Lightweight AAA for Cellular IP

As Mobile IP based communications networks become increasingly ubiquitous, current trust relationships employed in these networks will no longer remain adequate. With a large number of networks and many millions of roaming users, there is a need to put into place authentication, authorization and accounting (AAA) procedures for secure updating of router entries and accounting of network usage by mobiles. We present a lightweight AAA scheme for micro mobility based architectures which makes use of hash chain trees for efficient storage of hash values and fast authentication of datagrams. A node attaches the next unused hash value in a chain to each datagram, which can be used by intermediate routing nodes to verify the authenticity of the message. We give an overview of current AAA proposals for Mobile IP and the emerging area of micro mobility protocols, before presenting the design goals of our protocol and details of our solution. 1 AAA IN MOBILE IP The IETF has specified the Mobile IP [1] protocol for wide area mobility management. It enables a node to move freely from one point of connection on the Internet to another, without disrupting end-to-end TCP connectivity. Mobile nodes are required to securely register a care-of-address (COA) with their home agent (HA) while roaming in a foreign domain. If however security mechanisms are not employed, the network can be compromised through remote redirection attacks by malicious nodes. In addition, mechanisms are needed that allow foreign agents (FA) in the visited domain to verify the identity of mobile nodes and authorize connectivity based on local policies or the ability to pay for network usage. Figure 1 adapted from [2] shows the Mobile IP network model where a correspondent node is communicating with a roaming mobile node via the MN’s home agent. Figure 1: Mobile IP network model With the availability of low-cost handheld devices such as PDAs and wireless networking hardware, there has been a lot of interest in building Mobile IP based wireless access networks. However for such networks to become commercially viable, authentication and accounting procedures need to be put in place. Current work in the IETF is focusing on providing an infrastructure for authentication, authorization and accounting (AAA) services to the various entities in the network [3]. Figure 2 depicts the entities and the relationships between them. A foreign domain contains one or more AAA servers (AAAF) and multiple foreign agents. The FAs also known as attendants interact with a mobile node to authenticate its credentials. A foreign agent has a security association with its local AAA server, which in turn will have further security associations with other AAA servers. If the AAAF cannot verify the credentials of a mobile node, it will contact the MNs home AAA server (AAAH) with whom it must share a security association. A security association at a very minimum consists of a shared secret between two entities. Figure 2: Mobile IP/AAA entities and trust model In the AAA trust model for Mobile IP, a mobile node shares a security association SA1 with the AAA server in its home domain. The AAAH in turn shares a security association SA2 with the home agent. It is also necessary for the AAAH and the AAAF to share a security association SA3 in order that the AAA server in the foreign domain can verify the credentials of roaming mobile node. Finally the attendant must share a security association SA4 with the AAAF in order for it to allocate local resources to a mobile node. For scalability reasons the concept of brokers (AAAB) is employed which means that a foreign domain does not need to keep security associations with every possible home domain. Once a mobile node has been authenticated three session keys are generated by the AAAH. Each session AAAFn