[throwawaymath]

This is a great comment, but I just want to point out:

> Bcrypt is not a KDF and not a hash function

This is true, but it's also a good example of what I was saying in my other comment. bcrypt is an example of a password hashing function which is not itself a KDF, but which can be used to construct a KDF.

All password hashing functions can be used to construct key derivation functions or simply are key derivation functions. But not all password hashing functions are key derivation functions. Whether or not it would be advisable to use a given password hashing function as a KDF depends, of course. In bcrypt's case you can construct a reasonable KDF. For example: https://github.com/pyca/bcrypt/blob/master/README.rst