[Fix/Feat] Asymmetrical Noise-XX handshake for the validators

[ljedrz]

Replaces the gateway's challenge-response handshake with one built on the Noise XX pattern, where each side binds its Aleo identity to the session by signing the running Noise handshake hash. Identity is still the Aleo account key - the Noise static keys are per-connection and exist only to give the pattern a channel to bind to. The post-handshake traffic remains unencrypted.

The legacy handshake is still accepted, so validators can be upgraded one at a time. NOISE_HANDSHAKE_ACTIVATION_HEIGHT is None: nothing on mainnet initiates the new handshake yet, only devnets do.

Over 50% of the new code is tests, and much of the new plumbing can be reused if we want to utilize this handshake pattern with other node types as well.

Benefits:

• Relay/impersonation is closed. Each side signs its own session's handshake hash, and two sessions cannot share one, so a forwarded signature never verifies. Note: the relay would yield an eclipse, not a forgery - nothing attributable to the victim can be fabricated, and the attacker cannot speak for any other validator on that connection.
• The DoS asymmetry is inverted. The responder reads the initiator's cleartext hint and runs every cheap check - version, trusted, committee membership, already-connected - before deriving a single key. This makes the handshake initially more expensive for the initiator.
• Peer-pool mutation moved after the checks, so an unauthorized peer can no longer occupy a pool slot at all.
• Pre-authentication buffering drops 16x (1MiB -> 65535B) once legacy is retired.

As a small drive-by, there's also a hardening for the EventCodec's encoder, in its own commit.

CC #4140

[vicsn]

Can you enable the merge-workflow so we can make sure the upgrade-test succeeds? But before that tackle #4356 ?

[vicsn]

Looks amazing!

It would be great if we can truly consider the issues closed with one PR (ignoring the pruning of dead code). Therefore:

• should we also adjust the gateway handshake done by the bootstrap nodes?
• either we:
  • keep NOISE_HANDSHAKE_ACTIVATION_HEIGHT=V19 and introduce a new NOISE_HANDSHAKE_DEACTIVATION_HEIGHT=V20.
  • replace NOISE_HANDSHAKE_ACTIVATION_HEIGHT=V19 to a NOISE_HANDSHAKE_DEACTIVATION_HEIGHT=V19. As soon as a validator has upgraded, they attempt a noise handshake. If it fails, they retry with the legacy handshake. At NOISE_HANDSHAKE_DEACTIVATION_HEIGHT==V19 we assume all nodes upgraded and everyone is using noise.

[vicsn]

Can we set this to CONSENSUS_HEIGHT(ConsensusVersion::V19) (regrettably a runtime value)