Paper 2020/748

Anonymous probabilistic payment in payment hub

Tatsuo Mitani and Akira Otsuka

Abstract

Privacy protection and scalability are significant issues with blockchain. We propose an anonymous probabilistic payment under the general functionality for solving them. We consider the situation that several payers pay several payees through a tumbler. We have mediated the tumbler of the payment channel hub between payers and payees. Unlinkability means that the link, which payer pays which payee via the tumbler, is broken. A cryptographic puzzle plays a role in controlling the intermediation and execution of transactions. Masking the puzzle enables the payer and the payee to unlink their payments. The overview of the proposed protocol is similar to TumbleBit (NDSS 2017). We confirm the protocol realizes the ideal functionalities discussed in TumbleBit. The functionality required for our proposal is the hashed time lock contract that various cryptocurrencies use. This request is general, not restricted to any particular cryptocurrency. Our proposal includes a probabilistic payment. In probabilistic payment, one pays an ordinary mount with a certain probability. One pays a small amount as an expected value. One can run fewer transactions than a deterministic payment. It contributes scalability. We introduce a novel fractional oblivious transfer for probabilistic payment. We call it the ring fractional oblivious transfer (RFOT). RFOT is based on the ring learning with errors (RLWE) encryption. Our trick is based on the fact that an element of the ring is indistinguishable from the circular shifted element. We confirm that RFOT holds the properties of fractional hiding and binding presented in the DAM scheme (Eurocrypt 2017).