This answer to the question Can numbers be illegal? makes a good argument, and AFAIK it comports with the law. It follows other answers in observing that any piece of information can be encoded by numbers. Yes, there are pieces of information that are illegal to possess – e.g., child pornography, stolen intellectual property, financial numbers intended to commit theft or fraud. But it asserts, without reference to law, that if you don't know that application of the number your possession can't be illegal. So it begs the following two interesting questions:
Do information possession crimes always require mens rea?
I can't think of a circumstance in which one could be charged for a crime for possession without knowledge of the significance of the number. I know this is a "prove a negative" problem, but if anyone knows of a possession crime that does not require a guilty mind that would be noteworthy.
Is there a safe harbor for possession of an "illegal" number?
If you are found in possession of stolen property, even if you lack mens rea, you are not allowed to keep it. If you are found in possession of stolen data can you keep it if it also represents something you can possess?
E.g., if an encrypted version of your password database also happens to produce a JPEG-encoded image of child pornography, can you keep it if you show that you have a code that transforms it into information that is not child pornography?