Patent Publication Number: US-2009240957-A1

Title: Copy protection method, content playback apparatus, and ic chip

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-69508 filed on Mar. 18, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD 
     A copy protection method, etc., disclosed herein relates to a copy protection method for preventing a content recording medium from being illicitly copied, and further relates to a content playback apparatus that is compatible with the copy protection method, and an IC chip used in implementation of the copy protection method. 
     Many types of content recording media for recording various types of content, such as movies, music, and software, are offered on the market. Representative examples of the content recording media include DVDs, CDs, and memory cards. 
     For so-called copy protection techniques for preventing the content recording media from being illicitly used or illicitly copied, various techniques have been proposed so far and have also been widely put to practical use. Examples of the techniques include the following [Patent Document 1] and [Patent Document 2]. 
     According to an invention of [Patent Document 1], upon executing an application on a personal computer, the application reads an ID recorded in a non-rewritable area of a USB memory external to the personal computer, and when the ID is correct the application is executed. 
     According to an invention of [Patent Document 2], upon a recording operation, (1) in a distribution apparatus, an ID and a public key Kp are read from a medium and the ID and a common key Kw are encrypted by the public key Kp, and then the encrypted ID and common key Kw are recorded in the medium; and (2) content to be distributed is encrypted by the common key Kw and the encrypted content is stored in the medium. Upon a playback operation, (1) a terminal apparatus (playback apparatus) reads an ID that is not encrypted, an encrypted ID, and an encrypted common key Kw from a medium; (2) the terminal apparatus decrypts the encrypted ID and common key Kw by a secret key Ks held by the terminal apparatus; (3) the terminal apparatus compares the decrypted ID with the unencrypted ID read from the medium to verify that the IDs match each other; and (4) encrypted content is decrypted by the common key Kw obtained by decryption.
     [Patent Document 1] Japanese Laid-open Patent Publication No. 2003-288128   [Patent Document 2] Japanese Laid-open Patent Publication No. H11-250571   

     In conventional typical copy protection methods, a “secret key” is contained in playback apparatuses that are distributed in large numbers on the market. Hence, when the secret key is stolen from a playback apparatus, a common key contained in a content recording medium can be broken. In addition, since a public key is contained in the medium, a pirated edition of content can be easily produced. That is, such methods have a weak copy protection function. 
     An object of the present invention is therefore to provide a copy protection method with a further enhanced protection function compared to conventional methods. 
     Furthermore, another object of the present invention is to provide a content playback apparatus and an IC chip that are compatible with the copy protection method. 
     According to a copy protection method disclosed herein, illicit copying of a content recording medium is prevented by an IC chip which is a hardware chip. Since the IC chip has a unique chip ID originally recorded therein, the chip ID may be used for copy protection. Moreover, an encrypted chip ID obtained by encrypting the chip ID by a secret key known only to a specific manufacturer may be used. In addition, the IC chip stores a content ID that uniquely represents content recorded on a content recording medium to which the IC chip is added. The content ID is also encrypted by the secret key. 
     Playback of the content is allowed only when IDs respectively obtained by decrypting the encrypted chip ID and the encrypted content ID on a content playback apparatus and the original chip ID can be correctly reproduced in their original forms on the content playback apparatus. 
     Therefore, even if content (regardless of whether the content is encrypted or not) is copied by malicious third parties, the illicitly copied content cannot be eventually played back unless the content is correctly reproduced as described above. Accordingly, even if malicious third parties succeed in copying the content itself, the content cannot, after all, be played back, thus reducing the possibility of illicit copying. It is sufficient for an IC chip used herein to include at least a memory. Since a high-functionality portion of a CPU is not required, the IC chip is low in cost and small in size. 
     SUMMARY 
     An IC chip that can be added to a content recording medium and that has a chip ID which is non-rewritably and uniquely set and originally recorded therein, wherein the IC chip includes a writable/readable ID memory that stores an encrypted content ID obtained by encrypting a content ID that identifies content, and an encrypted chip ID obtained by encrypting the chip ID. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a first method disclosed in the present specification. 
         FIG. 2  is a diagram illustrating a second method disclosed in the present specification. 
         FIG. 3  is a diagram illustrating a specific example of a content playback apparatus  200 . 
         FIG. 4  is a flowchart illustrating a method performed by a manufacturing side  100 . 
         FIG. 5  is a flowchart illustrating a method performed by the side of the content playback apparatus  200 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a diagram illustrating a first method disclosed in the present specification and  FIG. 2  is a diagram illustrating a second method disclosed in the present specification. Note that, as described above, the first method is for when a content recording medium is manufactured and the second method is for when content is played back. 
     First, referring to a manufacturing side  100  in  FIG. 1 , a content recording medium  10  represents a content recording medium (hereinafter, also simply referred to as a recording medium) which is a target of copy protection. Content  11  shown at the far left of the drawing is burned (arrow A) onto the content recording medium  10 . The content  11  may be, for example, a movie, music, or software. Note that the content  11  may be encrypted or not encrypted and in either case a copy protection function in a copy protection method disclosed herein is not affected. 
     The portion to which attention should be directed is a block  12  shown at the far right of the drawing. The block  12  is the aforementioned IC chip. a unique chip ID (individual identification number)  13  is originally recorded in the IC chip  12 . Also, an ID memory  14  is provided in the IC chip  12 . 
     The first step of the copy protection method disclosed herein is to gather information on a chip ID and a content ID, which is illustrated as ID information  16 . A chip ID in the ID information  16  is, as illustrated by arrow B in  FIG. 1 , the chip ID  13  read out from the IC chip  12 . A content ID in the ID information  16  is prepared as follows. 
     First, a specific computation process is performed on the content  11  (see arrow C in  FIG. 1 ) to obtain a content ID  15 . An example of the specific computation process includes a hash function computation. By this computation, a “hash value” may be obtained. By using the hash function, for example, a hash value (content ID) of 128 bytes that uniquely identifies the content  11  of 5 gigabytes, for example, can be obtained. The content ID  15  thus obtained is entered as one piece of the ID information  16 . 
     In the second step, the ID information  16  is encrypted (see arrow E). The encryption is performed using a secret key  17 , whereby encrypted ID information  16 ′ is obtained. In this case, the secret key  17  is only known to a limited number of people such as a specific manufacturer (e.g., an IC chip manufacturer) and thus has a high level of confidentiality. 
     In this way, the encrypted ID information  16 ′ including an encrypted chip ID  13 ′ and an encrypted content ID  15 ′ is obtained. The ID information  16 ′ is then stored in the ID memory  14  in the IC chip  12 . 
     The IC chip  12  thus processed is added to a corresponding unique content recording medium  10  and the content recording medium  10  is distributed on the market for purchase by users. 
     A content recording medium  10  with an IC chip which is bought by a user on the market is set, for example, on a content playback apparatus (player) in a user&#39;s home. If the recording medium with an IC chip is one that is illicitly manufactured (e.g., a pirated edition), then playback cannot be performed. The prevention of the playback in this case is enabled by the second method. 
     Now, the second method will be explained with reference to  FIG. 2 . In  FIG. 2 , the above-described content playback apparatus (hereinafter, also simply referred to as a “playback apparatus”) is represented by reference numeral  200 . In the first step, content  21  is read out (arrow G) from a content recording medium  20  set on the playback apparatus  200 . Also, an encrypted chip ID  23 ′ and an encrypted content ID  25 ′, which are stored in an ID memory  24  in the IC chip  22 , and a chip ID  23  are read out (arrow H) from an IC chip  22  added to the content recording medium  20  to regenerate encrypted ID information  26 ′. 
     Then, in the second step, the computation process as the aforementioned specific computation process (arrow C in  FIG. 1 ) is performed on the content  21  read out (arrow G) to generate a content ID  25  (arrow C in  FIG. 2 ). 
     Furthermore, in the third step, the encrypted chip ID  23 ′ and the encrypted content ID  25 ′ that form the encrypted ID information  26 ′ are decrypted by a public key  27  (arrow I in  FIG. 2 ). In this way, decrypted ID information  26 ″ is obtained and a decrypted chip ID  23 ″ and a decrypted content ID  25 ″, e.g., an original chip ID and an original content ID, are reproduced. 
     In the fourth step, a match/mismatch between the respective IDs reproduced in the above-described manner is detected by a first comparing unit  31  and a second comparing unit  32 . The first comparing unit  31  compares the reproduced chip ID  23 ″ with the chip ID  23  read out from the IC chip  22 , to determine whether the IDs match (OK) or mismatch (NG). 
     In parallel with this, the second comparing unit  32  compares the reproduced content ID  25 ″ with the content ID  25  computed by the hash function, to determine whether the IDs match (OK) or mismatch (NG). 
     Thus, whether the content recording medium  20  is one that is illicitly copied or not may be detected. When results of the comparisons ( 31  and  32 ) both match (OK), the content recording medium  20  is an authentic product (e.g., the content recording medium  10 ) and thus the playback apparatus  200  can play back the content. In contrast, when at least one of the results of the comparisons ( 31  and  32 ) does not match (NG), the content recording medium  20  may be an illicitly copied product and thus the playback apparatus  200  cannot play back the content. Even if malicious third parties produce illicitly copied products, the products cannot, after all, be played back and thus are useless as products for sale. Accordingly, the third parties may not plan making such illicit copies from the beginning. 
     Examples of preventing such illicit copying include the following (a) and (b). Specifically, 
     (a) the content recording medium  10  having the IC chip  12  added thereto, shown at the far right of  FIG. 1 , is offered on the market. Suppose that a third party removes the IC chip  12  from the medium  10  and illicitly adds an IC chip of another recording medium. 
     Suppose that such a recoding medium is set on the playback apparatus  200 . If the IC chip  12  is used as is, two chip IDs match each other and thus a matching determination performed by the first comparing unit  31  is cleared. However, if two pieces of content are different, their hash values (content IDs) do not match each other and thus a matching determination performed by the second comparing unit  32  cannot be cleared (NG). As a result, content on the recording medium cannot be played back. 
     (b) Suppose that a third party produces an illicitly copied product in which a similar IC chip is added to a recording medium (e.g., a pirated edition) having illicitly copied content of the content recording medium  10 . Since a chip ID of the similar IC chip and a chip ID reproduced from an ID memory  24  do not match each other (chip IDs are all unique), a comparison result obtained by the first comparing unit  31  indicates “NG” and thus the content cannot be played back. Even if the third party manages to learn the chip ID of the IC chip  12 , the third party cannot learn the secret key  17  and thus can neither generate the original encrypted chip ID  13 ′ nor generate the same content ID as that of the authentic product. 
     The above-described IC chip  12  will be summarized. The IC chip can be added to a content recording medium  10  and has a chip ID  13  which is non-rewritably and uniquely set and originally recorded therein. The IC chip includes a writable/readable ID memory  14  that stores an encrypted content ID  15 ′ obtained by encrypting a content ID  15  that identifies the content  11 , and an encrypted chip ID  13 ′ obtained by encrypting the chip ID  13 . 
     The content ID  15  is generated from a computed value of n (n&lt;&lt;N) bytes obtained by performing a computation operation on N-byte digital data forming the content  11 , using a specific function. The specific function may be, for example, a hash function, and the computed value may be a hash value obtained using the hash function. 
     The content ID  15  and the chip ID  13  are encrypted by a first key ( 17 ), and the encrypted content ID  15 ′ and the encrypted chip ID  13 ′ are generated. The first key makes a pair with a second key ( 27 ) used to decrypt the encrypted content ID  15 ′ and the encrypted chip ID  13 ′ when the content  11  recorded on the content recording medium  10  is played back. In this case, the first key ( 17 ) is a secret key  17  that is secretly held only by a manufacturer of the IC chip  12 , and the second key ( 27 ) is a public key  27  publicly provided to each content playback apparatus  200  that plays back the content  11  recorded on the content recording medium  10 . 
     It is desirable that the IC chip  12  be manufactured by a manufacturer different from a manufacturer of the content recording medium  10  to further enhance the secrecy of the IC chip  12 . A content recording medium  10  having such an IC chip  12  added is new. The IC chip  12  may be added to the content recording medium  10  by, for example, bonding or embedding. 
     Next, a specific example of the content playback apparatus  200 , the concept of which is illustrated in  FIG. 2 , will be described. 
       FIG. 3  is a diagram illustrating a specific example of the content playback apparatus  200 . In the drawing, the content playback apparatus  200  has a first readout function unit  41  and a second readout function unit  42 . 
     The first readout function unit  41  reads out an encrypted content ID  25 ′ and an encrypted chip ID  23 ′ from an IC chip  22  added to a content recording medium  20 . The content recording medium  20  has an ID memory  24  that stores an encrypted content ID  15 ′ and an encrypted chip ID  13 ′ which are respectively obtained by encrypting, by a first key ( 17 ), a content ID  15  and a chip ID  13 . The content ID  15  is obtained by a specific process based on content  11  to uniquely identify the content  11 . The chip ID  13  is uniquely set and non-rewritably and originally recorded in an IC chip  12 . 
     The second readout function unit  42  reads out a chip ID  23  contained in the IC chip  22  itself. Although, as stated above, the content ID  15  and the chip ID  13  each are encrypted by the first key, e.g., the IDs are separately encrypted, encryption is not limited thereto and the content ID  15  and the chip ID  13  may be combined into one ID data unit and the ID data unit may be encrypted once. 
     The content playback apparatus  200  further has a decryption unit  43 . The decryption unit  43  decrypts the read encrypted content ID  25 ′ and encrypted chip ID  23 ′ with a second key ( 27 ) which makes a pair with the first key ( 17 ) and regenerates an original content ID  25 ″ and an original chip ID  23 ″. 
     The content playback apparatus  200  also has a content ID generation unit  44  that generates a content ID  25  obtained by performing the same process as the aforementioned specific process on content  21  recorded on the content recording medium  20 . 
     The content playback apparatus  200  has a playback allowance function unit  45  that allows playback of the content  21  only when decrypted data units (CH and CO) from the decryption unit  43  match output data units (CH and CO) from the second readout function unit  42  and the content ID generation unit  44  respectively. The playback allowance unit  45  includes a chip ID comparing unit  51  that detects a match/mismatch between the decrypted chip ID (CH) from the decryption unit  43  and the chip ID (CH) from the second readout unit  42 ; and a content ID comparing unit  52  that detects a match/mismatch between the decrypted content ID (CO) from the decryption unit  43  and the content ID (CO) from the content ID generation unit  44 . 
     When both comparison results from the two comparing units  51  and  52  match (OK), a second gate (corresponding to a switch)  54  is turned on through a first gate (corresponding to an AND)  53  and the content  21  of the authentic recording medium  20  (e.g., the content  11  of the original recording medium  10 ) is transferred to, for example, a movie/music playback unit (not shown). 
     Note that, as described above, the content ID  15  is a computed value of n (n&lt;&lt;N) bytes obtained by performing a computation operation on N-byte digital data forming the content  11 , using a specific function, and the specific function may be a hash function and the computed value may be a hash value obtained using the hash function. 
     The above-described  FIGS. 1 and 2  illustrate the first method (for manufacturing) and the second method (for playing back). These methods are represented by specific flowcharts below. 
       FIG. 4  is a flowchart illustrating a method performed by the manufacturing side  100  and  FIG. 5  is a flowchart illustrating a method performed by the side of the playback apparatus  200 . First,  FIG. 4  will be referred to. 
     In the drawing, at operation S 11 , a chip ID  13  that is originally recorded in an IC chip  12  and uniquely identifies the IC chip  12  is read out. 
     At operation S 12 , a content ID  15  that uniquely identifies content  11  recorded on a content recording medium  10  is generated. 
     At operation S 13 , the chip ID  13  and the content ID  15  are encrypted. 
     At operation S 14 , an encrypted chip ID  13 ′ and an encrypted content ID  15 ′ are recorded in the IC chip  12 . 
     At operation S 15 , the IC chip  12  storing the encrypted chip ID  13 ′ and the encrypted content ID  15 ′ is added to the content recording medium  10 . 
     The manufactured content recording medium  10  with an IC chip is supplied on the market. 
     Next, referring to  FIG. 5 , at operation S 21 , a content recording medium  20  having an IC chip  22  is set on a content playback apparatus  200 . The IC chip  22  stores an encrypted chip ID  13 ′ and an encrypted content ID  15 ′. The encrypted chip ID  13 ′ is obtained by encrypting, by a first key ( 17 ), a chip ID  13  which is uniquely set and non-rewritably and originally recorded in the IC chip. 
     The encrypted content ID  15 ′ is obtained by encrypting, by the first key ( 17 ), a content ID  15  generated by a specific process to uniquely identify a content  11  recorded on a content recording medium  10 . 
     At operation S 22 , a chip ID  23 , an encrypted chip ID  23 ′, and an encrypted content ID  25 ′ in the IC chip  22  are read out. 
     At operation S 23 , the read encrypted chip ID  23 ′ and encrypted content ID  25 ′ are decrypted by a second key ( 27 ) which makes a pair with the first key ( 17 ). 
     At operation S 24 , a match/mismatch between a chip ID  23 ″ and a content ID  25 ″ which have been decrypted and regenerated and the read chip ID  23  and a content ID  25  generated by the same process as the aforementioned specific process is detected. 
     At operation S 25 , only when results of the detections each match, playback of content  21  on the content playback apparatus  200  is allowed. The content  21  is exactly the same as the content  11  contained in the authentic recording medium  10 . 
     Points of the above-described copy protection methods are summarized as illustrated in the following (1) to (4).
     (1) A content ID corresponding to content is contained in a content recording medium by means of hardware (chip) to make duplication difficult.   (2) A content ID that is dependent on content is used to prevent an IC chip from being used (diverted) for other content.   (3) Under an environment in which only an allowed manufacturer (a manufacturer having a secret key) can manufacture a medium, a content ID and a chip ID are encrypted and the encrypted content ID and chip ID are written in an IC chip.   (4) To improve the security management of a manufactured content recording medium, an IC chip containing content information and a recording medium containing content itself can be separately manufactured.   

     Effects of the points are listed below in (a) to (d).
     (a) By using a copy protection method disclosed herein when software is put into a recording medium and the recording medium is sold, illicit duplication of the medium can be prevented and the authenticity of the software may be proved. Specifically, even if an authentic IC chip is removed from an authentic medium and the IC chip is added to another medium and then tampered software is put into the medium, by referring to a content ID in the IC chip, it can be easily found that the software is tampered or otherwise altered.   (b) A certain manufacturer manufactures IC chips in which content IDs are respectively written and distributes the IC chips to a plurality of medium manufacturers, whereby convenience in content management, such as the number of pieces of content manufactured and by which medium manufacturer a certain recording medium is manufactured, is improved. Specifically, by separating an IC chip manufacturer and a recording medium manufacturer, more strict content management is performed. If writing of content IDs in IC chips and manufacturing of recording media are left to a single manufacturer, it becomes difficult to externally grasp the number of burned chips manufactured, facilitating illicit activity.   (c) A chip ID which is a hardware chip cannot be copied. Also, an encrypted content ID cannot be tampered or otherwise altered. Therefore, even when only content is copied onto another recording medium, the content cannot be played back, helping to prevent illegal copying.   (d) Regardless of whether content is encrypted or not, even when only the content is copied onto another medium and the medium is distributed, unless a modified player that is configured not to check a chip ID is provided together with the medium, a user who receives the pirated medium cannot play back the illicit content. To produce a perfect pirated medium, a secret key known only to a manufacturer needs to be stolen and an IC chip in which nothing is written needs to be obtained. However, doing so is extremely difficult.