Time-Lock Puzzles (TLPs) are cryptographic protocols that enable a client to lock a message in such a way that a server can only unlock it after a specific time period. However, existing TLPs have certain limitations: (i) they assume that both the client and server always possess sufficient computational resources and (ii) they solely focus on the lower time bound for finding a solution, disregarding the upper bound that guarantees a regular server can find a solution within a certain time frame. Additionally, existing TLPs designed to handle multiple puzzles either (a) entail high verification costs or (b) lack generality, requiring identical time intervals between consecutive solutions. To address these limitations, this paper introduces, for the first time, the concept of a "Delegated Time-Lock Puzzle" and presents a protocol called "Efficient Delegated Time-Lock Puzzle" (ED-TLP) that realises this concept. ED-TLP allows the client and server to delegate their resource-demanding tasks to third-party helpers. It facilitates real-time verification of solution correctness and efficiently handles multiple puzzles with varying time intervals. ED-TLP ensures the delivery of solutions within predefined time limits by incorporating both an upper bound and a fair payment algorithm. We have implemented ED-TLP and conducted a comprehensive analysis of its overheads, demonstrating the efficiency of the construction.

翻译：时间锁谜题（TLP）是一类密码学协议，允许客户端加密消息，使得服务器只能在特定时间周期后解密密文。然而，现有TLP存在以下局限性：（i）它们假设客户端和服务器始终拥有充足的计算资源，（ii）仅关注求解的时限下限，而忽略了保证普通服务器能在确定时限内求解的上限约束。此外，现有可处理多谜题的TLP方案要么（a）验证成本高昂，要么（b）缺乏通用性，要求连续解谜的时间间隔完全相同。为突破这些限制，本文首次提出“委托式时间锁谜题”的概念，并实现了名为“高效委托式时间锁谜题”（ED-TLP）的协议。ED-TLP允许客户端和服务器将高计算开销任务委托给第三方辅助方，支持对解谜正确性的实时验证，并能高效处理时间间隔可变的多个谜题。通过引入时限上限约束与公平支付算法，ED-TLP能够确保在预定时限内交付解谜结果。我们对ED-TLP进行了原型实现与系统性开销分析，验证了该构造的高效性。