| Summary: | 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 <inline-formula> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula>, which allows us to aggregate approximately <inline-formula> <tex-math notation="LaTeX">$(1/p)$ </tex-math></inline-formula> transactions into one. Unfortunately, existing solutions do not allow for ticket transferability, and the smaller <inline-formula> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula>, the more difficult it is to use them in the real world. Here we propose <inline-formula> <tex-math notation="LaTeX">$\textsf {VeloCash}$ </tex-math></inline-formula>, Decentralized Probabilistic Micropayments with Transferability, which preserves anonymity. By introducing tamper-proof assumptions for sending and receiving the tickets, we make <inline-formula> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula> smaller. As a tamper-proof hardware assumption, <inline-formula> <tex-math notation="LaTeX">$\textsf {VeloCash}$ </tex-math></inline-formula> 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. <inline-formula> <tex-math notation="LaTeX">$\textsf {VeloCash}$ </tex-math></inline-formula> can detect double-spending attacks perfectly and revoke the adversary’s device.
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