Designing secure communication protocols is not an easy task. Cryptography is often necessary but does not always guarantee the security of protocols as several famous examples attest in the literature. Moreover, in the context of Wireless Sensor Networks (WSNs) the design is even more difficult due to the limited resources of sensor nodes that add extra constraints to take into account. During the life time of a secure WSN, one of the first crucial steps is the key establishment between two nodes. In this paper we propose four secure multihop key establishment protocols based on elliptic curve cryptography (ECC). For each protocol, we make a formal security proof using the automatic tool Scyther. Then, in order to evaluate their performances, we implemented them on testbeds using TelosB motes and TinyOS. Results allow us to estimate the overhead of our key establishment methods.