Enabling Deletion in Append-Only Blockchains (Short Summary / Work in Progress)

TL;DR

This paper proposes a novel blockchain architecture that allows for controlled deletion of data within specific contexts, addressing privacy and data management needs while maintaining core blockchain qualities.

Contribution

It introduces a tree of context chains with simultaneous validity, enabling context-specific deletion without compromising blockchain integrity.

Findings

Supports GDPR compliance through context-based deletion

Enables truncation and data rollover

Maintains blockchain security and consistency

Abstract

Conventional blockchain implementations with append-only semantics do not support deleting or overwriting data in confirmed blocks. However, many industry-relevant use cases require the ability to delete data, especially when personally identifiable information is stored or when data growth has to be constrained. Existing attempts to reconcile these contradictions compromise on core qualities of the blockchain paradigm, as they include backdoor-like approaches such as central authorities with elevated rights or usage of specialized chameleon hash algorithms in chaining of the blocks. In this technical report, we outline a novel architecture for the blockchain ledger and consensus, which uses a tree of context chains with simultaneous validity. A context chain captures the transactions of a closed group of entities and persons, thus structuring blocks in a precisely defined way. The resulting context isolation enables consensus-steered deletion of an entire context without side effects to other contextes. This architecture opens the possibility of truncation, data rollover and separation of concerns, and can help to fulfill the GDPR regulations.