You are looking at a specific version 20210304:150450 of this paper. See the latest version.

Paper 2021/211

GearBox: An Efficient UC Sharded Ledger Leveraging the Safety-Liveness Dichotomy

Bernardo David and Bernardo Magri and Christian Matt and Jesper Buus Nielsen and Daniel Tschudi

Abstract

Sharding is an emerging technique to overcome scalability issues on blockchain based public ledgers. Without sharding, every node in the network has to listen to and process all ledger protocol messages. The basic idea of sharding is to parallelize the ledger protocol: the nodes are divided into smaller subsets that each take care of a fraction of the original load by executing lighter instances of the ledger protocol, also called shards. The smaller the shards, the higher the efficiency, as by increasing parallelism there is less overhead in the shard consensus. In this vein, we propose a novel approach that leverages the sharding safety-liveness dichotomy. We separate the liveness and safety in shard consensus, allowing us to dynamically tune shard parameters to achieve essentially optimal efficiency for the current corruption ratio of the system. We start by sampling a relatively small shard (possibly with a small honesty ratio), and we carefully trade-off safety for liveness in the consensus mechanism to tolerate small honesty without losing safety. However, for a shard to be live, a higher honesty ratio is required in the worst case. To detect liveness failures, we use a so-called control chain that is always live and safe. Shards that are detected to be not live are resampled with increased shard size and liveness tolerance until they are live, ensuring that all shards are always safe and run with optimal efficiency. As a concrete example, considering a population of 10K parties, 30% corruption and 60-bit security, our design permits shards of size 200 parties in contrast to 6K parties in previous designs. Moreover, in this highly concurrent execution setting, it is paramount to guarantee that both the sharded ledger protocol and its sub protocols (e.g., the shards) are secure under composition. To prove the security of our approach, we present ideal functionalities capturing a sharded ledger as well as ideal functionalities capturing the control chain and individual shard consensus, which needs adjustable liveness. We further formalize our protocols and prove that they securely realize the sharded ledger functionality in the UC framework.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
Preprint. MINOR revision.
Keywords
ShardingBlockchainBitcoinTransaction ledgerLiveness-Safety dichotomy
Contact author(s)
bernardo @ bmdavid com,magri @ cs au dk,cm @ concordium com,jbn @ cs au dk,dt @ concordium com
History
2022-07-05: last of 3 revisions
2021-03-02: received
See all versions
Short URL
https://ia.cr/2021/211
License
Creative Commons Attribution
CC BY
Note: In order to protect the privacy of readers, eprint.iacr.org does not use cookies or embedded third party content.