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PROXY BASED AUTHENTICATION LOCALISATION SCHEME FOR HANDOVER<br />

6.5 Practical Implementations<br />

The proposed PBAL scheme can be implemented on networks without mak<strong>in</strong>g any<br />

changes to access routers. This is achieved by sett<strong>in</strong>g up a third-party fast AAA proxy<br />

for localis<strong>in</strong>g AAA requests. From the perspective of a mobile user, it <strong>in</strong>teracts with the<br />

FAP through an access network dur<strong>in</strong>g a handover, <strong>in</strong>stead of directly communicat<strong>in</strong>g<br />

with its home AAA server for authentication. In the PBAL, the access network acts as a<br />

pass-through [18] for AAA messages and does not have to understand the<br />

authentication method applied. The mobile user is <strong>in</strong> a position of redirect<strong>in</strong>g its AAA<br />

request to the correspond<strong>in</strong>g FAP <strong>in</strong> a handover. Such a redirection operation is<br />

supported by the EAP framework [18], on which various authentication methods can be<br />

applied. For example, the EAP-AKA def<strong>in</strong>es that the supplicant (e.g. a mobile user)<br />

may modify the realm portion to <strong>in</strong>fluence the AAA rout<strong>in</strong>g [74]. Keep<strong>in</strong>g the PBAL<br />

transparent to access networks is a clear advantage of implement<strong>in</strong>g the PBAL for fast<br />

authentication. This provides a large number of network operators with a choice of<br />

upgrad<strong>in</strong>g to a fast authentication scheme without reflash<strong>in</strong>g old access equipments.<br />

The trust association between the home AAA server and a fast AAA proxy can be set<br />

up us<strong>in</strong>g a pairwise key K hp as part of a roam<strong>in</strong>g agreement between the two operators.<br />

Elements of such a trust association may <strong>in</strong>clude cryptographic keys, negotiated cipher<br />

suites and other parameters. AAA protocols such as Remote Authentication Dial In<br />

User Service (RADIUS, RFC 2865 [49]) and Diameter (RFC 4072 [65]) can be used to<br />

negotiate the maximum key lifetime between the home AAA server and a fast AAA<br />

proxy. The same protocol can be used to manage the trust association K pa<br />

between the<br />

fast AAA proxy and each access network. The pre-shared keys for sett<strong>in</strong>g up trust<br />

associations can be statically configured or dynamically updated <strong>in</strong> a secure manner.<br />

From the perspective of a network operator, its trust association established with a thirdparty<br />

fast AAA proxy has twofold usage: 1) transfers its authentication authorities to a<br />

third-party entity for facilitat<strong>in</strong>g fast handover of its own subscribers; 2) obta<strong>in</strong>s<br />

localised authentication services when process<strong>in</strong>g AAA requests from other roam<strong>in</strong>g<br />

mobile users.<br />

In the PBAL, a fast AAA proxy can be <strong>in</strong>tegrated on an ord<strong>in</strong>ary AAA broker <strong>in</strong> the<br />

roam<strong>in</strong>g broker <strong>in</strong>frastructure [53, 87]. This avoids build<strong>in</strong>g new separated entities for<br />

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