University of Twente Student Theses


Redactable Blockchain : how to change the immutable and the consequences of doing so

Sartori, Damiano (2020) Redactable Blockchain : how to change the immutable and the consequences of doing so.

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Abstract:The immutability of a blockchain is undoubtedly one of its strongest features. However, the inability to change or delete data might be an undesirable feature in specific contexts in which personal data are at stake. We propose the architecture of a blockchain that allows for redactions of data under particular circumstances. We employ chameleon-hash functions with ephemeral trapdoor to substitute the standard hash functions used in the blockchain. We distribute the ephemeral trapdoor using a verifiable and weighted secret sharing schemes in which the data subject holds the strongest share of the trapdoor. To maintain a sufficient level of integrity and keep the tamper-evident property of a blockchain, we publish a Proof-of-Redaction. This mechanism serves to prove that history has been modified and that the network agreed on the redaction. We evaluate our proposal with blockchain and cryptography experts to validate our design. We show that, while the standard immutability is not maintained, a weaker version that accounts for authorized redactions is still achievable. The proposed architecture could have the ability to reduce the frictions between the immutability of a blockchain and the GDPR without improperly weakening an existing architecture.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:54 computer science
Programme:Computer Science MSc (60300)
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