  In this paper, we present Velocity, a decentralized market deployed on
Ethereum for trading a custom type of derivative option. To enable the smart
contract to work, we also implement a price fetching tool called PriceGeth. We
present this as a case study, noting challenges in development of the system
that might be of independent interest to whose working on smart contract
implementations. We also apply recent academic results on the security of the
Solidity smart contract language in validating our codes security. Finally, we
discuss more generally the use of smart contracts in modelling financial
derivatives.
