ZeroTrade: Privacy respecting assets trading system based on public ledger

Motivation. Public ledger is a decentralized book keeping technology and is believed to have the potential to revolutionize many areas. Besides handling crypto-currency, public ledger can be used to tokenize arbitrary assets, and then support trading of these asset tokens in a decentralized manner. With public ledger based token trading system, users do not necessarily convert their assets to currencies, but can exchange assets directly. It also avoids unnecessary transportation as the asset only needs to be physically transferred to its last owner. Furthermore, utilization of the public ledger does not require that users have to trust each other in order to trade tokens safely. However, using decentralized public ledger for trading asset tokens raises serious privacy concerns. Because token ownership information is stored on the public ledger and disclosed to the public, anyone can uncover users trading activities and history. For a token based asset trading platform, all tokens are unique and transactions are usually two-ways or multi-ways. In response to these challenges, we propose ZeroTrade, a privacy respecting heterogeneous assets trading system that leverages various cryptography tools to conceal the exchange trace of asset tokens and takes advantage of public ledger for guaranteeing fairness of asset token exchange. Solution. ZeroTrade involves trusted hubs that are responsible for converting assets to tokens and back, where trusted means that hubs will generate/accept valid tokens, and uses the public ledger to record all token exchange information. When two or more users want to exchange tokens with each other, each user picks an agent for the exchange. Asset tokens are first poured into a pool and users leverage agents to obliviously retrieve tokens from the pool in order to finish the exchange. The oblivious retrieving process cut off the connection between the original user and the agent. Therefore, one cannot determine the relationship between the original users who want to exchange tokens by observing information recorded on the public ledger. To implement the design, ZeroTrade leverages different cryptography tools including zero-knowledge proof and various encryption techniques. Considering various demands in token trade, ZeroTrade also supports operations like partial token trade and revocation. A preliminary evaluation of the performance shows that ZeroTrade only adds limited burden on top of the public ledger. More detailed information can be found in the full version of the paper. Conclusion. ZeroTrade provides a privacy friendly platform for asset trading based on public ledger. For the next step, we plan to implement a fully functional prototype and considering more complex token trading scenarios.