PoWVDF: Progressive Real-Time Block Rate Targeting.

In conventional PoW mining, miners iterate a nonce until the block header's hash falls below a predefined target. The mining time for a single block approximately follows an exponential distribution, resulting in a large variance in block generation time. Consequently, the generation time of a single block cannot accurately reflect mining power. Therefore, conventional PoW blockchains use the generation time of numerous blocks to evaluate mining power, leading to lengthy difficulty adjustment periods that cannot adapt to the fast-paced market. To seek better responsiveness to changing hashrate, an innovative consensus algorithm called Real-Time Block Rate Targeting (RTT) has been proposed. This consensus algorithm features shorter difficulty adjustment periods and improves the stability of block generation. In this paper, we demonstrate that the RTT consensus algorithm make chains more vulnerable to double-spending attacks, enabling attackers to conduct successful attacks at lower costs. To address this vulnerability, we propose the PoWVDF protocol, which combines Proof-of-Work and verifiable delay functions. This protocol maintains the advantages of RTT's shorter diffi-culty adjustment periods and stability of block generation while enhancing the security against double-spending attacks.