Post-Disaster Postmen: Encrypted Mail without a Network

So I just posted my brief mention of the novel Dignity, which, again, is a series of letters by one character to the assorted communities built from the abandoned ruins of unfinished developments. The character, N, mentions a few times that he’s concerned about details being leaked to authorities. As such, and given my recent interest in cryptography, it makes me wonder why they’re just sending plain, unencrypted paper letters, delivered by random people going between communities.

Part of that is that they’re trying to ditch ‘screens’, including tablets and the like. I get that. But regardless of the message the novel is trying to convey, I don’t believe you could just make technology go away. The genie’s out of the bottle. And so the root of the following idea is based on having tablets, or e-book readers. They could be readily charged with solar chargers like are becoming suddenly very popular amongst the DIY electronics crowd.

The idea is this. Public-key encryption, with a quick and dirty directory of people’s public keys in a text file. Alice bashes out a letter to Bob with his public key as would happen with email today. A community then puts all of the mail together for a courier. It’s loaded onto a common USB thumb drive, and the courier moves between communities as it is. As these couriers encounter one another, they copy all of their correspondence with each other, so both have a copy. A little like a manual bittorrent. If one gets lost or stolen, the contents are safe.

Once it gets there, everyone gets a copy of all of it. Bob’s private key will only unlock his segment of the file, the rest will still be gibberish. And boom, Bob can read his mail securely. The public keys will be safe and pseudo-signed as legit… a community will be able to vouch for whomever has their key listed in the directory, and Eve wouldn’t get a chance to go into the community center, claim she’s Bob, and replace his public key with hers.

It’s not completely foolproof: Eve could intercept a USB drive, infected with a virus, and put back into the system. This could cause some problems but with the assumption that the end-devices aren’t connected to a network, it would be effectively impossible to cause remote exploits like giving away locations or sending keylogs back to Eve.

Anyway. This is all an extremely preliminary idea. Specifics… well, there probably won’t be specifics. These labs are half-assed, don’t you know. But this popped into my head as a more secure method than just plain paper mail. And I do like thought experiments along these lines, lately.