0RTTlike

0RTTlike is a term used in network protocol discussions to describe mechanisms that aim to achieve zero or near-zero latency for initial data delivery by reusing previously established credentials. It is not an official standard, and its exact meaning can vary by context, but the core idea is to allow the client to send application data in the first exchange after initiating a connection, without waiting for a full new handshake.

In practice, 0RTTlike approaches rely on some form of cached state, such as pre-shared keys, session tickets, or other resumption data, to bootstrap encryption and authentication quickly. The client can attach data to the initial message that would normally be sent only after a complete handshake. Servers implementing 0RTTlike logic must carefully manage state to ensure data integrity and prevent misuse.

Security considerations are central to 0RTTlike concepts. The main risk is replay attacks, where previously captured data could be resent. Mitigations include strict replay protection, short time windows, binding data to fresh handshake context, and limiting what can be sent in the initial message. Key management complexity and potential exposure of resumed keys are additional concerns. Some 0RTTlike designs distinguish between data that is safe to send in the first flight and data that must wait for a full handshake.

Typical use cases involve scenarios requiring very low latency for repeated connections, such as high-frequency web services or IoT devices, where the performance benefits outweigh the security trade-offs in carefully controlled contexts. See also TLS 1.3 0-RTT, TLS resumption, and replay protection.