  In this paper, we explore new area/throughput trade- offs for the Girault,
Poupard and Stern authentication protocol (GPS). This authentication protocol
was selected in the NESSIE competition and is even part of the standard ISO/IEC
9798. The originality of our work comes from the fact that we exploit a fixed
key to increase the throughput. It leads us to implement GPS using the Chapman
constant multiplier. This parallel implementation is 40 times faster but 10
times bigger than the reference serial one. We propose to serialize this
multiplier to reduce its area at the cost of lower throughput. Our hybrid
Chapman's multiplier is 8 times faster but only twice bigger than the
reference. Results presented here allow designers to adapt the performance of
GPS authentication to their hardware resources. The complete GPS prover side is
also integrated in the network stack of the PowWow sensor which contains an
Actel IGLOO AGL250 FPGA as a proof of concept.
