Wireless Security.pdf - PDF Archive

Wireless Embedded System Security 613
The network topologies supported by ZigBee vary, but depending on the type of network
being deployed there are varying security considerations. In some ZigBee topologies,
all nodes are considered equal and the network is basically an ad hoc peer-to-peer
configuration. In some of the other topologies (star and tree forms), there must be a
coordinator that facilitates the network. In such a topology, the end-nodes can be of
reduced functionality to save cost, but there is an inherent problem: If the coordinator is
disabled, reduced-functionality end nodes cannot reestablish the network. One way to get
around this is to provide redundant full-function nodes that can all serve as a coordinator
(this is a good idea for reliability, not just security). ZigBee nodes can also function as
routers, directing communications between nodes that may not be able to communicate
directly (as would be the case if the distance between those nodes was too great, but the
router node bisected the path between them). If a ZigBee node is acting as a router, it is
important that any information being passed along cannot be compromised if the router
node is compromised.
The ZigBee protocol provides low-level security for communications between individual
nodes using AES and a message authentication code scheme, but this only protects the
data between nodes, not on the nodes themselves. Normally this would be OK if the nodes
in question were functioning as end-nodes, but if they are functioning as coordinators or
routers, it may be desirable to use a higher-level security scheme to protect that data. This
presents another interesting challenge due to the limited bandwidth of ZigBee and the
extremely limited resources that are likely to be found on ZigBee devices. A full-blown
security protocol like SSL will probably not work because of the extra overhead (especially
when you consider running RSA on a ZigBee node). In fact, a number of protocols, like
IPSEC, do not even make sense, since ZigBee networks are not based upon TCP/IP. What
would make more sense would actually be to use a simple AES-based scheme similar
to what is done later in the PIC case study. Authentication could be provided through a
password or key that is passed in encrypted form to the end device.
ZigBee is an exciting new technology that promises to bring a level of connectivity
never before seen. Depending on how it is deployed, it may also represent a security
challenge unlike any we have ever seen. What will be important to remember as ZigBee
devices are deployed in factories and homes around the world is that these devices will
probably not support a level of security equal to that of full-blown networking. Due to the
extremely limited resources, some devices may have no security at all, so it will be vital
to keep a constant vigil on what information is being sent over these networks. For these
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