[TLS] ECH AAD for HRR

[Stephen Farrell <[e-mail]>]

(Apologies for the acronym laden subject:-)

I'm more or less at the "code complete" stage of
implementing draft-13 incl. HRR. (If anyone wants
to try interop, for now please contact me, but I
should have a server up in a few days.) I'm sure
as usual I'll have gotten some details wrong, but
I wasn't clear about one thing:

- When sending the 2nd CH following HRR, the spec
calls for omitting the "enc" field of the ECH
extension ("enc" holds the sender's public HPKE
value that's re-used from the 1st CH).
- The AAD for that ECH encryption is the outer
CH with zeros replacing where the ciphertext will
go.
- I concluded that the sender's ECH public value
(the "enc" field) ought not be present in the
AAD in that case, as well as being omitted in
the ECH value, but it wasn't entirely clear to me
from the spec (and it'd work either way).

So my question is: did I get that right or not?

Thanks in advance,
S.