Here's a way to encrypt something with an <i>actual</i> timelock, which works because physics. More specifically, it works because there is a maximum speed that information can travel through space: the speed of light.<p>Step 1: Generate a large number of named public/private keypairs and put the private keys on a spacecraft. Also give the spacecraft a communication system and a long-lived RTG (an energy source getting its energy from the decay of some radioactive materials).<p>Step 2: Send the spacecraft to land on the surface a distant body in the solar system, such as one of the moons of Neptune.<p>Step 3: To encrypt a message such that it's guaranteed to not be cracked in less than some specified time, encrypt it several times, using the known named public keys.<p>To decrypt the message, you've got to send it out to the distant spacecraft and ask it to decrypt the outer layer of encryption, using the private key corresponding to the outer layer's public key. It does that and you get back a message but it might still have several layers of encryption. Repeat until all those layers are removed.<p>There are tricks to speed things up by sending a spacecraft out towards Neptune, but they don't speed things up too much (because spacecraft travel much slower than light). The amount of speedup possible is left as an exercise for the reader. There's still a lower bound on the required time until full decryption.<p>Inspired by the TOR network.