Firstly DCPs are not wrappers that contain MXFs. From what I remember DCP predates MXF.
From memory (its been 8 years since I've actually dealt with creating them) They are effectively zip files that contain JPEG2000, lots of metadata and some sound tracks.
Crucially, the authoring and encryption are controlled by a central authority. Each projector needs to be registered with a KDM to make sure it can receive decryption keys. http://www.artsalliancemedia.com/software/screenwriter#featu... is one system for managing projectors.
Getting a distribution DCP is pretty hard, also Keys are short lived. But, someone people create non-encrypted DCPs for various purposes.
If its a MXF, then that suggests its either from a finishing house, or more likely a producer's laptop. (ie how wolverine got leaked, a pissed up producer leaving an unencrypted laptop on a plane. Even though their flight was pointless, as there are many remote viewing systems about. )