There are multiple steps involved in establishing resilient communication between the MIG software in the Protected Environment and the graphics hardware.
1. Driver identity
The first step is that the driver is identity verified.
The Protected Environment software can now accept the driver on the system when playing premium content.
2. Diffie Hellman
Diffie Hellman is then used between the graphics hardware and vendor-supplied driver to establish the 2048-bit Diffie Hellman key.
This establishes a key that is known only to the graphics hardware and the driver. However, a man-in-the-middle attack has not yet been ruled out.
3. Hash to make session key
Next, the vendor-supplied driver passes the 2048-bit Diffie Hellman number to the Microsoft LDDM kernel-mode component that then applies an AES Davies-Meyer hash to produce the 128-bit session key. The graphics hardware also does an AES Davies-Meyer hash to obtain the session key. Neither the vendor-supplied driver nor the graphics hardware needs to remember the Diffie Hellman key (and it is actually preferable to forget it).
This establishes a session key that is known only to the graphics hardware and the Microsoft LDDM kernel-mode component. A man-in-the-middle attack has still not yet been ruled out.
4. Seeded HFS
Next, the graphics driver performs HFS, exercising some complex internal workings of the graphics chip to authenticate the graphics hardware. It uses some of the bits from the Diffie Hellman number as a seed value to tie together the authentication with the Diffie Hellman process, to mitigate man-in-the-middle attacks.
The graphics driver now trusts that the graphics hardware is genuine. It is now known that the Diffie Hellman process was not subject to a man-in-the-middle attack, so therefore the session key is OK.
5. Driver certificate
Next, the ProtectedDXVA software component checks the PVP-UAB certificate in the driver, to establish trust that the driver is genuine and conforms to all the PVP-UAB requirements.
The MIG software can now trust the graphics hardware.
6. Content key delivery
Next, the ProtectedDXVA component creates a content key and sends it to the graphics hardware whenever a new one is required for a new premium video stream. It sends it by having the Microsoft LDDM component encrypt the content key with the session key.
Now the content key is known to the ProtectedDXVA software component and the graphics hardware.
7. Content encryption
Finally, the ProtectedDXVA component encrypts a premium video stream using the content key, and then streams this to the graphics hardware, where it is decrypted on receipt.
The premium content has now been safely delivered from the MIG Protected Environment to the graphics hardware.
PVP-UAB Architecture - simplified view of the components that make up PVP-UAB
| 