Cryptology ePrint Archive: Report 2018/087

(Short Paper) A Wild Velvet Fork Appears! Inclusive Blockchain Protocol Changes in Practice

Alexei Zamyatin and Nicholas Stifter and Aljosha Judmayer and Philipp Schindler and Edgar Weippl and William J. Knottenbelt

Abstract: The loosely defined terms hard fork and soft fork have established themselves as descriptors of different classes of upgrade mechanisms for the underlying consensus rules of (proof-of-work) blockchains. Recently, a novel approach termed velvet fork, which expands upon the concept of a soft fork, was outlined. Specifically, velvet forks intend to avoid the possibility of disagreement by a change of rules through rendering modifications to the protocol backward compatible and inclusive to legacy blocks.We present an overview and definitions of these different upgrade mechanisms and outline their relationships. Hereby, we expose examples where velvet forks or similar constructions are already actively employed in Bitcoin and other cryptocurrencies. Furthermore, we expand upon the concept of velvet forks by proposing possible applications and discuss potentially arising security implications.

Category / Keywords: cryptographic protocols / Bitcoin, blockchain, consensus, fork, velvet fork

Original Publication (in the same form): 5th Workshop on Bitcoin and Blockchain Research, Financial Cryptography and Data Security 18

Date: received 22 Jan 2018, last revised 18 Apr 2018

Contact author: a zamyatin at imperial ac uk

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Version: 20180418:102934 (All versions of this report)

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