Forward-secure Key Evolution Protocol 
                in Wireless Sensor Networks **
     
               M.Klonowski, M.Kutylowski, 
            (Wroclaw University of Technology)
                 M.Ren, K.Rybarczyk
              (Adam Mickiewicz University, Poznan)

We consider a key distribution scheme for 
securing node-to-node communication in sensor networks. 
While most schemes in use are based on random predistribution, we 
consider a system of dynamic pairwise keys based on design due to Ren, Tanmoy and Zhou.
We design and analyze a variation of this scheme, in which
capturing a node does not lead to security threats for the past communication.
 
Instead of bit-flipping, we use a pseudorandom one-way function. 
While this immediately guarantees forward-security, it is not clear
whether the pseudorandom transformation of the keys does not lead to security problems
through a potentially reduced size of the keyspace or nonuniform probability 
distribution  of the keys. We show, in a rigid mathematical way, that this is not the case: after a relatively small number of transformations, 
with high probability each key can be reached and no key has probability significantly 
higher than for the uniform distribution.


*The 6th International Conference on Cryptology and Network Security (CANS) 2007
To appear in LNCS, Springer-Verlag