Angelo De Caro

The adoption of Distributed Ledger Technology (DLT) for critical financial infrastructures like Central Bank Digital Currencies (CBDCs) is hindered by a significant performance gap. Permissioned blockchains such as Hyperledger Fabric, which are conceptually suitable and have become popular platform used in many production deployments today, are nevertheless limited by architectural bottlenecks. Their monolithic peer design and consensus mechanisms prevent them from achieving the required scale for such demanding applications. This paper presents Fabric-X, a fundamental re-architecture of Hyperledger Fabric that addresses these challenges end-to-end. We have open-sourced Fabric-X as part of the Linux Foundation Decentralized Trust at github.com/hyperledger/fabric-x. We decompose the monolithic peer into independently scalable microservices for endorsement, validation, and committing. To maximize parallelism, we introduce a transaction dependency graph that enables the safe, concurrent validation of transactions across multiple blocks. Complementing the peer redesign, we introduce Arma, a novel sharded Byzantine Fault Tolerant (BFT) ordering service that dramatically increases throughput by ordering compact transaction digests rather than full transaction payloads. We implemented and benchmarked this framework with a UTXO-based CBDC application. Our evaluation demonstrates a peak throughput exceeding 100,000 transactions per second (TPS)—a multiple-orders-of-magnitude improvement over the standard implementation. This work proves that permissioned DLTs can be engineered for national-scale payment systems, providing a resilient and highly performant foundation for practical CBDC deployments and the integration of advanced, computationally intensive features.

In the wake of fraud scandals involving decentralized exchanges and the significant financial loss suffered by individuals, regulators are pressed to put mechanisms in place that enforce customer protections and capital requirements in decentralized ecosystems. Proof of liabilities (PoL) is such a mechanism: it allows a prover (e.g., an exchange) to prove its liability to a verifier (i.e., a customer). This paper introduces a fully privacy-preserving PoL scheme with short proofs. We store the prover's liabilities in a novel data structure, the sparse summation Verkle tree (SSVT), in which each internal node is a hiding vector commitment of its children and whose root commits to the sum of all the leaves in the tree. We leverage inner product arguments to prove that a user's liability is included in the total liabilities of the prover without leaking any information beyond the liability's inclusion. Our construction yields proofs of size Ologn N) where n is the arity of the SSVT and N is an upper bound on the number of users. Additionally, we show how to further optimize the proof size using aggregation. We benchmark our scheme using an SSVT of size 2256 and one of size 10^9 that covers the universe of all US social security numbers.