nd from the secret key Kcn of the correspondent node: First 64 bits HMAC_SHA1 (Kcn, (HoA | nonce I 0x00)) - CoT message contains the cryptographic information Care-of Keygen Token calculated from the address CoA, a random number (nonce) and the secret key Kcn of the correspondent node: First 64 bits HMAC_SHA1 (Kcn, (CoA | nonce | 0x01)) Following the procedure, the mobile node has the data it needs to build a Kbm secret key by hashing the received data: Kbm = SHA1 (Home Keygen Token | Care-of Keygen Token) The Binding Update message transmitted by the mobile node directly to the correspondent node contains the following cryptographic information: First 96 bits HMAC_SHA1 (Kbm, (CoA | CNA Binding Update)) S2c Tunnel Establishment When the correspondent node has validated the received Binding Update message, it responds with the Binding Acknowledgment message with the following cryptographic information: First 96 bits HMAC_SHA1 (Kbm, (CoA Binding Acknowledgement) The procedure is based on the assumption that no intruder can listen to both HoT and CoT messages, these messages using two different paths to join the mobile node. Interception remains possible if the malicious node is connected to the network of the correspondent node. The procedure is based on the shared Kbm secret that needs to be refreshed. Refreshment is left to the initiative of the correspondent node. An association change request Binding Update is denied through the Binding Error message. The mobile node must then restart the Return Routability procedure. 9.2. DSMIPv6 mechanism The MIPv6 mechanism was designed for a mobile connection to an IPv6 network. The DSMIPv6 (Dual-Stack Mobile IP version 6) mechanism takes into account the connection of the mobile to a public or private IPv4 network. This arrangement makes it possible to avoid unrolling the two MIPv4 and MIPv6 mechanisms when the mobile has a dual IPv4 and IPv6 stack. Several types of tunnel can be built between the mobile and the PGW entity that hosts the home agent functions: - an IPv6 pac