[openpgp] Forwarding for v6 follow-up

Hi everyone,

I'm following up about the forwarding proposal I presented today at the meeting. As it's supposed to be, I've got a possibly better alternative to the FKESK at lunch after the meeting.

My question to the working group is then: what do you prefer from the following two options?

## FKESK
This is the alternative presented earlier today. To convey the message information needed to decrypt for the forwardee KDF, we create a new packet: Forwarding Key Encrypted Session Key Packet.
An FKESK contains the PKESK info plus the transformed ciphertext:
- Version
- Key version
- Forwardee fingerprint
- Algorithm used (same code point as original)
- Forwarder public key material
- Original algorithm-specific data:
  - Original ciphertext
- Forwarded algorithm-specific data:
  - Transformed ciphertext

## New algorithm ID
We can re-use the PKESK and add the needed information into the algorithm specific data. No additional packet needed, just define a new codepoint e.g. "Forwarded X25519" (note that not all algorithms allow forwarding) so we'd have to do just a couple.
The PKESK for the forwarding algorithm is structured as follows:
- Version
- Key version
- Forwardee fingerprint
- Algorithm used (new code point)
- Algorithm-specific data:
  - Transformed ciphertext
  - Original ciphertext
  - Forwarder public key material

Any early feedback is appreciated, I'll then proceed to formalize it better in the draft. Thanks!

Cheers,
Aron

-- 
Aron Wussler 
Sent with ProtonMail, OpenPGP key 0x7E6761563EFE3930

_______________________________________________
openpgp mailing list -- [email protected]
To unsubscribe send an email to [email protected]

-----BEGIN PGP SIGNATURE-----
Version: ProtonMail

wqsEARYIAF0FgmiDvBEJEH5nYVY+/jkwNRQAAAAAABwAEHNhbHRAbm90YXRp
b25zLm9wZW5wZ3Bqcy5vcmcUFaNzGqRpcUVnUiTEiAfYFiEEi5WyUV9ru2q2
FJ1VfmdhVj7+OTAAADqzAP4mNrV5TsHCrwcgMJWhGBkRIAioEcpwh/vANJGn
fQFipAD+KIbrdS+tMaNl7COr9IF9xZJHmEA6RqSsUafzijFj0Qg=
=/hlI
-----END PGP SIGNATURE-----