Book Code for Prime Base

[tsofian]

As I rewrite Prime Base I'm considering using a book code to provide clues to the players. To be effective the code needs to reference a text that the characters will be able to access but that it is far less likely that the bad guys will have handy. I am considering the semi official goals of the Project.

Help the People
Contact Other Morrow Teams
Try and stay alive

This has acehilmnoprstvw, so doesn't have every letter. It might be rejected out of hand by none project cryptographers for that reason alone. Plus although it is a long running in character in game set of statements I'm not sure it would be written down that much in Project documentation.

Is it too obvious? Is it too obscure?