Information theoretic secrecy is combined with cryptographic secrecy to achieve
a secret-key exchange protocol in wireless networks. A network of transmitters,
which already have cryptographically secured channels between them, cooperate to
exchange a secret key with a new receiver at a random location, in the presence
of eavesdroppers at unknown locations. Two spatial point processes: A
homogeneous Poisson process and independently uniformly distributed points are
used for the spatial distributions of transmitters and eavesdroppers. Upper
bounds on the probability of existence of positive secrecy between the
cooperating transmitters and the receiver are derived. Simulations show that
cooperative transmitting provides a larger secrecy area than cooperative jamming
or cooperative relaying.