Drupal 6 Module Storing configuration setting in file
The Question was not so clear to me but I can suggest you 2 things.


You can use variable_set('salt', 'unique_hash'); in the .install file in hook_install(). Then this variable will be stored in the variables table. In hook_uninstall() you add variable_del('salt'); So this will remove the variable from the table if the module is uninstalled. You can access it via variable_get('salt', 'default_value'); Also if you want to change it then make a form text field and in the hook_submit for that form make a variable_set('salt', 'edited_value') call. This will update the variable in the variables table. Use user_access() to restrict all users to access it. 
The second is, to make a text file in the server file system and make it's permission as 644. Then read the file by php's fread() function and access the file value.