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So in general, isn't this equivalent to what Bcrypt and PBKDF2 do in terms of password storage security? PBKDF2, yes, pretty much. The only real difference is that salt/password are used the other way around, with the password mixed in at every step. Bcrypt, however, is different. In your case an attacker only needs a small amount of memory compared ...


Although your scheme is secure - especially with a random key of 32 bytes or higher - it won't offer any benefit over HMAC. It's therefore not recommended to use such a scheme. Also note that `bcrypt has been designed for key stretching which is deliberately not efficient. You have ample entropy in your key so there is no need for key stretching.


The question is how much is this schema secure? Not significantly more secure than sha256(m + k) is and may be less secure. An attacker who could arrange a collision for that would trivially also get a collision for the bcrypt hash of that, regardless of the salt value. While SHA-256 is collision resistant, there are MACs that have better bounds, like ...

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