I am looking for a cryptographic protocol that is as energy-efficient as possible. I am talking about battery drain. Alice wants to do a mutual authentication with Bob. Maybe symmetric is good, maybe asymmetric with PFS is better. I am interested in knowing the best state-of-the-art, non-patented solutions for this issue.
It would also be nice to know which primitives for hashes, ciphers, groups etc. tend to be most efficent. The context is for IoT devices.