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observations, the adversary may conclude that the session initiator is one of the Mesh
nodes that are in both rings.” [Wu and Li 2006]
3. The new Proposal
Our protocol employs a principle similar to that one presented by WuLi in their private
onion ring protocol. That is, it avoids that a node directly sends data (e.g., an access request
or uplink data) to the gateway router. Instead, nodes should wait for specific tokens
in order to anonymously communicate. However, other than using WuLi’s ring routing
approach, we propose a probabilistic routing protocol to make routes more flexible. As
such, our method overcomes the drawbacks of the former proposal of having a fixed ring
route topology.
3.1. Overview
Our proposal consists of three phases: the access phase, the downlink phase, and the uplink
phase. The access phase is intended to grant to mesh nodes anonymous access to
gateway services. The downlink phase follows the access phase and it aims at anonymously
delivering data to the requester. And finally, the uplink phase takes place when a
node wants to anonymously send uplink data to the gateway.
In the access phase, the gateway periodically generates access tokens and delivers
them to mesh nodes. The gateway delivers a token to one the nodes next to itself. After
receiving it, the node either forwards it to another hop or uses it to make an access request
to the gateway. In the former case, the node performs cryptographic operations on the
token before forwarding it. In the latter case, the mesh node modifies the token to obtain
a new one containing the node’s request. In either case, the nodes are free for choosing
the next hop. After the token visits a defined number of hops, the last hop sends it back to
the gateway.
The downlink phase works similar as proposed by WuLi. In this phase, the gateway
provides data from an Internet address requested by a specific mesh node. These
data are delivered as an onion packet through a given route, chosen by the gateway. Each
node in this route decrypts one layer of the onion to discover the next hop and then forwards
the packet to it. If the node is the requester, it will obtain the plain downlink data
after decrypting the onion’s layer. Finally, the uplink phase occurs when nodes want to
asynchronously send uplink data up to the gateway. This phase is based on the same idea
used in the access phase. In order to send uplink data, active nodes should wait until a
so-called uplink carrier arrives. As in the access phase, this carrier, or token, is cast in the
network by the gateway. The next procedures also follow as before, except that the active
node inserts uplink data into the token, instead of an access request.
3.2. Assumptions and Attack Model
The assumptions and the attack model of our scheme are similar to that ones employed
by Wu and Li in their scheme. An adversary can learn which Internet address is being
accessed, but it cannot confirm which mesh node performed a request to this address. This
means that the node that performed the request (i.e. the active node) is hidden within a
group of mesh nodes. In addition, each mesh node and the gateway are assumed to have
enough computer resources to perform the operations required.
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