deciphering someones personal journal?

[flamewolf393]

I want my character to keep a journal, but in a shorthand notation that only she understands, and leaving out a lot of detail. Its meant to be more of a reminder of things so she can transcribe into a real journal that is kept safe back home.

The point of this is because she is an infiltrator of cults and enemy ranks, but at the same time wants to keep a record of her deeds and motivations in case she ever has to explain anything worrisome to her superiors.

My question, is how difficult would it be for someone to decipher a journal like that if I get captured and they start going through my things? And is there anything simple I can do to make it more difficult?

[Rhunder]

I personally like switching letters so a=g b=h etc. It can be deciphered but it takes time. There's another thing you can do where the only way to read it is with a key and having random symbols. I forgot what that is called.

Writing in riddles is a safe thing to do since its for yourself later so you'll get the references. Like that guy with a fancy shirt in the third town I stayed at was a complete jerk. Only you and your party could possibly know what you are talking ab.

Than a combination of several codes is the safest way to go. Riddles, alternate letters, shifted through pig Latin, and then written backwards.

[BWR]

If you keep an obviously coded journal, it's going to look bad for you no matter what. The safest is the yugoloth route - a complex and pretty much uncrackable system of word and phrase substitutions that have specific meanings but which can't be extrapolated from what is actually written/said. Using different names for people, using different words, specific phrases for other things etc.. If done properly it can look pretty innocuous. If done improperly it is obviously hiding (http://www.youtube.com/watch?v=Qs_AebOXkAY) (ffw to about 11.30) something but you can't tell what.
Apart from that, the old system of writing normally but having every X letter be part of the important words is less likely to awaken suspicion. Unless you are unusually observant and seriously paranoid, this sort of thing is hard to detect, especially if you have irregular intervals between important letters, intentional misspellings, etc.

Mechanically, I'd go with a Linguistics roll - the PC has to make a roll (can take 20) and that's the DC for anyone who wants to crack the code. For a straight letter substitution code, that is.

[Firest Kathon]

There are two important questions here:

How do you hide the information? To make sure nobody finds it by accident, e.g. during a routine inspection or something similar.
How do you encrypt the information? The OP pointed out the situation that the character is caught (and not merely suspected), so hiding the fact that she did write something down is not that important anymore.


For the first point, beyond simply hiding the journal, I'll point to the Wikipedia article about Steganography (http://en.wikipedia.org/wiki/Steganography).
For the second point, we are talking about encryption. A simple letter-substitution will not stand up to any serious effort. There are non-technological encryption methods which would hold up even to (basic) computer analysis, such as the Solitaire cypher (http://en.wikipedia.org/wiki/Solitaire_%28cipher%29) (longer description (https://www.schneier.com/solitaire.html)). I'm sure there are others, but don't have the time to look for them now. Most secure would be a one-time pad (http://en.wikipedia.org/wiki/One-time_pad) (with the second copy stored safely at home base with the main journal), but you'd have to keep those hidden as well.

Combine both points for maximum security.

Edited to add:
From a mechanical perspective, I would make Forgery vs. Decipher Script (3.5) or opposing Linguistics (Pathfinder) checks. Let the encryption method give modifiers on the checks for the writer, maybe -5 for the Ceasar up to +20 for the Solitaire cypher. If the reader has indications/proof about the method used, give a +5 circumstance bonus. Writer may take 10, reader may take 20. Properly applied OTP would of course be unbreakable.

Let's put it to the test:
Writer: Lvl 5 rogue, 8 ranks, Int 16: +11
Reader: Lvl 15 Paladin, 18 Ranks, Int 14: +20

Using the Solitaire cypher, the writer takes 10 and gets 41. The reader takes 20 and gets 40, so the cypher is quite secure. If he had taken skill focus, he would have been able to decipher it. Looks good to me.

[Extra Anchovies]

Mechanically, I'd go with a Linguistics roll - the PC has to make a roll (can take 20) and that's the DC for anyone who wants to crack the code. For a straight letter substitution code, that is.

This. Remember, regardless of how you choose to encode it out-of-game, the method you use to code it in-game has to be something your character is smart enough to try. I think either Decipher Script or Speak Language Linguistics is the skill for this; maybe the code has a Decipher Script DC of 20+Int modifier+Decipher Script ranks+Linguistics ranks?

[flamewolf393]

I wasnt thinking of using actual codes and cyphers, but more of just a personally developed shorthand notation. Like abbreviating words, leaving out details, having a complete lack of context, maybe doing it in an obscure language I learned for this exact purpose, things like that.

I dont want to have to reverse crack an actual cypher, just have enough in it to keep the record of events straight in my own head to transcribe it to a real, safely kept journal later on.