[openpgp] Re: I-D Action: draft-ietf-openpgp-persistent-sy mmetric-keys-02.txt

Hi all,

I've (finally) published a new version of draft-ietf-openpgp-
persistent-symmetric-keys, apologies that it took so long.

I've taken some time to consider the various options that were discussed
at the interim meeting and afterwards, and landed on the feeling that
we may be introducing too many nobs. Do we really need multiple new
algorithms for persistent symmetric keys, with room for future
expansion? AEAD seems pretty solid and already has its own registry
with room for expansion. HMAC less so, but do we really need it?

I realized that no, we don't, we could simply use AEAD as a MAC, too,
by passing the input as additional data, and the empty string as the
message to encrypt.

This allows us to more cleanly use the special algorithm ID value 0
for persistent symmetric keys, which obviates the need to rename packets
and registries.

This also simplifies the implementation and reduces the number of
primitives we're introducing to OpenPGP.

If we really want to introduce HMAC or KMAC at a later date after all
for whatever reason, plenty of nobs remain to do so, such as in a new
packet or packet version, or a new algorithm ID anyway, and so on.

Hopefully this seems reasonable; I'll also present the changes more in
depth at the session tomorrow, if time allows.

Best,
Daniel

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