Money transfer is an abstraction that realizes the core of cryptocurrencies. It has been shown that, contrary to common belief, money transfer in the presence of Byzantine faults can be implemented in asynchronous networks and does not require consensus. Nonetheless, existing implementations of money transfer still require a quadratic message complexity per payment, making attempts to scale hard. In common blockchains, such as Bitcoin and Ethereum, this cost is mitigated by payment channels implemented as a second layer on top of the blockchain allowing to make many off-chain payments between two users who share a channel. Such channels only require on-chain transactions for channel opening and closing, while the intermediate payments are done off-chain with constant message complexity. But payment channels in-use today require synchrony, therefore they are inadequate for asynchronous money transfer systems. In this paper, we provide a series of possibility and impossibility results for payment channels in asynchronous money transfer systems. We first prove a quadratic lower bound on the message complexity of on-chain transfers. Then, we explore two types of payment channels, unidirectional and bidirectional. We define them as shared memory abstractions and prove that in certain cases they can be implemented as a second layer on top of an asynchronous money transfer system whereas in other cases it is impossible.
翻译:货币转移是一个抽象的抽象,它认识到了隐蔽的核心。 已经表明,与共同的信念相反,在拜占庭断层面前的货币转移可以在非同步的网络中实施,不需要协商一致。 尽管如此,货币转移的现有实施仍需要每支付一个四级信息复杂度,因此难以扩大规模。在Bitcoin和Etheum等共同的连锁链中,这种成本通过在块链上第二层实施支付渠道而得到缓解,使两个共享频道的用户能够进行许多离链付款。这种渠道只需在链式交易中打开和关闭频道,中间付款则以固定的信息复杂程度进行离链式支付。但是,目前使用的支付渠道需要同步,因此它们不足以适应不同步的货币转移系统。在本文中,我们为不稳的货币转移系统提供了一系列可能性和不可能的结果。我们首先证明,在电链转移的复杂程度上存在一种四级更低的分级的连接。 然后,我们探索两种类型的支付渠道,即电路的打开和关闭,中间传输系统作为共同的双向系统,我们又可以确定一个共同的存储系统。