: Public key cryptography (PKC) has been considered for a long time to be computationally too expensive for small battery powered devices. However, PKC turned out to be very beneficial for issues such as key distribution, authentication etc. In the recent years first research groups started to cope with the challenges applying PKC in resource-constrained environments. One result is that in particular ECC seems to be very suitable for such environments, because it provides the same level of security as RSA does while requiring much shorter keys. In this paper we evaluate the power consumption resulting from using various PKC approaches with respect to calculations and transmission of signatures etc. Our findings here clearly indicate that software realisations of PKC lead to relatively long duty cycles (operating intervals) which in turn require significant amount of energy. In contrast, the energy required for computation is negligible if the PKC is performed by power efficient hardwar...