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[Wu and Li 2006] which claims to defend against those attacks, assuming a global and
aggressive adversary. However, their solution is vulnerable to a number of attacks due
to problems in the protocol design, which were pointed out by the authors. We propose
a new protocol based on some of Wu and Li’s ideas. However, our solution does not
suffer from the problems of the former proposal. In addition, it enables multiple nodes
to communicate using a single data carrier, which makes our scheme more effective than
Wu and Li’s proposal, namely WuLi.
This paper is organized as follows: the next section presents an outline of WuLi’s
scheme and its drawbacks. After that, in Section 3, we present our new protocol. Next,
we sketch the security analysis of our solution. Section 4 presents the works related to
our solution. Finally, in Section 5, we conclude this work.
2. A Summary of WuLi’s Proposal and Its Drawbacks
In order to provide anonymous communication in WMN, WuLi proposed the private
onion ring protocol. In that protocol, they applied the concept of onion routing
[Syverson et al. 1997] to obtain data confidentiality and to achieve source anonymity.
The entire protocol relies on the security of the so-called private onion ring, which is
an anonymously constructed route for nodes’ communication. As the name suggests, the
route has a ring topology, where the gateway is both the beginning and the end of it. Before
presenting this topology, they proposed an open route approach. In this approach,
the communication starts at the gateway and could end at any mesh node. However, the
approach had a serious anonymity vulnerability, which were solved by employing the ring
solution.
Their protocol works as follows. First, the gateway sends an request carrier to
the first node of the ring. Each node encrypts the carrier (using a symmetric key shared
between the node and the gateway) and then forwards it to the next hop in the ring. When a
node wants to make an access request, it replaces the carrier with a new one containing its
request. If more than one node tries to request access in the same access session, always
the node closer to the gateways gets granted, since the requester erases the previous ones.
After knowing the requester, the gateway sends a downlink onion through the ring, in
order to provide the requested data. Nodes peel off one layer and forward the onion to
another hop. When the onion arrives at the active node, it obtains the plain downlink data,
and then replaces it with uplink data. After that, the active node encrypts the onion and
sends it to the next hop. These procedures continue until the onion returns to the gateway.
WuLi’s private onion ring solution overcomes the drawbacks of the open route
approach. However, the ring topology still have some problems. The rings established by
the gateway make the route fixed and easy for an adversary launching privacy attacks. In
addition, if a node goes down, a new ring must be re-established. This topology dynamics
may make the scheme too inefficient. Malicious nodes could also utilize it to launch
powerful DoD attacks against the WMN. Besides, ring route is vulnerable to the so-called
intersection attacks based on user profile. This vulnerability is pointed out by the authors
as the main problem of the protocol: “Assume that a Mesh node initiates a session to
connect to an Internet address through a ring. Later it is included in new ring, through
which it visits the same address again. Both visits are observed by the adversary that
monitors the Gateway router. If the address only has very special visitors, based on the
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