The “key” is the mapping of cipher alphabet to message alphabet.
There has to be a secret to be cryptography. The meaning has to be hidden without the secret information (though primitive/weak attempts can have a small enough search space to be brute forced). But the content being hidden without that information is the entirety of what the word means.
no. replacement cyphers are cryptography, too.
The “key” is the mapping of cipher alphabet to message alphabet.
There has to be a secret to be cryptography. The meaning has to be hidden without the secret information (though primitive/weak attempts can have a small enough search space to be brute forced). But the content being hidden without that information is the entirety of what the word means.