Zero-knowledge for homomorphic key-value commitments with applications to privacy-preserving ledgers

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: double-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 formally describe a specific application of commitments to key-value maps to scalable anonymous
ledgers. We 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.