cryptography is as simple as putting numbers,letters, made up symbols on a piece of paper, or a sign, and then making a rubric for what those symbols mean ( the secret or secrets). those who have the rubric, are thus the 'keyholders' that can decipher the meaning behind the characters.

2 kids making a secret language to pass notes at school only they can read is cryptography

an inside joke between two friends at a party that only they get is cryotography

sharing secrets without publicizing the meaning behind the message