Offline Submission With RSA Time-Lock Puzzles
The authors introduce a non-interactive RSA time-lock puzzle scheme whose level of difficulty can be arbitrarily chosen by artificially enlarging the public exponent. Solving a puzzle for a message m means for Bob to encrypt m with Alice's public puzzle key by repeated modular squaring. The number of squarings to perform determines the puzzle complexity. This puzzle is non-parallelizable. Thus, the solution time cannot be shortened significantly by employing many machines and it varies only slightly across modern CPUs. Alice can quickly verify the puzzle solution by decrypting the cipher-text with a regular private key operation.