Section: 5.5.4.3 UE-initiated authentication and key agreement procedure initiation
Content: Upon receiving a ProSe direct link establishment request from the 5G ProSe remote UE or the 5G ProSe end UE including the SUCI or the CP-PRUK ID of the 5G ProSe remote UE or the 5G ProSe end UE, for establishing a secure PC5 unicast link as specified in 3GPP TS 24.554[ Proximity-services (ProSe) in 5G System (5GS) protocol aspects; Stage 3 ]  [19E] when the security for 5G ProSe communication via 5G ProSe UE-to-network relay or 5G ProSe UE-to-UE relay is performed over control plane as specified in 3GPP TS 33.503[ Security Aspects of Proximity based Services (ProSe) in the 5G System (5GS) ]  [56], the UE shall: a) allocate a PRTI value as specified in subclause 5.5.4.2; b) create a RELAY KEY REQUEST message; c) set the PRTI IE of the RELAY KEY REQUEST message to the allocated PRTI value; d) set the relay key request parameters IE of the RELAY KEY REQUEST message with SUCI or the CP-PRUK ID, relay service code, and nonce_1 received from the of the 5G ProSe remote UE or the 5G ProSe end UE; e) send the RELAY KEY REQUEST message; and f) start the timer T3527 upon sending the RELAY KEY REQUEST message.