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1. Quorum subsumption for heterogeneous quorum systems

   https://doi.org/10.4230/LIPIcs.DISC.2023.28  

   Li, Xiao; Chan, Eric; Lesani, Mohsen (January 2023, Leibniz International Proceedings in Informatics (LIPIcs):37th International Symposium on Distributed Computing (DISC 2023))

   Oshman, Rotem (Ed.)

   Byzantine quorum systems provide higher throughput than proof-of-work and incur modest energy consumption. Further, their modern incarnations incorporate personalized and heterogeneous trust. Thus, they are emerging as an appealing candidate for global financial infrastructure. However, since their quorums are not uniform across processes anymore, the properties that they should maintain to support abstractions such as reliable broadcast and consensus are not well-understood. It has been shown that the two properties quorum intersection and availability are necessary. In this paper, we prove that they are not sufficient. We then define the notion of quorum subsumption, and show that the three conditions together are sufficient: we present reliable broadcast and consensus protocols, and prove their correctness for quorum systems that provide the three properties. 

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2. Flow-limited authorization for consensus, replication, and secret sharing

   https://doi.org/10.3233/JCS-230048  

   Mondal, Priyanka; Algehed, Maximilian; Arden, Owen (October 2023, Journal of Computer Security)

   Calzavara, Stefano; Naumann, David (Ed.)

   Availability is crucial to the security of distributed systems, but guaranteeing availability is hard, especially when participants in the system may act maliciously. Quorum replication protocols provide both integrity and availability: data and computation is replicated at multiple independent hosts, and a quorum of these hosts must agree on the output of all operations applied to the data. Unfortunately, these protocols have high overhead and can be difficult to calibrate for a specific application’s needs. Ideally, developers could use high-level abstractions for consensus and replication to write fault-tolerant code that is secure by construction. This paper presents Flow-Limited Authorization for Quorum Replication (FLAQR), a core calculus for building distributed applications with heterogeneous quorum replication protocols while enforcing end-to-end information security. Our type system ensures that well-typed FLAQR programs cannot fail (experience an unrecoverable error) in ways that violate their type-level specifications. We present noninterference theorems that characterize FLAQR’s confidentiality, integrity, and availability in the presence of consensus, replication, and failures, as well as a liveness theorem for the class of majority quorum protocols under a bounded number of faults. Additionally, we present an extension to FLAQR that supports secret sharing as a form of declassification and prove it preserves integrity and availability security properties. 

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3. Hamraz: Resilient Partitioning and Replication

   https://doi.org/10.1109/SP46214  

   Li, Xiao; Houshmand, Farzin (January 2022, S&P'22 (IEEE Symposium on Security and Privacy))

   Inter-organizational systems where subsystems with partial trust need to cooperate are common in healthcare, finance and military. In the face of malicious Byzantine attacks, the ultimate goal is to assure end-to-end policies for the three aspects of trustworthiness: confidentiality, integrity and availability. In contrast to confidentiality and integrity, provision and validation of availability has been often sidestepped. This paper guarantees end-to-end policies simultaneously for all the three aspects of trustworthiness. It presents a security-typed object-based language, a partitioning transformation, an operational semantics, and an information flow type inference system for partitioned and replicated classes. The type system provably guarantees that well-typed methods enjoy noninterference for the three properties, and that their types quantify their resilience to Byzantine attacks. Given a class and the specification of its end-to-end policies, the Hamraz tool applies type inference to automatically place and replicate the fields and methods of the class on Byzantine quorum systems, and synthesize trustworthy-by-construction distributed systems. The experiments show the resiliency of the resulting systems; they can gracefully tolerate attacks that are as strong as the specified policies. 

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4. Hamband: RDMA Replicated Data Types

   https://doi.org/10.1145/3519939.3523426  

   Houshmand, Farzin; Saberlatibari, Javad; Lesani, Mohsen (January 2022, PLDI'22 (ACM SIGPLAN Conference on Programming Language Design and Implementation))

   Data centers are increasingly equipped with RDMAs. These network interfaces mark the advent of a new distributed system model where a node can directly access the remote memory of another. They have enabled microsecond-scale replicated services. The underlying replication protocols of these systems execute all operations under strong consistency. However, strong consistency can hinder response time and availability, and recent replication models have turned to a hybrid of strong and relaxed consistency. This paper presents RDMA replicated data types, the first hybrid replicated data types for the RDMA network model. It presents a novel operational semantics for these types that considers three distinct categories of methods and captures their re- quired coordination, and formally proves that they preserve convergence and integrity. It implements these semantics in a system called Hamband that leverages direct remote accesses to efficiently implement the required coordination protocols. The empirical evaluation shows that Hamband outperforms the throughput of existing message-based and SMR-based implementations by more than 4x. 

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5. Vote Them Out: Detecting and Eliminating Byzantine Peers

   https://doi.org/10.1145/3357223.3365442  

   Tran, Tuan; Mondal, Priyanka; Shadmon, Roy; Mallikarjun, Manthan; Alvaro, Peter; Arden, Owen (November 2019, SoCC '19: Proceedings of the ACM Symposium on Cloud Computing)

   null (Ed.)

   Byzantine Fault Tolerant (BFT) protocols are designed to ensure correctness and eventual progress in the face of misbehaving nodes [1]. However, this does not prevent negative effects an adversary may have on performance: a faulty node may significantly affect the latency and throughput of the system without being detected. This is especially true in speculative protocols optimized for the best-case where a single leader can force the protocol into the worst case [3]. Systems like Aardvark [2] that are designed to maximize worst-case performance tolerate byzantine behavior without necessarily detecting who the perpetrator is. By forcing regular view changes, for example, they mitigate the effects of leaders who deliberately delay dissemination of messages, even if this behavior would be difficult to prove to a third party. Byzantine faults, by definition, can be difficult to detect. An error of 'commission', such as a message with a mismatching digest, can be proven. Errors of 'omission', such as delaying or failing to relay a message, as a rule cannot be proven, and the node responsible for these types of omission faults may not appear faulty to all observers. Nevertheless, we observe that they can reliably be detected. Designing protocols that detect and eject nodes is challenging for two reasons. First, some behaviors are observed by a subset of honest nodes and cannot be objectively proven to a third party. Second, any mechanism capable of ejecting nodes could be subverted by Byzantine nodes to eject honest nodes. This paper presents the Protocol for Ejecting All Corrupted Hosts (Peach, a mechanism for detecting and ejecting faulty nodes in Byzantine fault tolerant (BFT) protocols. Nodes submit votes to a trusted configuration manager that replaces faulty nodes once a threshold of votes are received. We implement Peach for two BFT protocol variants, a traditional pbft-style three-phase protocol and a speculative protocol, and evaluate its ability to respond to Byzantine behavior. This work makes the following contributions: (1) We present and prove a necessary and sufficient constraint on cluster membership guaranteeing that any nodes causing performance degradation via acts of omission will be detected. (2) We present an agreement protocol, PEACHes, in which replicas pass votes about their subjective local observations of possible omissions to a TTP. (3) We show how the separation of detection and effectuation allows fine-grained detection of malicious behavior that is compatible and easily integrated with existing systems. (4) We present DecentBFT, an extension of BFT-Smart to which we added a speculative fast path (similar to Zyzzva) and integrated PEACHes. (5) We show DecentBFT rapidly detects and mitigates a variety of performance attacks that would have gone undetected by the state of the art. 

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