Restructure LP packet format so cleartext fields (receiver_idx, counter)
are always first, enabling trivial header parsing for routing before
session lookup. Protocol version and reserved fields are now encrypted
in the inner payload for encrypted packets.
Wire format change:
- Before: proto(1B) + reserved(3B) + receiver_idx(4B) + counter(8B)
- After: receiver_idx(4B) + counter(8B) | proto(1B) + reserved(3B) + ...
Key changes:
- Add OuterHeader struct (12 bytes) for routing/replay protection
- Update serialize_lp_packet/parse_lp_packet for unified format
- parse_lp_header_only now returns OuterHeader
- Gateway handler uses OuterHeader for session lookup
- Update DESIGN.md with new wire format diagrams
Security improvement: Only receiver_idx and counter visible after PSK
establishment (was also exposing protocol version and reserved).
durch
b05113e522