Paper 2018/1135

PoTS - A Secure Proof of TEE-Stake for Permissionless Blockchains

Sébastien Andreina, Jens-Matthias Bohli, Ghassan O. Karame, Wenting Li, and Giorgia Azzurra Marson

Abstract

Proof-of-Stake (PoS) protocols have been actively researched for the past few years. PoS finds direct applicability in permissionless blockchain platforms and emerges as one of the strongest candidates to replace the largely inefficient Proof of Work mechanism that is currently plugged in the majority of existing permissionless blockchain systems. Although a number of PoS variants have been proposed, these protocols suffer from a number of security shortcomings. Namely, most existing PoS variants are either subject to the nothing at stake, the long range, or the stake grinding attacks which considerably degrade security in the blockchain. These shortcomings do not result from a lack of foresight when designing these protocols, but are inherently due to the ease of manipulating "stake" when compared to other more established variants, such as "work". In this paper, we address these problems and propose a secure Proof of Stake protocol, PoTS, that leverages Trusted Execution Environments (TEEs), such as Intel SGX, to ensure that each miner can generate at most one block per "height" for strictly increasing heights—thus thwarting the problem of nothing at stake and a large class of long-range attacks. In combination with TEEs, PoTS additionally uses cryptographic techniques to also prevent grinding attacks and protect against posterior corruption. We show that our protocol is secure, in the sense of well-established cryptographic notions for blockchain protocols, down to realistic hardware assumptions on TEE and well-established cryptographic assumptions. Finally, we evaluate the performance of our proposal by means of implementation. Our evaluation results show that PoTS offers a strong tradeoff between security of performance of the underlying PoS protocol.