tokens: ['The', 'VX', 'control', 'function', 'VCF', 'and', 'VUE', 'could', 'use', 'a', 'share', 'key', 'to', 'do', 'mutual', 'authentication', 'and', 'establish', 'a', 'secure', 'channel', 'based', 'on', 'PSK', 'TLS', 'The', 'preshared', 'key', 'could', 'be', 'derived', 'during', 'the', 'AKA', 'procedure', 'when', 'the', 'VUE', 'attach', 'to', 'the', 'network', 'through', 'UU', 'interface', 'The', 'new', 'key', 'hierarchy', 'based', 'on', 'the', 'GPP', 'TS', '', '', 'is', 'presented', 'as', 'follows', 'Figure', '', 'Key', 'Hierarchy', 'Based', 'on', 'TS', '', 'According', 'to', 'the', 'VX', 'architecture', 'defined', 'in', 'the', 'TS', '', 'there', 'is', 'no', 'communication', 'interface', 'between', 'VCF', 'and', 'MME', 'but', 'VCF', 'could', 'communicate', 'with', 'HSS', 'through', 'V', 'interface', 'so', 'VCF', 'could', 'acquires', 'key', 'or', 'materials', 'from', 'HSS', 'The', 'new', 'branch', 'of', 'key', 'derivation', 'is', 'that', 'the', 'VUE', 'and', 'HSS', 'derives', 'a', 'root', 'key', 'KVX', 'respectively', 'for', 'VX', 'service', 'during', 'AKA', 'procedure', 'and', 'then', 'VUE', 'and', 'VCF', 'derive', 'a', 'preshared', 'key', 'KPSK', 'from', 'KVX', 'respectively', 'The', 'VUE', 'and', 'VCF', 'could', 'utilize', 'the', 'KPSK', 'and', 'PSK', 'TLS', 'protocol', 'to', 'perform', 'mutual', 'authentication', 'and', 'establish', 'a', 'secure', 'channel', 'on', 'user', 'plane', 'Note', 'This', 'solution', 'does', 'not', 'address']