  We propose a privacy-preserving billing protocol for local energy markets
(PBP-LEMs) that takes into account market participants' energy volume
deviations from their bids. PBP-LEMs enables a group of market entities to
jointly compute participants' bills in a decentralized and privacy-preserving
manner without sacrificing correctness. It also mitigates risks on individuals'
privacy arising from any potential internal collusion. We first propose a
novel, efficient, and privacy-preserving individual billing scheme, achieving
information-theoretic security, which serves as a building block. PBP-LEMs
utilizes this scheme, along with other techniques such as multiparty
computation, Pedersen commitments and inner product functional encryption, to
ensure data confidentiality and accuracy. Additionally, we present three
approaches, resulting in different levels of privacy and performance. We prove
that the protocol meets its security and privacy requirements and is feasible
for deployment in real LEMs. Our analysis also shows variations in overall
performance and identifies areas where overhead is concentrated based on the
applied approach.
