CSS Module
6-9
6.3 CSS Module
The CSS module descrambles encrypted data stored on DVD discs. It
can accept DVD data from both PC DVD drives (2048 bytes/sector) and
stand-alone DVD player drives (2064 bytes/sector). In PC DVD drive
applications, the CSS module generates random number sequences in
the form of challenge and response data for disc key and title key
authentication (see Sections
6.3.1 and
6.3.2). Following disc key
extraction and title key decryption, the CSS module descrambles
audio/video data from the DVD disc at a rate of one byte every four
system clock cycles. In stand-alone DVD player drive applications, the
title key decryption period is 12 bytes/sector prior to DVD data
descrambling and continuous transfer for decoding (see
Figure 6.12).The CSS module features ve programmable operating modes
(Register 178, bits [2:0] in Section
4.3). These include:
Bypass Mode
Disc Key Extraction (DK) Mode
Audio/Video Descramble (AV_Desc) Mode
Disc Key Authentication/Extraction (Auth_DK) Mode
Title Key Authentication/Decryption (Auth_TK) Mode
The Bypass Mode is the default mode wherein the CSS module is
bypassed for decoding nonencrypted DVD data. For PC DVD drive
applications, the CSS module descrambles DVD data in the Auth_DK,
Auth_TK, and AV_Desc modes (see Sections
6.3.1 and
6.3.2). When
descrambling data from a stand-alone DVD player drive, the CSS module
operates in the DK and AV_Desc modes (see Section
6.3.3).The CSS module can generate eight distinct host interrupts for reporting
event status and errors (see Register 176 in Section
4.3). Its internal
registers can also be software reset to default settings without affecting
other L64021 registers and without erasing decrypted disc and title keys
(see Register 178, bit 3 in Section
4.3).6.3.1 Disc Key Authentication/Extraction (PC DVD Drive)
Figure 6.6 contains a control ow by which the disc key is authenticated
and extracted from a DVD inserted into a PC DVD drive. Bank switching
for Registers 180 through 189 is applied to meet the challenge/response
data order restrictions of the PC DVD drive. This contol ow is presented
from the perspective of the host.