DCMA: You must use Ford Gas in Ford Cars or Else We Repo The Car

Or does the DCMA make my decrypting a DVD (which I own) using unauthorized software (i.e. not part of the consortium) illegal, period?

When someone sells you something (e.g., a phonograph, or phonograph recording) they can claim that the warrantee is void [1] if you use other than *their* parts (phonograph needles, licensed phonographs), but they cannot tell the govt that they are harmed by your use of unapproved gear. The DCMA folks need to understand this. Badly. [1] An OEM may not be always be able to void a warrantee for objectively bogus reasons, e.g., a car manufacturer probably couldn't get away with dropping a drive-train warrantee because you used generic oil that fullfilled published specs.