Anais - Engenharia de Redes de Comunicação - UnB

We consider two kinds of computer-bounded adversaries: an insider and an outsider.
The insider is a malicious node in the set of nodes that compose the mesh network.
It can perform any task that other mesh nodes are able to, such as forwarding packets,
checking packets type, and making an access request to the gateway. The outsider is a
malicious node that is not in the set of nodes that compose the mesh network. It can monitor
the mesh nodes and the gateway activities. Also, it can determine which web activities
are performed by the gateway on behalf of mesh nodes. We assume a small number of
insiders and one or few outsiders. Insiders and outsiders may cooperate to launch attacks
against mesh nodes’ privacy. They may inject or modify traffic, try to replay messages,
jam nodes’ communication, etc. Also, we consider that the nodes cannot stop the message
flow.
3.3. The Data Carrier
The data carrier is a specific purpose packet periodically issued by the gateway router.
When a node wants to either make an access request or send uplink data to the gateway,
it has to wait for the appropriate data carrier. If a node wants to make an access request,
then it uses the access carrier; if it wants to send uplink data, it should use the uplink
carrier. Both carriers, however, have the same basic structure and they will be addressed
in this section as data carrier.
The data carrier consists of two well-defined parts. The first part is called
onioned data and the second one is called encrypted route information. The onioned
data part is composed of a multilayer encrypted data, i.e. an onion. It is built by successively
encrypting the received data carrier at each mesh node. As an onion, the
onioned data may be constructed by either employing a symmetric cryptosystem, such
as AES [Daemen and Rijmen 2002], or an asymmetric cryptosystem, such as El Gamal
[Gamal 1985]. Here we employ a symmetric cryptosystem to build the onion. Throughout
this paper we denote E X (·) a ciphertext using the symmetric or public key X.
The onioned data has the following general format:
E kr (...E k2 (E k1 (data 1 ), data 2 )..., data r ), where k i is a symmetric key shared between
the gateway and a node i, and data i is the plain data inserted by each mesh node
i; data r is the data corresponding to the last node of a route of length r. Note that
this approach enables multiple nodes using the same carrier to communicate with the
gateway. Additionally, data i could be just padding bits in case a node has no data to
include into the carrier.
As stated before, the data carrier is just a packet abstraction. The actual packets
are the access and the uplink carriers. Hence, data i is actually a request (denoted as req)
if the packet is an access carrier, the req is composed of {reqId, url, N i }, where reqId
is the request’s identification generated by the requester node, url is the Internet address
that the node wants to access and N i is the node’s identification. Differently, if the packet
is an uplink carrier, the data will be uplink = {url, updata, N i }, where url is the web
destination of the uplink data, and updata is the uplink traffic the active node is sending.
The second part of the carrier, the encrypted route information, consists of a set
of nodes’ encrypted secret parameters. A node’s secret parameter is a unique information
about the node, which, later on, will work as the node’s identification. Precisely, when
the carrier returns to the gateway, it uses these parameters to identify which nodes the
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