"Check-Before-you-Solve": Verifiable Time-lock Puzzles
Jiajun Xin, Dimitrios PapadopoulosHong Kong
IEEE Symposium on Security and Privacy 2025 · Day 2 · Blockchain II
In the realm of modern cryptography and decentralized systems, **time-lock puzzles (TLPs)** have emerged as a foundational primitive, enabling a variety of applications from secure auctions to blockchain front-running resistance. These puzzles are designed such that generating them is computationally easy, but solving them requires a predetermined, sequential computational effort, often denoted as *t* steps. This inherent asymmetry ensures that a solution can only be revealed after a specified time delay, regardless of parallel processing power. However, a critical vulnerability arises from this very property: there is no inherent mechanism to verify the legitimacy or content of a time-lock puzzle *before* expending the significant computational resources required to solve it. An attacker could exploit this by generating arbitrary, meaningless puzzles and falsely claiming they contain valuable information, thereby wasting the computational power of solvers.