The HDCP Master Key

Pastebin has the HDCP master key that we talked about in a post last week. This is the encryption protocol used for HDMI content protection on media such as Blu-Ray and High Definition cable television.

The master key array is a 40×40 set of 56-bit hex used to generate the key sets. You get one brief paragraph at the top of the document explaining what to do with this information. If you ask us we’re more interested in how this set was determined. So for some background information read the key selection vector (KSV) Wikipedia page. That points us to an interesting discussion proposing that if 40 unique device-specific KSVs can be captured, they could be used to reverse-engineer the master key. And finally, a bit of insight from a Reddit user (make your own decision on the dependability of this information) commenting on the value of having the master key.

In his comment, [iHelix150] covers the revocation system that HDCP uses to ban devices that are being used to circumvent copy protection. He says that having the master key makes it possible to push your own revocation lists onto devices. Each time a list is written to your device (TV, Blu-ray, etc.) the version number field for the list is updated. If you push an update with nothing on the revocation list, and set the version number to a binary value of all 1’s it will prevent any more rewrites of the list. This means that any previously banned hardware will be allowed back into the chain or trust.

So far this probably means nothing for you. But it’s fun to watch the cat-and-mouse involved in the DRM struggle, isn’t it?