International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Matthias Fitzi

Publications

Year
Venue
Title
2020
TCC
Ledger Combiners for Fast Settlement 📺
Blockchain protocols based on variations of the longest-chain rule—whether following the proof-of-work paradigm or one of its alternatives—suffer from a fundamental latency barrier. This arises from the need to collect a sufficient number of blocks on top of a transaction-bearing block to guarantee the transaction’s stability while limiting the rate at which blocks can be created in order to prevent security-threatening forks. Our main result is a black-box security-amplifying combiner based on parallel composition of m blockchains that achieves \Theta(m)-fold security amplification for conflict-free transactions or, equivalently, \Theta(m)-fold reduction in latency. Our construction breaks the latency barrier to achieve, for the first time, a ledger based purely on Nakamoto longest-chain consensus guaranteeing worst-case constant-time settlement for conflict-free transactions: settlement can be accelerated to a constant multiple of block propagation time with negligible error. Operationally, our construction shows how to view any family of blockchains as a unified, virtual ledger without requiring any coordination among the chains or any new protocol metadata. Users of the system have the option to inject a transaction into a single constituent blockchain or---if they desire accelerated settlement---all of the constituent blockchains. Our presentation and proofs introduce a new formalism for reasoning about blockchains, the dynamic ledger, and articulate our constructions as transformations of dynamic ledgers that amplify security. We also illustrate the versatility of this formalism by presenting robust-combiner constructions for blockchains that can protect against complete adversarial control of a minority of a family of blockchains.
2008
TCC
2007
ASIACRYPT
2007
TCC
2006
TCC
2006
TCC
2005
JOFC
2005
JOFC
2004
CRYPTO
2004
EUROCRYPT
2003
EUROCRYPT
2002
EUROCRYPT
2001
CRYPTO
1999
ASIACRYPT
1998
CRYPTO

Program Committees

PKC 2008
Asiacrypt 2003