International Association
for Cryptologic Research

Inventory matching is a standard mechanism for trading financial stocks by which buyers and sellers can be paired. In the financial world, banks often undertake the task of finding such matches between their clients. The related stocks can be traded without adversely impacting the market price for either client. If matches between clients are found, the bank can offer the trade on advantageous rates. If no match is found, the parties have to buy or sell the stock in the public market, which introduces additional costs. A problem with the process as it is presently conducted is that the involved parties must share their order to buy or sell a particular stock, along with the intended quantity (number of shares) to the bank. Clients are concerned that if this information ``leaks'' somehow, other market participants will become aware of their intentions, and thus cause the price to move adversely against them before their transaction is concluded. We provide a solution that enables the clients to match their orders efficiently with reduced market impact while maintaining privacy. In the case where there are no matches, no information is revealed. Our main cryptographic innovation is a secure linear comparison protocol for computing the minimum between two quantities with malicious security. We report benchmarks of our Prime Match system, which runs in production, and is adopted by a large bank in the US (J.P. Morgan). Prime Match is the first MPC solution running live in the financial world.