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data, such as the nodes’ secret parameters, which are encrypted with the gateway’s public
key. Finally, since we assume computer-bounded adversaries, and thus cannot break
into symmetric or asymmetric cryptosystems, it can be claimed that data confidentiality
is secure.
In order to enhance anonymity, we enforce the use of non-deterministic routes
for packet routing. In the access and uplink phases, each mesh node randomly forwards
carriers to one of the hops in its range. After r hops, carriers have travelled through a
random route. Any attempt of manipulating the route part of the carrier is easily verified
by the gateway by checking the nodes’ shared key against the onioned data. Having nondeterministic
route make it difficulty for an adversary, even for a global one, to target
specific nodes in privacy attacks In the downlink phase, routes for message delivery are
properly selected by the gateway, so that they are different for each downlink session.This
approach makes the downlink route also non-deterministic, in the sense that no one, but
the gateway, knows the entire route; nodes only know their previous and next hops. Nondeterministic
routes approach also turns infeasible the so-called intersection attack, the
main problem of WuLi’s protocol. WuLi’s solution reveals the ring’s ID included in
every packets. As their topology is fixed, the intersection attack becomes viable. In our
protocol, is difficulty to correlate the web activities observed at the gateway with specific
mesh nodes, since they are not include in deterministic routing paths.
The protocol is secure against a global outsider which may cooperate with a small
number of insiders. In this context, a number of attacks could be launched aiming at
breaching mesh user’s privacy. An attacker could, for example, record the nodes’ encrypted
secret parameters from previous access or uplink sessions. Then the attacker may
then try to reuse them in a replay attack. This would allow the adversary to control the
length of the route and thus weakening the anonymous communication protocol. The adversary
could, indeed, perform this. However the attack will not be successful, as the first
part of the data carrier(the onioned data) requires encryption which requires the knowledge
of the node’s shared key. When the carrier returns to the gateway, a broken carrier
can be easily verified, by checking each onion layer. This kind of attack may only be
successful if the attacker controls at least r − 1 nodes in the network, where r is the previously
defined length of the route. In this scenario, the attacker could intentionally forward
the carrier to the compromised nodes and lastly forward to a target node. Hence r should
be large enough to avoid this kind of attack, but shall not be so large, as the carrier’s size
increases along the route.
4. Related Work
Anonymity in Wireless Mesh Networks has gained attention in the literature. Wu
and Li designed a robust protocol to protect against aggressive global adversaries
[Wu and Li 2006]. They employ both cryptography and redundancy to protect against
traffic analysis and flow tracing attacks. However, their Private Onion Ring protocol
is mainly vulnerable to the so-called intersection attack. To overcome this problem,
[Li et al. 2009] proposed a new protocol based on a multilayer onion ring approach. In
[Wu et al. 2006], the authors propose the use of multi-path communication to achieve privacy.
However, the protocol cannot defend against a powerful global attacker who is able
to observe most traffic in the network.
Another solution related to ours is the one proposed in [Islam et al. 2008], where
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