Protocols for Secure Communication in Wireless Sensor Networks

6.5. Extended Interleaved Authentication 195
messages are correct. With more nodes being compromised, this rate quickly
falls. This is due to the fact that the “doors” in this scenario are a bottleneck
through which all messages have to pass. If the attacker happens to select
nodes in such an area, all messages from the respective room will be subject to
manipulation.
6.5 Extended Interleaved Authentication
The simple Canvas scheme provides basic protection against message manipulations
that are carried out in unstructured attackes. But a highly structured
attack, such as a partitioning attack, can render the Canvas scheme ineffective.
We will now show that by introducting shortcuts in the authentication graph,
structured attacks can be mitigated as well. They effectively force the attacker
to become active (i.e. compromise nodes) in the close vicinity of the target
location.
6.5.1 Protocol Description
We describe here a protocol that extends the basic Canvas scheme, i.e. all
checks that are made when using Canvas only are made here as well. The
extended protocol provides an additional layer of security that specifically addresses
the weakness of Canvas that a cluster of compromised nodes can manipulate
all messages that pass through nodes in this cluster.
The proposed scheme extends the basic Canvas scheme in the following
way. Each node maintains a (small) number of security relationships with
nodes that are not within its k-hop neighbourhood but distributed throughout
the whole network. These long-range links are used for authenticating messages
that are sent to remote locations. Having a direct security relationship
between the source of the message and a node that is close to the receiver,
large, potentially compromised, parts of the network can be bypassed. An attacker
will only be able to tamper with messages if he is active within close
range of the receiving node.
The long-range security relationships of nodes will be called “shortcuts”,
and the remote peer of a node will be called a “shortcut node”. The security of
this extended scheme is based on two principles:
1. If the distance between the sender of a message and its target location is
less than δ, i.e. d(A,P) ≤ δ, it is sufficient to Canvas-authenticate the
message. This is based on the consideration that if the attacker is active
in the vicinity of the target location, there is a certain probability that