Unit:
Κατεύθυνση / ειδίκευση Υπολογιστικά Συστήματα: Λογισμικό και Υλικό (ΣΥΣ)Πληροφορική
Author:
Polydouri Andrianna
Supervisors info:
Άγγελος Κιαγιάς, Αναπληρωτής Καθηγητής, Τμήμα Πληροφορικής κ' Τηλεπικοινωνιών, Εθνικό κ' Καποδιστριακό Πανεπιστήμιο Αθηνών
Original Title:
A Study on Superlight Clients under Velvet Fork
Translated title:
A Study on Superlight Clients under Velvet Fork
Summary:
Superlight blockchain clients learn facts about the blockchain state while requiring only polylogarithmic communication in the total number of blocks.
For proof-of-work blockchains two known constructions exist: Superblock and FlyClient.
Unfortunately, none of them can be deployed to existing blockchains as they require changes at the consensus layer and at least a soft fork to implement.
In this work, we investigate how a blockchain can be upgraded to support superblock clients without a soft fork. We show that it is possible to implement the needed changes without modifying the consensus protocol and by requiring only a minority of miners to upgrade, a process termed a "velvet fork'' in the literature. While previous work conjectured that Superblock and FlyClient clients can be safely deployed using velvet forks as-is, we show that previous constructions are insecure. We describe a novel class of attacks, called "chain-sewing'', which arise in the velvet fork setting: an adversary can cut-and-paste portions of various chains from independent forks, sewing them together to
fool a superlight client into accepting a false claim.
We show how previous velvet fork constructions can be attacked via chain-sewing.
Next we put forth the first provably secure velvet superblock client construction which we show secure against adversaries that are bounded by 1/3 of the upgraded honest miner population.
Main subject category:
Technology - Computer science
Keywords:
distributed systems, blockchains, superlight clients, velvet fork
