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A. Zamyatin, N. Stifter, A. Judmayer, P. Schindler, E. Weippl, W.J. Knottenbelt:
"A Wild Velvet Fork Appears! Inclusive Blockchain Protocol Changes in Practice";
Talk: 5th Workshop on Bitcoin and Blockchain Research at Financial Cryptography and Data Security 2018, Curacao, Santa Barbara Beach Resort; 2018-03-02; in: "Proceedings of Bitcoin 2018", Sprinter Lecture Notes in Computer Science, (2018).

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 in [22]. 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.