At what layer to hash a password

[Robin Wood <robin () digininja org>]

When developing a web app using a presentation (html generation not
browser side), application and database layer approach at what level
should you encode a password that is on its way into a database? I'm
generally thinking of hashing as the main encoding method but anything
could be used.

If you go for presentation layer then you could end up needing to
update multiple areas of the code if you change the encoding method
changes. You can pass this off to a function but in some situations
you could still end up having to make multiple updates. The advantage
of this layer is that the password is protected for its whole journey
down the stack and into the database so even if it leaks in a debug or
error log for example the plaintext isn't leaked. You could also have
a problem if you use multiple different presentation layers keeping
them all in sync and ensuring they all have the correct functionality
to perform the encoding.

At the other end if you do the encoding at the database layer then you
only have a single point to change to update the algorithm so this is
better from a coding point of view but there is the potential for the
password to leak out on its way there.

This leaves application layer, might be the best as you can pull all
the setting calls into a single place but there is still chance of
some leakage.

I prefer the presentation layer from a security point of view but from
clean coding I'd rather do it at database layer the same way I encode
timestamps to what will go into the database at the last minute.

What do other people think?

Robin



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