How Do I Send You a Christmas Present, And Know You Won’t Open It Until Christmas Day?

How can we properly secure things? Well, we sure make the effort so large to crack them, that no-one could afford the effort to break it. If is takes me a little bit of work to change the clock on a computer, it is probably worth it to me to do it, if there is a good reward. But if I require to purchase all the computing power in the world to change something, it is probably outwith my budget. In a blockchain world, work load becomes a key test of the security of systems.

So let’s say that I do not trust anything, and especially not you! I don’t even trust the clock on a computer or on a network (as someone may change it).

How would I send you your Christmas present now, even though we have many days to go to the big day? I know that you will cheat and change the clock on your computer and reveal the present, so I need to stop that. And you are also sneaky enough to change the network time server clock. If I write a program to reveal an encryption key based on the time on the system, you are likely to open your present early.

I have a plan which will cost you a great deal of effort to break it.

Now I need an encrypted box with your present in in, and then I create a black box which has the encryption key in it. I now want…