Say you have computer files
you want no-one to see. You could use PGP
or a similar program to encrypt
them, however if someone breaks into your house and makes a copy of the PGP file, they might be able to eventually break it, and you'll never know, because you'll get back to your house and see the file is still there.
What you can do, is this:
1. Generate enough truly random numbers, from 0 to 255. (Enough in this case is the length in bytes of the file you wish to store, and "truly random" means not using a pseudorandom number generator, but rather, either a hardware solution which measures radioactive decay, or software measuring something such as hard disk times / webcam input- point the webcam at a lavalamp or something)
2. Store these numbers on a disk.
3. XOR the file with these numbers, and store that on a separate disk.
You now have two disks with what is essentially random data on them. A person wanting to view your top-secret file needs both disks in order to decrypt the data.
So you keep one disk in a vault (or other place where it is unlikely to be found), and the other disk on your person, at all times. Do not let it out of your sight, ever.
If someone tries to mug you for the disk, try your best to destroy it. If you can't do that, get to the other disk as soon as possible and destroy that. (This is of course assuming that the data is better destroyed than seen by others)
Once one of the disks has been destroyed, the other just contains random data. So the information is theoretically lost forever.
If, by some weird coincidence, you don't get mugged for the disk, and you want to view the data again, you get both disks, and XOR the contents together. This will produce the original data.