Time-lock puzzle with examinable evidence of unlocking time

Abstract

Rivest et. al. proposed a time-lock puzzle based on the RSA crypto algorithm. To unlock the puzzle a player has to perform a computation which has a well understood time complexity. However,i n that puzzle scheme there is no way for a player to examine whether a puzzle has been constructed in good order and to play a puzzle may foolishly risk wasting a very lengthy time on trying to solve an intractable problem. This weakness prohibits the time-lock puzzle from any applications that involve distrusted parties (most imaginable applications do involve distrusted parties). We propose a new RSA-based time-lock puzzle which includes an efficient protocol to let a player examine the time needed for unlocking.