Double key encryption is a simple method for sending encrypted messages while avoiding the key distribution problem. There is a very nice way to illustrate how double key encryption works, using pre digital age things:
Suppose Alice wants to send Bob a message written on a scroll. She can put the scroll in a box, lock it with a padlock and send to Bob, but then Bob must have a key to Alice's lock. On the other hand, if the box can be locked with two padlocks, this problem can be avoided - Alice will send the box to Bob, locked with her padlock. Bob will then lock the box with his padlock and send it back to Alice. Alice will remove her lock and send the box again to Bob who can now open it because it is locked only with his lock.
So how is this related to storytelling? well back in the days when the best place by the fire was kept for the storytellers, this was exactly how they were casting their spell. Sure, they had prepared narratives and moral messages, but when they sat with their audience and started telling stories, they became engaged in an interactive process. They would quickly adapt the story to the responses of the audience, replacing characters and objects with local ones, adding to the plot or omitting from it, based on the taste of those who listen. But the storyteller made sure, not to make the story too obvious. Only to bring it to a point where the listeners could decipher it with their own mental keys.
Now you might be asking yourself if the same principle can be applied to a written story, to a case where the writer has no direct interaction with the readers. Well the answer is yes. The published text represents the final phase of the process. It is the story, ciphered with the mental keys of the readers. Every writer knows that the interactive process is occurring in the earlier phases of the creative work, in the research phase, and in the development of the plot and characters. A writer should always think about the readers. Who are day? How am I going to engage them in deciphering my story?
In fact, this is what distinguishes a story from just any text, that it echos with the readers inner world. It is something that the human brain is wired to do very well. It's what enables us to interact in the unique way that we call, "culture".