The movie files in this case are not meant for consumers. They're only decrypted on specialised equipment not accessible to the general public. If you manage to get your hands on a DCP file there's nothing you can do to decrypt it without access to the specific projector system it was intended for (unless someone screwed up somewhere of course)
Sure, they make it look all secure, pass it through all that crypto and stuff but ultimately it has to be passed to the projector chip in some form which is unencumbered to be turned into light. At which point it's fairly trivial to dump. Anti-tampers on the case are probably fairly limited.
If they have been any kind of smart when designing them, the decoded stream takes a limited, shielded, and highly tamper resistant path to the projector chip, and each and every critical component are paired with each other such that switching one of the out automatically destroy all keys.
What tech is used on UHD consumer Bluerays?