VeloCash: Anonymous Decentralized Probabilistic Micropayments With Transferability

Micropayments are one of the challenges in cryptocurrencies. Micropayments on the blockchain have the problem that the fee is high for the transfer amount. As a countermeasure, a method called Layer-two has been proposed to consolidate transactions outside the blockchain and improve the blockchain's throughput. As one of the existing Layer-two schemes, Decentralized Probabilistic Micropayments have been proposed. The winning amount is registered in the blockchain, and the lottery tickets are issued to be won with probability p, which allows us to aggregate approximately (1/p) transactions into one. Unfortunately, existing solutions do not allow for ticket transferability, and the smaller p, the more difficult it is to use them in the real world. Here we propose VeloCash, Decentralized Probabilistic Micropayments with Transferability, which preserves anonymity. By introducing tamper-proof assumptions for sending and receiving the tickets, we make p smaller. As a tamper-proof hardware assumption, VeloCash uses Attested Execution Secure Processors, a formal abstraction of secure processors with attested execution functionality and Direct Anonymous Attestation to achieve anonymity for sending and receiving tickets. VeloCash can detect double-spending attacks perfectly and revoke the adversary's device.