Inria Ericsson Ericsson University of Murcia University of Murcia This document specifies a Pre-Shared Key (PSK) authentication method for the Lightweight Authenticated Key Exchange (LAKE) protocol. The PSK method provides mutual authentication, ephemeral key exchange, identity protection, and quantum resistance while incurring lower computational costs than the public-key authentication methods specified for LAKE. It is suited for systems where nodes share a PSK provided out-of-band (external PSK) and enables efficient session resumption with less computational overhead when the PSK is provided from a previous LAKE session (resumption PSK). This document details the PSK message flow, key derivation changes, message formatting, processing, and security considerations.