Doom9's Forum - View Single Post - Understanding AACS (including Subset-Difference)

xyz987 · 5th March 2007, 02:45

Well, i have read the whole thing about HDDVD Segment Keys, and it is just a system to determine which Sequence Key was used to decrypt a movie, so it doesn't affect to an attacker who publishes just one Sequence Key.

Segment Keys are just to face the problem of an attacker publishing a decrypted movie (not the key, but the movie). AACS needs to know which is the Sequence Key that has been used to decrypt it, so some frames of the movie vary slightly from a Sequence Key to another, so AACS LA can know which SK was used to decrypt a pirated movie available on Internet.

Nothing of this affects our attacker. He is publishing his SK (just one), so AACS LA knows which is the compromised SK anyway.

BTW AACS LA guys have designed a far good system. Segment Keys give them 62-63 bits of information about the Sequence Key (hence they use 6 SKBs), and a Sequence Key is 64 bit long.

Edit: BluRay is also using 6 SKBs (section 6.2.1 of BluRay Prerecorded spec).

5th March 2007, 02:45	#133 \| Link
xyz987 Registered User Join Date: Dec 2006 Posts: 142	Well, i have read the whole thing about HDDVD Segment Keys, and it is just a system to determine which Sequence Key was used to decrypt a movie, so it doesn't affect to an attacker who publishes just one Sequence Key. Segment Keys are just to face the problem of an attacker publishing a decrypted movie (not the key, but the movie). AACS needs to know which is the Sequence Key that has been used to decrypt it, so some frames of the movie vary slightly from a Sequence Key to another, so AACS LA can know which SK was used to decrypt a pirated movie available on Internet. Nothing of this affects our attacker. He is publishing his SK (just one), so AACS LA knows which is the compromised SK anyway. BTW AACS LA guys have designed a far good system. Segment Keys give them 62-63 bits of information about the Sequence Key (hence they use 6 SKBs), and a Sequence Key is 64 bit long. Edit: BluRay is also using 6 SKBs (section 6.2.1 of BluRay Prerecorded spec). Last edited by xyz987; 5th March 2007 at 03:01.