
Cross-Chain Deals and Adversarial Commerce - mad44
http://muratbuffalo.blogspot.com/2019/12/cross-chain-deals-and-adversarial.html
======
EthanHeilman
_Disclaimer:_ I am a researcher in this space and also CTO of a company
(Arwen.io) which builds cross-chain atomic swaps.

To me, one of the more powerful properties of blockchain-based
cryptocurrencies is that they overcome a long standing impossibility result in
cryptography:

fair exchange, i.e. atomic swaps, are impossible without a trusted third party
[0].

Cryptocurrency-backed blockchains do this by modifying the underlying
assumptions behind that impossibility result in two ways [1]:

1\. it adds the assumption that at least one side of the exchange is trading a
blockchain asset,

2\. it the treats the blockchain holding that asset as a trusted party.

To someone outside the world of cryptocurrency this may seem like an odd set
of assumptions. However if what you want to exchange is a blockchain asset,
assumption 1 and 2 is very reasonable. Valuing a blockchain asset already
assumes that the blockchain is trustworthy because the value and ownership of
the asset requires a trustworthy blockchain.

A very cool result is that a party can perform a fair-exchange between a
cryptocurrency and the solution to a problem in NP. For instance the ZKCP
(Zero Knowledge Contingent Payment) protocol has been used to perform a fair-
exchange of bitcoins for the solution to a Sudoku puzzle [2]. SIA coin uses a
slightly different model to enable users to prove and collect cryptocurrency
for storing another users data [3].

Taken to its logical conclusion, this seems like it would allow substituting
information or math for currency. Could we build an economic in which hard
currency is backed by proof-of-storage or solutions to problems in NP? When I
was a teenager I read Richard Brautigan's poem in which a man replaces his
plumping with poetry [4]. It was one of reasons I got into cross-chain trading
research as it inspired me to think about how to replace cash with
computation. Hopefully it works out better than for the protagonist of that
poem who ends up living in YMCA. Brautigan, writing 50 years ago, captures
both the promise [5] and downsides of information technology ecology projects
like cybernetics and cryptocurrency.

[0]: On the impossibility of fair exchange without a trusted third party
[https://pdfs.semanticscholar.org/208b/22c7a094ada20736593afc...](https://pdfs.semanticscholar.org/208b/22c7a094ada20736593afcc8c759c7d1b79c.pdf)

[1]: The Arwen Trading Protocols (Full Version)
[https://eprint.iacr.org/2020/024.pdf](https://eprint.iacr.org/2020/024.pdf)

[2]: The first successful Zero-Knowledge Contingent Payment
[https://bitcoincore.org/en/2016/02/26/zero-knowledge-
conting...](https://bitcoincore.org/en/2016/02/26/zero-knowledge-contingent-
payments-announcement/)

[3]: sia - about [https://sia.tech/technology](https://sia.tech/technology)

[4]: Homage to The San Francisco YMCA by Richard Brautigan
[http://www.rewindreduceandrecycle.com/richard-brautigans-
hom...](http://www.rewindreduceandrecycle.com/richard-brautigans-homage-to-
the-san-francisco-ymca/)

[5]: All Watched Over by Machines of Loving Grace by Richard Brautigan
[https://en.wikipedia.org/wiki/All_Watched_Over_by_Machines_o...](https://en.wikipedia.org/wiki/All_Watched_Over_by_Machines_of_Loving_Grace)
[https://allpoetry.com/All-Watched-Over-By-Machines-Of-
Loving...](https://allpoetry.com/All-Watched-Over-By-Machines-Of-Loving-Grace)

