Many sensor network applications require secure communication between sensor nodes and the sink. This paper presents a key distribution scheme based on the well known Elliptic Curve Diffie-Hellman key exchange mechanism. The DHB-KEY scheme is performed in two stages. The first stage is carried out in a secure environment before network deployment. The second stage is carried out periodically using a single broadcast message. Each node arrives at a unique key it shares with the sink. This paper presents a first evaluation and a prototype implementation of the protocol. We have found that the presented key distribution approach uses energy and communication resources efficiently and has a low deployment complexity.