Invited Talks
Krzysztof Pietrzak
Title
New proof systems for sustainable blockchains: proofs of space and verifiable delay functions
Abstract
The distinctive feature of Bitcoin is that it achieves decentralisation in an open setting where everyone can join. This is achieved at a high price, honest parties must constantly dedicate more computational power towards securing Bitcoin's blockchain than is available to a potential adversary, which leads to a massive waste of energy; at its hitherto peak, the electricity used for Bitcoin mining equaled the electricity consumption of Austria. In this lecture I will discuss how disk-space, instead of computation, can be used as a resource to construct a more sustainable blockchain. We will see definitions and constructions of "proof of space" and "verifiable delay functions", and how they can be used to construct a Blockchain with similar dynamics and security properties as the Bitcoin blockchain.
Biography
Krzysztof Pietrzak received his masters and PhD from ETH Zurich, then did postdocs at ENS Paris and CWI Amsterdam. Since 2011 he heads the cryptography group at the recently founded Institute of Science and Technology Austria (IST Austria). He is interested in theoretical and applied aspects of cryptography, including pseudorandomness/entropy, (black-box) lower bounds, leakage-resilience, memory-hard functions, crypto for light-weight devices and proof systems for sustainable blockchains. He is the recipient of an ERC starting and consolidator grant and three Eurocrypt best paper awards.
Elaine Shi
Title
Streamlined blockchains: A simple and elegant approach (tutorial)
Abstract
A blockchain protocol (also called state machine replication) allows a set of nodes to agree on an ever-growing, linearly ordered log of transactions. In this tutorial, we present a new paradigm called “streamlined blockchains”. This paradigm enables a new family of protocols that are extremely simple and natural: every epoch, a proposer proposes a block extending from a notarized parent chain, and nodes vote if the proposal’s parent chain is not too old. Whenever a block gains enough votes, it becomes notarized. Whenever a node observes a notarized chain with several blocks of consecutive epochs at the end, then the entire chain chopping off a few blocks at the end is final. By varying the parameters highlighted in blue, we illustrate two variants for the partially synchronous and synchronous settings respectively. We present very simple proofs of consistency and liveness. We hope that this tutorial provides a compelling argument why this new family of protocols should be used in lieu of classical candidates (e.g., PBFT, Paxos, and their variants), both in practical implementation and for pedagogical purposes.
Biography
Elaine Shi is an Associate Professor in Cornell University. Her research interests include cryptography, randomized algorithms, foundations of blockchains, distributed systems, and the intersection of formal methods and cryptography. She was the recipient of a Packard Fellowship and a Sloan Fellowship.
