This paper presents a new approach of dynamic symmetric key distribution for encrypting the communication between two nodes in a wireless sensor network (WSN). The distribution of a shared key can be performed by any sensor node and does not always require that it is performed by the base station (BS). Each node can be selected by one of its neighbor nodes in order to distribute a pair-wise key for a communication between two nodes. The selection is based on the local computation of a trust value granted by the requesting nodes. This scheme considerably reduces the cost of communication between the BS and the nodes when setting up pair-wise keys between neighboring nodes. Trust is also used to discard keys that were allocated by untrustworthy nodes.