As for real time-release - how about just using conventional encryption, and require it to be brute-forced?
Depending on how fine grained you want the release to be, you could also take the inverse of Moore's law, work out how big a key you need to have it unbreakable in less than the desired time, add in whatever fudge factors you feel like based on how much it would be worth to the opponent to get early access, then lock up the secret and throw away the key.
The problem here is that it is probablistic when they are going to be able to unlock it. If the search space will take a total of 10 years to exhaustively search, there is a 50% chance that they will find the key within 5 years, 10% chance that it will be found in 1 year, etc. So, if you are lucky, it will be found in about the time you want it to be. If you aren't it will be found in a few milli-seconds. There is also the problem that your intended recipeient will need to expend just as much work as your advesary to decrypt the message. This might not be a disadvantage in the case of a "broadcast" message, but otherwise it might be. Good idea - but I would say not pratical.... Now, if we just had an objects between 1 and 10 light years away that you could bounce lasers off of...... ;-) Dan ------------------------------------------------------------------ Dan Oelke Alcatel Network Systems droelke@aud.alcatel.com Richardson, TX