Defining DLT Immutability: A Qualitative Survey of Node Operators

TL;DR

This paper explores the concept of immutability in permissionless blockchains, revealing that strict immutability is unrealistic and proposing a practical, governance-dependent definition based on node operator insights.

Contribution

It introduces the concept of Practical Immutability, a nuanced understanding of immutability contingent on governance and stakeholder trust, based on qualitative analysis.

Findings

Rewrites are more common than generally acknowledged.

Immutability is conditional on governance legitimacy.

Stakeholder trust influences ledger stability.

Abstract

Immutability is a core design goal of permissionless public blockchain systems. However, rewrites are more common than is normally understood, and the risk of rewrite, cyberattack, exploit, or black swan event is also high. Taking the position that strict immutability is neither possible on these networks nor the observed reality, this paper uses thematic analysis of node operator interviews to examine the limits of immutability in light of rewrite events. The end result is a qualitative definition of the conditional immutability found on these networks, which we call Practical Immutability. This is immutability contingent on the legitimate governance demands of the network, where network stakeholders place their trust in the governance topology of a network to lend it legitimacy, and thus manage ledger state.