Privacy Preserving Payments in Credit Networks: Enabling trust with privacy in online marketplaces

A credit network models trust between agents in a distributed environment and enables payments between arbitrary pairs of agents. With their flexible design and robustness against intrusion, credit networks form the basis of several Sybil-tolerant social networks, spam-resistant communication protocols, and payment systems. Existing systems, however, expose agents’ trust links as well as the existence and volumes of payment transactions, which is considered sensitive information in social environments or in the financial world. This raises a challenging privacy concern, which has largely been ignored by the research on credit networks so far. This paper presents PrivPay, the first provably secure privacypreserving payment protocol for credit networks. The distinguishing feature of PrivPay is the obliviousness of transactions, which entails strong privacy guarantees for payments. PrivPay does not require any trusted third party, maintains a high accuracy of the transactions, and provides an economical solution to network service providers. It is also general-purpose trusted hardwarebased solution applicable to all credit network-based systems. We implemented PrivPay and demonstrated its practicality by privately emulating transactions performed in the Ripple payment system over a period of four months.