Digital contents are typically sold online through centralized and custodian marketplaces, which requires the trading partners to trust a central entity. We aim to develop Databarter, a fair protocol which, assuming the cryptographic hash of the file of interest is known to the buyer, should be trust-free and lets a buyer purchase data for a previously agreed monetary amount, while guaranteeing the integrity of the contents. The goal of the project is to come up with a protocol that prevents misbehavior and that guarantees that any deviation from the expected participants' behavior results in a negative financial payoff; i.e. honest behavior must correspond to a subgame perfect Nash equilibrium. We aim to minimize the necessary protocol costs, i.e. if buyer and seller behave honestly, Databarter's execution should at most require four blockchain transactions. The actual data is exchanged must be privacy preserving and without writing the whole data to the blockchain. We ideally want databarter to enable flexible peer-to-peer setting where multiple parties can fairly sell a file to a buyer.