What's the problem with `H(salt||H(pepper||password))`? If `H` is a good PRF, it should work fine (you want `KDF(salt, H(pepper||password))` to protect against

What's the problem with `H(salt||H(pepper||password))`? If `H` is a good PRF, it should work fine (you want `KDF(salt, H(pepper||password))` to protect against guessing attacks). In any case, if you pepper is exposed and you don't have a good pepper rotation scheme, you are no worse than if you started with no pepper at all.