Protocols for Secure Communication in Wireless Sensor Networks

6.2. Basic Interleaved Authentication 167
Algorithm 5 canvas-auth(A,P,m,C)
Global values:
X: ID of current node
k: Parameter of the Canvas schme
Input:
A: message source
P: destination location
m: message text
C: authentication information
Output:
Return modified authentication information
1: C ′ := C \ {(_,X,_,_) ∈ C} ⊲ Remove all MACs for X
2: for i in {1...k} do
3: V := prefetch-hop(i)
4: cXV := cXV + 1
5: a := {A,P,m,cXV }KXV
6: C ′ := C ′ ∪ {(X,V,cXV ,a)}
7: end for
8: return C ′
The fundamental message acceptance rules for the Canvas authentication
scheme are shown in Table 6.1. Messages are marked with flags that denote
their type. Here, only type DIRECT is used, which indicates that the authentication
of the message is completely handled locally, i.e. at each hop. Later, we
will see another type, SHORTCUT, which extends the authentication of messages
to larger distances. The format of messages is explained in Table 6.2.
The destination location of a message is specified by geographic coordinates.
Table 6.3 lists the remaining parameters that are being used in rules. The
distance function d yields the geographic distance between a node and a location.
τ is a global parameter that determines the acceptable deviation from
the exact destination location. If a node is located within a range of τ from a
destination location, this node is qualified to be the final receiver of a message.
This means that this node will not further relay the message. It could, however,
inform the nodes in its vicinity that it has received the message. There could be
multiple nodes that are qualified to receive a message for a certain destination,
and multiple messages addressed to the same destination could be received by
different nodes. It is up to a higher system layer, such as a clustering protocol
or the application itself, to coordinate the activities of all these nodes.
Another global parameter denoting a geographic distance is δ. This parameter
denotes the maximum distance over which Canvas-authenticated messages
should be forwarded. If δ = ∞, there is no limit on that distance, and full
reachability is maintained. For variations of the basic authentication scheme