Discussing Bitcoin Softchains, Sidechains Using PoW Fraud Proofs – Bitcoin Magazine

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In this episode of “The Van Wirdum Sjorsnado,” hosts Aaron van Wirdum and Sjors Provoost were once again joined by Ruben Somsen. This time, they discussed one of Ruben’s own proposals, called “softchains.”

Softchains are a type of two-way peg sidechain that utilizes a new type of consensus mechanism: proof-of-work fraud proofs (or, as Provoost prefers to call them, “proof-of-work fraud indicators”). Using this consensus mechanism, users don’t validate the content of each block, but instead only check the proof-of-work header, like simplified payment verification (SPV) clients do. By using proof-of-work fraud proofs, users do validate the entire content of blocks any time a blockchain fork occurs. This offers a security model in between full node security and SPV security.

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Somsen explained that by using proof-of-work fraud proofs for sidechains to create softchains, Bitcoin full nodes could validate entire sidechains at minimal cost. This new model might be useful for certain types of sidechains, most notably “block size increase” sidechains that do nothing fancy but do offer more transaction capacity. Van Wirdum, Provoost and Somsen also discussed some of the downsides of the softchain model.


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