LFCS Seminar: 20 November 2018 - David Tse and Pramod Viswanath

Title:  Deconstructing the Blockchain to Approach Physical Limits

Abstract:

The concept of a blockchain was invented by Satoshi Nakamoto to maintain a distributed ledger for an electronic payment system, Bitcoin. In addition to its security, important performance measures of a blockchain protocol are its transaction throughput, confirmation latency and confirmation reliability. These measures are limited by two underlying physical network attributes:  communication capacity and speed-of-light propagation delay. Existing systems operate far away from these physical limits. In this work we introduce Prism, a new blockchain protocol, which can provably achieve 1) security against up to 50% adversarial hashing power; 2) optimal throughput up to the capacity C of the network; 3) confirmation latency for honest transactions proportional to the propagation delay D, with confirmation error probability exponentially small in the bandwidth-delay product CD ; 4) eventual total ordering of all transactions. Our approach to the design of this protocol is based on deconstructing the blockchain into its basic functionalities and systematically scaling up these functionalities to approach their physical limits. This is joint work with Vivek Bagaria, Sreeram Kannan, Giulia Fanti and Pramod Viswanath. The full paper can be found at https://arxiv.org/abs/1810.08092. 

Bio: David Tse received the B.A.Sc. degree in systems design engineering from University of Waterloo in 1989, and the M.S. and Ph.D. degrees in electrical engineering from Massachusetts Institute of Technology in 1991 and 1994 respectively. From 1995 to 2014, he was on the faculty of the University of California at Berkeley. He is currently the Thomas Kailath and Guanghan Xu Professor at Stanford University. He received the Claude E. Shannon Award in 2017 and was elected member of the U.S. National Academy of Engineering in 2018. Previously, he received a NSF CAREER award in 1998, the Erlang Prize from the INFORMS Applied Probability Society in 2000 and the Frederick Emmons Terman Award from the American Society for Engineering Education in 2009. He is a coauthor, with Pramod Viswanath, of the text Fundamentals of Wireless Communication, which has been used in over 60 institutions around the world. He received best paper awards from IEEE Information Theory, Communications and Signal Processing societies, and is the inventor of the proportional-fair scheduling algorithm used in all third and fourth-generation cellular systems.

Title: Why Blocks and Why Chains; A First Principles (Re)Design of Blockchains

 Speaker: Pramod Viswanath

 Abstract: 

Today's blockchains do not scale in a meaningful way. As more nodes join the system, the efficiency of the system (computation, communication, and storage) degrades, or at best stays constant. Furthermore, the security of the permission less system imposes limitations on the core performance metrics of throughput, latency and confirmation probability. We take a first principle approach to the blockchain ecosystem addressing each of the various components holistically. Our approach is characterized by seeking fundamental limits (those prescribed by the physics of the underlying network) to performance and designing algorithms that attain them. This research is informed by decades of experience in information theory, coding theory,  algorithms, wireless communication and packet networks. This talk will highlight

key outcomes of this research program, including Prism (a new consensus algorithm that guarantees information theoretically optimal throughput, latency, reliability), Spider (a new networking protocol for off-chain payment channels),  Polyshard (a new coded storage architecture), and Dandelion (a new network privacy layer).

References:

https://arxiv.org/abs/1810.08092

https://arxiv.org/abs/1809.10361

https://arxiv.org/abs/1809.05088

https://arxiv.org/abs/1809.07468

Bio: Pramod Viswanath received the Ph.D. degree in EECS from UC Berkeley in2000. From 2000 to 2001, he was a member of research staff at Flariontechnologies, NJ. Since 2001, he is on the faculty at University of Illinois atUrbana Champaign in Electrical and Computer Engineering, where he currently is a professor. He is a coauthor, with David Tse, of the text Fundamentals of Wireless Communication, which has been used in over 60 institutions around the world. He is coinventor of the opportunistic beamforming method and codesigner of Flash-OFDM communication algorithms adapted into fourth-generation cellular systems.