Cryptology ePrint Archive: Report 2016/757

Redactable Blockchain -- or -- Rewriting History in Bitcoin and Friends

Giuseppe Ateniese and Bernardo Magri and Daniele Venturi and Ewerton Andrade

Abstract: We put forward a new framework that makes it possible to re-write and/or compress the content of any number of blocks in decentralized services exploiting the blockchain technology. As we argue, there are several reasons to prefer an editable blockchain, spanning from the necessity to remove improper content and the possibility to support applications requiring re-writable storage, to "the right to be forgotten".

Our approach generically leverages so-called chameleon hash functions (Krawczyk and Rabin, NDSS '00), which allow to efficiently determine hash collisions given a secret trapdoor information. We detail how to integrate a chameleon hash function in virtually any blockchain-based technology, for both cases where the power of redacting the blockchain content is in the hands of a single trusted entity and where such a capability is distributed among several distrustful parties (as is the case in Bitcoin).

We also report on a proof-of-concept implementation of a redactable blockchain, building on top of Nakamoto's Bitcoin core. The implementation only requires minimal changes to the way current client software interprets information stored in the blockchain and to the current blockchain, block, or transaction structures. Moreover, our experiments show that the overhead imposed by a redactable blockchain is small compared to the case of an immutable one.

Category / Keywords: cryptographic protocols / Blockchain, Bitcoin, Chameleon hash functions

Original Publication (with major differences): IEEE EuroS&P 2017

Date: received 5 Aug 2016, last revised 11 May 2017

Contact author: bernardomagri21 at gmail com

Available format(s): PDF | BibTeX Citation

Note: Fixed fonts in the PDF file.

Version: 20170511:210619 (All versions of this report)

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