WBN 2022

Workshop date: June 6, 2022
Location: The workshop will be held as a live event in the US Eastern Time mirror over Zoom. Please see the Sigmetrics main conference page for details on how to register and participate.

Speaker: Ovia Seshadri

Abstract: Proof-of-work (PoW) consensus generates blocks at random time instants, and consequently, adds weight to the blockchain at these random instants. This unsteady increase in chain weight over time along with the large network delay of blocks is the root cause of many security and performance problems such as high block confirmation time, high fork resolution times and vulnerability to double-spend attacks. In my talk, I will describe a signaling scheme of PoW called Anchors that can be implemented on any PoW blockchain system to improve performance. Through emulations, we show anchors' ability to reduce fork resolution times and prevent forks. We also show how anchors strengthen the system against double-spend attacks and reduce block confirmation times by half.

Bio: Ovia Seshadri is nearing the end of her PhD from IIT Delhi where she is working on the security and performance of blockchain systems. Prior to her PhD journey, she gained her master's in software engineering and worked as a data warehouse modeller. She has been a visiting scholar to IBM India Research Labs. Her other topics of interest include distributed systems and databases.

Speaker: Mohammad Alizadeh

Abstract: The success of blockchains has given rise to large-scale deployments of Byzantine fault tolerant (BFT) consensus protocols over wide area networks. A central feature of such networks is variable communication bandwidth across nodes and across time. Bandwidth variability creates stragglers that slow down the progress of standard BFT protocols. This talk presents DispersedLedger, an asynchronous BFT protocol that provides near-optimal throughput over variable bandwidth networks. The core idea of DispersedLedger is to enable nodes to propose, order, and agree on blocks of transactions without having to download their full content. To achieve consensus, nodes merely download a small fraction of a proposed block, allowing them to agree that the block is available within the network and unmalleable. Then, asynchronously, each node downloads the agreed-upon blocks at its own pace. I’ll describe DispersedLedger’s design and evaluation, including experiments on a geo-distributed Internet deployment in which DispersedLedger achieves 2x better throughput and 74% better latency than state-of-the-art asynchronous protocols.

Bio: Mohammad Alizadeh is an Associate Professor in the EECS Department at MIT, and a member of CSAIL. Before joining MIT, he completed his Ph.D. at Stanford University, and spent a couple of years at a datacenter networking startup, Insieme Networks, and Cisco. He works in the areas of computer networks and systems. His research aims to improve the performance, robustness, and ease of management of future networks and cloud computing systems. His current research centers on network protocols and algorithms for large-scale datacenters, programmable switching architectures, and learning-based networked systems. He is also broadly interested in performance modeling and analysis of computer systems and bridging theory and practice in computer system design.

Speaker: Giulia Fanti

Abstract: Most permissionless blockchain networks run on peer-to-peer (P2P) networks, which offer flexibility and decentralization at the expense of performance (e.g., network latency). Historically, this tradeoff has not been a bottleneck for most blockchains. However, an emerging host of blockchain-based applications (e.g., decentralized finance) are increasingly sensitive to latency; users who can reduce their network latency relative to other users can accrue (sometimes significant) financial gains. In this work, we initiate the study of strategic latency reduction in blockchain P2P networks. We first define two classes of latency that are of interest in blockchain applications. We then show empirically that a strategic agent who controls only their local peering decisions can manipulate both types of latency, achieving 60% of the global latency gains provided by the centralized, paid service bloXroute, or, in targeted scenarios, comparable gains. Finally, we show that our results are not due to the poor design of existing P2P networks. Under a simple network model, we prove that an adversary can always manipulate the P2P network's latency to their advantage, provided the network experiences sufficient peer churn and transaction activity.

Bio: Giulia Fanti is an assistant professor of Electrical and Computer Engineering at Carnegie Mellon University. She has a courtesy appointment in the Computer Science Department and is a part of CyLab. Her group’s research focus is on the security and privacy implications of data transparency and sharing. As part of this focus, her research interests span the algorithmic and theoretical foundations of distributed systems, machine learning, and privacy-enhancing technologies. She is also a co-director of CyLab Africa alongside Assane Gueve.

Speaker: Bhaskar Krishnamachari

Abstract: Blockchain technology is bringing fundamental new capabilities pertaining to decentralized trust and enabling micropayments for data. I will present results from research at USC touching on both the core technology and its application to the internet of things. These include a new mobile-oriented blockchain protocol, a middleware to decentralize publish-subscribe brokers, smart contracts to enable cheat-proof peer-to-peer trading of digital goods, and a streaming data payment protocol.

Bio: Bhaskar Krishnamachari is Professor and Ming Hsieh Faculty Fellow in Electrical and Computer Engineering Engineering at the Viterbi School of Engineering, University of Southern California. He has been a faculty member in the Department of Electrical and Computer Engineering since 2002. He also holds a joint appointment in the Department of Computer Science. He is the Director of the Center for Cyber-Physical Systems and the Internet of Things, and the Autonomous Networks Research Group, and Co-Director of the Ming Hsieh Institute for Electrical Engineering as well as the USC Center for Human Applied Reasoning and the Internet of Things. His research interests are focused on the design and analysis of algorithms, protocols, and applications for next generation networks and distributed systems. These include the internet of things, connected vehicles, robotic networks, dispersed computing, and blockchain systems. On these topics, his research spans the entire spectrum from theoretical design and analysis of algorithms to prototype software implementations and empirical evaluations of protocols and applications. He has co-authored over 300 technical articles on these topics, including conference and workshop best-paper awards at ACM/IEEE IPSN (2004, 2010), ACM MSWiM (2006), ACM MobiCom (2010), IEEE SECON (2012, Runner-Up), IEOM (2018), IEEE BigMM (2019), IEEE VNC (2021), COMSNETS-MINDS (2022). He has authored a textbook titled Networking Wireless Sensors, published by Cambridge University Press, and co-authored a book titled Blockchain and the Supply Chain: concepts, strategies and practical applications published by Kogan Page Publishers in 2019. Collectively his work has been cited more than 31,000 times and he has an H-index of 79 (per Google Scholar).

Speaker: Joachim Neu

Abstract: Spamming attacks are a serious concern for consensus protocols, as witnessed by recent outages of a major blockchain, Solana. They cause congestion and excessive message delays in a real network due to its bandwidth constraints. In contrast, longest chain (LC), an important family of consensus protocols, has previously only been proven secure assuming an idealized network model in which all messages are delivered within bounded delay. This model-reality mismatch is further aggravated for Proof-of-Stake (PoS) LC where the adversary can spam the network with equivocating blocks. Hence, we extend the network model to capture bandwidth constraints, under which nodes now need to choose carefully which blocks to spend their limited download budget on. To illustrate this point, we show that 'download along the longest header chain', a natural download rule for Proof-of-Work (PoW) LC, is insecure for PoS LC. We propose a simple rule 'download towards the freshest block', formalize two common heuristics 'not downloading equivocations' and 'blocklisting', and prove in a unified framework that PoS LC with any one of these download rules is secure in bandwidth-constrained networks. In experiments, we validate our claims and showcase the behavior of these download rules under attack. By composing multiple instances of a PoS LC protocol with a suitable download rule in parallel, we obtain a PoS consensus protocol that achieves a constant fraction of the network's throughput limit even under worst-case adversarial strategies. Joint work with Srivatsan Sridhar, Lei Yang, David Tse, Mohammad Alizadeh.

Bio: Joachim is a PhD student at Stanford working with David Tse on Internet-scale open-participation consensus (in more hype terms: the technical foundations of blockchains). His current research focus is provable consensus security for next-generation Ethereum, and provable security and performance of proof-of-stake consensus under bandwidth constraints and network-level attacks. While a Masters student at Technical University of Munich and a visiting student researcher at MIT, EPFL, and KAUST, he published in information and coding theory. He has been supported by Protocol Labs PhD Fellowship, Ethereum Foundation, Stanford Graduate Fellowship, and German Academic Scholarship Foundation.

Speaker: Gopal Pandurangan

Abstract: Performing computation in the presence of faulty and malicious (Byzantine) nodes is a central problem in distributed computing and networks. Even after several decades of research in Byzantine protocols, a major drawback is that the vast majority of the protocols either work with complete networks, or the few that do work for sparse (bounded degree) networks, are not fully-distributed --- in those protocols, nodes are required to have initial knowledge of the entire network topology. This drawback makes such protocols not applicable to real-world communication networks such as Peer-to-Peer (P2P) networks, which are typically sparse, bounded degree (where nodes initially have only local knowledge of themselves and their neighbors), and highly dynamic with churn (nodes join and leave the network continuously).

In this talk, we will give an overview of our research on fully-distributed Byzantine protocols for sparse, bounded degree, dynamic P2P networks that can tolerate a large number of Byzantine nodes. In particular, we will discuss protocols for the fundamental problems of Byzantine agreement (consensus), Byzantine leader election, and Byzantine storage and search.

Bio: Gopal Pandurangan is a professor in the department of computer science at the University of Houston and a VAJRA visiting professor at the Indian Institute of Technology at Madras. He received his Ph.D. in computer science from Brown University in 2002. His research interests are in theory and algorithms for distributed computing, networks, and large-scale data. He has published over 125 refereed papers in these areas. His work has appeared in JACM, SICOMP, ACM TALG, STOC, FOCS, SODA, PODC, SPAA, DISC, and INFOCOM. His research has been supported by research grants from the US National Science Foundation, the US-Israel Binational Science Foundation, and the Singapore Ministry of Education.

Speaker: Ling Ren

Abstract: What is fundamentally novel about Bitcoin's longest-chain consensus protocol over class Byzantine Fault Tolerant (BFT) protocols? One key innovation is its support for dynamic participation. The Bitcoin protocol has operated for over a decade, during which it has witnessed a billionfold increase as well as big sudden drops in the participation level (represented by the total hashing rate). But to support this phenomenal level of robustness, longest-chain protocols suffer from long latency as a fundamental trade-off. Classic BFT protocols, on the other hand, can achieve constant latency but cannot make progress under dynamic participation. In this talk, I will present a protocol that simultaneously supports dynamic participation and achieves constant latency. The core technique is to extend the classic BFT approach from static quorum size to dynamic quorum size, i.e., according to the current participation level, while preserving important properties of static quorums. Joint work with Atsuki Momose.

Bio: Ling Ren is an assistant professor in the Department of Computer Science at the University of Illinois at Urbana-Champaign. Prior to joining the University of Illinois, he obtained his Ph.D. from MIT and worked at VMware Research. His research interests include security, cryptography, and distributed algorithms. He has won several awards including NSF CAREER Award, Google privacy research award, VMware Early Career Faculty Grant, Top Picks in Hardware and Embedded Security, and Best Paper Runner-Up and Best Student Paper at CCS.

Speaker: Kartik Nayak

Abstract: Safety, liveness, and privacy are three critical properties required for any privacy-preserving proof-of-stake (PoS) blockchain. To obtain safety and liveness, PoS blockchains typically elect parties proportional to their stake, and only the elected parties send messages in the protocol. To obtain privacy, privacy-preserving PoS systems hide the identity of the stakeholders that propose blocks to the system. Intuitively, these measures should provide us with all of the three properties.

In this talk, we will show this intuition is incorrect under some circumstances. In particular, if the adversary can cause some network delays between a victim party and other parties, then there is an inherent tension between privacy and safety and liveness even if the underlying network is an ideal anonymous broadcast channel. We will discuss stake inference attacks where such an adversary can precisely learn a party's stake by injecting some transactions into the system. To defend against such attacks, we will discuss a differentially-private stake distortion mechanism to trade-off between the three properties in the system.

Bio: Kartik Nayak is an assistant professor in the Department of Computer Science at Duke University. He works in the areas of security, applied cryptography, distributed computing, and blockchains. Before joining Duke University, he spent a year as a postdoctoral researcher at VMware Research. Before that, he graduated from the University of Maryland, College Park. He has served on program committees of several top-tier conferences such as ACM CCS, PODC, Asiacrypt, and PoPETS. Kartik is a recipient of the 2016 Google Ph.D. fellowship in Security. His research is funded by NSF Awards, VMware Early Career Grant Award, Novi, and Ethereum Foundation.

Speaker: Soubhik Deb

Abstract: Transaction-order-manipulation attacks have become extremely common in public blockchains, costing hundreds of millions of dollars. In these blockchains, a miner can unilaterally determine the order of transactions inside a block, and this ordering is not checked by other users, leaving room for the miner to manipulate the order for its own benefit. This gap is also evident from existing security results for permissionless blockchains which only focus on the security properties of consistency and liveness. However, consistency and liveness do not provide any guarantees on the relationship between the order in which transactions arrive into the network and the finalized order in the ledger. The ordering is important because the fees associated with the transactions and the value of the native tokens at different points in the ledger can depend on the ordering. The importance of fair ordering is underscored by massive front-running attacks in various decentralized finance (DeFi) projects on popular blockchains. A fair ordering of transactions would mean that if one transaction was transmitted before another one then this ordering would be maintained in the final ledger. This workshop will focus on introducing order manipulation in blockchains and explain how fair ordering protocols can be used to mitigate such manipulation in order to achieve a FIFO ordering.

Bio: Soubhik is a third year Ph.D. student at the University of Washington Department of Electrical and Computer Engineering. His goal is to design, develop and deploy systems that are based on blockchain, in order to push for democratization and permissionless innovation in digital platforms. He previously graduated from IIT Bombay with a Bachelors and Masters in Electrical Engineering.

Shaileshh Bojja Venkatakrishnan (The Ohio State University)
Sreeram Kannan (University of Washington - Seattle)