[bitcoin-dev] The first successful Zero-Knowledge Contingent Payment

Sergio Demian Lerner sergio.d.lerner at gmail.com
Fri Feb 26 23:06:40 UTC 2016


It a property of the SKCP system that the person who performed the trusted
setup cannot extract any information from a proof?

In other words, is it proven hard to obtain information from a proof by the

On Fri, Feb 26, 2016 at 6:42 PM, Gregory Maxwell via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:

> I am happy to announce the first successful Zero-Knowledge Contingent
> Payment (ZKCP) on the Bitcoin network.
> ZKCP is a transaction protocol that allows a buyer to purchase
> information from a seller using Bitcoin in a manner which is private,
> scalable, secure, and which doesn’t require trusting anyone: the
> expected information is transferred if and only if the payment is
> made. The buyer and seller do not need to trust each other or depend
> on arbitration by a third party.
> Imagine a movie-style “briefcase swap” (one party with a briefcase
> full of cash, another containing secret documents), but without the
> potential scenario of one of the cases being filled with shredded
> newspaper and the resulting exciting chase scene.
> An example application would be the owners of a particular make of
> e-book reader cooperating to purchase the DRM master keys from a
> failing manufacturer, so that they could load their own documents on
> their readers after the vendor’s servers go offline. This type of sale
> is inherently irreversible, potentially crosses multiple
> jurisdictions, and involves parties whose financial stability is
> uncertain–meaning that both parties either take a great deal of risk
> or have to make difficult arrangement. Using a ZKCP avoids the
> significant transactional costs involved in a sale which can otherwise
> easily go wrong.
> In today’s transaction I purchased a solution to a 16x16 Sudoku puzzle
> for 0.10 BTC from Sean Bowe, a member of the Zcash team, as part of a
> demonstration performed live at Financial Cryptography 2016 in
> Barbados. I played my part in the transaction remotely from
> California.
> The transfer involved two transactions:
> 8e5df5f792ac4e98cca87f10aba7947337684a5a0a7333ab897fb9c9d616ba9e
> 200554139d1e3fe6e499f6ffb0b6e01e706eb8c897293a7f6a26d25e39623fae
> Almost all of the engineering work behind this ZKCP implementation was
> done by Sean Bowe, with support from Pieter Wuille, myself, and Madars
> Virza.
> Read more, including technical details at
> https://bitcoincore.org/en/2016/02/26/zero-knowledge-contingent-payments-announcement/
> [I hope to have a ZKCP sudoku buying faucet up shortly. :) ]
> _______________________________________________
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> bitcoin-dev at lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
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