Reparo: Publicly Verifiable Layer to Repair Blockchains

Sri Aravinda Krishnan Thyagarajan, Adithya Bhat, Bernardo Magri, Daniel Tschudi, Aniket Kate

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


Although blockchains aim for immutability as their core feature, several instances have exposed the harms with perfect immutability. The permanence of illicit content inserted in Bitcoin poses a challenge to law enforcement agencies like Interpol, and millions of dollars were lost in buggy smart contracts in Ethereum. A line of research then spawned on redactable blockchains with the aim of solving the problem of redacting illicit contents from both permissioned and permissionless blockchains. However, all the existing proposals follow the build-new-chain approach for redactions, and cannot be integrated with existing running blockchains, such as Bitcoin and Ethereum. This work demonstrates that the traditional build-new-chain approach for blockchain redactions is not necessary. We present Reparo (In the Harry Potter universe, ‘ Reparo ’ is a spell that repairs objects), a publicly verifiable layer on top of any blockchain to perform repairs, ranging from fixing buggy contracts to removing illicit contents from the chain. We present an efficient instantiation of Reparo over Ethereum (with proof of work based consensus) for repairing smart contract bugs. In this protocol, any Ethereum user may propose a repair and a deliberation process ensues resulting in a decision that complies with the repair policy of the chain and is publicly verifiable. A repair operation (for instance, fixing a bug in a contract) is then performed according to the repair proposal and the state of Ethereum is updated accordingly. Reparo ’s advantages are multi-fold: (i) Since Reparo follows a layer design, it helps facilitate additional functionalities for Ethereum while maintaining the same provable security guarantees; (ii) Reparo can be easily tailored to different consensus requirements (like proof of stake), does not require heavy cryptographic machinery, and thus, can be integrated with other existing blockchains (such as Bitcoin, Cardano) as well. We evaluate Reparo with Ethereum mainnet and show that the cost of fixing several prominent smart contract bugs is almost negligible. For instance, the cost of repairing the prominent Parity Multisig wallet bug with Reparo is as low as 0.00005 % of the Ethers that can be retrieved after the fix.

Original languageEnglish
Title of host publicationFinancial Cryptography and Data Security - 25th International Conference, FC 2021, Virtual Event, March 1-5, 2021, Revised Selected Papers, Part II
EditorsNikita Borisov, Claudia Diaz
PublisherSpringer Berlin
Number of pages20
ISBN (Print)9783662643303
Publication statusPublished - 23 Oct 2021

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume12675 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


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