#4: Encryption and Data Hiding

[RPGnet Columns]

http://www.rpg.net/columns//hack//hack4.phtml

Summary:

How and what to encrypt, and why.

Go to the column (http://www.rpg.net/columns//hack//hack4.phtml) for more information.

[torbenm]

The Romans used a very simple mechanical encryption device: Sender and receiver both had identical conical rods. The sender would wrap a ribbon around his rod and write the message on the rod, across the ribbon edges. When the ribbon is unwound, the letters would be in apparently random order on the ribbon, but when wound on the receivers code-rod, it would be readable again.

This is, obviously, not that difficult to crack, but the Romans presumably relied on the idea that few interceptors would guess how the encryption was done. This is, btw, all too common even today: People rely on keeping the encryption algorithm secret in the hope that this will make it harder to crack. But it is difficult to keep such things secret, and if there is any undetected weakness in the algorithm (which is more likely if the algorithm is known to only a few people), your encryption is compromised.

One thing to note for games: The movie cliche of savants being able to "read" encrypted text directly is just that -- it doesn't work in practice except for simple substitution cyphers. Also, having even one instance of a plaintext/cyphertext pair is an immense help in breaking any code, so in a spy story, obtaining such a pair could be a good story hook.

[Clay]

That's a good story hook, and I'll have to put that up on my website (see signature).