Jim,
I would like to offer a suggestion and a word of caution concerning F.J.B. suggestions for secure and private communications.
The suggestion is the computer media containing the data. Instead of trying to find a small thumb drive or a thumb drive in some nondescript package, one should look at the MicroSD card. These generally come with an SD card carrier and SD card writers are inexpensive and small. Once removed from the carrier, the MicroSD card measures only 11x15x1 mm (.43x..59x.04 inches) and is available in sizes up to 64 GB. This extremely small gadget can easily be hidden in clothing or elsewhere.
The warning has to do with encoding and decoding book ciphers. One method used by code-breakers is to look for word frequency using identical cipher text symbols, so the way to beat the code-breakers in this case is to use multiple cipher-text symbols for the intended word. In the example, the word safe was represented as 2-37-17. If that word or others were used multiple times in the message, or in different messages for that matter, this could give the code breakers a starting point. The way around this is to find the same word “safe” someplace else within the key books, so that perhaps 2-73-5 and 3-21-89 also reference the same word. The apparent randomness of the cipher-text makes it harder to break. – L.V.Z. in Ohio
JWR Replies: I agree with your warning on book codes. Just as with a “one time pad”, you should not use the same code sequence twice. If using a “book code”, simply draw a line through the word, so that you don’t use the same word position code again.