A probabilistic key agreement scheme for sensor networks without key   predistribution
  The dynamic establishment of shared information (e.g. secret key) between two entities is particularly important in networks with no pre-determined structure such as wireless sensor networks (and in general wireless mobile ad-hoc networks). In such networks, nodes establish and terminate communication sessions dynamically with other nodes which may have never been encountered before, in order to somehow exchange information which will enable them to subsequently communicate in a secure manner. In this paper we give and theoretically analyze a series of protocols that enables two entities that have never encountered each other before to establish a shared piece of information for use as a key in setting up a secure communication session with the aid of a shared key encryption algorithm. These protocols do not require previous pre-distribution of candidate keys or some other piece of information of specialized form except a small seed value, from which the two entities can produce arbitrarily long strings with many similarities. 
V. Liagkou, E. Makri, P. Spirakis and Y.C. Stamatiou