Paper 2021/1678

Zero-Knowledge for Homomorphic Key-Value Commitments with Applications to Privacy-Preserving Ledgers

Matteo Campanelli and Felix Engelmann and Claudio Orlandi

Abstract

Commitments to key-value maps (or, authenticated dictionaries) are an important building block in cryptographic applications, including cryptocurrencies and distributed file systems. In this work we study short commitments to key-value maps with two additional properties: full-hiding (both keys and values should be hidden) and homomorphism (we should be able to combine two commitments to obtain one that is the ``sum'' of their key-value openings). Furthermore, we require these commitments to be short and to support efficient transparent zero-knowledge arguments (i.e., without a trusted setup). As our main contribution, we show how to construct commitments with the properties above as well as efficient zero-knowledge arguments over them. We additionally discuss a range of practical optimizations that can be carried out depending on the application domain. Finally, we show a specific application of commitments to key-value maps to scalable anonymous ledgers. Our contribution there is to formalize multi-type anonimity ledgers and show how to extend QuisQuis (Fauzi et al., ASIACRYPT 2019). This results in an efficient, confidential multi-type system with a state whose size is independent of the number of transactions.

Note: Minor typographical changes.