WO2008106691A1 - Dvd download - Google Patents

Abstract

In one embodiment, a method of configuring a DVD-R formatted recorder to record 2X wobble discs is provided that includes: configuring a wobble PLL within the recorder to lock on the first sub-harmonic of a wobble input signal from the 2X wobble disc to produce a wobble clock output signal; determining whether the wobble clock output signal is phased properly so that the recorder may decode land prepit (LPP) addresses; and if the wobble clock output signal is not phased properly, unlocking and relocking the wobble PLL.

Description

DVD DOWNLOAD

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/892,466, filed March 1, 2007, U.S. Provisional Application No. 60/892,471, filed March 1, 2007, and U.S. Provisional Application No. 60/938,396, filed May 16, 2007. The contents of these three applications are incorporated by reference in their entirety.

TECHNICAL FIELD The present invention relates generally to digital rights management. More particularly, the present invention relates to the secure access of storage mediums.

BACKGROUND

Digital content such as movies stored under the Digital Video Disc (DVD) format represents a considerable source of profits to a content provider such as a studio. For example, it has been estimated that approximately 50% of a DVD purchase price represents the costs of manufacture, distribution, and promotion such that the profit margins on DVD sales range from 50% to 60%, a considerably higher profit margin than that developed during the era of VHS sales. To protect such valuable property, the content scrambling system (CSS) was developed under the control of the DVD Copy Control Association. All conventional read-only DVDs (DVD-ROMs) are encrypted according to the CSS protocol using a 40-bit title key. It has since been shown (through the efforts of hackers who cracked the CSS encryption and published programs that decrypt CSS- protected content) that 40-bit keys are not very robust in that even brute force attempts to crack such encryption may be performed relatively quickly using conventional desktop computers. However, at the time the DVD format was developed, U.S. government export controls limited the export of more-sophisticated encryption protocols. Although not very robust, the CSS standard has been very successful in that many millions of DVD-ROM players have been sold that practice the CSS protocol. Under the CSS protocol, every DVD-ROM player has a subset of 409 available player keys. The DVD-ROM content is encrypted according to the title key. The title key itself is encrypted according to a disc key that is itself encrypted according to a media key block. Conventional DVD-ROM discs have their media key block in a lead-in area of the disk. Each media key block has a table having an entry according to each player key such that each entry in the table corresponds to a hash of the disc key with the corresponding player key. A DVD-ROM player may thus read the appropriate entry in the media key block (corresponding to player keys the player has been instantiated with) and recover the disc key through an appropriate hash of the table entry with the player key. Another entry in the media key block represents a hash of the disc key itself so that the player may verify it has correctly recovered the disc key by performing this self -hash of the disc and checking the results against the corresponding media key block entry. Having recovered the disc key, the DVD-ROM player may then read the encrypted title key and recover the title key using the disc key, whereupon the DVD-ROM player may begin decrypting the corresponding video content so that it may be displayed to a user. Recordable DVD formats have also been developed. For example, DVD-R,

DVD+R, DVD+RW, and DVD-RAM are all formats recognized by the DVD forum. However, to protect their valuable DVD-ROM sales, these formats are not compatible with conventional DVD-ROM players. In other words, a user may burn a DVD-R (for example) disc but such a disc cannot normally be played on a DVD-ROM player. This is because all recordable DVD formats record their data on a grooved disk that is modulated in sinusoidal fashion so that a drive can read and compare it with a timing signal for precise rotation of a disc. The DVD-ROM format, on the other hand, has no wobble. This incompatibility ultimately represented a problem for the DVD industry because the growth rates for DVD sales have matured. Seeing the success of the growing music download business, the DVD industry realized that the downloading of DVD-formatted content could bolster flagging DVD sales. However, there was a built-in impediment to such downloading in that existing DVD recorder/players were incompatible with CSS recording. As a result, the DVD forum promulgated a DVD Download Disc for CSS Managed Recording (DVD- Download) standard. Under this standard, special DVD-R discs were created that have a "2X" wobble frequency (0.2814 MHz) that is twice is fast as the standard DVD-R wobble frequency of 0.1407 MHz.

Although the DVD-Download standard thus allows content providers to begin to grow sales analogous to the growth enjoyed by the music download industry, a problem arises in that the conventional DVD-R system-on-chip (SOC) used within DVD-R recorders is incompatible with the DVD-Download system. Thus, a manufacturer must produce a custom SOC to support the DVD-Download standard, which is a very expensive undertaking. Accordingly, there is a need in the art for cost effective adaptations of conventional DVD SOCs to support the DVD-Download standard. In addition, another problem arises in that a CSS-compatible format such as the

DVD-Download format requires each disc to have the appropriate media key block. It is cumbersome and expensive for the disc manufacturer to create blank media-key-block- containing-DVD-Download-compatible discs before shipping to an end user, who would then record the disc using a DVD-Download-compatible recorder. Accordingly, there is a need in the art for media key block initialization procedures for DVD-Download- compatible recorders. SUMMARY

In accordance with one aspect of the invention, a method of configuring a DVD-R formatted recorder to record 2X wobble discs is provided that includes: configuring a wobble PLL within the recorder to lock on the first sub-harmonic of a wobble signal from the 2X wobble disc to produce a wobble clock output signal; determining whether the wobble clock output signal is phased properly so that the recorder may decode land prepit (LPP) addresses; and if the wobble clock output signal is not phased properly, unlocking and relocking the wobble PLL.

In accordance with another aspect of the invention, a method of configuring a DVD-R recorder to record 2X wobble discs, the DVD-R recorder including a wobble PLL having a square wave input is provided. The method includes: providing a phase-locked loop to lock to a 2X wobble signal; dividing a output from the phase-locked loop by two to produce a square -wave IX signal; and providing the square-wave IX signal to the wobble PLL so that the wobble PLL may lock to the IX square-wave signal to produce a IX wobble clock output signal.

In accordance with another aspect of the invention, a method of initializing a 2X wobble disc at a DVD-R recorder is provided that includes: generating a pseudo-random number; generating a disc key from the pseudo-random number; retrieving a plurality of player keys from a memory; generating a media key block using the player keys and the generated disc key; and writing the media key block to the 2X wobble disc.

In accordance with another aspect of the invention, a method of initializing a 2X wobble disc at a DVD-R recorder is provided that includes: generating a random number; selecting a disc key from a stored plurality of disc keys based on the random number; retrieving a plurality of player keys from a memory; generating a media key block using the player keys and the selected disc key; and writing the media key block to the 2X wobble disc. These and other aspects of the invention will become more apparent from the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the relationship between a IX wobble signal and the land prepits

(LPPs) and the resulting wobble clock for a conventional DVD-R disc. Figure 2 illustrates a phase-locked loop (PLL) configured to lock on the first subharmonic for operation within a DVD-R DVD Download recorder according to an embodiment of the invention.

Figure 3 illustrates the relationship between a 2X wobble signal and the land prepits and the resulting wobble clock as derived by the PLL of Figure 2. Figure 4 illustrates 2X wobble circuitry that may be added to a conventional DVD-

R recorder to enable recording on 2X wobble discs.

DETAILED DESCRIPTION

Reference will now be made in detail to one or more embodiments of the invention.

While the invention will be described with respect to these embodiments, it should be understood that the invention is not limited to any particular embodiment. On the contrary, the invention includes alternatives, modifications, and equivalents as may come within the spirit and scope of the appended claims. Furthermore, in the following description, numerous specific details are set forth to provide a thorough understanding of the invention. The invention may be practiced without some or all of these specific details. In other instances, well-known structures and principles of operation have not been described in detail to avoid obscuring the invention.

As discussed earlier, both the DVD-R and DVD+R formats use a wobbled disc (as do other recordable DVD formats). However, the DVD-R and the competing DVD+R differ on how the player/recorder determines the position of the laser beam on the disk. In the DVD-R format, special lands denoted as land prepits (LPPs) are formed on every other wobble as shown in Figure 1. These prepits are absent in the DVD+R format. In a conventional DVD-R player-recorder, an optical pickup unit (OPU) includes several photodetectors so that a push-pull signal may be formed (among other optical signals such as focus error signal and a tracking error signal). This push-pull signal will be denoted as a wobble input signal in the following discussion. Because the sinusoidal wobble signal is noisy, conventional DVD-R systems typically process the raw sinusoidal wobble signal through a non-linear circuit such as a comparator to form a square-wave wobble signal. A tracking circuit such as a phase-locked loop locks to the square-wave wobble signal to generate a wobble clock such as wobble clock 100 illustrated in Figure 1. Because the wobble clock results from a locking synchronous with the IX wobble signal, each positive zero crossing of the wobble clock is synchronous with the positive zero crossing of the sinusoidal IX wobble signal. Each LPP is located 90 degrees (a quarter cycle) before the positive zero crossing of the IX wobble as shown in Figure 1. This relationship is expected by a DVD-R SOC - in other words, a DVD-R SOC expects to detect each LPP before the positive zero crossing of the wobble clock. However, if the PLL locks to a 2X wobble signal, such an expectation is violated.

To provide a solution so as to allow a conventional DVD-R SOC to record on a 2X wobble DVD Download disc, the firmware of the DVD-R recorder player is programmed such that the voltage-controlled oscillator (VCO) in the PLL operates at ¹A the frequency seen in the wobble signal. For example, a typical DVD-R SOC will have a circuit such as a register that controls the nominal frequency relationship between the wobble input signal and the VCO output signal. The SOCs firmware may be programmed to write to this register so as to create the desired nominal frequency relationship as will be discussed further. Most PLLs can operate in a phase-only mode wherein the PLL' s phase detector will measure the phase error of the nearest zero crossing (of the push-pull signal) relative to the divided-down VCO clock output signal. To effect a lock to the desired sub-harmonic, the SOCs firmware may first allow the PLL to lock onto the 2X wobble input signal. In such a case, the nominal frequency relationship between the input and output frequencies for the PLL is 1:1. The SOCs firmware would then force a nominal 2:1 relationship between the input and output frequencies though, for example, a write to a register that controls the VCO's nominal operating frequency. Because the PLL's VCO is then nominally set to operate at Vi the actual wobble frequency (2X wobble), the PLL should lock to the first subharmonic (IX wobble) of the wobble input signal. Turning now to Figure 2, a PLL 200 is illustrated that receives a wobble input signal 205 that is obtained from a DVD Download disc (thus oscillating at 0.2814 MHz or 2X wobble frequency). Because the VCO within PLL 200 is programmed to nominally operate at Vi the wobble input signal's frequency, a VCO output signal 210 feeds back to the PLL as a reference signal Fref oscillating at a IX wobble rate (0.1407 MHz). The VCO output signal may thus form a IX wobble clock that is processed by the SOC in a conventional fashion. It will be appreciated that PLL's generally have two modes of operation. In a first mode of operation, the PLL uses a phase detector to compare a feedback signal derived from the VCO output signal to the wobble input signal. In a second mode of operation, the PLL uses a phase/frequency detector to compare the feedback signal to the wobble input signal. A phase detector mode of operation would be desired for 2X wobble operation because such a mode of operation makes the PLL insensitive to media imperfections that produce extra or missing cycles in the wobble input signal. A 2X wobble signal is illustrated in Figure 3. In the DVD Download format, an

LPP is encoded on every other cycle of the 2X wobble. It may be seen that a IX wobble clock 210 as discussed with regard to Figure 2 has the proper phase relationship with each LPP in that each LPP occurs 90 degrees before a positive zero crossing of IX wobble clock 210. However, note that PLL 200 could have locked 180 degrees out of phase with the relationship shown in Figure 3. Thus, whereas Figure 3 shows each LPP 45 degrees before the positive zero crossing of IX wobble clock 210, an equally valid lock for PLL 200 would have each LPP occur 225 degrees before each positive zero crossing. To place the LPP in the desired phase relationship of 90 degrees before each zero crossing (as discussed with regard to Figure 1), PLL 200 is programmed so as to produce a 45 degree phase shift in IX wobble clock 210. The two possible LPP positions would thus be either -90 degrees or -270 degrees with respect to each wobble clock positive zero crossing. Because the standard SOC expects the -90 degree relationship, such a phase relationship is compatible with conventional DVD-R address decoding of the LPPs. At -270 degrees, however, the standard SOC will typically fail to decode LPP addresses. The DVD-R recorder/player firmware may thus be programmed to unlock and relock the PLL (through, for example, a toggling of an acquire/track signal 215 shown in Figure 2) until valid prepit addresses are decoded. Alternatively, the prepit address decoder in the SOC could be programmed (through an appropriate change in the firmware) to operate at -45 degree (such as shown with regard to Figure 3) rather than at a -90 degree window as discussed with regard to Figure 1. In such an embodiment, the SOC may still be programmed to unlock and relock the PLL until valid prepit addresses are detected since a -45 degree detection window would fail if the prepits were locked at -225 degrees with respect to the IX wobble clock positive zero crossings. Rather than have a PLL lock onto the first sub-harmonic, an external divide-by-2 flip-flop could be used to divide down a square-wave version of the 2X wobble signal. To interface with this external circuitry, an existing SOC must have the necessary input pins or pads. For example, it is common for an SOC to provide an output pin that carries the square-wave wobble input signal that would ordinarily be provided to the SOCs wobble PLL. In addition, it is common for an SOC to provide an input pin such that a user may force the SOCs wobble PLL to lock to a test signal provided over this input pin rather than to the square-wave wobble input signal that it would ordinarily otherwise lock to. To provide this externally-provided input signal to the existing PLL within the SOC, an external PLL 400 may be provided as shown in Figure 4. This PLL 400 receives the square-wave wobble input signal oscillating at the 2X wobble frequency to provide a 2X wobble square wave VCO output signal 405. PLL 400 runs in a phase-detector mode of operation through a track command from the SOCs firmware so as to filter the square- wave wobble input signal so that extra/missing wobble cycles (which will typically occur occasionally due to media imperfections) do not upset the resulting wobble clock. It will be appreciated that PLL 400 may also have a phase/frequency detector mode of operation if the SOCs firmware drives PLL 400 with an acquire command. Thus, the firmware should drive the acquire/track command input to PLL 400 so that it operates in a phase only mode during write operations but initially locks in a phase/frequency mode to prevent locks to a harmonic of the square-wave 2X wobble input signal. A divide-by-2 flip-flop 410 receives a VCO output signal 405 from external PLL 400 to produce a filtered IX wobble clock signal 415. Assuming that a DVD SOCs wobble PLL has a provision to lock to an externally-provided signal, the SOCs wobble PLL (not illustrated) may lock to square wave signal 415 so as to operate in a conventional fashion. As discussed previously, the resulting IX wobble clock may be correctly phased or it may have locked 180 degrees out of a desired phase relationship to the LPPs. Conventional SOCs typically provide an output pin that carries the LPP signal. To force the phase of the external divide by two to a known state, a second flip-flop 420 may be clocked off the LPP signal to latch signal 415 when the LPP signal is pulsed to provide a wobble phase signal 425. The recorder/player firmware may then receive the phase signal 425 using, for example, a general purpose input output (GPIO) pin (not illustrated). Firmware filtering may then reject the occasional false LPP and monitor the phase 425 after the wobble is locked. If the phase is incorrect prior to a write operation, the firmware may reset the phase by unlocking and relocking PLL 400. Alternatively, a multiplexer may be provided (not illustrated) that selects between signal 415 and an inverted version of signal 415 to provide the wobble clock to the wobble PLL. If the firmware detects that phase signal 425 is not in the proper phase relationship to the LPP signal, it would then command a selection through the multiplexer of the inverted version of signal 415.

When a disc is inserted into a drive having the additional hardware shown in Figure 4, a firmware algorithm should determine the type of disc and either enable or disable this additional hardware depending upon whether the disc has a 2X wobble. For example, if the 2X wobble is not detected, the firmware would enable a bypass of the 2X wobble circuitry shown in Figure 4. Each DVD Download disc is encrypted according to the CSS protocol. As discussed previously, it is cumbersome to require a manufacturer to insert the media key block into each blank DVD Download disc. Thus, in addition to detecting whether a disc has a 2X wobble characteristic of DVD Download discs, the recorder firmware may also detect whether a 2X wobble disc has been recorded to. If no data is seen, the firmware would initiate a random number generator to generate a 40-bit disc key. The drive firmware would include the 409 (or currently active) CSS player keys. The drive firmware may thus then perform the CS S -prescribed cryptographic methods to generate the CSS media key block using the 409 stored player keys and the generated disc key. The newly- generated CSS media key may then be written to the disc lead-in control data zone as specified in the CSS protocol. Advantageously, the probability of any one drive creating an identical media key block as compared to another drive is very small (approximately 2^"

4Ck

Alternatively, each drive may have a subset (one or more) of disc keys stored in its firmware. The drive firmware would include the 409 (or currently active) player keys.

Upon detecting a new DVD Download disc, the drive generates a random number to select a disc key from the disc key set stored in its firmware. The media key block may then be generated and written to the disc as discussed previously. It will be appreciated that the available disc key sets in such an embodiment could then be controlled by the DVD Copy Control Association but the media key blocks would still vary randomly from disc to disc, with the probability of duplicate media key blocks dependent on the number of disc keys available at any given drive.

Regardless of how the drive generates its media key block, the CSS player keys may be stored in a secure encrypted format in the drive non- volatile memory such as a flash memory. If the disc keys are also stored by the drive (rather than being randomly generated), the stored disc key set would also be stored in an encrypted fashion in the nonvolatile memory. Only upon detection of a new DVD Download disc would the drive decrypt these keys and start the disc initialization process. In addition, the necessary algorithms may be implemented in RAM that is internal to the drive microprocessor such that key signals do not appear on external microprocessor busses. Moreover, the drive firmware may be configured so that it will only accept authenticated cipher text for firmware downloads. In such an embodiment, the existing drive firmware would download the update file to local memory so that it may be decrypted and authenticated before the flash or other non-volatile memory is updated.

The above-described embodiments of the present invention are merely meant to be illustrative and not limiting. It will thus be obvious to those skilled in the art that various changes and modifications may be made without departing from this invention in its broader aspects. The appended claims encompass all such changes and modifications as fall within the true spirit and scope of this invention

Claims

WHAT IS CLAIMED IS

1. A method of configuring a DVD-R recorder to record 2X wobble discs, comprising: configuring a wobble PLL within the recorder to lock on the first sub-harmonic of a wobble input signal from the 2X wobble disc to produce a wobble clock output signal; determining whether the wobble clock output signal is phased properly so that the recorder may decode land prepit (LPP) addresses; and if the wobble clock output signal is not phased properly, unlocking and relocking the wobble PLL.

2. The method of claim 1, wherein configuring the wobble PLL comprises: configuring a VCO within the wobble PLL to have a nominal 1:1 frequency relationship with the wobble input signal so that the wobble clock output signal oscillates at a 2X frequency; and reconfiguring the VCO to have a nominal 2: 1 frequency relationship with the wobble input signal so that the wobble clock output signal oscillates at a IX frequency.

3. The method of claim 2, wherein configuring and reconfiguring the VCO comprises writing to a register that controls the nominal frequency relationship between the wobble input signal and the wobble clock output signal.

4. The method of claim 2, further comprising configuring the PLL to operate in a phase detector mode of operation while in the nominal 2: 1 frequency relationship.

5. A method of configuring a DVD-R recorder to record 2X wobble discs, the DVD-R recorder including a wobble PLL having a mode of operation in which it responds to an externally-provided signal provided through an input port, the DVD-R recorder also providing an access to a wobble input signal, comprising: providing a phase-locked loop to lock to a 2X wobble input signal provided through the access; dividing a output from the phase-locked loop by two to produce a square- wave IX signal; and providing the square- wave IX signal to the wobble PLL through the input port so that the wobble PLL may lock to the square-wave IX signal to produce a IX wobble clock output signal.

6. The method of claim 5, wherein the DVD-R recorder provides access to an LPP signal, the method further comprising: latching the IX wobble clock output signal responsive to a pulsing of the LPP signal to produce a phase signal; and determining if the phase signal indicates a proper phase relationship of the IX wobble clock output signal to the LPP signal.

7. The method of claim 6, further comprising: if the phase signal indicates an improper phase relationship, unlocking and relocking the external PLL.

8. The method of claim 6, further comprising: if the phase signal indicates an improper phase relationship, inverting the IX wobble clock output signal.

9. A method of initializing a 2X wobble disc at a DVD-R recorder, comprising: generating a random number; generating a disc key from the random number; retrieving a plurality of player keys from a memory; generating a media key block using the player keys and the generated disc key; and writing the media key block to the 2X wobble disc.

10. The method of claim 9, further comprising: downloading video content; and writing the video content in a CSS-protected fashion to the 2X wobble disc.

11. A method of initializing a 2X wobble disc at a DVD-R recorder, comprising: generating a random number; selecting a disc key from a stored plurality of disc keys based on the random number; retrieving a plurality of player keys from a memory; generating a media key block using the player keys and the selected disc key; and writing the media key block to the 2X wobble disc.

2. The method of claim 11, further comprising: downloading video content; and writing the video content in a CSS-protected fashion to the 2X wobble disc.