Paper 2017/1067

Regulating Storage Overhead in Existing PoW-based Blockchains

Frederik Armknecht, Jens-Matthias Bohli, Ghassan O. Karame, and Wenting Li

Abstract

Proof of Work (PoW) blockchains regulate the frequency and security of extensions to the blockchain in a decentralized manner by adjusting the difficulty in the network. However, analogous decentralized measures to regulate the replication level of the associated transactions and blocks data are completely missing so far. We argue that such measures are required as well. On the one hand, the smaller the number of replicas, the higher the vulnerability of the system against compromises and DoS-attacks. On the other hand, the larger the number of replicas, the higher the storage overhead, and the higher the operational blockchain cost are. In this paper, we propose a novel solution, EWoK (Entangled proofs of WOrk and Knowledge), that regulates in a decentralized manner the minimum number of replicas that should be stored by miners in the blockchain. EWoK achieves this by tying replication to the only directly-incentivized process in PoW-blockchains – which is PoW itself. EWoK only incurs small modifications to existing PoW protocols and is fully compliant with the specifications of existing mining hardware. Our implementation results confirm that EWoK can be easily integrated within existing mining pool protocols, such as GetBlockTemplate and Stratum mining, and does not impair the mining efficiency.