I have an old site running Osclass 3.9.0 and imported to the new vers 8x install

All my passwords no longer work.  No admin, no users.   

So what changed.   Is there a way to edit the PHP files to use the old passwords?   I see a place where it sets a has to an environment variable.  Is this set in a db someplace?

Hash may use some newer library, but I don't recall there should be any such impact.
It would be mentioned in changelog