TIDE: A Novel Approach to Constructing Timed-Release Encryption

In ESORICS 2021, Chvojka et al. introduced the idea of taking a time-lock puzzle and using its solution to generate the keys of a public key encryption (PKE) scheme [12]. They use this to define a timed-release encryption (TRE) scheme, in which the secret key is encrypted `to the future' using a time-lock puzzle, whilst the public key is published. This allows multiple parties to encrypt a message to the public key of the PKE scheme. Then, once a solver has spent a prescribed length of time evaluating the time-lock puzzle, they obtain the secret key and hence can decrypt all of the messages. In this work we introduce TIDE (TIme Delayed Encryption), a novel approach to constructing timed-release encryption based upon the RSA cryptosystem, where instead of directly encrypting the secret key to the future, we utilise number-theoretic techniques to allow the solver to factor the RSA modulus, and hence derive the decryption key. We implement TIDE on a desktop PC and on Raspberry Pi devices validating that TIDE is both efficient and practically implementable. We provide evidence of practicality with an extensive implementation study detailing the source code and practical performance of TIDE.