The MKB is encrypted in a subset difference tree approach. In order to decrypt it, a device must know the right Processing Key (P) which is available via the subset-difference tree process.Essentially, the set of Device Keys are arranged in a tree such that any given Device Key can be used to find lower level Processing keys. The processing keys at higher position in the tree than the given set of Device Keys are not reachable.A given set of Device Keys give access to a given set of Processing keys, it is to say to a given set of decodable MKB.
