A Nonoutsourceable Puzzle Under GHOST Rule

Blockchain technology has attracted a lot of attention in recent years. Applications of blockchain are not only restricted to cybercurrencies, but have also been extended to other areas such as finance, e-health, music, and other business. One of the key components of blockchain is the design for miners who are responsible for adding new transactions (blocks) by solving a puzzle and receive some rewards in return. As a result, miners tend to join centralized mining pools to outsource their computing resources in order to gain more steady rewards, which may affect the security and fairness of the system. This motivates the researchers to propose nonoutsourceable puzzles. However, existing nonoutsourceable puzzles do not work well under the high-rate transaction processing protocol (GHOST). In this paper, we propose the first nonoutsourceable puzzle that can satisfy all security requirements of GHOST. Our experimental results show that our puzzle is practical.