ed in the response of the IKE_INIT_SA exchange response or in the IKE AUTH exchange request. It also indicates the certification authority for the required certificate. 7.1.2.2.6. AUTH block The authentication (AUTH) block contains the authentication digest (signature or seal) for the third-party authentication. The block also specifies the method used. 7.1.2.2.7. Ni and Nr blocks Nonce initiator (Ni) and nonce responder (Nr) blocks contain a random number generated by the initiator and responder. These numbers are used in the creation of derived keys. 7.1.2.2.8. N block The notification (N) blocks contain error messages indicating the reason why the security association cannot be established. The N block also contains status messages that an SA management process wishes to communicate to a remote process. 7.1.2.2.9. D block The delete (D) block includes the SPI of the SA that the message source wishes to delete. For an AH or ESP, it is possible to specify several SPI values. It is also possible to string several D blocks together in a single IKEv2 message. 7.1.2.2.10. V block The vendor ID (V) block announces that the message source is capable of accepting private extensions of the IKEv2 protocol. These extensions can involve the introduction of new blocks, new types of exchange or new notification information. SWu Tunnel Establishment 7.1.2.2.11. TS block The traffic selector (TS) block identifies the flows for which the ESP/AH security association is implemented. Flow determination is based on the following information: - the type of data encapsulated by the IP header, stated in the Protocol fields of the IPv4 header or the Next Header field of the IPv6 header; - the range of source and destination IP addresses; - the range of source and destination port numbers if the IP header encapsulates UDP or TCP segments; - the ICMP message type and code. 7.1.2.2.12. SK block The SK (encrypted and authenticated) block is always located at the end of the IKEv2 message. The encryption and integrity algorithms for the IKEv