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  1. This paper studies Byzantine reliable broadcast (BRB) under asynchronous networks, and improves the state-of-the-art protocols from the following aspects. Near-optimal communication cost: We propose two new BRB protocols for n nodes and input message M that has communication cost O(n|M| +n^2 log n), which is near-optimal due to the lower bound of Ω(n|M| +n^2). The first BRB protocol assumes threshold signature but is easy to understand, while the second BRB protocol is error-free but less intuitive. Improved computation: We propose a new construction that improves the computation cost of the state-of-the-art BRB by avoiding the expensive online error correction on the input message, while achieving the same communication cost. Balanced communication: We propose a technique named balanced multicast that can balance the communication cost for BRB protocols where the broadcaster needs to multicast the message M while other nodes only needs to multicast coded fragments of size O(|M|/n + log n). The balanced multicast technique can be applied to many existing BRB protocols as well as all our new constructions in this paper, and can make every node incur about the same communication cost. Finally, we present a lower bound to show the near optimality of our protocol in termsmore »of communication cost at each node.« less
    Free, publicly-accessible full text available July 1, 2023
  2. Asynchronous verifiable secret sharing (AVSS) protocols protect a secret that is distributed among N parties. Dual-threshold AVSS protocols guarantee consensus in the presence of T Byzantine failures and privacy if fewer than P parties attempt to reconstruct the secret. In this work, we construct a dual-threshold AVSS protocol that is optimal along several dimensions. First, it is a high-threshold AVSS scheme, meaning that it is a dual-threshold AVSS with optimal parameters T < N/3 and P < N - T. Second, it has O(N^2) message complexity, and for large secrets it achieves the optimal O(N) communication overhead, without the need for a public key infrastructure or trusted setup. While these properties have been achieved individually before, to our knowledge this is the first protocol that is achieves all of the above simultaneously. The core component of our construction is a high-threshold AVSS scheme for small secrets based on polynomial commitments that achieves O(N^2 log(N)) communication overhead, as compared to prior schemes that require O(N^3) overhead with Tmore »a large secret F.« less
  3. Blockchain is the technology used by developers of cryptocurrencies, like Bitcoin, to enable exchange of financial “coins” between participants in the absence of a trusted third party to ensure the transaction, such as is typically done by governments. Blockchain has evolved to become a generic approach to store and process data in a highly decentralized and secure way. In this article, we review blockchain concepts and use cases, and discuss the challenges in using them from a governmental viewpoint. We begin with reviewing the categories of blockchains, the underlying mechanisms, and why blockchains can achieve their security goals. We then review existing known governmental use cases by regions. To show both technical and deployment details of blockchain adoption, we study a few representative use cases in the domains of healthcare and energy infrastructures. Finally, the review of both technical details and use cases helps us summarize the adoption and technical challenges of blockchains.
  4. We present Chios, an intrusion-tolerant publish/subscribe system which protects against Byzantine failures. Chios is the first publish/subscribe system achieving decentralized confidentiality with fine-grained access control and strong publication order guarantees. This is in contrast to existing publish/subscribe systems achieving much weaker security and reliability properties. Chios is flexible and modular, consisting of four fully-fledged publish/subscribe configurations (each designed to meet different goals). We have deployed and evaluated our system on Amazon EC2. We compare Chios with various publish/subscribe systems. Chios is as efficient as an unreplicated, single-broker publish/subscribe implementation, only marginally slower than Kafka and Kafka with passive replication, and at least an order of magnitude faster than all Hyperledger Fabric modules and publish/subscribe systems using Fabric.