  Many existing timed-release encryption schemes uses time-lock puzzles to
avoid relying on a trusted timeserver or a key holder which could be a weak
spot in data security. However, it is unavoidable to consume massive computing
power for solving time-lock puzzles and it is difficult for encryptors to
predict the amount of time to solve a puzzle by decryptors. In this study, an
efficient dual-purpose proof-of-work consensus allows users to release a
time-locked content, which is encrypted by an asymmetric key encryption scheme
on a blockchain, without trust in any third-party agents. The release time is
predictable as the block time in a proof-of-work blockchain is adaptively
controlled. The mining work is reproposed so that once a new block was mined on
the blockchain network, time-lock puzzles were also solved immediately. No
additional work is required to reveal the time-locked contents and the
encryption is secured by monetary incentive mechanisms since it would be very
costly to arrange an attack attempt, which must overtake the total hash rate of
the whole blockchain network.
