[moviuro]

The salt has to be random, and stored locally.

You propose a new hashing algorithm that does: IP -> h. If the salt depends on the IP, you can create a rainbow table offline.

If you can generate the salt on the machine (on the fly), you need an algorithm that must run on the machine - what do you base that on? Hostname? local IP addresses? Hardware?... And known_hosts(5) can't be moved to a new machine anymore, as it's tied to a machine.

[mikorym]

I think what I have in mind is essentially a customisation option. And I think your answer (and others) does make a good case that there is not a more general solution to this at the moment (and not even conceptually).

As a custom solution there are many ways to solve this if we introduce a third parameter (such as simply encrypting your files with a password). I think however the point that many people are making is that the debate is about what the default should be, and without introducing a third factor.

The two step de-hash case (IP hash + salt) suggests interesting research topics on whether there are ways to have other combinations e.g.: (IP hash + x) or (IP hash + x + y) but with the assumption that we don't want any further apriori information. The point that you are making is that in fact we only have one variable (the IP) and the salt is simply a obfuscation step. Any other approach requires more parameters (hardware, fingerprints, etc.).