E.1 General aspects

33.1793GPPRelease 13Security of Mission Critical Push To Talk (MCPTT) over LTETS

E.1.0 Introduction

MIKEY-SAKKE as defined in IETF RFC 6509 [11] is used to transport Group Master Keys (GMKs) from a Group Management Server to a Group Management Client on a MCPTT UE and Private Call Keys (PCKs) between MCPTT UEs.

The GMK is encrypted to the UID generated from the receiving user’s MCPTT ID and current time period. It is signed using the UID generated from the URI associated to the Group Management Server and current time period. Similarly, the PCK is encrypted to the UID generated from the receiving user’s MCPTT ID and current time period. It is signed using the UID generated from the initiating user’s MCPTT ID and current time period. Details of this process are defined in IETF RFC 6508 [10] and IETF RFC 6507 [9]. The generation of the MIKEY-SAKKE UID is defined in clause F.2.1.

The GMK and PCK shall be 16 octets in length.

E.1.1 MIKEY common fields

If the transmitter requires an ACK for a transmission this is indicated by setting the V-bit in the MIKEY common header. For distribution of GSKs for one-to-many communications, the V-bit shall not be set.

Each MIKEY message contains the timestamp field (TS). The timestamp field shall be TS type NTP-UTC (TS type 0), and hence is a 64-bit UTC time.