Title of Invention	DATA PLAYBACK METHOD AND DATA PROCESSING APPARATUS
Abstract	The present invention is provided with a data playback method for reading protected digital data from a recording medium (101) and playing the read protected digital data (113), the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original data, and (ii) a bytecode (112) that outputs a byte value for use in restoring modified digital data, the data playback method comprising a first step of reading the protected digital data from the recording medium, and subjecting the read protected digital data to decryption which corresponds to the encryption, to generate modified digital data; characterized by the bytecode recorded on the recording medium; a second step of reading the bytecode from the recording medium and obtaining the byte value by executing the bytecode so as to cause the bytecode to self-rewrite part thereof; a third step of subjecting the generated modified digital data to a restoration operation in order to generate restored digital data, the restoration operation being a fixed operation that uses the byte value; and a fourth step of playing the generated restored digital data, wherein a control step of controlling such that the second step is performed before the first step.

Title of Invention

DATA PLAYBACK METHOD AND DATA PROCESSING APPARATUS

Abstract

The present invention is provided with a data playback method for reading protected digital data from a recording medium (101) and playing the read protected digital data (113), the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original data, and (ii) a bytecode (112) that outputs a byte value for use in restoring modified digital data, the data playback method comprising a first step of reading the protected digital data from the recording medium, and subjecting the read protected digital data to decryption which corresponds to the encryption, to generate modified digital data; characterized by the bytecode recorded on the recording medium; a second step of reading the bytecode from the recording medium and obtaining the byte value by executing the bytecode so as to cause the bytecode to self-rewrite part thereof; a third step of subjecting the generated modified digital data to a restoration operation in order to generate restored digital data, the restoration operation being a fixed operation that uses the byte value; and a fourth step of playing the generated restored digital data, wherein a control step of controlling such that the second step is performed before the first step.

Full Text	Technical Field The present invention relates to a method for storing digitized data of content which is a copyrighted work such as a movie, on a large-capacity medium such as a digital optical disc, and enabling only specific terminals to completely acquire the data. In particular, the present invention relates to a technique for playing content data that is recorded on a large-capacity medium and has been encrypted and modified in order to protect copyright. Background Art With increases in capacity of storage media in recent years, systems that distribute contents, which are copyrighted works such as movies, that have been digitized and stored on media such as digital optical discs are becoming prevalent. In such a system, it is necessary toprotect the copyright of a content such that playback, copying and the like of the content is carried out onlyunder limitations defined by an agreement with the copyright holder. A general system for protecting copyrighted works from dishonest copying and the like, in other words copying and the like without the permission of the copyright holder, has a structure whereby digital content is encrypted with a content key managed by the copyright holder, recorded on a disc, and is only able to be decrypted by a terminal that has a corresponding content key. A party wishing to obtain the content key must obey stipulations relating to copyright protection agreed on with the copyright holder. As one example of such a system, Patent Document 1 discloses a method for protecting a content key that is for encrypting and decrypting content data, by generating the content key based on a seed key and time-variable data. Patent Document 1: Japanese Patent Application Publication No. 2000-100069 Disclosure of the Invention Problem to be Solved by the Invention Although the content key must be managed strictly so that it is not exposed to an outside party in this case, it is possible that the content key will be exposed dishonestly due to some kind of accident or occurrence. Once the content key is exposed, there is a danger that a content key for future content will be exposed using the same method. It is therefore assumed that dishonest usage of future content will not be able to be prevented. The prior art is vulnerable to this kind of attack because the content data is protected only by content keys that are protected by a prescribed method. In view of the described problem, the present invention has an object of providing a data playback method and a data processing apparatus according to which, if a method is discovered to break content protection due to some kind of accident or occurrence, other content will not be able to be used dishonestly using the same method. Means to Solve the Problem In order to achieve the stated object, the present invention is a data playback method for reading protected digital data from a recording medium and playing the read protected digital data, the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original digital data, and (ii) modified restoration-use information which has been generated by modifying restoration-use information that is for use in restoring modified digital data, the data playback method including: a first step of reading the protected digital data from the recording medium, and subjecting the read protected digital data to decryption which corresponds to the encryption, to generate modified digital data; a second step of subjecting the generated modified digital data to restoration which corresponds to the modification, withuseof the restoration-use information, togenerate restored digital data; a third step of playing the generated restored digital data; a fourth step of reading the modified restoration-use information from the recording medium, and, with use of the read modified restoration-use information, generating the restoration-use information in a format used in processing in the second step; and a control step of controlling such that the fourth step is executed before the first step. Here, the generation of the restoration-use information in the fourth step may be executed before the playing of the restored digital data, and the first step, the second step, and the third step may be executed in parallel during the playing of the restored digital data. Here, the modification of the restoration-use information may be modification that makes the restoration-use information software-tamper-resistant. Here, the digital data may be composed of a plurality of pieces of content, and execution processing of the restoration-use information may differ for each piece of content. Here, the protected digital data may have been generated by encrypting the original digital data and then modifying the encrypted digital data, in the first step, instead of the decryption, the read protected digital data may be subjected to restoration that corresponds to the modification, with use of the restoration-use information, to generate encrypted digital data, and in the second step, instead of the restoration, the encrypted digital data may be subjected to decryption that corresponds to the encryption, to generate the restored digital data. Furthermore, the present invention is a data playback method for reading protected digital data from a recording medium and playing the read protected digital data, the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original digital data, and (ii) modified restoration-use information whichhas been generated by modifying restoration-use information that is for use in restoring modified digital data, the data playback method including: a first step of reading the protected digital data from the recording medium, and subjecting the read protected digital data to decryption which corresponds to the encryption, to generate modified digital data; a second step of subjecting the generated modified digital data to restoration which corresponds to the modification, with use of the restoration-use information, to generate restored digital data; a third step of playing the generated restored digital data; and a fourth step of, before the first step, reading the modified restoration-use information from the recording medium, and subjecting the read modified restoration-use information to restoration that corresponds to the modification, to generate unmodified restoration-use information. Furthermore, the present invention is a data processing apparatus that reads protected digital data from a recording medium and plays the read protected digital data, the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original digital data, and (ii) modified restoration-use information which has been generated by modifying restoration-use information that is for use in restoring modified digital data, the data processing apparatus including: a reading unit operable to read the protected digital data and the modified restoration-use information from the recording medium; a decryption unit operable to subject the read protected digital data to decryption corresponding to the encryption, to generate modified digital data; a restoration unit operable to subject the generated modified digital data to restoration corresponding to the modification, with use of the restoration-use information, to generate restored digital data; a playback unit operable to play the generated restored digital data; a generation unit operable to read the modified restoration-use information from the recording medium, and with use of the read modified restoration-use information, generate the restoration-use information in a format used in processing by the restoration unit; and a control unit operable to control such that the generation of the restoration-use information by the generation unit is executed before the decryption by the decryption unit. Here, the control unit may control such that the generation of the restoration-use information is executed before playback of the restored digital data, and such that the decryption by the decryption unit, the restoration by the restoration unit and the playback by the playback unit are performed in parallel during playback of the restored digital data. Here, the modification of the restoration-use information may be modification that makes the. restoration-use information software-tamper-resistant. Here, the digital data may be composed of a plurality of pieces of content, and execution processing of the restoration-use information may differ for each piece of content. Here, the protected digital data may have been generated by encrypting the original digital data and then modifying the encrypted digital data, in the decryption unit, instead of the decryption, the read protected digital data may be subjected to restoration that corresponds to the modification, with use of the restoration-use information, to generate encrypted digital data, and in the restoration unit, instead of the restoration, the encrypted digital data may be subjected to decryption that corresponds to the encryption, to generate the restored digital data. Here, the present invention is a data processing apparatus that reads protected digital data from a recording medium and plays the read protected digital data, the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original digital data, and (ii) modified restoration-use information which has been generated by modifying restoration-use information that is for use in restoring modified digital data, the data processing apparatus including: a reading unit operable to read the protected digital data and the modified restoration-use information from the recording medium; a decryption unit operable to subject the read protected digital data to decryption corresponding to the encryption, to generate modified digital data; a restoration unit operable to subj ect the generated modified digital data to restoration corresponding to the modification, with use of the restoration-use information, to generate restored digital data; a playback unit operable to play the generated restored digital data; a generation unit operable to read the modified restoration-use information from the recording medium, and subject the modified restoration-use information to restoration corresponding to the modification, to generate unmodified restoration-use information; and a control unit operable to control such that the generation of the restoration-use information by the generation unit is executed before the decryption by the decryption unit. Effects of the Invention According to the described invention, content is dually protected according to an operation or the like and encryption. The significance of this is as follows. If a unified method is employed to encrypt each content, and the restoration processing or the like using restoration-use information or the like is different for each content, even if the encryption of a content is broken dishonestly, other content will be protected according to transformation that uses the restoration information or the like. This provides even stronger protection of copyright of content or the like. Furthermore, according to the present invention, transformation of the restoration-use information is executed before decryption. The significance of this is as follows. The present invention is effective in cases such as when the Fig. 7 shows an example of restoration processing of modified content data in an embodiment of the present invention; Fig. 8 shows an example of restoration-use bytecodes being generated from TRS bytecodes according to self-rewriting in an embodiment of the present invention; and Fig. 9 shows an example of restoration processing of protected content according to switching of a playback order of TS data in an embodiment of the present invention. Description of Numerical References 101 recording medium 102 content playback apparatus 111 playback control information 112 TRS bytecodes 113 protected content data 114 encrypted content key 115 revocation information 121 disc reading unit 122 playback control unit 123 user operation reception unit 124 TRS bytecode execution unit 125 decryption unit 126 content data restoration processing unit 127 decoder 128 content key generation unit 129 revocation information processing unit 130 device key storage unit 501 encryption key-use TRS bytecodes 502 encrypted restoration-use bytecodes 701 bit string of unit of modification of modified content data 702 parameter used in XOR operation 703 bit string of unit of modification after restoration 801 pre-execution codes 802 post-execution codes 803 restoration-use bytecodes 901 reading order in decryption unit 125 902 reading order in decoder 127 Best Mode for Carrying Out the Invention The following describes a best mode for carrying out the invention, with reference to the drawings. The recording medium used in the present invention has recorded thereon content data that is protected according to encryption with a content key and data modification by an operation that is different to the encryption. Also recorded on the recording medium with the content data is the content key and a program for executing an inverse operation to the aforementioned operation, which are also in a protected state. The content key is protected by revocation i n formation that enabl es the content key to be used only by an author i zed data processing apparatus that has permission to use the content data, and is recorded together with the revocation information. The program is protected by being subjected to TRS (being subjected to processing to make data software-tamper-resistant). The procedure used to record the content data includes a step of encrypting the content data with the content key, and a step of data modification according to an operation that is different to the encryption. The procedure also includes a step of recording the content key in a protected state to the recording medium, and a step of recording a program for executing an inverse operation to the aforementioned operation to the recording medium. Here, the program is in a protected state that is achieved using a different method of protection to the method used to protect the content key. The procedure further includes a step of protecting the content key according to revocation information that enables the content key to be used only by an authorized data processing apparatus that has permission to use the content data. The procedure further includes a step of protecting the program by subjecting it to TRS. Pig. 1 shows the structure of a recording medium and a content playback apparatus of an embodiment of the present invention. A recording medium 101 has recorded thereon playback control information 111, TRS (Tamper-resistant Software) bytecodes .112, protected content data 113, an encrypted content key 114, and revocation information 115. The recording medium 101 is assumed to be a BD (Blu-Ray Disc) for instance, but is not limited to being so. Note that in the present Description, "TRS bytecodes" denotes codes generated by subjecting bytecodes to processing for making data software-tamper-resistant. In the present embodiment, it is assumed that one content is composed of a plurality of pieces of MPEG2-TS (Motion Picture Expert Group 2- Transport Stream) data. It is the playback control information 111 that defines the playback order of the pieces of data for playing the content. The TRS bytecodes 112 (one example of modified restoration-use information) are one or more bytecodes (one example of restoration- use information) that has been subject to processing to put software into a state in which secret information, processing contents and the like included in the software cannot be ascertained by an act of analysis. Specific execution contents of the bytecodes are described later. Note that although an example of bytecodes is given in the present embodiment, an execution program other than bytecodes may be used. The protected content data 113 (one example of protected digital data) is data generated by subjecting plaintext MPEG2-TS (one example of digital data) that can be output as video by a decoder to encryption processing using the content key, and modification processing in which an XOR operation or the like with a particular value is performed. The encrypted content key 114 is data generated by encrypting, with a media key, the content key for decrypting the content data. ■ The following describes the revocation information 115. A key management organization has a collection of a plurality of device keys and a plurality of media keys. The key management organization allocates one of the device keys, and a key identification number for the device key, to each of content playback apparatuses 102, and gives the respective allocated device key and key identification number to each content playback apparatus 102. The key management organization also allocates one media key to the recording medium 101. Next, the key management organization encrypts the media key respectively using the each of the device keys allocated to the content playback apparatuses 102, to generate encrypted media keys, and generates a list of the encrypted media keys and key identification numbers that correspond to all the device keys . This list is the revocation information 115. A drawback of this simple method is that the size of the data of the revocation information 115 will be unrealistically large if there is a large number of content playback apparatuses 102. Therefore, the method disclosed in "Digital Content Hogo-you Kagi Kanri Houshiki (Key Management Method for Protecting Digital Content)" (Nakano, Ohmori and Tatebayashi, Symposium on Cryptography arid Information Security 2001, SCIS2001, 5A-5, Jan. 2001) may be used to compress the size of the data of the revocation information 115. A method to be used is not limited to this method, and any other method for compressing the size of the data of the revocation information 115 may be used. The content playback apparatus 102 is composed of a disc reading unit 121, a playback control unit 122, a user operation reception unit 123, a TRS bytecode execution unit 124, a decryption unit 125, a content data restoration processing unit 126, a decoder 127, a content key generation unit 128, a revocation information processing unit 129, and a device key storage unit 130. One implementation example of these components is the disc reading unit 121 being a BD drive, and the other components being realized by a computer composed of a CPU, a work memory, an HDD and the like. '■':" Here, the description of the structure of the recording medium 101 and the content playback apparatus 102 pertaining to an embodiment of the present invention is completed. Description of Content Playback Processing The following describes content playback processing, with use of Fig. 2. The content playback processing starts upon the user operation reception unit 123 receiving a content playback start request from the user via the user operation reception unit 123. Upon the content playback start request being received, the revocation information processing unit 129 performs revocation checking processing with respect to the content playback apparatus 102 (S201) . Details of the revocation checking processing are given later. Subsequently, the processing branches depending on whether or not generation of the media key is successful in the revocation checking processing at S201 (S202). If generation of the media key succeeds in the revocation checking processing at S201, the playback control unit 122 performs selection of the protected content data 113 (step S203). ; If generation of the media key fails in the revocation checking processing at S201, notification is issued that the content playback apparatus 102 is revoked, and the processing ends (S208) . After the processing at S203 ends, the TRS bytecbdes 112 necessary for playback of the selected protected content data 113 are read, and the TRS bytecode execution unit 124 performs TRS bytecode execution processing (S204) . Details of the TRS bytecode execution processing are given later. Note that the processing up to this point is pre-processing that is performed before the content is displayed. In accordance with the playback control information 111, the playback control unit 122 instructs reading of the protected content data 113. The content key generation unit 128 and the decryption unit 125 perform decryption of the read protected content data 113. (S205) . Hereinafter, the data obtained as a result of decrypting the protected content data 113 is called modified content data (one example of modified digital data). The encryption used in the encryption of the protected content is AES (Advanced Encryption Standard), but is not limited to being so. Since decryption processing is performed repeatedly during content playback until the end of the protected content data 113, restoration (S206) and decoding of content (S207), which are described later, are executed in parallel. Details of decryption processing of the protected content data 113 are given later. The content data restoration processing unit 126 performs restoration processing on the modified content data output by the decryption unit 125 (S206) . The restoration processing is executed in units of aligned units, each of which is composed of a predetermined number of MPEG2-TS packets in MPEG2-TS data, or executed in units of sectors, each of which is the unit of recording on the recording medium 101. During content playback, decryption processing of the protected content data 113 (S205) and decoding of content which is described later (S207) are executed in parallel. Details of restoration processing of the modified content data are given later. The restored content data is decoded in the decoder 127, and is output to a device that displays video, such as a television monitor (S207) . During content playback, decryption of the protected content data 113 (S205) and restoration of the modified content data (S206) are executed in parallel. The content playback processing ends when playback of all the content data ends. Here, the description of the content playback processing is completed. Revocation Checking Processing of the Content Playback Apparatus 102 The following describes revocation checking processing of the content playback apparatus 102. The revocation checking processing is processing that starts after the start of content playback in Fig. 2, and is for checking that the content playback apparatus 102 is not revoked, according to the revocation information 115 recorded on the recording medium 101. The revocation checking processing corresponds to step S201. The revocation information processing unit 129 reads the device key obtained from the device key storage unit 130 (S301). The device key is information that can be used to specify the content playback apparatus 102, and is unique to the content playback apparatus 102. Next, the revocation information processing unit 129 reads the revocation information 115 recorded on the recording medium 101 (S302), and generates the media key with use of the read device key and the revocation information 115 (S303). The media key cannot be generated if the content playback apparatus 102 is revoked. Details about generating the media key with use of the device key and the revocation information 115 can be found in National Technical Report Vol. 43, No. 3, pp. 118-122 (Engineering Administration Center, Matsushita Electric Industrial Company, June 18, 1997) . Here, the description of the revocation checking processing of the content playback apparatus 102 is completed. TRS bytecode execution processing The following describes TRS bytecode execution processing (corresponding to step S204 of Fig. 2), with use of Fig. 4. The TRS bytecode execution unit 124 obtains the TRS bytecodes 112 necessary for playback of the instructed content, from the recording medium 101 (S401). The TRS bytecode execution unit 124 executes the obtained TRS bytecodes 112, thereby outputting restoration-use bytecodes (S402) . The restoration-use bytecodes are bytecodes executed in the content data restoration processing unit 126. The following describes a specific example of restoration processing of modified content data in the content restoration processing unit 126 at S206, with use of Fig. 7. In Fig. 7, an explanation is given about processing of bytecodes for restoring the content data by performing an XOR operation of the modified content data and a certain value by executing the restoration-use bytecodes . 701 expresses a bit sequence that is the unit of modification of the modified content data. A parameter 702 shows a parameter for performing an XOR operation for restoring the modified content data. The parameter 702 is specified in the restoration-use bytecodes. The content restoration processing unit 126 outputs, as plaintext content data 703, the result of performing the XOR operation on the unit of modification 701 of modified content data and the parameter 702 by executing the restoration-use bytecodes . The entire modified content data is restored by repeatedly executing the described processing. . The execution processing is assumed to be an XOR operation using the modified content data with a specific byte sequence in the bytecodes, with a value in a specific address of the data to be restored, or with a combination of those values. However, the execution processing is not limited to being an operation mentioned above. The execution processing may alternatively be a combination of several operations that incur a relatively small processing load, such as a ROT. The processing executed according to restoration-use bytecodes may differ for each content. ' .- Furthermore, the TRS bytecodes 112 may be data generated by concatenating encryption key-use TRS bytecodes 501 and encrypted restoration-use bytecodes 502 (one example of modified restoration-use information), as shown in Fig. 5. In such a case, the encryption key-use TRS bytecodes 501 are executed by the TRS bytecode execution unit 124, to output an encryption key for the encrypted restoration-use bytecodes 502. The output encryption key and encrypted restoration-use bytecodes 502 are transmitted to the decryption unit 125, which generates restoration-use bytecodes . The generated restoration-use bytecodes are transmitted to the content restoration unit 126, and the processing continues. Furthermore, in the above example, the restoration-use bytecodes that are output are different bytecodes to the TRS bytecodes 112 recorded on the recording medium 101. However, the restoration-use bytecodes that are output may be bytecodes generated in TRS bytecode execution processing at S204 in which the TRS bytecodes 112 self-rewrite part of their own codes. The following describes the TRS bytecode execution processing at S204 for generating restoration-use bytecodes 803 by self-rewriting, with use of Fig. 8. In Fig. 8, pre-execution codes 801 of the TRS bytecodes 112 are executed according to the TRS bytecode execution processing at S204, thereby self-rewriting into post-execution codes 802 to output restoration-use bytecodes 803. Here, when executing the restoration-use bytecodes 803 in the content restoration processing unit 126, the post-execution codes 802 generated according to the rewriting in the TRS bytecode execution processing at S204 will not be rewritten again. And, during content playback, the decryption of the protected content data 113 at step S205 in Fig. 2 and the restoration of the modified content data at S206 in Fig. 2 can be executed in parallel without distortion occurring in the displayed video. Decryption Processing' of Protected Content Data 113 The following describes decryption processing of protected content data 113 (corresponding to S205 of Fig. 2), with use of Fig. 6. The content key generation unit 128 obtains the encrypted content key 114 from the recording medium 101 via the disc reading unit 121 (S601). ■ '' \ Next, the content key generation unit 128 obtains, from the revocation information processing unit 129, the media key that was generated in the revocation checking processing of the content playback apparatus 102 at S201 in Fig. 2, and decrypts the encrypted content key 114 (S602). The decryption unit 125 obtains the protected content data 113 from the recording medium 101 via the disc reading unit 121 (S603) . The decryption unit 125 obtains the content key from the content key generation unit 128, and decrypts the protected content data 113 (S604) . The modified content data output as a result of the decryption is transmitted to the content restoration processing unit 126. Here, the description of the decryption processing of the protected content data 113 is completed. Note that although in the present embodiment the protected content data 113 is generated by subjecting plaintext content data to modification processing and then encryption, the plaintext content data may instead be encrypted and then subject to modification ' processing. In this case, the order of S205 and S206 in Fig. 2 is switched. Furthermore, although in the present embodiment the restoration-use bytecodes are output in the TRS bytecode execution processing at S204 in Fig. 2, a fixed-length byte value (one example of restoration-use information) may be output as the output of the TRS bytecode execution processing at S204. In this case, the restoration processing of the modified content data at S206 uses the value output as a result of the TRS bytecode execution processing atS204, in a fixed operation processing, for example an XOR operation on the modified content data and the output value of S204. Furthermore, in the present embodiment, although operation processing such as an XOR operation is performed on the modified content data in the restoration of modified content at S206 in Fig. 2, the content may be protected by changing the reading order and playback order of the MPEG2-TS files that compose the content. The following describes this processing with use of Fig. 9. The playback control information 111 expresses that the content is composed of four TS files a to d, and, as a reading order 901 in the decryption unit 125, that these TS files are read in the following order: TS data b, TS data a, TS data d, TS data c. In Fig. 2, the protected content data 113 corresponding to each of the TS data files is read in accordance with the playback control information 111, and the decryption of the protected content data 113 at S205 is performed. data correspond respectively to the predetermined number of sets of TRS bytecodes, and correspond respectively to the predetermined number of encrypted content keys. (2) The protected content data 113 is generated in a manner such as the following by a content distribution apparatus. ' At least part of one piece of MPEG2-TS data is subjected to an XOR operation with a certain value, and the part is replaced with the obtained operation result. Then, using the content key, an encryption algorithm that implements AES, for instance, is applied, thereby generating the protected content data 113. (3) The revocation information 115 includes a plurality of encrypted media keys. The encrypted media keys correspond respectively to a plurality of devices, and have attached thereto a device identifier of the corresponding device, for instance. Here, the devices are, for instance, content playback apparatuses. A key management server apparatus possessed by the key management organization encrypts the media key using each of the device keys allocated to devices that are not revoked, thereby generating encrypted media keys. Each of the device keys allocated to a revoked device is used to encrypt predetermined detection information, thereby generating encrypted media keys. Here, the predetermined detection information has a fixed value, for example the value XN0". «*• The revocation information processing unit 129 selects an encrypted media key that corresponds to the content playback apparatus 102, and decrypts the selected encrypted media key using the device key obtained from the device key storage unit 130, to obtain decrypted information. Here, if the decrypted information is "0", the content playback apparatus 102 is considered to be revoked, and generation of the media key is considered to have failed. If the obtained decrypted information is not w0", the content playback apparatus 102 is not revoked and the generation of the media key succeeds, and therefore the decrypted information is considered to be the media key. (4) The TRS bytecode execution processing may be an ROT, which is a rotation operation. One example of a rotation operation is as follows. J- For instance, ROT2(X) shows subjecting 32-bit data X to a 2-bit circular shift to the left. Subjecting 32-bit data X to a 2-bit circular shift to the left denotes separating the data X into its highest 2 bits XI and its lowest 30 bits X2, and shifting X2 to the highest 30 bits of the data X and shifting XI to the lowest 2 bits 1: of the data X. C-,i'; (5) The TRS bytecodes 112 shown in Pig. 8 include, for instance, (i) encrypted data that is a predetermined plain text that has been encrypted, (ii) a decryption-use computer program for decrypting the encrypted data, and (iii) a rewriting-use computer 2C program for the TRS bytecodes 112 to self-rewrite the pre-execution codes 801 using the plaintext obtained according to the decryption. When the TRS bytecodes 112 are executed, the encrypted data included in the TRS bytecodes 112 are decrypted by the decryption-use computer program, thereby generating a plaintext. Then the . .> rewri ting-use computer program rewrites the pre-execution codes 801 that are part of the TRS bytecodes 112, with the generated plaintext. The restoration-use bytecodes 803 that include the post-execution codes 802 which are the overwritten part is generated in this way. (6) When the switching of the TS data shown in Fig. 9 is performed, the restoration-use bytecodes include, for instance, two instructions such as the following. SWAP TS data b, TS data a (instruction 1) SWAP TS data d, TS data c (instruction 2) Here, the instruction SWAP A, B" shows switching of the playback order of WA" and XXB" that are TS data. When the instruction *SWAP A, B" is executed, the playback order is switched such that the TS data UB" is played first, and then the TS data VXA" is played. When the aforementioned instruction 1 and instruction 2 are executed, as described above, the playback order of the TS data is as follows: TS data a, TS data b, TS data c, TS data d. Modification Examples The present invention has been described based on, but is not limited to, the above embodiment. Cases such as the following are included in the present invention. (1) Each described apparatus is, specifically, a computer system composed of a microprocessor, a ROM, a RAM, a hard disk unit, a display unit, a keyboard, a mouse, and the like. A computer program is stored in the RAM or the hard disk unit. The computer program is composed of a plurality of instruction codes showing instructions with respect to a computer in order to have predetermined functions achieved. The apparatus achieves predetermined functions by the microprocessor operating according to the computer program. Inother words, the microprocessor reads one of the instructions included in the computer program at a time, decodes the read instruction, and operates in accordance with the result of the decoding. (2) All or part of the compositional elements of each apparatus may be composed of one system LSI (Large Scale Integrated circuit) . The system LSI is a super-multifunctional LSI on which a plurality of compositional units are manufactured integrated on one chip, and is specifically a computer system that includes a microprocessor, a ROM, a RAM, or the like. A computer program is stored in the RAM. The system LSI achieves its functions by the microprocessor operating according to the computer program. Furthermore, the units that are the compositional elements of each of the apparatuses may be realized separately with individual chips, or part or all may be included on one chip. Here, the LSI may be an IC, a system LSI, a super LSI, or ultra LSI, depending on the degree of integration. Furthermore, the integration of circuits is not limited to being realized with LSI, but may be realized with a special-purpose circuit or a general-use processor. Alternatively, the integration may be realized with use of a FPGA (field programmable gate array) that is programmable after manufacturing of the LSI, or a re-configurable processor that enables re-configuration of the connection and settings of circuit cells in the LSI. (3) Part or all of the compositional elements of each apparatus may be composed of a removable IC card or a single module. The IC card or the module is a computer system composed of a microprocessor, a ROM, a RAM, or the like. The IC card or the module may include the aforementioned super-multifunctional LSI. The IC card or the module achieves its functions by the microprocessor operating according to computer program. The IC card or the module may be tamper-resistant. • (4) The present invention may be methods shown by the above. Furthermore, the methods may be a computer program realized by a computer, and may be a digital signal of the computer program. Furthermore, the present invention may be a computer-readable recording medium such as a flexible disk, a hard disk, a CD-ROM, anMO, aDVD, aDVD-ROM, aDVD-RAM, aBD (Blu-rayDisc) or a semiconductor memory, that stores the computer program or the digital signal. Furthermore, the present invention may be the computer program or the digital signal recorded on any of the aforementioned recording media. Furthermore, the present invention may be the computer program or the digital signal transmitted on a electric communication network, a wireless or wired communication network, a network of which the Internet is representative, or a data broadcast or the like. Furthermore, the present invention may be a computer system that includes a microprocessor and a memory, the memory storing the computer program, and the microprocessor operating according to the computer program. Furthermore, by transferring the program or the digital signal to the recording medium, or by transferring the program or the digital signal via a network or the like, the program or the digital s ignal may be executed by another independent computer system. (5) The present invention may be any combination of the above-described embodiment and modifications. Industrial Applicability The recording medium having recorded thereon content data that has been encrypted and modified to protect copyright and the information necessary for playback of the content data, the data processing method, and the data processing apparatus of the present invention are useful in fields such as the field of packaged media. Furthermore, the apparatuses and recording medium of the present invention can be used managerially, and repeatedly and continuously in a content distribution industry that creates content requiring copyright protection, and distributes the content. Furthermore, the apparatuses and recording medium of the present invention can be used managerially, and repeatedly and continuously in an electronic device manufacturing industry. WE CLAIM: 1. A data playback method for reading protected digital data from a recording medium (101) and playing the read protected digital data (113), the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original data, and (ii) a bytecode (112) that outputs a byte value for use in restoring modified digital data, the data playback method comprising: a first step of reading the protected digital data from the recording medium, and subjecting the read protected digital data to decryption which corresponds to the encryption, to generate modified digital data; characterized by the bytecode recorded on the recording medium; a second step of reading the bytecode from the recording medium and obtaining the byte value by executing the bytecode so as to cause the bytecode to self-rewrite part thereof; a third step of subjecting the generated modified digital data to a restoration operation in order to generate restored digital data, the restoration operation being a fixed operation that uses the byte value; and a fourth step of playing the generated restored digital data, wherein a control step of controlling such that the second step is performed before the first step. 2. The data playback method as claimed in claim 1, wherein the acquisition of the byte value in the second step is executed before the playing of the restored digital data, and the first step, the third step, and the fourth step are executed in parallel during the playing of the restored digital data. 3. The data playback method as claimed in claim 1, wherein the bytecode recorded on the recording medium is protected by a software tamper-resistant method, and the second step executes the bytecode after canceling the protection on the bytecode. 4. The data playback method as claimed in claim 1, wherein the digital data is composed of a plurality of pieces of content, and the bytecode outputs a different byte value for each piece of the content. 5. The data playback method as claimed in claim 1, wherein the protected digital data has been generated by encrypting the original digital data and then modifying the encrypted digital data, in the first step, instead of the decryption, the read protected digital data is subjected to the restoration operation, with use of the byte value, to generate encrypted digital data, and in the third step, instead of the restoration operation, the encrypted digital data is subjected to decryption that corresponds to the encryption, to generate the restored digital data. 6. A data processing apparatus that reads protected digital data from a recording medium (101) and plays the read protected digital data (113), the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original digital data, and (ii) a bytecode (112) that outputs a byte value for use in restoring modified digital data, the data processing apparatus comprising: a reading unit (121) operable to read the protected digital data and the bytecode from the recording medium; a decryption unit (125) operable to subject the read protected digital data to decryption corresponding to the encryption, to generate modified digital data; an acquisition unit (124) operable to read the bytecode from the recording medium and obtain the byte value by executing the bytecode so as to cause the bytecode to self-rewrite part thereof; a restoration unit (126) operable to subject the generated modified digital data to restoration operation in order to generate restored digital data, the restoration operation being a fixed operation that uses the byte value; and a playback unit (122) operable to play the generated restored digital data; a control unit operable to control with such that the acquisition of the byte value by the acquisition unit is performed before the decryption by the decryption unit, wherein the control unit controls such that the acquisition of the byte value is executed before playback of the restored digital data, and such that the decryption by the decryption unit, the restoration by the restoration unit and the playback of the restored digital data. 7. The data processing apparatus as claimed in claim 6, wherein the bytecode recorded on the recording medium is protected by a software tamper-resistant method, and the acquisition unit executed the bytecode after canceling the protection on the bytecode. 8. The data processing apparatus as claimed in claim 6, wherein the digital data is composed of a plurality of pieces of content, and the bytecode outputs a different byte value for each piece of the content. 9. The data processing apparatus as claimed in claim 6, wherein the protected digital data has been generated by encrypting the original digital data and then modifying the encrypted digital data, in the decryption unit, instead of the decryption, the read protected digital data is subjected to the restoration operation, with use of the byte value, to generate encrypted digital data, and in the restoration unit, instead of the restoration operation, the encrypted digital data is subjected to decryption that corresponds to the encryption, to generate the restored digital data. ABSTRACT TITLE: DATA PLAYBACK METHOD AND DATA PROCESSING APPARATUS The present invention is provided with a data playback method for reading protected digital data from a recording medium (101) and playing the read protected digital data (113), the recording medium having recorded thereon (i) the protected digital data which has been generated by modifying and encrypting original data, and (ii) a bytecode (112) that outputs a byte value for use in restoring modified digital data, the data playback method comprising a first step of reading the protected digital data from the recording medium, and subjecting the read protected digital data to decryption which corresponds to the encryption, to generate modified digital data; characterized by the bytecode recorded on the recording medium; a second step of reading the bytecode from the recording medium and obtaining the byte value by executing the bytecode so as to cause the bytecode to self-rewrite part thereof; a third step of subjecting the generated modified digital data to a restoration operation in order to generate restored digital data, the restoration operation being a fixed operation that uses the byte value; and a fourth step of playing the generated restored digital data, wherein a control step of controlling such that the second step is performed before the first step.

Full Text

Technical Field
The present invention relates to a method for storing
digitized data of content which is a copyrighted work such as a movie,
on a large-capacity medium such as a digital optical disc, and enabling
only specific terminals to completely acquire the data. In particular,
the present invention relates to a technique for playing content
data that is recorded on a large-capacity medium and has been encrypted
and modified in order to protect copyright.
Background Art
With increases in capacity of storage media in recent
years, systems that distribute contents, which are copyrighted works
such as movies, that have been digitized and stored on media such
as digital optical discs are becoming prevalent. In such a system,
it is necessary toprotect the copyright of a content such that playback, copying and the like of the content is carried out onlyunder limitations
defined by an agreement with the copyright holder. A general system
for protecting copyrighted works from dishonest copying and the like,
in other words copying and the like without the permission of the
copyright holder, has a structure whereby digital content is encrypted
with a content key managed by the copyright holder, recorded on a
disc, and is only able to be decrypted by a terminal that has a
corresponding content key. A party wishing to obtain the content
key must obey stipulations relating to copyright protection agreed
on with the copyright holder.

As one example of such a system, Patent Document 1
discloses a method for protecting a content key that is for encrypting
and decrypting content data, by generating the content key based
on a seed key and time-variable data.
Patent Document 1: Japanese Patent Application Publication
No. 2000-100069
Disclosure of the Invention
Problem to be Solved by the Invention
Although the content key must be managed strictly so
that it is not exposed to an outside party in this case, it is possible
that the content key will be exposed dishonestly due to some kind
of accident or occurrence. Once the content key is exposed, there
is a danger that a content key for future content will be exposed
using the same method. It is therefore assumed that dishonest usage
of future content will not be able to be prevented. The prior art
is vulnerable to this kind of attack because the content data is
protected only by content keys that are protected by a prescribed
method.
In view of the described problem, the present invention
has an object of providing a data playback method and a data processing
apparatus according to which, if a method is discovered to break
content protection due to some kind of accident or occurrence, other
content will not be able to be used dishonestly using the same method.
Means to Solve the Problem
In order to achieve the stated object, the present invention
is a data playback method for reading protected digital data from
a recording medium and playing the read protected digital data, the

recording medium having recorded thereon (i) the protected digital
data which has been generated by modifying and encrypting original
digital data, and (ii) modified restoration-use information which
has been generated by modifying restoration-use information that
is for use in restoring modified digital data, the data playback
method including: a first step of reading the protected digital data
from the recording medium, and subjecting the read protected digital
data to decryption which corresponds to the encryption, to generate
modified digital data; a second step of subjecting the generated
modified digital data to restoration which corresponds to the
modification, withuseof the restoration-use information, togenerate
restored digital data; a third step of playing the generated restored
digital data; a fourth step of reading the modified restoration-use
information from the recording medium, and, with use of the read
modified restoration-use information, generating the
restoration-use information in a format used in processing in the
second step; and a control step of controlling such that the fourth
step is executed before the first step.
Here, the generation of the restoration-use information
in the fourth step may be executed before the playing of the restored
digital data, and the first step, the second step, and the third
step may be executed in parallel during the playing of the restored
digital data.
Here, the modification of the restoration-use information may
be modification that makes the restoration-use information
software-tamper-resistant.
Here, the digital data may be composed of a plurality
of pieces of content, and execution processing of the restoration-use

information may differ for each piece of content.
Here, the protected digital data may have been generated by
encrypting the original digital data and then modifying the encrypted
digital data, in the first step, instead of the decryption, the read
protected digital data may be subjected to restoration that
corresponds to the modification, with use of the restoration-use
information, to generate encrypted digital data, and in the second
step, instead of the restoration, the encrypted digital data may
be subjected to decryption that corresponds to the encryption, to
generate the restored digital data.
Furthermore, the present invention is a data playback
method for reading protected digital data from a recording medium
and playing the read protected digital data, the recording medium
having recorded thereon (i) the protected digital data which has
been generated by modifying and encrypting original digital data,
and (ii) modified restoration-use information whichhas been generated
by modifying restoration-use information that is for use in restoring
modified digital data, the data playback method including: a first
step of reading the protected digital data from the recording medium,
and subjecting the read protected digital data to decryption which
corresponds to the encryption, to generate modified digital data;
a second step of subjecting the generated modified digital data to
restoration which corresponds to the modification, with use of the
restoration-use information, to generate restored digital data; a
third step of playing the generated restored digital data; and a
fourth step of, before the first step, reading the modified
restoration-use information from the recording medium, and subjecting
the read modified restoration-use information to restoration that

corresponds to the modification, to generate unmodified
restoration-use information.
Furthermore, the present invention is a data processing
apparatus that reads protected digital data from a recording medium
and plays the read protected digital data, the recording medium having
recorded thereon (i) the protected digital data which has been
generated by modifying and encrypting original digital data, and
(ii) modified restoration-use information which has been generated
by modifying restoration-use information that is for use in restoring
modified digital data, the data processing apparatus including: a
reading unit operable to read the protected digital data and the
modified restoration-use information from the recording medium; a
decryption unit operable to subject the read protected digital data to decryption corresponding to the encryption, to generate modified
digital data; a restoration unit operable to subject the generated
modified digital data to restoration corresponding to the modification,
with use of the restoration-use information, to generate restored
digital data; a playback unit operable to play the generated restored
digital data; a generation unit operable to read the modified
restoration-use information from the recording medium, and with use
of the read modified restoration-use information, generate the
restoration-use information in a format used in processing by the
restoration unit; and a control unit operable to control such that
the generation of the restoration-use information by the generation
unit is executed before the decryption by the decryption unit.
Here, the control unit may control such that the generation
of the restoration-use information is executed before playback of
the restored digital data, and such that the decryption by the

decryption unit, the restoration by the restoration unit and the
playback by the playback unit are performed in parallel during playback
of the restored digital data.
Here, the modification of the restoration-use information may
be modification that makes the. restoration-use information
software-tamper-resistant.
Here, the digital data may be composed of a plurality
of pieces of content, and execution processing of the restoration-use
information may differ for each piece of content.
Here, the protected digital data may have been generated by
encrypting the original digital data and then modifying the encrypted
digital data, in the decryption unit, instead of the decryption,
the read protected digital data may be subjected to restoration that
corresponds to the modification, with use of the restoration-use
information, to generate encrypted digital data, and in the
restoration unit, instead of the restoration, the encrypted digital
data may be subjected to decryption that corresponds to the encryption,
to generate the restored digital data.
Here, the present invention is a data processing apparatus
that reads protected digital data from a recording medium and plays
the read protected digital data, the recording medium having recorded
thereon (i) the protected digital data which has been generated by
modifying and encrypting original digital data, and (ii) modified
restoration-use information which has been generated by modifying
restoration-use information that is for use in restoring modified
digital data, the data processing apparatus including: a reading
unit operable to read the protected digital data and the modified
restoration-use information from the recording medium; a decryption

unit operable to subject the read protected digital data to decryption
corresponding to the encryption, to generate modified digital data;
a restoration unit operable to subj ect the generated modified digital
data to restoration corresponding to the modification, with use of
the restoration-use information, to generate restored digital data;
a playback unit operable to play the generated restored digital data;
a generation unit operable to read the modified restoration-use
information from the recording medium, and subject the modified
restoration-use information to restoration corresponding to the
modification, to generate unmodified restoration-use information;
and a control unit operable to control such that the generation of
the restoration-use information by the generation unit is executed
before the decryption by the decryption unit.
Effects of the Invention
According to the described invention, content is dually
protected according to an operation or the like and encryption. The
significance of this is as follows.
If a unified method is employed to encrypt each content, and
the restoration processing or the like using restoration-use
information or the like is different for each content, even if the
encryption of a content is broken dishonestly, other content will
be protected according to transformation that uses the restoration
information or the like. This provides even stronger protection of
copyright of content or the like.
Furthermore, according to the present invention,
transformation of the restoration-use information is executed before
decryption. The significance of this is as follows.
The present invention is effective in cases such as when the

Fig. 7 shows an example of restoration processing of modified
content data in an embodiment of the present invention;
Fig. 8 shows an example of restoration-use bytecodes being
generated from TRS bytecodes according to self-rewriting in an
embodiment of the present invention; and
Fig. 9 shows an example of restoration processing of protected
content according to switching of a playback order of TS data in
an embodiment of the present invention.
Description of Numerical References
101 recording medium
102 content playback apparatus
111 playback control information
112 TRS bytecodes
113 protected content data
114 encrypted content key
115 revocation information

121 disc reading unit
122 playback control unit
123 user operation reception unit
124 TRS bytecode execution unit
125 decryption unit
126 content data restoration processing unit
127 decoder
128 content key generation unit
129 revocation information processing unit
130 device key storage unit
501 encryption key-use TRS bytecodes

502 encrypted restoration-use bytecodes
701 bit string of unit of modification of modified content
data
702 parameter used in XOR operation
703 bit string of unit of modification after restoration

801 pre-execution codes
802 post-execution codes
803 restoration-use bytecodes

901 reading order in decryption unit 125
902 reading order in decoder 127
Best Mode for Carrying Out the Invention
The following describes a best mode for carrying out the
invention, with reference to the drawings.
The recording medium used in the present invention has recorded
thereon content data that is protected according to encryption with
a content key and data modification by an operation that is different
to the encryption. Also recorded on the recording medium with the
content data is the content key and a program for executing an inverse
operation to the aforementioned operation, which are also in a
protected state. The content key is protected by revocation
i n formation that enabl es the content key to be used only by an author i zed
data processing apparatus that has permission to use the content
data, and is recorded together with the revocation information. The
program is protected by being subjected to TRS (being subjected to
processing to make data software-tamper-resistant).
The procedure used to record the content data includes
a step of encrypting the content data with the content key, and a

step of data modification according to an operation that is different
to the encryption. The procedure also includes a step of recording
the content key in a protected state to the recording medium, and
a step of recording a program for executing an inverse operation
to the aforementioned operation to the recording medium. Here, the
program is in a protected state that is achieved using a different
method of protection to the method used to protect the content key.
The procedure further includes a step of protecting the content key
according to revocation information that enables the content key
to be used only by an authorized data processing apparatus that has
permission to use the content data. The procedure further includes
a step of protecting the program by subjecting it to TRS.
Pig. 1 shows the structure of a recording medium and a
content playback apparatus of an embodiment of the present invention.
A recording medium 101 has recorded thereon playback control
information 111, TRS (Tamper-resistant Software) bytecodes .112,
protected content data 113, an encrypted content key 114, and
revocation information 115. The recording medium 101 is assumed to
be a BD (Blu-Ray Disc) for instance, but is not limited to being
so. Note that in the present Description, "TRS bytecodes" denotes
codes generated by subjecting bytecodes to processing for making
data software-tamper-resistant.
In the present embodiment, it is assumed that one content
is composed of a plurality of pieces of MPEG2-TS (Motion Picture
Expert Group 2- Transport Stream) data. It is the playback control
information 111 that defines the playback order of the pieces of
data for playing the content.
The TRS bytecodes 112 (one example of modified restoration-use

information) are one or more bytecodes (one example of restoration- use
information) that has been subject to processing to put software
into a state in which secret information, processing contents and
the like included in the software cannot be ascertained by an act
of analysis. Specific execution contents of the bytecodes are
described later. Note that although an example of bytecodes is given
in the present embodiment, an execution program other than bytecodes
may be used.
The protected content data 113 (one example of protected
digital data) is data generated by subjecting plaintext MPEG2-TS
(one example of digital data) that can be output as video by a decoder
to encryption processing using the content key, and modification
processing in which an XOR operation or the like with a particular
value is performed.
The encrypted content key 114 is data generated by encrypting,
with a media key, the content key for decrypting the content data.
■ The following describes the revocation information 115.
A key management organization has a collection of a plurality of
device keys and a plurality of media keys. The key management
organization allocates one of the device keys, and a key identification
number for the device key, to each of content playback apparatuses
102, and gives the respective allocated device key and key
identification number to each content playback apparatus 102. The
key management organization also allocates one media key to the
recording medium 101. Next, the key management organization encrypts
the media key respectively using the each of the device keys allocated
to the content playback apparatuses 102, to generate encrypted media
keys, and generates a list of the encrypted media keys and key

identification numbers that correspond to all the device keys . This
list is the revocation information 115. A drawback of this simple
method is that the size of the data of the revocation information
115 will be unrealistically large if there is a large number of content
playback apparatuses 102. Therefore, the method disclosed in
"Digital Content Hogo-you Kagi Kanri Houshiki (Key Management Method
for Protecting Digital Content)" (Nakano, Ohmori and Tatebayashi,
Symposium on Cryptography arid Information Security 2001, SCIS2001,
5A-5, Jan. 2001) may be used to compress the size of the data of
the revocation information 115. A method to be used is not limited
to this method, and any other method for compressing the size of
the data of the revocation information 115 may be used.
The content playback apparatus 102 is composed of a disc
reading unit 121, a playback control unit 122, a user operation
reception unit 123, a TRS bytecode execution unit 124, a decryption
unit 125, a content data restoration processing unit 126, a decoder
127, a content key generation unit 128, a revocation information
processing unit 129, and a device key storage unit 130. One
implementation example of these components is the disc reading unit
121 being a BD drive, and the other components being realized by
a computer composed of a CPU, a work memory, an HDD and the like.
'■':" Here, the description of the structure of the recording
medium 101 and the content playback apparatus 102 pertaining to an
embodiment of the present invention is completed.
Description of Content Playback Processing
The following describes content playback processing, with use
of Fig. 2.
The content playback processing starts upon the user operation

reception unit 123 receiving a content playback start request from
the user via the user operation reception unit 123.
Upon the content playback start request being received,
the revocation information processing unit 129 performs revocation
checking processing with respect to the content playback apparatus
102 (S201) . Details of the revocation checking processing are given
later.
Subsequently, the processing branches depending on whether
or not generation of the media key is successful in the revocation
checking processing at S201 (S202).
If generation of the media key succeeds in the revocation
checking processing at S201, the playback control unit 122 performs
selection of the protected content data 113 (step S203).
; If generation of the media key fails in the revocation
checking processing at S201, notification is issued that the content
playback apparatus 102 is revoked, and the processing ends (S208) .
After the processing at S203 ends, the TRS bytecbdes 112
necessary for playback of the selected protected content data 113
are read, and the TRS bytecode execution unit 124 performs TRS bytecode
execution processing (S204) . Details of the TRS bytecode execution
processing are given later. Note that the processing up to this point
is pre-processing that is performed before the content is displayed.
In accordance with the playback control information 111,
the playback control unit 122 instructs reading of the protected
content data 113. The content key generation unit 128 and the
decryption unit 125 perform decryption of the read protected content
data 113. (S205) . Hereinafter, the data obtained as a result of
decrypting the protected content data 113 is called modified content

data (one example of modified digital data). The encryption used
in the encryption of the protected content is AES (Advanced Encryption
Standard), but is not limited to being so. Since decryption processing
is performed repeatedly during content playback until the end of
the protected content data 113, restoration (S206) and decoding of
content (S207), which are described later, are executed in parallel.
Details of decryption processing of the protected content data 113
are given later.
The content data restoration processing unit 126 performs
restoration processing on the modified content data output by the
decryption unit 125 (S206) . The restoration processing is executed
in units of aligned units, each of which is composed of a predetermined
number of MPEG2-TS packets in MPEG2-TS data, or executed in units
of sectors, each of which is the unit of recording on the recording
medium 101. During content playback, decryption processing of the
protected content data 113 (S205) and decoding of content which is
described later (S207) are executed in parallel. Details of
restoration processing of the modified content data are given later.
The restored content data is decoded in the decoder 127,
and is output to a device that displays video, such as a television
monitor (S207) . During content playback, decryption of the protected
content data 113 (S205) and restoration of the modified content data
(S206) are executed in parallel.
The content playback processing ends when playback of all the
content data ends.
Here, the description of the content playback processing
is completed.
Revocation Checking Processing of the Content Playback

Apparatus 102
The following describes revocation checking processing of the
content playback apparatus 102.
The revocation checking processing is processing that starts
after the start of content playback in Fig. 2, and is for checking
that the content playback apparatus 102 is not revoked, according
to the revocation information 115 recorded on the recording medium
101. The revocation checking processing corresponds to step S201.
The revocation information processing unit 129 reads the
device key obtained from the device key storage unit 130 (S301).
The device key is information that can be used to specify the content
playback apparatus 102, and is unique to the content playback apparatus
102.
Next, the revocation information processing unit 129 reads
the revocation information 115 recorded on the recording medium 101
(S302), and generates the media key with use of the read device key
and the revocation information 115 (S303).
The media key cannot be generated if the content playback
apparatus 102 is revoked. Details about generating the media key
with use of the device key and the revocation information 115 can
be found in National Technical Report Vol. 43, No. 3, pp. 118-122
(Engineering Administration Center, Matsushita Electric Industrial
Company, June 18, 1997) .
Here, the description of the revocation checking processing
of the content playback apparatus 102 is completed.
TRS bytecode execution processing
The following describes TRS bytecode execution processing
(corresponding to step S204 of Fig. 2), with use of Fig. 4.

The TRS bytecode execution unit 124 obtains the TRS bytecodes
112 necessary for playback of the instructed content, from the
recording medium 101 (S401).
The TRS bytecode execution unit 124 executes the obtained
TRS bytecodes 112, thereby outputting restoration-use bytecodes
(S402) . The restoration-use bytecodes are bytecodes executed in the
content data restoration processing unit 126.
The following describes a specific example of restoration
processing of modified content data in the content restoration
processing unit 126 at S206, with use of Fig. 7. In Fig. 7, an
explanation is given about processing of bytecodes for restoring
the content data by performing an XOR operation of the modified content
data and a certain value by executing the restoration-use bytecodes .
701 expresses a bit sequence that is the unit of modification of
the modified content data. A parameter 702 shows a parameter for
performing an XOR operation for restoring the modified content data.
The parameter 702 is specified in the restoration-use bytecodes.
The content restoration processing unit 126 outputs, as plaintext
content data 703, the result of performing the XOR operation on the
unit of modification 701 of modified content data and the parameter
702 by executing the restoration-use bytecodes . The entire modified
content data is restored by repeatedly executing the described
processing.
. The execution processing is assumed to be an XOR operation
using the modified content data with a specific byte sequence in
the bytecodes, with a value in a specific address of the data to
be restored, or with a combination of those values. However, the
execution processing is not limited to being an operation mentioned

above. The execution processing may alternatively be a combination
of several operations that incur a relatively small processing load,
such as a ROT. The processing executed according to restoration-use
bytecodes may differ for each content.
' .- Furthermore, the TRS bytecodes 112 may be data generated
by concatenating encryption key-use TRS bytecodes 501 and encrypted
restoration-use bytecodes 502 (one example of modified
restoration-use information), as shown in Fig. 5. In such a case,
the encryption key-use TRS bytecodes 501 are executed by the TRS
bytecode execution unit 124, to output an encryption key for the
encrypted restoration-use bytecodes 502. The output encryption key
and encrypted restoration-use bytecodes 502 are transmitted to the
decryption unit 125, which generates restoration-use bytecodes . The
generated restoration-use bytecodes are transmitted to the content
restoration unit 126, and the processing continues.
Furthermore, in the above example, the restoration-use
bytecodes that are output are different bytecodes to the TRS bytecodes
112 recorded on the recording medium 101. However, the
restoration-use bytecodes that are output may be bytecodes generated
in TRS bytecode execution processing at S204 in which the TRS bytecodes
112 self-rewrite part of their own codes. The following describes
the TRS bytecode execution processing at S204 for generating
restoration-use bytecodes 803 by self-rewriting, with use of Fig.
8. In Fig. 8, pre-execution codes 801 of the TRS bytecodes 112 are
executed according to the TRS bytecode execution processing at S204,
thereby self-rewriting into post-execution codes 802 to output
restoration-use bytecodes 803. Here, when executing the
restoration-use bytecodes 803 in the content restoration processing

unit 126, the post-execution codes 802 generated according to the
rewriting in the TRS bytecode execution processing at S204 will not
be rewritten again. And, during content playback, the decryption
of the protected content data 113 at step S205 in Fig. 2 and the
restoration of the modified content data at S206 in Fig. 2 can be
executed in parallel without distortion occurring in the displayed
video.
Decryption Processing' of Protected Content Data 113
The following describes decryption processing of protected
content data 113 (corresponding to S205 of Fig. 2), with use of Fig.
6.
The content key generation unit 128 obtains the encrypted
content key 114 from the recording medium 101 via the disc reading
unit 121 (S601).
■ '' \ Next, the content key generation unit 128 obtains, from
the revocation information processing unit 129, the media key that
was generated in the revocation checking processing of the content
playback apparatus 102 at S201 in Fig. 2, and decrypts the encrypted
content key 114 (S602).
The decryption unit 125 obtains the protected content data
113 from the recording medium 101 via the disc reading unit 121 (S603) .
The decryption unit 125 obtains the content key from the
content key generation unit 128, and decrypts the protected content
data 113 (S604) . The modified content data output as a result of
the decryption is transmitted to the content restoration processing
unit 126.
Here, the description of the decryption processing of the
protected content data 113 is completed.

Note that although in the present embodiment the protected
content data 113 is generated by subjecting plaintext content data
to modification processing and then encryption, the plaintext content
data may instead be encrypted and then subject to modification
' processing. In this case, the order of S205 and S206 in Fig. 2 is
switched.
Furthermore, although in the present embodiment the
restoration-use bytecodes are output in the TRS bytecode execution
processing at S204 in Fig. 2, a fixed-length byte value (one example
of restoration-use information) may be output as the output of the
TRS bytecode execution processing at S204. In this case, the
restoration processing of the modified content data at S206 uses
the value output as a result of the TRS bytecode execution processing
atS204, in a fixed operation processing, for example an XOR operation
on the modified content data and the output value of S204.
Furthermore, in the present embodiment, although
operation processing such as an XOR operation is performed on the
modified content data in the restoration of modified content at S206
in Fig. 2, the content may be protected by changing the reading order
and playback order of the MPEG2-TS files that compose the content.
The following describes this processing with use of Fig. 9. The
playback control information 111 expresses that the content is
composed of four TS files a to d, and, as a reading order 901 in
the decryption unit 125, that these TS files are read in the following
order: TS data b, TS data a, TS data d, TS data c. In Fig. 2, the
protected content data 113 corresponding to each of the TS data files
is read in accordance with the playback control information 111,
and the decryption of the protected content data 113 at S205 is performed.

data correspond respectively to the predetermined number of sets
of TRS bytecodes, and correspond respectively to the predetermined
number of encrypted content keys.
(2) The protected content data 113 is generated in a manner
such as the following by a content distribution apparatus.
' At least part of one piece of MPEG2-TS data is subjected
to an XOR operation with a certain value, and the part is replaced
with the obtained operation result. Then, using the content key,
an encryption algorithm that implements AES, for instance, is applied,
thereby generating the protected content data 113.
(3) The revocation information 115 includes a plurality of
encrypted media keys. The encrypted media keys correspond
respectively to a plurality of devices, and have attached thereto
a device identifier of the corresponding device, for instance. Here,
the devices are, for instance, content playback apparatuses.
A key management server apparatus possessed by the key
management organization encrypts the media key using each of the
device keys allocated to devices that are not revoked, thereby
generating encrypted media keys. Each of the device keys allocated
to a revoked device is used to encrypt predetermined detection
information, thereby generating encrypted media keys. Here, the
predetermined detection information has a fixed value, for example
the value XN0". «**•
The revocation information processing unit 129 selects
an encrypted media key that corresponds to the content playback
apparatus 102, and decrypts the selected encrypted media key using
the device key obtained from the device key storage unit 130, to
obtain decrypted information. Here, if the decrypted information

is "0", the content playback apparatus 102 is considered to be revoked,
and generation of the media key is considered to have failed. If
the obtained decrypted information is not w0", the content playback
apparatus 102 is not revoked and the generation of the media key
succeeds, and therefore the decrypted information is considered to
be the media key.
(4) The TRS bytecode execution processing may be an ROT,
which is a rotation operation. One example of a rotation operation
is as follows.
J- For instance, ROT2(X) shows subjecting 32-bit data X to a 2-bit
circular shift to the left. Subjecting 32-bit data X to a 2-bit
circular shift to the left denotes separating the data X into its
highest 2 bits XI and its lowest 30 bits X2, and shifting X2 to the
highest 30 bits of the data X and shifting XI to the lowest 2 bits
1: of the data X.
C-,i'; (5) The TRS bytecodes 112 shown in Pig. 8 include, for
instance, (i) encrypted data that is a predetermined plain text that
has been encrypted, (ii) a decryption-use computer program for
decrypting the encrypted data, and (iii) a rewriting-use computer
2C program for the TRS bytecodes 112 to self-rewrite the pre-execution
codes 801 using the plaintext obtained according to the decryption.
When the TRS bytecodes 112 are executed, the encrypted data
included in the TRS bytecodes 112 are decrypted by the decryption-use
computer program, thereby generating a plaintext. Then the
. .> rewri ting-use computer program rewrites the pre-execution codes 801
that are part of the TRS bytecodes 112, with the generated plaintext.
The restoration-use bytecodes 803 that include the post-execution
codes 802 which are the overwritten part is generated in this way.

(6) When the switching of the TS data shown in Fig. 9
is performed, the restoration-use bytecodes include, for instance,
two instructions such as the following.
SWAP TS data b, TS data a (instruction 1)
SWAP TS data d, TS data c (instruction 2)
Here, the instruction *SWAP A, B" shows switching of the playback
order of WA" and XXB" that are TS data. When the instruction *SWAP
A, B" is executed, the playback order is switched such that the TS
data UB" is played first, and then the TS data VXA" is played.
When the aforementioned instruction 1 and instruction
2 are executed, as described above, the playback order of the TS
data is as follows: TS data a, TS data b, TS data c, TS data d.
Modification Examples
The present invention has been described based on, but is not
limited to, the above embodiment. Cases such as the following are
included in the present invention.
(1) Each described apparatus is, specifically, a computer
system composed of a microprocessor, a ROM, a RAM, a hard disk unit,
a display unit, a keyboard, a mouse, and the like. A computer program
is stored in the RAM or the hard disk unit. The computer program
is composed of a plurality of instruction codes showing instructions
with respect to a computer in order to have predetermined functions
achieved. The apparatus achieves predetermined functions by the
microprocessor operating according to the computer program. Inother
words, the microprocessor reads one of the instructions included
in the computer program at a time, decodes the read instruction,
and operates in accordance with the result of the decoding.
(2) All or part of the compositional elements of each

apparatus may be composed of one system LSI (Large Scale Integrated
circuit) . The system LSI is a super-multifunctional LSI on which
a plurality of compositional units are manufactured integrated on
one chip, and is specifically a computer system that includes a
microprocessor, a ROM, a RAM, or the like. A computer program is
stored in the RAM. The system LSI achieves its functions by the
microprocessor operating according to the computer program.
Furthermore, the units that are the compositional elements
of each of the apparatuses may be realized separately with individual
chips, or part or all may be included on one chip. Here, the LSI
may be an IC, a system LSI, a super LSI, or ultra LSI, depending
on the degree of integration.
Furthermore, the integration of circuits is not limited to
being realized with LSI, but may be realized with a special-purpose
circuit or a general-use processor. Alternatively, the integration
may be realized with use of a FPGA (field programmable gate array)
that is programmable after manufacturing of the LSI, or a
re-configurable processor that enables re-configuration of the
connection and settings of circuit cells in the LSI.
(3) Part or all of the compositional elements of each
apparatus may be composed of a removable IC card or a single module.
The IC card or the module is a computer system composed of a
microprocessor, a ROM, a RAM, or the like. The IC card or the module
may include the aforementioned super-multifunctional LSI. The IC
card or the module achieves its functions by the microprocessor
operating according to computer program. The IC card or the module
may be tamper-resistant.
• (4) The present invention may be methods shown by the

above. Furthermore, the methods may be a computer program realized
by a computer, and may be a digital signal of the computer program.
Furthermore, the present invention may be a computer-readable
recording medium such as a flexible disk, a hard disk, a CD-ROM,
anMO, aDVD, aDVD-ROM, aDVD-RAM, aBD (Blu-rayDisc) or a semiconductor
memory, that stores the computer program or the digital signal.
Furthermore, the present invention may be the computer program or
the digital signal recorded on any of the aforementioned recording
media.
Furthermore, the present invention may be the computer
program or the digital signal transmitted on a electric communication
network, a wireless or wired communication network, a network of
which the Internet is representative, or a data broadcast or the
like.
Furthermore, the present invention may be a computer system
that includes a microprocessor and a memory, the memory storing the
computer program, and the microprocessor operating according to the
computer program.
Furthermore, by transferring the program or the digital
signal to the recording medium, or by transferring the program or
the digital signal via a network or the like, the program or the
digital s ignal may be executed by another independent computer system.
(5) The present invention may be any combination of the
above-described embodiment and modifications.
Industrial Applicability
The recording medium having recorded thereon content data
that has been encrypted and modified to protect copyright and the

information necessary for playback of the content data, the data
processing method, and the data processing apparatus of the present
invention are useful in fields such as the field of packaged media.
Furthermore, the apparatuses and recording medium of the present invention can be used managerially, and repeatedly and
continuously in a content distribution industry that creates content
requiring copyright protection, and distributes the content.
Furthermore, the apparatuses and recording medium of the present
invention can be used managerially, and repeatedly and continuously
in an electronic device manufacturing industry.

WE CLAIM:
1. A data playback method for reading protected digital data from a recording
medium (101) and playing the read protected digital data (113), the recording
medium having recorded thereon (i) the protected digital data which has been
generated by modifying and encrypting original data, and (ii) a bytecode (112)
that outputs a byte value for use in restoring modified digital data, the data
playback method comprising:
a first step of reading the protected digital data from the recording
medium, and subjecting the read protected digital data to decryption which
corresponds to the encryption, to generate modified digital data;
characterized by the bytecode recorded on the recording medium;
a second step of reading the bytecode from the recording medium and
obtaining the byte value by executing the bytecode so as to cause the bytecode
to self-rewrite part thereof;
a third step of subjecting the generated modified digital data to a
restoration operation in order to generate restored digital data, the restoration
operation being a fixed operation that uses the byte value; and
a fourth step of playing the generated restored digital data, wherein a
control step of controlling such that the second step is performed before the first
step.
2. The data playback method as claimed in claim 1, wherein
the acquisition of the byte value in the second step is executed before the
playing of the restored digital data, and the first step, the third step, and the
fourth step are executed in parallel during the playing of the restored digital
data.

3. The data playback method as claimed in claim 1, wherein
the bytecode recorded on the recording medium is protected by a
software tamper-resistant method, and
the second step executes the bytecode after canceling the protection on
the bytecode.
4. The data playback method as claimed in claim 1, wherein
the digital data is composed of a plurality of pieces of content, and
the bytecode outputs a different byte value for each piece of the content.
5. The data playback method as claimed in claim 1, wherein
the protected digital data has been generated by encrypting the original
digital data and then modifying the encrypted digital data,
in the first step, instead of the decryption, the read protected digital data
is subjected to the restoration operation, with use of the byte value, to generate
encrypted digital data, and
in the third step, instead of the restoration operation, the encrypted digital
data is subjected to decryption that corresponds to the encryption, to generate
the restored digital data.
6. A data processing apparatus that reads protected digital data from a recording
medium (101) and plays the read protected digital data (113), the recording
medium having recorded thereon (i) the protected digital data which has been
generated by modifying and encrypting original digital data, and (ii) a bytecode
(112) that outputs a byte value for use in restoring modified digital data, the
data processing apparatus comprising:

a reading unit (121) operable to read the protected digital data and the
bytecode from the recording medium;
a decryption unit (125) operable to subject the read protected digital data
to decryption corresponding to the encryption, to generate modified digital data;
an acquisition unit (124) operable to read the bytecode from the recording
medium and obtain the byte value by executing the bytecode so as to cause the
bytecode to self-rewrite part thereof;
a restoration unit (126) operable to subject the generated modified digital
data to restoration operation in order to generate restored digital data, the
restoration operation being a fixed operation that uses the byte value; and
a playback unit (122) operable to play the generated restored digital data;
a control unit operable to control with such that the acquisition of the byte
value by the acquisition unit is performed before the decryption by the
decryption unit, wherein the control unit controls such that the acquisition of the
byte value is executed before playback of the restored digital data, and such that
the decryption by the decryption unit, the restoration by the restoration unit and
the playback of the restored digital data.
7. The data processing apparatus as claimed in claim 6, wherein
the bytecode recorded on the recording medium is protected by a
software tamper-resistant method, and
the acquisition unit executed the bytecode after canceling the protection
on the bytecode.
8. The data processing apparatus as claimed in claim 6, wherein
the digital data is composed of a plurality of pieces of content, and
the bytecode outputs a different byte value for each piece of the content.

9. The data processing apparatus as claimed in claim 6, wherein
the protected digital data has been generated by encrypting the original
digital data and then modifying the encrypted digital data,
in the decryption unit, instead of the decryption, the read protected digital
data is subjected to the restoration operation, with use of the byte value, to
generate encrypted digital data, and
in the restoration unit, instead of the restoration operation, the encrypted
digital data is subjected to decryption that corresponds to the encryption, to
generate the restored digital data.

ABSTRACT

TITLE: DATA PLAYBACK METHOD AND DATA PROCESSING
APPARATUS
The present invention is provided with a data playback method for reading protected
digital data from a recording medium (101) and playing the read protected digital data
(113), the recording medium having recorded thereon (i) the protected digital data
which has been generated by modifying and encrypting original data, and (ii) a
bytecode (112) that outputs a byte value for use in restoring modified digital data, the
data playback method comprising a first step of reading the protected digital data from
the recording medium, and subjecting the read protected digital data to decryption
which corresponds to the encryption, to generate modified digital data; characterized by
the bytecode recorded on the recording medium; a second step of reading the bytecode
from the recording medium and obtaining the byte value by executing the bytecode so
as to cause the bytecode to self-rewrite part thereof; a third step of subjecting the
generated modified digital data to a restoration operation in order to generate restored
digital data, the restoration operation being a fixed operation that uses the byte value;
and a fourth step of playing the generated restored digital data, wherein a control step
of controlling such that the second step is performed before the first step.

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Patent Number

258845

Indian Patent Application Number

1702/KOLNP/2007

PG Journal Number

07/2014

Publication Date

14-Feb-2014

Grant Date

11-Feb-2014

Date of Filing

14-May-2007

Name of Patentee

PANASONIC CORPORATION

Applicant Address

1006, OAZA KADOMA, KADOMA SHI, OSAKA 571 8501, JAPAN

Inventors:

#	Inventor's Name	Inventor's Address
1	SENICHI ONODA	C/O MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. 1006, OAZA KADOMA, KADOMA-SHI, OSAKA 571-8501
2	KAORU MURASE	C/O MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. 1006, OAZA KADOMA, KADOMA-SHI, OSAKA 571-8501
3	MASAYA MIYAZAKI	C/O MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. 1006, OAZA KADOMA, KADOMA-SHI, OSAKA 571-8501
4	MASAYA YAMAMOTO	C/O MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. 1006, OAZA KADOMA, KADOMA-SHI, OSAKA 571-8501

PCT International Classification Number

G06F 21/24

PCT International Application Number

PCT/JP2005/020470

PCT International Filing date

2005-11-08

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2004-326512	2004-11-10	Japan