Stochastic Modeling of Intrusion-Tolerant Server Architectures for Dependability and Performance Evaluation

Coordinated Science Laboratory was formerly known as Control Systems LaboratoryDARPA / F30602-00-C-017

Dumbo-MVBA: Optimal Multi-valued Validated Asynchronous Byzantine Agreement, Revisited

Multi-valued validated asynchronous Byzantine agreement (MVBA), proposed in the elegant work of Cachin et al. (CRYPTO \u2701), is fundamental for critical fault-tolerant services such as atomic broadcast in the asynchronous network. It was left as an open problem to asymptotically reduce the $O(ln^2+n^2*lambda+n^3)$ communication (where $n$ is the number of parties, $l$ is the input length, and $lambda$ is the security parameter). Recently, Abraham et al. (PODC \u2719) removed the $n^3$ term to partially answer the question when input is small. However, in other typical cases, e.g., building atomic broadcast through MVBA, the input length $l >= n*lambda$, and thus the communication is dominated by the $ln^2$ term and the problem raised by Cachin et al. remains open. We fill the gap and answer the remaining part of the above open problem. In particular, we present two MVBA protocols with $O(ln+n^2*lambda)$ communicated bits, which is optimal when $l >= n*lambda$. We also maintain other benefits including optimal resilience to tolerate up to $n/3$ adaptive Byzantine corruptions, optimal expected constant running time, and optimal $O(n^2)$ messages. At the core of our design, we propose asynchronous provable dispersal broadcast (APDB) in which each input can be split and dispersed to every party and later recovered in an efficient way. Leveraging APDB and asynchronous binary agreement, we design an optimal MVBA protocol, Dumbo-MVBA; we also present a general self-bootstrap framework Dumbo-MVBA* to reduce the communication of any existing MVBA protocols

Dumbo: Faster Asynchronous BFT Protocols

HoneyBadgerBFT, proposed by Miller et al. [32] as the first practical asynchronous atomic broadcast protocol, demonstrated impressive performance. The core of HoneyBadgerBFT (HB-BFT) is to achieve batching consensus using asynchronous common subset protocol (ACS) of Ben-Or et al., constituted with $n$ reliable broadcast protocol (RBC) to have each node propose its input, followed by $n$ asynchronous binary agreement protocol (ABA) to make a decision for each proposed value ($n$ is the total number of nodes). In this paper, we propose two new atomic broadcast protocols (called Dumbo1, Dumbo2) both of which have asymptotically and practically better efficiency. In particular, the ACS of Dumbo1 only runs a small $k$ (independent of $n$) instances of ABA, while that of Dumbo2 further reduces it to constant! At the core of our techniques are two major observations: (1) reducing the number of ABA instances significantly improves efficiency; and (2) using multi-valued validated Byzantine agreement (MVBA) which was considered sub-optimal for ACS in [32] in a more careful way could actually lead to a much more efficient ACS. We implement both Dumbo1, Dumbo2 and deploy them as well as HB-BFT on 100 Amazon EC2 t2.medium instances uniformly distributed throughout 10 different regions across the globe, and run extensive experiments in the same environments. The experimental results show that our protocols achieve multi-fold improvements over HoneyBadgerBFT on both latency and throughput, especially when the system scale becomes moderately large

Voices Raised, Issue 06

Included in this issue: Immaculate Mary; Grants augment women’s research; Mentoring grows; Women’s Studies take root in the neighborhood; Solution-oriented VP to retire; Muslim students strive to educate, support; Don’t let stress ruin your holidays; Dining services dishes up more than you’d expect; Marianist Images Across Campus; Confronting Disrespect: We Owe it to Each Other.https://ecommons.udayton.edu/wc_newsletter/1005/thumbnail.jp

Parsimonious Asynchronous Byzantine-Fault-Tolerant Atomic Broadcast

Atomic broadcast is a communication primitive that allows a group of n parties to deliver a common sequence of payload messages despite the failure of some parties. We address the problem of asynchronous atomic broadcast when up to t n/3 parties may exhibit Byzantine behavior. We provide the first protocol with an amortized expected message complexity of per delivered payload. The mos

Architecting dependable systems using virtualization

We propose new methods of leveraging virtualization for addressing system dependability issues. Using combinatorial modeling, we analyze multiple design choices when a single physical server is used to host multiple virtual servers. Our results show that unless certain conditions (e.g., regarding the reliability of the hypervisor and the number of VMs) are met, virtualization could decrease the reliability of a single physical node. In light of the prevailing ad-hoc approach to virtualization and the general inclination to move services out of the operating system into the virtualization layer, our results point out the need for a more cautious and rigorous approach.

Semi-Passive Replication in the Presence of Byzantine Faults

Semi-passive replication is a variant of passive replication that does not rely on a group membership service. Défago et al. [4] defined the semi-passive replication concept in the crash fault model and described a semi-passive replication algorithm based on a lazy consensus algorithm. In this paper, we consider semipassive replication and lazy consensus for a Byzantine fault model. We present lazy Byzantine consensus algorithms for two system models: 1) a system with synchronous communication and partially synchronous processing, and 2) an asynchronous system augmented with unreliable fault detectors for Byzantine faults. We prove that our algorithms provide safety and liveness. Our algorithms are optimal in good runs, having a latency degree of 2. We describe how our algorithms can be tuned to obtain the desired levels of fault resilience or efficiency in the presence of faults. We also present optimizations to improve the performance of the algorithms