  We construct a privacy-preserving, distributed and decentralized marketplace
where parties can exchange data for tokens. In this market, buyers and sellers
make transactions in a blockchain and interact with a third party, called
notary, who has the ability to vouch for the authenticity and integrity of the
data.
  We introduce a protocol for the data-token exchange where neither party gains
more information than what it is paying for, and the exchange is fair: either
both parties gets the other's item or neither does. No third party involvement
is required after setup, and no dispute resolution is needed.
