DMs Guide to Cryptography

[TheElf]

Anyone can try to protect his secrets, even if he has to write them down. Magic users can use specialized spells for this purpose, but the rest has no access to theese spells, so they need a different method: Cryptic messages, specialized alphabets and similar tricks serve them well. But how can you make an encrypted note, and how your players can break the cyphers? The modern cryptography are based on complex mathematical formulas, and it is unlikely that it would work without computers. But there are some old methods. We can offer a guide for these tricks.

Secret alphabet: You can just use a secret alphabet. One sign for one letter, it is real easy to make, and it is real easy to break with the proper knowledge. Your players just have to check the most frequently used symbols, and they know, that they represent the most common letter in your language, and from that point, they have a good chance to decrypt the message. It is best for long messages, or a lot of different messages made using the very same alphabet. A short message is impossible to break in this way.

Hidden dictionary:

Want a harder cypher? It is easy: Just open a book, you can use as handout, and the words in the cryptic message should be replaced by a page number, and another number telling which word should be used from the page. You can encrypt the numbers in the way noted above, and you can use more books for this encryption. It is realy easy. Your players have a fair chance if they wanna break this cypher. You can make it a bit harder, if you use some more complex cypher. There are numerous tricks, like encoding letter pairs, or the difference between the two letters (in their position in the ABC), and so on. But making it harder to decrypt takes away some time, so it is best if you use the simple method detailed above, with time limits. Speaking about time limits: We will have a new house rule about time limits and intelligence soon.

[UncleDave]

Yes! I'm a bit of a fan of cryptography. Both of the ones described by Elf were commonly used. Heres a couple more.

Caesar code: also known in modern times as "kellogs code", this was a code supposedly used by Caeser himself, where you simply shift the characters of the alphabet a certain number of characters. for example, "hello" with a code shift of +1 would become "ifmmp". This is a simple code, easy to break, but better than nothing. It would probably be good enough to stop ogres or kobolds, if they can read in the first place!

Code talking: Its fairly well known now that the US used Navajo speakers to relay secret messages. This worked because so few people spoke the language. For extra security, the message could be encoded first, and THEN translated!

Steganography: You dont need to encrypt things to keep them hidden. You can hide a message inside another message. Remember "The Eagle has landed"? That's a simple example. Drug dealers have also been known to use this technique, speaking of selling carpets when they really mean drugs. But a truly impressive steganographer will take a genuine message and change the wording to include a hidden meaning. This may or may not be difficult to decode... but the really difficult part is realising that there is something there to be decoded in the first place!

I dont know if theres any rules about such a thing in d20. You would certainly need knowledge of cryptography to encrypt in any meaningful way, but you should get at least some chance to decrypt whether you have the skill or not.

Cheers!

[Tzeentch]

There are plenty of sites on cryptography, if you want to get into serious cryptography I'd recommend using more "underground" sites like www.neworder.box.sk

Then again here is a starter for the beginners:
http://www.cryptographyworld.com/

I find those good starting points for the masses

[TheElf]

I think modern day cryptography that depends on our current knowledge of math and also on the fact we have information in mostly digital format, makes it hard to use in most games, and in modern settings the characters can use tools to decipher texts and don't have to work on their own.