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Department of Computer Science - University of Cyprus

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Colloquium Coordinator: Demetris Zeinalipour

Colloquium: Distributed Ledger Objects: Formalization, Implementation and Applications, Dr. Chryssis Georgiou (University of Cyprus, Cyprus), Tuesday, November 9, 2021, 10:00-11:15 EET.

The Department of Computer Science at the University of Cyprus cordially invites you to the Colloquium entitled:

Distributed Ledger Objects: Formalization, Implementation and Applications


Speaker: Dr. Chryssis Georgiou
Affiliation: University of Cyprus, Cyprus
Category: Colloquium
Location: Zoom (with Registration), URL https://ucy.zoom.us/meeting/register/tJEodeGtqjMqHNUHb7J594oxL2rYHizue6zb (directions)
Date: Tuesday, November 9, 2021
Time: 10:00-11:15 EET
Host: Prof. Andreas Pitsillides (cspitsil-AT-cs.ucy.ac.cy)
URL: https://www.cs.ucy.ac.cy/colloquium/index.php#cs.ucy.2021.georgiou

There is no doubt that cryptocurrencies and (public or private) distributed ledgers (blockchains) have the potential to impact our society. However, most experts do not clearly differentiate between the coin, the ledger that supports it, and the service both provide. Instead they get very technical, talking about the cryptographic mechanisms involved, the mining used to maintain the ledger or the smart contract technology. Moreover, when they are asked for details, it is often the case that there is no formal specification of the protocols, algorithms, and the service provided; in many cases “the code is the spec”. In this talk I will overview recent attempts in formalizing the properties of distributed ledgers from a distributed computing point of view. In particular, I will first define the notion of a ledger object as a sequence of records, and provide the operations and properties that such an object should support. Implementing a ledger object on top of (possibly geographically dispersed) computing devices gives rise to the Distributed Ledger Object (DLO). Distribution introduces challenges on the consistency of the ledger in each participant. I will present a DLO implementation that provides linearizable consistency guarantees in a distributed asynchronous setting in which both servers (that maintain the ledger object) and clients (that access the object) are prone to Byzantine (malicious) failures; the implementation uses an Atomic Broadcast service. As an application of the formalism I will introduce the Atomic Appends problem, which emerges when the exchange of digital assets between multiple clients may involve appending multiple records to distinct ledgers (DLOs) in an atomic way. This abstracts the emerging problem of blockchain interconnection. Building on the DLO implementation, I will present an algorithmic solution for the Atomic Appends problem under an asynchronous distributed setting where both clients and the servers may be Byzantine. Finally, I will introduce the notion of the Distributed Grow-only Set Object (DSO) and demonstrate how eventually consistent DSOs can be used to obtain consensus-free solutions to the Atomic Appends problem.

Short Bio:
Chryssis Georgiou is an Associate Professor in the Department of Computer Science at the University of Cyprus. He holds a Ph.D. (December 2003) and M.Sc. (May 2002) in Computer Science & Engineering from the University of Connecticut and a B.Sc. (June 1998) in Mathematics from the University of Cyprus. His research interests span the Theory and Practice of Fault-tolerant Distributed Computing with a focus on Algorithm Design and Analysis. Recent research topics include the Specification and Implementation of Distributed Ledgers, the Design and Implementation of Fault-tolerant and Strongly Consistent Distributed Storage Systems, the Design and Analysis of Self-stabilizing Distributed Systems and the Application of Machine Learning in Acceptance and Commitment Therapy. He has published more than 100 articles in journals and peer-reviewed conference proceedings in his area of study and he has co-authored two books on Robust Distributed Cooperative Computing. A book he had co-edited on the Principles of Blockchain Systems has just been published. He has served on several Program Committees of conferences in Distributed and Parallel Computing and on the Steering Committees of DISC (2008-2010, 2010-2012) and ACM PODC (2013- 2015). He was recently elected to serve for a three-year term as the Steering Committee Chair of ACM PODC (2021-2024). In 2015 he served as the General Chair of PODC 2015, and in 2017 as the Track Program Committee co-Chair (Stabilizing Systems: Theory and Practice Track) of SSS 2017. In 2018, 2019 and 2021 he was the General co-Chair of the workshops ApPLIED 2018, 2019, and 2021 (co-located with PODC 2018, DISC 2019, and PODC 2021 respectively), while in 2020 he co-chaired the PC committee of NETYS 2020. As of January 2018, he is on the Editorial Board of Information Processing Letters (subject area: Distributed Computing). His research has been funded by the University of Cyprus, the Cyprus Research and Innovation Foundation, and the European Commission. More information at: www.cs.ucy.ac.cy/~chryssis .

This colloquium is part of the speaker's procedure for evaluation and promotion from Associate Professor to Professor.

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