Explain how Cookie key and passwords work together in Prestashop

[ameagher]

Hi,

I've been having some problems with Prestashop when I move to a new server!

It relates to this post:
http://www.prestashop.com/forums/viewthread/3352/installation_configuration___upgrade/settings_dot_inc_dot_php_problems

I have tried the remedies and the second solution, removing the cookie key, seems to work .... for a while .... then I get a 500 Internal Server Error.

I would like to know the reasoning behind how the cookie/password/md5 works.

If there is a general reference to this I would be happy to read up on it, if not could someone please explain the process so I can put this to rest once and for all?

Many Thanks,
Anthony