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Old 12-03-2004, 09:02 PM   #1
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can any one give a hand on CSS problem(Content Scramble System)

Hi folks, I am doing a CSS research now, but having a problem for a long time which still can not find the answers of it, I just wonder that does anyone knows about this?

1 problem :In CSS encryption, it used 2 LFSR to produce the random bits stream, and XOR with the plaintext to generate the ciphertext, but every LFSR has a period in which can only generate serveral unique key stream bits, and after this period, repeated bits stream will appear, so how do you know the plaintext has the same size as the random bits both LFSRs can generate since the LFSRs can only generate certain amount of random bit stream? what happen if the all the plaintext have not been encrypted and both LFSRs already finish to generate all the random bits?

2 problem: for 2 LFSR, it is initialised by the bits which are XORed between the first 5 bytes of the title keys and the sector keys, the question is that where are those two keys come from? are there come from the actual data of the DVD? if it does, in which part of DVD it resides.

3 problem: when try to play the DVD, it uses the player key to decrypt the disk key on the DVD, the player key of the DVD is assigned by the manufactory when produce the DVD, so how about the disk keys on the DVD, where is it come from then? furthermore, the disk keys are used to decrypt the title keys, but when CSS scramble the DVD, the title key in the DVD wasnt encrypted by anything? so why need a disk key to decrypt it?

4 problem: for CSS, it has 4 modes, each of which might or might not use the bit-wise invertor as follows:
Mode LFSR-17 LFSR-25
Authentication Yes No
Session Key No No
Title Key No Yes
Data Yes No
why is that? how is this come from?

5 problem: for CSS, there are someways to hack it, such as it uses 40 bits key, so brute force can easliy breaks, so why didnot the people use brute force to break it rather than hack the player key from the DVD produced by XINE? and are there any other ways and hack the CSS?

If anyone knows about this, please tell me as much as you can, I do need this in a hurry~~~ Thank you very much


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