A question for cryptography/networking nerds.
To protect from replay attacks, Shadowsocks 2022 requires clients to send a timestamp (in every packet) which servers verify and reject a packet if it differs by more than N minutes from the current server-side time.
TLS 1.3 protects from replays in a different way, it generates a new ephemeral encryption key for every handshake, so any old conversation replay is invalid.
What if i remove timestamp verification in my ss-inspired protocol, and make a key exchange handshake instead?
A handshake packet would be encrypted with a pre-shared key (like every packet in regular ss), server sends a new key in it, and then the rest of the conversation is encrypted with this newly generated psk.
What am i missing? Is this approach safe?
@darkcat09 sounds good to me. The downside I can think of is the cost of the extra handshake packet. If the entire conversation is short like only a couple of packets, then that could be a significant overhead. But it's good to avoid relying on time, it can easily happen that someone is manipulated into having wrong time.
