How to ensure that a file can only be decrypted after a specific date?

Technology CommunityCategory: CryptographyHow to ensure that a file can only be decrypted after a specific date?
VietMX Staff asked 3 years ago

I have seen this done for video game releases. Customers are allowed to download an encrypted copy of the game in advance. Then, when the release time comes, the game company simply releases the key. That way, people can start playing immediately when the game is released, without needing to wait for a download.

Or (all answers are valid):

  1. You may be interested inĀ time-lock puzzles. The idea is to be able to make a problem instance that is easy to build but expensive to open, where the cost is configurable. Of course this does not guarantee a release at a specific date; rather, it guarantees a minimum effort to unlock the puzzle. Conversion between effort and date depends on how hard attackers try. In other words, if an attacker wants to get your file earlier, he just has to buy a faster computer.
  2. Time is relative, but the speed of light is absolute. Put the decryption key sufficient distance away from the attackers. No powerful computer can overcome that. For example, you can use a mirror at some x/2 light years away, and then transmit the key to that mirror. Assuming no-one is able to sniff/disturb it, you’d have the appropriate delay of x years.
  3. Carefully place a spaceship broadcasting the decryption key in orbit around a black hole. The pull of gravity will delay the message until the appropriate time.