Bengt is working on a little nuclear thing in his basement, and it's making him a bit paranoid. He's sure that shady government agents and whatnot are spying on him. For this reason, he needs a secure way to send messages to his "contacts", as he says. Now, there are various useful methods for encryption, so that should be doable, but Bengt is afraid the "agents" will capture him and force him to give them the key. So, what he needs is a way to encrypt
two messages to the same cipher text - one real, and one innocuous, so that if he is questioned, he can give them the second key, and they will find the innocuous message.
We can assume that Bengt and his contact - let's call her Alice, shall we - are able to meet beforehand and exchange keys, if need be. After that, they need to be able to send several messages only using channels where the "enemy" can read. All the data has to be possible to interpret as an innocuous message.
- What methods can you think of for doing this?
- What if they can't meet beforehand, and every message sent has to have this double-encryption quality?
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