HDMI uses copy protection system called HDCP. And I have know for some years that HDMI copy protection broken. But based on recent information that has popped out it seems that it is even more broken that I thought that it was. Hackaday tells that HDMI breakout lets you sniff HDCP crypto keys and points to HDCP is dead. Long live HDCP. A peek into the curious world of HDMI copy protection… article for more details.
HDCP is dead. Long live HDCP. A peek into the curious world of HDMI copy protection… is interesting reading. It says that HDCP is thoroughly, comprehensively, irredeemably and very publicly broken. Normally, if something is this badly broken, particularly in the security world, at least some effort will be made to replace it with something that actually works. But still HDCP is pushed to users (because HDCP, although broken, cannot and will not be defeated by the general public).
The article has lost of interesting details to prove that HDCP is broken. The article shows how easy it is to exploit the vulnerabilities. Basically you just need a HDMI breakout cable (which is quite easy to build) and suitable logic analyzer to look at the data. HDCP key exchange is done over the DDC (Display Data Channel) that is basically an I2C serial bus, living on pins 15 (clock) & 16 (data) with ground on pin 17. A hdmi-sniff HDMI DDC (I2C) inspection tool tool can be found on the Aperture Labs tools page (it works with Bus Pirate).