been strong objection to specifying our own padding scheme

- There is no _need_ for normative specification to ensure
interoperability: so long as the serialization is valid JSON, we are
good.

A note (I am not sure where it would be) might look something like:

"Note: Some algorithms used for key wrapping place constraints on the
payload size. For example AES-KW requires the payload to be a multiple
of 8 bytes in length and RSA-OAEP places a restriction on the length.
For key formats that offer flexibility in serialization of a given key
(for exmaple JWK), implementations may choose to adapt the
serialization to the constraints of the wrapping algorithm."

Comments ?

...Mark