CaSPR Lab


Conditional Electronic Payments


Digital payments are the electronic version of cash: they cannot be traced to the users that spend them and even though they are trivial to duplicate, they cannot be spent more than once without risking detection. In this project we introduce a novel conditional e-cash protocol allowing future anonymous cashing of bank-issued e-money only upon the satisfaction of an agreed-upon public condition. Payers are able to remunerate payees for services that depend on future, yet to be determined outcomes of events. Moreover, payees are able to further transfer payments to third parties. Once the payment is complete, any double-spending attempt by the payer will reveal its identity; no double-spending by any of payees in the payee transfer-chain is possible. Payers can not be linked to payees or to ongoing or past transactions. The flow of cash within the system is thus both correct and anonymous.

Conditional E-Payments with Transferability"
Bogdan Carbunar, Larry Shi, Radu Sion.
Journal of Parallel and Distributed Computing (JPDC), Volume 71, Issue 1, January 2011

"Conditional E-Cash"
Larry Shi, Bogdan Carbunar, Radu Sion.
In Proceedings of the 11th Financial Cryptography and Data Security (FC), Trinidad/Tobago, February 2007 [18%] [pdf]

While the initial applications of conditional e-cash were thought to concern mostly online trading of financial securities, prediction markets, and betting systems, we have soon identified several other domains. One such domain is in the computation outsourcing framework. Initiated by volunteer computing efforts, the computation outsourcing problem has potential for adoption in the growing market of networked set-top-boxes and mobile devices. In the following paper we study the problem of providing secure payments in exchange for outsourced CPU cycles. Previous contributions have almost exclusively tackled only one side of the problem -- offering incentives for volunteer participation and preventing worker laziness. This makes sense in volunteer computing environments where the outsourcer has little to gain from incorrectly rewarding honest participation. However, this assumption is no longer valid in general computation outsourcing frameworks, where anybody can outsource computations. We propose a solution that simultaneously ensures correct remuneration for jobs completed on time and prevents worker laziness. Our solution relies on an offline bank to generate and redeem payments; the bank is oblivious to interactions between outsourcers and workers. In particular, the bank is not involved in job computation or verification. Our experiments show that the solution is efficient: the bank can perform hundreds of payment transactions per second and the overheads imposed on outsourcers and workers are negligible.

"Fair Payments for Outsourced Computations"
Bogdan Carbunar, Mahesh Tripunitara.
In Proceedings of the 7th IEEE International Conference on Sensor, Ad Hoc and Mesh Communications and Networks (SECON)[21%]. Boston, June 2010 [pdf]

nother application domain is anonymous micropayments for electronic services, such as anonymizers. In the following paper we design and analyse a first set of practical anonymous mechanisms for (networked) service payment. Specifically we report on implementing software for network routing micropayment in TOR. We then explore additional general purpose micropayment protocols for networked service deployments of increasingly complex requirements (such as cloud and p2p-hosted services). The solutions are extremely efficient (e.g., bandwidth and latency overheads of under 4\% and 0.4 ms respectively in the TorPay implementation with out of band payment), provide full anonymity (both sender and receiver side), and support throughputs of thousands of transactions per second.

"XPay: Practical Anonymous Payments for Tor Routing and Other Networked Services"
Yao Chen, Radu Sion, Bogdan Carbunar.
In Proceedings of the 8th ACM Workshop on Privacy in the Electronic Society (WPES), Chicago, November 2009 [pdf]