It is interesting to have a mystery about cryptography.

But I think many mysteries misunderstand the meaning of "code" -- something both authors and readers know, of course.

A cipher is a message that

(1) can only be carried in a way that is open to the entire world,

yet

(2) can only be decrypted by a specific person.

If the public message in (1) above contains the decryption hint in (2), the cipher cannot achieve its purpose.

Also, if it is something that can only be deciphered by the qualities (abilities) of the person, it is not a cipher because it is not a message to a specific person.

And if no one can decrypt it, it is not even a "cipher." It is just a string of characters.

In other words, in a strict sense, the ciphers that appear in novels, dramas, and movies are not 'ciphers.

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I am watching a digest of the drama "Not to Mention Mystery" on YouTube.

All I know is that 'I shouldn't talk about these things to people I'm watching drama with,' much less 'I shouldn't talk about the principles of the RAS cipher in a way that I'm good at.