> I have just PRed a draft version of two BIPs I recently wrote.
> https://github.com/bitcoin/bips/pull/362

Thanks for the feedback and IRC discussions.

I have overhauled both BIPs.
https://github.com/bitcoin/bips/pull/362/files#diff

Main changes for the encryption BIP:
* No message wrapping. Once encryption is established, everything is
encrypted. No timeout.
* Added MAC: proposed AEAD is now ChaCha20-Poly1305 with an alternative
for AES256-GCH
* Independent ECDH negotiation and independent secrets for the symmetric
cipher for both communication directions
* Optimized message format and message-batch-option for encrypted data

It could be that the p2p performance for Chacha20-poly1305 encrypted
message is slightly better then the current plaintext message format
(dropping the network magic and the sha256 per message).

P2p authentication BIP:
* No message wrapping. Peers keep the state once authenticated.
* Simplified and auth now requires encrypted channels.


Some answers...

> How does a peer know what messages the other peer requires to be
authenticated?

This is not covered by the auth BIP. Peers could agree on a protocol
extension outside of any BIP.
Once auth is possible, new BIPs could be written. Things like only
allowing filtering (or other services) to authenticated peers (and
disabling NODE_BLOOM).

> How does banning in this specific case enable fingerprinting as
opposed to any other banning?

Current nodes ignore a unknown message with a command like "auth".
Banning would allow a requesting peer to identify nodes that support
auth and attack them over different channels ("ah, ... this guy supports
auth, they must have some secret data, lets attack over SSH).

>> This proposal is backward compatible. Non supporting peers will
ignore the <code>auth</code> message.
> ... and not process it at all? How is that backward compatible?

Depends how we define backward compatibility. :-)
Peers supporting this "extension" can still interact with older peers.

> This proposal is backward compatible. Non supporting peers will ignore
the > <code>enc*</code> messages.

Current p2p implementation ignores any unknown command.


</jonas>