KR20070058288A - Method and apparatus for descrambling av stream - Google Patents

Abstract

A method and an apparatus for descrambling an AV(Audio Visual) stream are provided to quickly process a descramble work for a scramble loaded in the middle of AV contents. A confirming unit(69) confirms information for correcting a modified part of a stream with respect to the first packet among packets composing the stream modified by a scramble, and extracts position information of the second packet necessary for confirming the information among the packets from the confirmed information. If the confirmed information indicates that modification by the scramble exists in the first packet, an overwrite unit(71) overwrites a descramble value for correcting the modified part of the first packet on a position of the modified part of the first packet.

Description

 Method and apparatus for descrambling AV stream {Method and apparatus for descrambling AV stream}

1 is a block diagram of a player according to a conventional descramble method.

2 is a structural diagram of a calibration table according to a conventional descramble method.

3 is a structural diagram of a calibration entry according to a conventional descramble method.

4 is a diagram illustrating a descrambling operation according to a conventional descramble method.

5 is a diagram illustrating a problem of a conventional descramble method.

6 is a block diagram of a player according to an embodiment of the present invention.

8 is a diagram illustrating a calibration table checking operation according to an exemplary embodiment of the present invention.

9 is a structural diagram of a calibration entry according to one preferred embodiment of the present invention.

11 is a block diagram of a player according to an embodiment of the present invention.

12-13 are flowcharts of a content restoration method according to an embodiment of the present invention.

The present invention relates to a method and apparatus for restoring AV content from an AV (Audio Visual) stream stored in a disc, and more particularly, to a method and apparatus for descrambled an AV stream modified due to scramble.

The Advanced Access Content System (AACS) standard, the next-generation optical disc protection system, applies the Broadcast Encryption Scheme to allow players with device key sets revoked due to hacker attacks. Encrypted content cannot be decrypted. The broadcast encryption method assigns a different device key set to each of a plurality of players, and does not store the intermediate key value encrypted with the discarded device key set on a disk distributed in public. The player having the game cannot acquire this intermediate key value, and as a result, cannot obtain the content decryption key.

However, since the number of device key sets is limited, and the number of players to which the device key set should be allocated continues to increase, there is a case where the same device key set is assigned to multiple players. If any one of these players is hacked and the device key set of this player is exposed, there is a problem that other players with the same device key set should also be discarded.

In order to solve this problem, a scramble-based renewability scheme has emerged. This method scrambles in the middle of the content when storing the content on disk, and encrypts it according to the AACS standard. Therefore, in order to restore the original content, the player must decode the stream stored on the disc according to the AACS standard, and then unscramble the middle of the content.

According to this method, content code, which serves to solve scramble, is stored on the disk. This content code is executed before the content is played back to determine whether there is a problem with the content being played. For example, it is determined whether the player has exposed the device key set, whether illegal copies of the content are running, and the like. As a result, descramble is performed only when it is determined that there is no problem in content reproduction, and descramble is not performed when it is determined that there is a problem. In other words, once the player is sold, it is difficult to update it again, but in the case of a disc, the content level can be updated by inserting the content code as described above for each disc.

1 is a block diagram of a player according to a conventional descramble method.

Referring to FIG. 1, a player 2 according to a conventional descramble includes a track buffer 21, a decryption unit 22, a buffer 23, a demux 24, Decoder 25, a virtual machine 26 for protecting AV content included in the AV stream, player information database 27, SP register 28, arithmetic unit 29 and overwriting It is comprised by the part 30.

The track buffer 21 reads out the AV stream from the disc 1 and temporarily stores the AV stream in order to correspond to the decoding processing speed in the decryption section 22. The AV stream stored in the track buffer 21 is an AV stream in encrypted form.

The decryption unit 22 decrypts the AV stream stored in the track buffer 21 using the title key Kt corresponding to the AV stream stored in the track buffer 21 according to the AACS standard.

The buffer 23 temporarily stores the AV stream decrypted by the decryption unit 22 in order to correspond to the decoding processing speed in the decryption unit 25. The AV stream stored in the buffer 23 is an AV stream that is deformed due to scramble and encoded according to the Moving Picture Experts Group (MPEG) -2 standard.

The demux 24 demuxes the AV stream stored in the buffer 23 according to the MPEG-2 standard to restore encoded AV content and original AV content from the AV stream stored in the buffer 23. Extract the information. In particular, the demux 24 retrieves a Program Map Table (PMT) packet including a masked fix-up table from the AV stream stored in the buffer 23, and extracts a mask correction table from the PMT packet. do.

The calibration table is a table in which descramble information for correcting the deformed portion of the deformed AV stream due to the scramble in the middle of the AV stream is recorded. The mask correction table is an exclusive OR of the values of the correction table and the secret parameter values so that the values of the correction table cannot be easily understood. Those skilled in the art can understand that the term mask may be expressed by the term obfuscate.

2 is a structural diagram of a calibration table according to a conventional descramble method.

Referring to FIG. 2, the field "SP_ID" indicates an ID of a secret parameter value used for an exclusive OR of a calibration table. &Quot; FixUpEntry " represents a calibration entry which is substantial information for correcting the deformation due to scramble.

3 is a structural diagram of a calibration entry according to a conventional descramble method.

Referring to Fig. 3, the "type_indicator" field indicates the processing type of the calibration table. That is, the value "00b" of this field indicates that there is no deformation due to scramble, "01b" indicates that there is deformation due to scramble, and "10b" indicates that it is forensic. The "FM_ID_bit_position" field indicates the bit position of the forensic mark ID for forensic marking. The "relative_SPN (Source Packet Number) _1" field indicates a relative packet number from the PMT packet to the first modified packet. The "relative_SPN_2" field indicates a relative packet number from the PMT packet to the second modified packet. The "byte_position_1" field indicates the start byte position of transform data in the first packet. The "byte_position_2" field indicates the start byte position of transform data in the second packet. "overwrite_value_1" represents the first value to be overwritten. The "overwrite_value_2" field indicates a second value to be overwritten.

The decoder 25 restores the original AV content by decoding the AV content extracted by the demux 24 according to the MPEG-2 standard.

The content code 26 for protecting the AV content included in the AV stream reads the content code for securing the AV content included in the AV stream stored in the disc 1 from the disc 1, and By executing the content code, a secret parameter value, a secret parameter ID, and a forensic mark ID are generated. In more detail, the content code 26 for protecting the AV content included in the AV stream is determined by comparing the player information stored in the player information database 27 with the player information obtained as a result of executing the content code. Determines whether the player has exposed the device key set, and as a result, generates a secret parameter value, a secret parameter ID, and a forensic mark ID only when it is determined that the player has not exposed the device key set. If it is determined to be a player, the secret parameter value, secret parameter ID, and forensic mark ID are not generated.

Forensic marks are not involved in the direct protection of AV content like secret parameters, but if the content with forensic marks is played in a compromised player, a mark specific to this player is created on this content. After this content is exposed to the public, the content owner can identify the compromised player by checking the forensic mark on the exposed content.

The SP register 28 stores secret parameter values, secret parameter IDs, and forensic mark IDs generated by the content code 26 for protecting AV content included in the AV stream.

The calculation unit 29 restores the original calibration table by performing an exclusive OR (XOR) on the secret parameter values stored in the SP register 28 and the mask correction table extracted by the demux 24. Since the mask correction table is an exclusive OR operation performed on the secret correction values with respect to the original correction table, the operation unit 29 once again exclusively sets the mask correction table to the same values as the secret parameter values used in the exclusive OR operation. Restore the original calibration table by performing the OR operation.

The overwrite unit 30 overwrites the descrambled value in the deformed position of the packet deformed by the scramble among the data packets stored in the buffer 23 based on the calibration table restored by the operation unit 29. Descrambles the scrambled portion of the data packets stored in < RTI ID = 0.0 >

4 is a diagram illustrating a descrambling operation according to a conventional descramble method.

4, the demux 24 searches for a PMT packet including a calibration table descriptor among packets constituting the AV stream output from the buffer 23, and outputs a mask calibration table in the PMT packet. The calculation unit 29 restores the original calibration table by exclusive OR of the calibration table and secret parameter values output from the demux 24. The overwrite unit 30 knows the relative positions of the first packet and the second packet deformed due to scrambled from the values of the "relative_SPN_1" field and the "relative_SPN_2" field of the calibration table restored by the calculating unit 29, respectively. And overwrite the descramble values in these locations.

5 is a diagram illustrating a problem of a conventional descramble method.

Referring to FIG. 5, when the overwrite unit 30 attempts to overwrite a descramble value at a position of a transport stream stored in the buffer 23, the PMT packet, which is the basis of this position calculation, is stored in the buffer 23. Instead, the demux 24 has already been demuxed. For this reason, there is a problem that it is not easy to calculate the position of the modified part of the transport stream stored in the buffer 23. In addition, when the position calculation of the modified part of the transport stream stored in the buffer 23 is not performed quickly, there is a problem that the modified part of the transport stream stored in the buffer 23 may be output as it is. Therefore, a device using a low specification CPU (Central Processing Unit) such as a mobile terminal is unable to process descrambling in software due to such a speed limitation.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a method and an apparatus capable of quickly processing a descrambling operation for a scramble in the middle of an AV content. The present invention also provides a computer-readable recording medium having recorded thereon a program for executing the method on a computer.

The descrambling method according to the present invention for solving the technical problem comprises the steps of identifying information for correcting the modified portion of the stream with respect to the first packet of the packets constituting the modified stream due to scramble; Obtaining location information of a second packet requiring identification of information for correcting a modified portion of the stream of the packets from the identified information; And selectively descrambled the stream based on the identified information.

In order to solve the above other technical problem, the present invention provides a computer-readable recording medium having recorded thereon a program for executing the above descrambling method on a computer.

According to another aspect of the present invention, a descrambler according to the present invention checks information for calibrating a deformed portion of a stream with respect to a first packet among packets constituting a deformed stream due to scramble, and confirms the information. A verification unit for extracting location information of a second packet requiring verification of the information from the received information; And if the checked information indicates that the first packet is deformed due to the scrambling, overwriting an overwrite of a descramble value for correcting the deformed portion of the first packet at a position of the deformed portion of the first packet. It includes a writing unit.

The computer-readable recording medium which records the data structure according to the present invention for solving the above technical problem is a computer having a data structure including fields representing information for correcting the deformed portion of the stream deformed due to scramble. 12. A record carrier readable by means of: a first field indicating substantial information for calibrating the deformed portion of the information; And a second field indicating position information of a second packet requiring confirmation of the information from the first packet among the information.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

6 is a block diagram of a player according to an embodiment of the present invention.

Referring to FIG. 6, the player 6 according to the present embodiment includes a track buffer 61, a decryption unit 62, a buffer 63, a demux 64, a decoder 65, and a virtual machine 66. And a player information database 67, an SP register 68, a FUT confirming section 69, a calculating section 70, and an overwriting section 71. In particular, the AV stream input to the player 6 according to the present embodiment is a stream in which calibration tables divided from the entire calibration table are muxed. Each of the calibration tables contains information for calibrating two modified portions of the entire modified portions of the stream. Those skilled in the art may understand that each of the calibration tables may be referred to as calibration table entries in terms of being partitioned from the entire calibration table.

The track buffer 61 reads out the AV stream from the disc 5 and temporarily stores this AV stream in order to correspond to the decoding processing speed in the decryption unit 62. The AV stream stored in the track buffer 61 is an AV stream in encrypted form.

The decryption unit 62 decrypts the AV stream stored in the track buffer 61 using the title key Kt corresponding to the AV stream stored in the track buffer 61 according to the AACS standard.

The buffer 63 temporarily stores the AV stream decrypted by the decryption unit 62 in order to correspond to the decoding processing speed in the decryption unit 65. The AV stream stored in the buffer 63 is modified due to scramble and is an AV stream encoded in the MPEG-2 standard.

The demux 64 demuxes the AV stream stored in the buffer 63 according to the MPEG-2 standard to restore the encoded AV content and the original AV content from the AV stream stored in the buffer 63. Extract the information. According to this embodiment, the demux 64 does not extract the mask correction entry from the AV stream stored in the buffer 63 unlike the conventional art. This function is responsible for the FUT check unit 69.

 The decoder 65 restores the original AV content by decoding the AV content extracted by the demux 64 according to the MPEG-2 standard.

The virtual machine 66 reads the content code for protecting the AV content contained in the AV stream stored in the disk 5 from the disk 5, and executes the content code to execute the secret parameter value, the secret parameter ID, and the forensic expression. Create a mark ID. More specifically, the virtual machine 66 compares the player information stored in the player information database 67 with the player information obtained as a result of executing the content code to determine whether the player 6 has exposed the device key set. As a result, a secret parameter value, a secret parameter ID, and a forensic mark ID are generated only when it is determined that the player key set is not exposed, and the secret parameter value is determined when the device key set is revealed. Do not generate secret parameter IDs and forensic mark IDs.

The SP register 68 stores secret parameter values, secret parameter IDs, and forensic mark IDs generated by the virtual machine 66.

The FUT confirming section 69 checks a calibration table which is a table in which information for correcting the modified portion of the AV stream is recorded for any PMT packet among the packets constituting the AV stream stored in the buffer 63. do. The FUT confirming unit 69 may check the calibration table more quickly by performing only checking of the calibration table for the PMT packets.

7 is a structural diagram of a calibration table according to an embodiment of the present invention.

Referring to FIG. 7, the "SP_ID" field indicates an ID of a secret parameter value and is not masked. The "FixUpEntry" field indicates a calibration entry, which is substantial information for correcting the deformation due to scramble, and is masked. The "Offset_SPN_to_next_FixUP" field indicates relative position information of the next PMT packet which needs to check the calibration table from the current PMT packet and is not masked.

The FUT confirming unit 69 extracts the ID of the secret parameter value from the "SP_ID" field of the calibration table shown in FIG. The FUT confirming unit 69 extracts the relative position information of the next PMT packet requiring the confirmation of the calibration table from the current PMT packet from the "Offset_SPN_to_next_FixUP" field of the calibration table shown in FIG.

8 is a diagram illustrating a calibration table checking operation according to an exemplary embodiment of the present invention.

The player 6 may play from the beginning of the AV stream stored in the disc or play from the middle according to the user's selection. Accordingly, the FUT confirming section 69 checks the calibration table for the PMT packet first appearing from the playback start point selected by the user. To this end, as shown in FIG. 8, each of the PMT packets of the AV stream includes a calibration table. However, not all correction tables included in the PMT packets include a mask correction entry which is substantial information for correcting the modified portion of the AV stream. That is, some of the PMT packets include a mask correction entry, while others only include relative position information of PMT packets requiring verification of the correction table. However, there are PMT packets including bit positions of forensic mark IDs for forensic marking among PMT packets corresponding to the latter.

Referring to FIG. 8, the FUT confirming unit 69 checks the calibration table for PMT packets existing between the next PMT packets that need to be checked from the current PMT packet with reference to the relative position information of the next PMT packet. Omit and immediately check the calibration table for the next PMT packet that needs to check the calibration table. Here, the relative position information of the next PMT packet refers to a relative packet number indicating how many packets are the next PMT packet that needs to check the calibration table from the current PMT packet. That is, the FUT checker 69 checks the calibration table for the next PMT packet present at the position corresponding to the value of the number of the current PMT packet plus the relative packet number of the next PMT packet.

For example, if the playback start point selected by the user is the left arrow 810 shown in Fig. 8, the FUT checker 69 checks the calibration table for the PMT packet A 81 first appearing from this point. do. Subsequently, the FUT confirming section 69 extracts a relative packet number of the next PMT packet, that is, PMT packet B 82, which needs to confirm the calibration table from the calibration table of the PMT packet A 81, and refers to the PMT packet B Check the calibration table for (82). Subsequently, the FUT confirming section 69 extracts, from the calibration table of the PMT packet B 82, the relative packet number of the next PMT packet, i.e., the PMT packet D 84, which needs confirmation of the calibration table. Check the calibration table for (84). In this case, the calibration table check for the PMT packet C 83 is omitted. This is because PMT packet C 83 is a PMT packet which does not require confirmation of the calibration table.

If the playback start point selected by the user is the right arrow 820 shown in Fig. 8, the FUT confirming section 69 checks the calibration table for the PMT packet C 83 first appearing from this point. Subsequently, the FUT confirming section 69 extracts, from the calibration table of the PMT packet C 83, the relative packet number of the next PMT packet, i.e., the PMT packet D 84, which needs confirmation of the calibration table. Check the calibration table for (84). In this case, the calibration table check for the PMT packet C 83 is performed. This is because the PMT packet C 83 is a PMT packet that first appears from the playback start point selected by the user although the PMT packet does not require confirmation of the calibration table.

That is, the FUT confirming section 69 checks the calibration table for the PMT packet first appearing from any playback start point selected by the user, and thereafter without having to check the calibration table for all PMT packets. Check the calibration table only for PMT packets that require verification.

Referring back to FIG. 7, the FUT checker 69 extracts a mask correction entry from the “FixUpEntry” field of the calibration table shown in FIG. 7.

The operation unit 70 restores the original calibration entry by exclusive OR of the secret parameter value stored in the SP register 68 and the mask correction entry extracted by the FUT check unit 69. Since the mask correction entry is an exclusive OR operation performed on the original calibration entry with a secret parameter value, the operation unit 68 once again converts the mask correction entry to the same value as the secret parameter value used for the exclusive OR operation. Restore the original calibration entry by performing the operation.

However, the ID of the secret parameter value stored in the SP register 68 and the ID used for the exclusive OR of the mask correction entry extracted by the FUT confirming unit 69 must match each other. That is, the calculating unit 70 extracts a secret parameter value corresponding to the ID used for the exclusive OR of the mask correction entry extracted by the FUT confirming unit 69 from the SP register 68, and this and the FUT confirming unit 69 The original correction entry is restored by exclusive OR of the mask correction entries extracted by the "

9 is a structural diagram of a calibration entry according to one preferred embodiment of the present invention.

Referring to Fig. 9, the "type_indicator" field indicates the processing type of the calibration table. That is, the value "00b" of this field indicates that there is no deformation due to scramble, "01b" indicates that there is deformation due to scramble, and "10b" indicates that it is forensic. The "FM_ID_bit_position" field indicates the bit position of the forensic mark ID for forensic marking. The "relative_SPN (Source Packet Number) _1" field indicates a relative packet number from the PMT packet to the first modified packet. The "relative_SPN_2" field indicates a relative packet number from the PMT packet to the second modified packet. The "byte_position_1" field indicates the start byte position of transform data in the first packet. The "byte_position_2" field indicates the start byte position of transform data in the second packet. "overwrite_value_1" represents the first value to be overwritten. The "overwrite_value_2" field indicates a second value to be overwritten.

The overwrite section 71 selectively descrambles the modified portion of the AV stream stored in the buffer 63 based on the calibration entry restored by the calculating section 70. In more detail, the overwrite unit 71 indicates that the value of the "type_indicator" field of the calibration entry restored by the operation unit 70 is "00b", that is, there is no deformation due to scramble. The value of the remaining fields is ignored without overwriting the descramble value for correcting the modified part of the AV stream stored in the. In addition, the overwrite unit 71 indicates that the value of the "type_indicator" field of the calibration entry restored by the operation unit 70 is "01b", that is, there is a deformation due to scramble, so that the overwrite of the AV stream stored in the buffer 63 is performed. By overwriting the descramble value for correcting the modified portion of the packet at the position of the modified portion of one of the packets, scrambled in the middle of the AV stream is released.

In addition, the overwrite unit 71 indicates that the value of the "type_indicator" field of the calibration entry restored by the operation unit 70 is "10b", that is, a forensic expression, and the forensic mark ID indicated by the "FM_ID_bit_position" field of the calibration entry. Only when bit is 1, the descramble value for correcting the modified portion of this packet is overwritten at the position of the modified portion of any of the packets of the AV stream stored in the buffer 63.

10 illustrates a descramble operation according to an embodiment of the present invention.

Referring to FIG. 10, the FUT confirming unit 69 extracts a mask correction entry from a PMT packet including a mask correction entry among PMT packets requiring verification of the correction table. Subsequently, the operation unit 70 restores the original calibration table by performing exclusive OR on the secret parameter value stored in the SP register 68 and the mask correction entry extracted by the FUT check unit 69. Subsequently, the overwrite unit 71 determines the value of the "relative_SPN (Source Packet Number) _1" field of the calibration entry, that is, the relative packet number of the first modified packet to the number of the current PMT packet confirmed by the FUT confirming unit 69. Compute the packet number of the first modified packet by adding.

In this way, since the overwrite unit 71 calculates the position of the deformed portion of the deformed packet due to the scramble based on the number of the PMT packet including the mask correction entry, the PMT packet including the mask correction entry is stored in the buffer 63. ), You do not have to consider how many additional packets have been missed since then. Subsequently, the overwrite unit 71 determines the value of the "byte_position_1" field of the calibration entry, that is, the value of "overwrite_value_1" of the calibration entry from the start byte position of the transformation data, in the packet corresponding to the packet number of the first transform packet. Overwrite the first value to be overwritten.

 Subsequently, the overwriting unit 71 determines the value of the "relative_SPN (Source Packet Number) _2" field of the calibration entry, that is, the relative packet number of the second modified packet, to the number of the current PMT packet confirmed by the FUT confirming unit 69. Compute the packet number of the second modified packet by adding. Subsequently, the overwrite section 71 determines the value of the "byte_position_2" field of the calibration entry, that is, the value of "overwrite_value_2" of the calibration entry from the start byte position of the transformation data in the packet corresponding to the packet number of the second modified packet, that is, Overwrite the second value to be overwritten.

11 is a block diagram of a player according to an embodiment of the present invention.

Referring to FIG. 11, the player 10 according to the present embodiment includes a track buffer 101, a decryption unit 102, a buffer 103, a demux 104, a decryption unit 105, and a virtual machine 106. And a player information database 107, an SP register 108, an arithmetic unit 109, and an overwriting unit 110. The player 10 according to the present embodiment is almost the same as the player 6 shown in FIG. 6, but the demux 104 performs the function of the FUT checker 69 together with the conventional demux function.

In addition to the above-described configuration, the player may be designed in various forms, but those skilled in the art may understand that the essential features of the configuration are the same.

12-13 are flowcharts of a content restoration method according to an embodiment of the present invention.

12-13, the content restoration method according to the present embodiment is composed of the following steps. The content reconstruction method according to the present embodiment is composed of steps that are processed in time series in the player 6 shown in FIG. Therefore, even if omitted below, the contents described above with respect to the player 6 shown in FIG. 6 also apply to the content restoration method according to the present embodiment.

In step 121, the player 6 reads the AV stream from the disc 5, and temporarily stores the AV stream. The stored AV stream in step 121 is an encrypted AV stream.

In step 122, the player 6 decrypts the AV stream stored in step 121 using the title key Kt corresponding to the AV stream stored in step 121 according to the AACS standard.

In step 123, the player 6 temporarily stores the decrypted AV stream in step 122. The AV stream stored in step 123 is transformed due to scramble and is an AV stream encoded according to the MPEG-2 standard.

In step 124, the player 6 reads the content code for protecting the AV content contained in the AV stream stored in the disk 5 from the disk 5, and executes the content code to execute the secret parameter value, secret parameter ID. Generate for, and forensic mark IDs.

In step 125 the player 6 stores the secret parameter value, the secret parameter ID, and the forensic mark ID generated in step 124.

In step 126, the player 6 checks the calibration table for the PMT packet first appearing from the playback start point selected by the user among the packets constituting the AV stream stored in step 123.

In step 127 the player 6 extracts the ID of the secret parameter value from the "SP_ID" field of the calibration table identified in step 126 or 136, extracts the mask correction entry from the "FixUpEntry" field, and from the "Offset_SPN_to_next_FixUP" field. From the current PMT packet, the relative packet number of the next PMT packet that requires confirmation of the calibration table is extracted.

In step 128 the player 6 restores the original correction entry by exclusive OR of the secret parameter value stored in step 125 and the mask correction entry extracted in step 127.

In step 129, the player 6 proceeds to step 136 when the value of the "type_indicator" field of the calibration entry restored in step 128 is "00b", and proceeds to step 130 when the value of the "type_indicator" field is "01b". If the value of the "type_indicator" field is "10b", the flow proceeds to step 135.

In step 130 the player 6 calculates the packet number of the first modified packet by adding the value of the "relative_SPN (Source Packet Number) _1" field of the calibration entry identified in step 126 to the number of the current PMT packet, The value of "overwrite_value_1" of the calibration entry is overwritten from the position corresponding to the value of the "byte_position_1" field of the calibration entry in the packet corresponding to the number.

Further, in step 130, the player 6 calculates the packet number of the second modified packet by adding the value of the "relative_SPN (Source Packet Number) _2" field of the calibration entry identified in step 126 to the number of the current PMT packet, The value of "overwrite_value_2" of the calibration entry is overwritten from the position corresponding to the value of the "byte_position_2" field of the calibration entry in the packet corresponding to this packet number.

In step 131 the player 6 selects this packet at the position of the modified portion of any of the packets of the AV stream stored in step 123 only if the bit of the forensic mark ID indicated by the "FM_ID_bit_position" field of the calibration entry is one. Override the descramble value to correct the deformation.

In step 132, the player 6 proceeds to step 133 if there is a next PMT packet that needs to be checked in the calibration table at a position corresponding to a value obtained by adding the relative packet number of the PMT packet to the number of the current PMT packet. If there is no next PMT packet, the flow proceeds to step 134.

In step 133, the player 6 checks the calibration table for the next PMT packet that exists at the position corresponding to the value of the number of the current PMT packet extracted in step 127 and then the relative packet number of the PMT packet, and in step 134 Proceed to step 127 at the same time.

In step 134, the player 6 restores the encoded AV content and the original AV content from the AV stream stored in step 123 by demuxing the descrambled AV stream in steps 124 to 135 according to the MPEG-2 standard. Extract a variety of information for

In step 135, the player 6 restores the original AV content by decoding the AV content extracted in step 134 according to the MPEG-2 standard.

Meanwhile, the above-described embodiments of the present invention can be written as a program that can be executed in a computer, and can be implemented in a general-purpose digital computer that operates the program using a computer-readable recording medium. In addition, the structure of the data used in the above-described embodiment of the present invention can be recorded on the computer-readable recording medium through various means.

The computer-readable recording medium may be a magnetic storage medium (for example, a ROM, a floppy disk, a hard disk, etc.), an optical reading medium (for example, a CD-ROM, DVD, etc.) and a carrier wave (for example, the Internet). Storage medium).

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

According to the present invention, by checking the calibration table for any one PMT packet of the packets constituting the modified AV stream due to scramble, and by obtaining the position information of the next PMT packet that needs to check the calibration table from this calibration table There is an effect that it is possible to quickly find the position of the PMT packet which needs to check the calibration table from the AV stream. Accordingly, the speed of the descramble operation is increased, and the system load due to the descramble is reduced, so that a device using a low specification CPU such as a mobile terminal can process the descramble by software.

Claims (18)

(a) identifying information for correcting the modified portion of the stream with respect to a first one of the packets constituting the modified stream due to scramble; (b) obtaining, from the identified information, location information of a second packet requiring identification of information for correcting a modified portion of the stream of the packets; And and (c) selectively descrambles the stream based on the identified information. The method of claim 1, And the step (c) descrambles the stream if the identified information indicates that there is a deformation due to the scramble. The method of claim 1, (d) identifying the information with respect to the second packet by referring to the obtained location information; And and (e) selectively descrambles the stream based on the information identified in step (d). The method of claim 1, And the confirmation unit confirms information for correcting the modified portion of the stream with respect to the first packet first appearing from the playback start point selected by the user. The method of claim 1, And the position information is relative position information from the first packet to the second packet. The method of claim 5, (d) omitting the checking of the information regarding the packets existing between the first packet and the second packet with reference to the obtained relative position information, and confirming the information with respect to the second packet; And (e) descrambling the stream selectively based on the information identified in step (d). The method of claim 5, The relative position information is a packet number indicating how many packets the second packet is from the first packet, (d) checking the information on the second packet present at a position corresponding to a value obtained by adding the number of packets to the number of the first packet; And (e) descrambling the stream selectively based on the information identified in step (d). The method of claim 1, The first packet and the second packet are PMT (Program Map Table) packets according to the Moving Picture Experts Group (MPEG) -2 standard, wherein each of the PMT packets includes information for correcting the packet. Descramble method. A non-transitory computer-readable recording medium having recorded thereon a program for executing the method of claim 1. Checking information for correcting the modified portion of the stream with respect to the first of the packets constituting the modified stream due to scramble, and from the identified information of the second packet that needs to confirm the information of the packets A verification unit for extracting location information; And If the identified information indicates that the first packet is deformed due to the scramble, an overwrite that overwrites a descramble value for correcting the deformed portion of the first packet at a position of the deformed portion of the first packet Descrambling device comprising a portion. The method of claim 10, The extracting unit checks the information with respect to the second packet with reference to the extracted position information, The overwrite unit may descramble a descrambled value for correcting the deformed portion of the second packet at a position of the deformed portion of the second packet when the checked information indicates that the second packet has a deformation caused by the scrambling. A descrambling device, characterized in that overwriting. The method of claim 10, And the confirmation unit confirms information for correcting the modified portion of the stream with respect to the first packet first appearing from the playback start point selected by the user. The method of claim 10, And the position information is relative position information from the first packet to the second packet. The method of claim 13, The extracting unit omits checking of the information on the packets existing between the first packet and the second packet with reference to the obtained relative position information, and confirms the information on the second packet. The overwrite unit may descramble a descrambled value for correcting the deformed portion of the second packet at a position of the deformed portion of the second packet when the checked information indicates that the second packet has a deformation caused by the scrambling. A descrambling device, characterized in that overwriting. The method of claim 13, The relative position information is a packet number indicating how many packets the second packet is from the first packet, The extracting unit checks the information with respect to the second packet present in the position corresponding to the value of the number of the packet plus the number of the first packet, The overwrite unit may descramble a descrambled value for correcting the deformed portion of the first packet at a position of the deformed portion of the second packet when the checked information indicates that the second packet has a deformation caused by the scrambling. A descrambling device, characterized in that overwriting. The method of claim 10, The first packet and the second packet are PMT (Program Map Table) packets according to the Moving Picture Experts Group (MPEG) -2 standard, wherein each of the PMT packets includes information for correcting the packet. Descramble device. A computer-readable recording medium having recorded a data structure including fields representing information for correcting a deformed portion of a deformed stream due to scramble, A first field representing substantial information for correcting the deformed portion of the information; And And a second field indicating position information of a second packet requiring identification of said information from said first packet of said information. The computer-readable recording medium having recorded thereon a data structure. The method of claim 17, And the first field is masked and the second field is not masked.

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