original idea of Tobias Specht.
Objective: Having a dictionary in clear text in archive beside isolated catalogue.
the dictionary contains a hash of path+filename+...+salt and associate all necessary attribute used for a differential backup.
the target is to be able to do a differential backup based on an encrypted isolated catalogue without providing any key for that isolated catalogue.
Documentation has to warn the user about the risk, may it be very improbable of a hash collision and the consequences of such event.
More details in the discussion at the libdar_api mailing list in the thread "dar encryption - RSA" initiated by Tobias Specht