Quote from: jago25_98 on July 30, 2012, 03:28:14 AM

Idea 2) Additional factor: Share the private key between 4 execs. 2 of the group are required to decrypt the code. 4 not 2 in case one of the pair dies.

Shamir's Secret Sharing Scheme (http://point-at-infinity.org/ssss/) can do this. You can split the private key into N encrypted secret strings and give them to different people. The original private key can only be reconstructed if X secrets are combined.

Quote from: jago25_98 on July 30, 2012, 03:28:14 AM

Idea 3) Time based auth. Have a factor that only becomes clear when a certain time happens. Hard to implement in practice? Could it be something such as how light falls on the earth or something stranger? How could this work in practice?

The closest thing I can think of to what you describe is having some third party only give you what you ask for at a certain time.

Another option that might be somewhat applicable is Encryption based on Time Reversal Transformations (http://comjnl.oxfordjournals.org/content/32/3/241.full.pdf (Skip to the Discussion section)). It's where you have some data, apply some rule to it to change it, and do that over and over again for X steps. There's no easy shortcut to skip steps. To decrypt it you would have to apply the rules in reverse and go through each step backwards until you got to your original data. This isn't measured in time exactly, because if you encrypt something on a slow computer, a fast computer would be able to reverse it quicker.