Post-Quantum EDHOC - Initiator and Responder using signature and/or KEM

This document specifies two extensions to the Ephemeral Diffie- Hellman over COSE (EDHOC). These two protocol versions aim to provide quantum-resistance to the original EDHOC protocol, while reducing message-complexity with respect to parallel drafts. The document defines: (1) a 3-message quantum-resistant EDHOC proposal when the Initiator knows the Responder; in this version, the Initiator authenticates using a signature, while the Responder uses a KEM; (2) a 3-or-4-message quantum-resistant EDHOC proposal, which proposes a tradeoff between message-complexity and computational overhead.