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They're only there as an easy-to-read example, the library fully supports binary keys if that's what you're getting at?

A secure storage system shouldn't allow passwords as keys. If passwords are a thing that is going to happen, the API should be structured so that those passwords get run through a KDF. That's what he's getting at.

You're absolutely right.

PBKDF2 incoming.

You can do that, but a better API design is one that simply ensures keys are always random. KDF'd passwords are still weaker than real cryptographic keys.

A common design pattern is to use KDF keys as key-encrypting keys wrapping fully random keys. The system in steady-state relies only on the fully random key; the KDF key, depending on the design, can sometimes be kept offline. This is how SSH and GPG handle keys: note how the actual keys the system uses are fully random and totally out of the user's hands.

But you might not need any of this mechanism at all; it might be totally possible to design this system such that keys are simply blobs, generated via urandom by reading crypt.Rand.

I suspect the parent is wondering why it isn't using a KDF.

https://en.wikipedia.org/wiki/Key_derivation_function

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