Abstract:
A recording device performs recording on a recording medium such as a DVD, and playback compatibility of the recording medium is increased. In circumstances such as when a standard is established after the manufacture of a playback apparatus, there are playback devices that physically cannot read information for decrypting encrypted data from a predetermined area of the recording medium due to the specifications of the playback apparatus, and therefore the playback apparatus cannot use the recording medium. In order for the recording medium to be able to be used in such a playback apparatus, the recording device reads data recorded in the predetermined area of the recording medium, and records the read data in another area that is readable by the playback apparatus.

Description:
This application claims benefit to the provisional U.S. Application No. 60/650,132, filed Feb. 7, 2005. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a recording device that records data onto a recording medium, and in particular to technology for improving the playback compatibility of recording media. 
     2. Description of the Related Art 
     DVDs, on which content such as a movie can be recorded in high quality, are widely used as package media for distributing content. Content is recorded onto DVDs as digital data. Compared to analog data, digital data undergoes much less degredation during copying, and the value of the content is diminished very little by copying. If recording media containing unauthorized copies of content are distributed to the market at cheap prices, the number of consumers who purchase legitimate package media falls, and there is the fear that holders of rights such as copyrights on content will incur extensive losses. 
     For this reason, copyright protection technology such as CPRM (Content Protection for Recordable media) is used to protect the rights of right-holders. CPRM is copyright protection technology used when recording content or other data to a writable recording medium. A recording device encrypts the data before recording it to the recording medium, in order to prevent unauthorized copying of the data. Here, the data is encrypted using information prerecorded in a predetermined area of the recording medium. Taking the example of the DVD-RAM standard, the recording device encrypts the data with use of an MKB (Media Key Block) recorded in an Initial Zone of the recording medium, a media ID recorded in a BCA (Burst Cutting Area), and the like. 
     Note that regarding disk layouts in DVD standards, the disk layouts of the DVD+RW standard and the DVD-RAM standard are described in non-patent documents 1 and 2 respectively.
     Non-patent document 1: ECMA-337, 3rd Edition—December, 2005.   Non-patent document 2: ECMA-272, 2nd Edition—June, 1999.   

     BRIEF SUMMARY OF THE INVENTION 
     Problems Solved by the Invention 
     As described in the above non-patent documents, the disk layout is different depending on the DVD standard. Since there are cases in which the recording positions of data are different depending on the disk layout, it is possible that a playback device will not be able to utilize a recording medium on which data has been recorded according to an incompatible standard. For this reason, manufacturers normally design their playback devices to be compatible with as many established standards as possible, such that there is no detriment to users of their playback devices. 
     However, when a standard is established after a playback device has been manufactured, it is possible that the playback device will not be able to decrypt encrypted data that has been recorded on a recording medium according to the newly established standard, due to specification-related constraints of the playback device. 
     For example, if the media ID and other decryption information used in processing for decrypting the encrypted data is recorded in an inner circumferential portion of a disk-shaped recording medium, and a reading unit of a playback device for reading data from the recording medium physically cannot read the inner circumferential portion of the disk, the playback device will not be able to decrypt the encrypted data the decryption information. Given that in this case the information necessary for decrypting the encrypted data physically cannot be read, a countermeasure such as updating a playback processing program of the playback device would have no effect. This is not preferable since the inability to utilize the data on the recording medium is not only a detriment to the user of the playback device, but also diminishes the number of choices of methods by which a content holder can distribute their content to potential content users. 
     Therefore, an aim of the present invention is to provide a recording device that records data to a recording medium in such away that even a playback device incompatible with a standard of the recording medium due to specification-related constraints can utilize the data that has been recorded onto the recording medium according to the standard. 
     Means to Solve the Problems 
     In order to solve the above problem, the present invention is a recording device that performs recording on a recording medium, such that a first area of the recording medium has prerecorded therein decryption information used in decryption processing for decrypting encrypted data, the recording device including: a read unit operable to read the decryption information from the first area; and a record unit operable to record the read decryption information in a second area of the recording medium, the second area being readable by a device that physically cannot read data in the first area. 
     Effects of the Invention 
     According to this structure, the recording device reads the decryption information from the first area, and records the read decryption information to the second area. 
     Accordingly, even a device that physically cannot read data from the first area of the recording medium will be able to decrypt the encrypted data recorded on the recording medium since the device can read the decryption information from the second area. 
     If some kind of information is recorded in the second area, and furthermore the information is illegitimate decryption information, the playback device can decrypt the encrypted data with use of the illegitimate decryption information, whereby it is possible that the rights of a right-holder are not sufficiently protected. Also, if the decryption information recorded in the second area has been corrupted due to a recording failure or another reason, the playback device cannot decrypt the encrypted data. 
     Here, the recording device may further include: a detection unit operable to detect that certain information is recorded in the second area; a determination unit operable to, if the certain information is recorded in the second area, determine whether the decryption information recorded in the first area and the certain information are identical; and an overwrite unit operable to, when the determination unit has determined that the decryption information and the certain information are not identical, overwrite the certain information in the second area with the decryption information. 
     This structure enables reliably recording legitimate decryption information in the second area. 
     Also, the decryption information may be a key block. 
     Also, the decryption information may be a media ID that identifies the recording medium. 
     Also, the second area may be a buffer area included in a lead-in area of the recording medium. 
     Also, the first area may be an initial zone of the recording medium. 
     Also, the present invention is an integrated circuit used in a recording device that performs recording on a recording medium, a first area of the recording medium having prerecorded therein decryption information used in decryption processing for decrypting encrypted data, the integrated circuit including: a read processing unit operable to perform processing for reading the decryption information from the first area; and a record processing unit operable to perform processing for recording the read decryption information in a second area of the recording medium, the second area being readable by a device that physically cannot read data in the first area. 
     Also, the present invention is a control program for causing processing to be executed by a recording device that performs recording on a recording medium, a first area of the recording medium having prerecorded therein decryption information used in decryption processing for decrypting encrypted data, the control program including the steps of: reading the decryption information from the first area; and recording the read decryption information in a second area of the recording medium, the second area being readable by a device that physically cannot read data in the first area. 
     There are playback devices that can read from both the first and second areas of the recording medium depending on the standard. If the decryption information is recorded in the second area, such playback devices can read the decryption information from either the first or second area. 
     However, there are cases in which the information recorded in the second area is illegitimate information recorded by an illegitimate recording device. In such cases, decrypting the encrypted data with use of the illegitimate information recorded in the second area of the recording medium is disadvantageous to a holder of a data copyright etc. 
     Here, the present invention is a playback device that reads encrypted data from a recording medium and controls execution of decryption processing for decrypting the read encrypted data, the recording medium including a first area and a second area, decryption information used in the decryption processing having been prerecorded in the first area before recording of the encrypted data by a recording device, the encrypted data having been generated by encrypting, with use of the decryption information, data targeted for recording, certain information being recorded in the second area, and the playback device including: a determination unit operable to determine whether the decryption information recorded in the first area and the certain information recorded in the second area are identical; and a control unit operable to control execution of the decryption processing, according to a result of the determination. 
     According to this structure, the playback device determines whether the information recorded in the first and second areas is identical. The execution of the decryption processing is controlled according to the result of the determination. 
     Accordingly, even if illegitimate information is recorded in the second area, the execution of the decryption processing can be controlled, such that there is no disadvantage to the right-holder etc. 
     Here, the control unit may execute the decryption processing only when the determination unit has determined that the decryption information recorded in the first area and the certain information recorded in the second area are identical. 
     According to this structure, in a playback device that can read from both the first and second areas depending on the standard, the decryption processing is performed only if the information recorded in the second area is identical to the decryption information recorded in the first area. Therefore, there is no disadvantage to the right-holder etc. even if illegitimate information is recorded in the second area. 
     Also, the control unit may suppress the decryption processing when the determination unit has determined that the decryption information recorded in the first area and the certain information recorded in the second area are not identical. 
     According to this structure, an illegitimate user gains no advantage by recording illegitimate information in the second area, since the decryption processing is suppressed if the information recorded in the second area is illegitimate. This potentially suppresses the recording of illegitimate information in the second area by illegitimate users. 
     Nonetheless, simply the fact that the information recorded in the second area is not identical to the decryption information recorded in the first area does necessarily mean that the information in the second area was recorded by an illegitimate user. For example, the information recorded in the second area may have been corrupted by degredation of or damage to the recording medium after the decryption information had been recorded in the second area by a legitimate user. 
     In other words, if the information recorded in the second area is not identical to the decryption information recorded in the first area due to damage to the recording medium etc., the playback device cannot decrypt the encrypted data even though it can read the decryption information from the first area. Therefore, in this case, use of the data on the recording medium is restricted even though the rights of the right-holder etc. are not being violated, which is unfairly disadvantageous to the user of the playback device. 
     Here, when the determination unit has determined that the decryption information recorded in the first area and the certain information recorded in the second area are not identical, the control unit may execute the decryption processing with use of the decryption information read from the first area. 
     This structure enables preventing the unfair disadvantage to the user of the playback device in the aforementioned case. 
     Also, the present invention is an integrated circuit used in a playback device that reads encrypted data from a recording medium and controls execution of decryption processing for decrypting the read encrypted data, the recording medium including a first area and a second area, decryption information used in the decryption processing having been prerecorded in the first area before recording of the encrypted data by a recording device, the encrypted data having been generated by encrypting, with use of the decryption information, data targeted for recording, certain information being recorded in the second area, the integrated circuit including: a determination processing unit operable to perform processing for determining whether the decryption information recorded in the first area and the certain information recorded in the second area are identical; and a control processing unit operable to perform processing for controlling execution of the decryption processing, according to a result of the determination. 
     Also, the present invention is a control program for causing processing to be executed by a playback device that reads encrypted data from a recording medium and controls execution of decryption processing for decrypting the read encrypted data, the recording medium including a first area and a second area, decryption information used in the decryption processing having been prerecorded in the first area before recording of the encrypted data by a recording device, the encrypted data having been generated by encrypting, with use of the decryption information, data targeted for recording, certain information being recorded in the second area, the control program including the steps of: determining whether the decryption information recorded in the first area and the certain information recorded in the second area are identical; and controlling execution of the decryption processing, according to a result of the determination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram showing a recording device  1000  of the present invention; 
         FIG. 2  is a functional block diagram showing a playback device  3000  that reads data from a recording medium  2000  and decrypts the read data; 
         FIG. 3  shows a disk layout of the recording medium  2000 ; 
         FIG. 4  is a flowchart showing processing performed by the recording device  1000 ; 
         FIG. 5  is a flowchart showing processing performed by the playback device  3000 ; 
         FIG. 6  is a functional block diagram showing a playback device  3100 ; and 
         FIG. 7  is a flowchart showing processing performed by the playback device  3100 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following describes an embodiment of a recording device pertaining to the present invention, with reference to the drawings. 
     Overview 
     The recording device of the present invention records AV data to a recording medium compatible with CPRM (Content Protection for Recordable Media). Before recording is performed, the AV data is encrypted with use of information prerecorded on the recording medium. Here, the encryption method is CPRM. The information prerecorded on the recording medium includes an MKB (Media Key Block), which is a block of keys, as well as MKB validation data and a media ID. 
     The MKB is prerecorded in an area of the recording medium called the Initial Zone. The MKB validation data and the media ID are prerecorded in a BCA (Burst Cutting Area) in the Initial Zone. 
     The recording device encrypts the AV data with use of the MKB, the media ID and the like. Also, in order for a playback device that physically cannot read the MKB, the media ID and the like from the recording medium due to specification-related constraints to be able to decrypt the AV data with use of the MKB etc., the recording device also records the MKB etc. in a predetermined area of the recording medium that is readable by the playback device. This enables the playback device to read the MKB etc. from the recording medium and decrypt the AV data. The present embodiment is an exemplary case in which the recording device records the MKB etc. in a buffer zone  2  of the recording medium. 
     Furthermore, if information has already been recorded in the buffer zone  2 , the recording device verifies whether the recorded information includes the MKB, media ID and the like that are prerecorded in the Initial Zone of the recording medium, and overwrites the MKB, media ID and the like in the buffer zone  2  according to a result of the verification. 
     Also, the playback device can read the information recorded in the buffer zone  2  of the recording medium, even though it is unable to read the information recorded in the Initial Zone of the recording medium. 
     The following is a detailed description of the present embodiment. 
     Structure 
       FIG. 1  is a functional block diagram showing a recording device  1000  of the present invention. Note that a recording medium  2000  is also shown in  FIG. 1 . 
     As shown in  FIG. 1 , the recording device  1000  includes a device key storage unit  101 , an MKB processing unit  102 , a check unit  103 , a key conversion unit  104 , an encryption unit  105 , and an AV pack storage unit  106 . The encryption unit  105  includes a title key generation subunit  111 , a title key combination subunit  112 , a title key encryption subunit  113 , a DCL_CCI generation subunit  114 , an intermediate key generation subunit  115 , a content key generation subunit  116 , and an AV pack encryption subunit  117 . 
     The device key storage unit  101  stores a device key allocated to the recording device  1000 . 
     The MKB processing unit  102  reads the MKB from the Initial Zone of the recording medium  2000 , and generates a media key (Km) by decrypting the read MKB with use of the device key stored in the device key storage unit  101  of the recording device  1000 . The MKB processing unit  102  also records the generated media key in the buffer zone  2  of the recording medium  2000 . 
     The check unit  103  calculates a hash value for the MKB recorded in the Initial Zone, and verifies the validity of the MKB by comparing the calculated hash value to the MKB validation data recorded in the BCA. The check unit  103  also detects that some kind of information is recorded in the buffer zone  2 , and upon detecting that an MKB is recorded in the buffer zone  2 , calculates a hash value for the MKB recorded in the buffer zone  2 , and verifies the validity of the MKB recorded in the buffer zone  2  by comparing the calculated hash value to the MKB validation data. Also, upon detecting that a media ID is recorded in the buffer zone  2 , the check unit  103  verifies the validity thereof by performing a comparison with the media ID recorded in the BCA. The media ID recorded in the buffer zone  2  is determined to be valid if, for example, a result of the aforementioned comparison is that the media IDs are the same. 
     The key conversion unit  104  reads the media ID recorded in the BCA, and with use of the read media ID, converts the MKB read by the MKB processing unit  102 , thereby generating a unique media key (Kmu). The key conversion unit  104  also records the media ID read from the BCA in the buffer zone  2 . 
     The encryption unit  105  encrypts AV data received as an input from the AV pack storage unit  106  in a 2,048-byte AV pack format, and records the encrypted data in a data area of the recording medium  2000 . The AV data encrypted by the encryption unit  105  is recorded in the data area in a 2,048-byte encrypted AV pack format. The first 128 bytes of the 2,048 bytes in the encrypted AV pack make up a plain-text unencrypted portion, and the remaining 1,920 bytes make up an encrypted portion. The first 128 bytes of the 2,048-byte AV pack received as input from the AV pack storage unit  106  are used to generate a content key (Kc) for encrypting the AV data, and are also recorded in the data area as the plain-text unencrypted portion. The encryption unit  105  also encrypts the remaining 1,920 bytes of the 2,048-byte AV pack with use of the content key, and records the generated encrypted data in the data area as the encrypted portion. 
     The following describes details of the function blocks constituting the encryption unit  105 . 
     The title key generation subunit  111  generates a title key. The title key generation subunit  111  outputs the generated title key (Kt) to the title key combination subunit  112  and the intermediate key generation subunit  115 . 
     The title key combination subunit  112  combines an arbitrary value V and the title key generated by the title key generation subunit  111 . 
     The title key encryption subunit  113  encrypts the title key combined with the arbitrary value V by the title key combination subunit  112 , with use of the unique media key generated by the key conversion unit  104 , thereby generating an encrypted title key. The title key encryption subunit  113  records the generated encrypted title key in the data area. 
     The DCL_CCI generation subunit  114  generates copy control information etc. of the AV data as DCL_CCI, and records the generated DCL_CCI in the data area. The DCL_CCI generation subunit  114  also outputs analog protection information (APSTB: Analog Protection Single Trigger Bit) to the intermediate key generation subunit  115 . 
     The intermediate key generation subunit  115  receives the APSTB from the DCL_CCI generation subunit  114 , and generates an intermediate key (Ki) by combining the received APSTB with the title key received from the title key generation subunit  111 . The intermediate key generation subunit  115  outputs the generated intermediate key to the content key generation subunit  116 . 
     The content key generation subunit  116  receives an input of the first 128 bytes (Dtkc) of the 2,048-byte AV pack, and generates a content key by converting the received intermediate key with use of the received first 128 bytes of the AV pack. Note that as described above, the first 128 bytes of the AV pack are recorded in the data area as the plain-text unencrypted portion. 
     The AV pack encryption subunit  117  encrypts the remaining 1,920 bytes of the 2,048-byte AV pack with use of the content key generated by the content key generation subunit  116 , and records the encrypted data in the data area as the encrypted portion. 
     The AV pack storage unit  106  stores the AV data. 
     The following describes a structure of the playback device. 
       FIG. 2  is a functional block diagram showing a playback device  3000  that reads data from the recording medium  2000  and performs decryption processing on the read data. 
     As shown in  FIG. 2 , the playback device  3000  includes a device key storage unit  301 , an MKB processing unit  302 , a key conversion unit  303 , a decryption unit  304 , and an AV pack playback processing unit  305 . The decryption unit  304  includes a title key decryption subunit  311 , a DCL_CCI storage subunit  312 , an intermediate key generation subunit  313 , a content key generation subunit  314 , and an AV pack decryption subunit  315 . 
     The device key storage unit  301  stores a device key of the playback device  3000 . 
     The MKB processing unit  302  reads the MKB recorded in the buffer zone  2  of the recording medium  2000 , and decrypts the read MKB with use of the device key stored by the device key storage unit  301  of the playback device  3000 , thereby generating a media key. 
     The key conversion unit  303  reads the media ID recorded in the buffer zone  2 , and with use of the read media ID, converts the media key generated by the MKB processing unit  302 , thereby generating a unique media key. 
     The decryption unit  304  reads the encrypted AV pack from the data area of the recording medium  2000 , and decrypts the read encrypted AV pack to obtain the AV data. The decryption unit  304  outputs the obtained AV data to the AV pack playback processing unit  305 . The decryption unit  304  also reads the DCL_CCI from the data area and stores the read DCL_CCI. 
     The following describes details of the function blocks constituting the decryption unit  304 . 
     The title key decryption subunit  311  reads the encrypted title key from the data area of the recording medium  2000 , and decrypts the read encrypted title key with use of the unique media key generated by the key conversion unit  303 , thereby generating a title key. 
     The DCL_CCI storage subunit  312  stores the DCL_CCI read from the data area. 
     The intermediate key generation subunit  313  receives the analog protection information (APSTB) included in the DCL_CCI recorded in the data area, and combines the received analog protection information with the title key generated by the title key decryption subunit  311 , thereby generating an intermediate key. The intermediate key generation subunit  313  outputs the generated intermediate key to the content key generation subunit  314 . 
     The content key generation subunit  314  converts the intermediate key received from the intermediate key generation subunit  313 , with use of the first 128 bytes of the encrypted AV pack read from the data area, thereby generating a content key. 
     The AV pack decryption subunit  315  decrypts the remaining 1,920 bytes of the encrypted AV pack with use of the content key generated by the content key generation subunit  314 . 
     The AV pack playback processing unit  305  performs video output and playback processing on the AV data obtained by the decryption unit  304 . 
     Note that although not depicted, the recording device  1000  and the playback device  3000  include a reading unit for reading data from the recording medium  2000 . Also, the above constituent elements constitute a computer system composed of specifically a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and operate in accordance with a program. A portion of the processing, such as the encryption processing, may be performed by a dedicated processor. 
     Data 
     The following describes the disk layout of the recording medium  2000 . 
       FIG. 3  shows the disk layout of the recording medium  2000 . Note that the DVD+RW standard is described as an example in the present embodiment. 
     As shown in  FIG. 3 , the Initial Zone is included in an inner drive area of the recording medium  2000 . A media ID and MKB validation data are prerecorded in the BCA of the Initial Zone. The information recorded in the BCA cannot be tampered with. An MKB is also prerecorded in the Initial Zone. Also, the buffer zone  2  is included in a lead-in area. 
     In the present embodiment, the recording device  1000  records the MKB and the media ID that were read from the Initial Zone of the recording medium  2000  in the buffer zone  2  of the recording medium  2000 . Also, as described above, the playback device  3000  cannot read the information recorded in the Initial Zone, and performs decryption processing using the MKB and the media ID that were recorded in the buffer zone  2  by the recording device  1000 . 
     Operations 
     The following describes operations performed by the recording device  1000  of the present invention. 
       FIG. 4  is a flowchart showing processing performed by the recording device  1000 . 
     As shown in  FIG. 4 , the recording device  1000  reads the buffer zone  2  of the recording medium  2000 , and judges whether the MKB and media ID are recorded therein (step S 41 ). 
     If the judgment is negative (step S 41 :NO), the recording device  1000  judges whether a sufficient amount of free space is available in the buffer zone  2  for writing the MKB and media ID (step S 42 ), and ends processing if the amount of free space is insufficient (step S 42 :NO). If a sufficient amount of free space is available in the buffer zone  2  (step S 42 :YES), the recording device  1000  judges whether the MKB and media ID are recorded in the Initial Zone, and ends processing if the judgment is negative (step S 43 :NO). If the MKB and media ID are recorded in the Initial Zone (step S 43 :YES), the recording device  1000  acquires the MKB and media ID from the Initial Zone (step S 44 ). The recording device  1000  records the acquired MKB and media ID in the buffer zone  2  (step S 45 ). 
     Upon completing the processing of step S 45 , the recording device  1000  encrypts the AV data stored in the AV pack storage unit  106 , with use of the MKB, media ID, title key, etc., and records the encrypted AV data in the Data area (step S 46 ). 
     Also, if the MKB and media ID have been judged in step S 41  to be recorded in the buffer zone  2  (step S 41 :YES), the recording device  1000  reads the MKB recorded in the buffer zone  2 , as well as reads the MKB validation data from the Initial Zone, and the check unit  103  verifies that the MKB recorded in the buffer zone  2  is valid (step S 47 ). 
     Processing ends if the MKB is not valid (step S 47 :NO). If the MKB is valid (step S 47 :YES), the check unit  103  similarly verifies that the media ID recorded in the buffer zone  2  is valid (step S 48 ). 
     If the media ID is not valid (step S 48 :NO), the recording device  1000  overwrites the media ID recorded in the buffer zone  2  with the media ID recorded in the Initial Zone (step S 49 ). If the media ID is valid (step S 48 :YES), the recording device  1000  does not perform the overwrite processing. Thereafter, the recording device  1000  encrypts the AV data stored in the AV pack storage unit  106 , with use of the MKB, media ID, title key, etc., and records the encrypted AV data in the data area (step S 46 ). Note that as mentioned in detail in the description of the encryption unit  105 , the encryption processing in step S 46  is performed similarly to encryption processing in CPRM. Also, although in the above description processing ends if the MKB is not valid (step S 47 :NO), the present invention is not limited to this. Instead, the recording device  1000  may overwrite the MKB recorded in the buffer zone  2  with the MKB recorded in the Initial Zone. Also, although in the above description the recording device  1000  overwrites the media ID recorded in the buffer zone  2  with the media ID recorded in the Initial Zone (step S 49 ) if the media ID is not valid (step S 48 :NO), the present invention is not limited to this. Instead, processing may end if the media ID is not valid. 
     The following describes operations performed by the playback device  3000 . 
       FIG. 5  is a flowchart showing processing performed by the playback device  3000 . 
     As shown in  FIG. 5 , the playback device  3000  judges whether the MKB and media ID are recorded in the buffer zone  2  (step S 51 ). If the judgment is affirmative (step S 51 :YES), the playback device  3000  acquires the MKB and media ID from the buffer zone  2  (step S 52 ). 
     Upon acquiring the MKB and media ID (step S 52 ), the playback device  3000  decrypts the AV data with use of the acquired MKB and media ID (step S 53 ). 
     Also, processing ends if the playback device  3000  judges in step S 51  that the MKB and media ID are not recorded in the buffer zone  2  (step S 51 :NO). 
     Supplementary Remarks 
     Although a recording device pertaining to the present invention has been described based on the above embodiment, variations such as the following are also possible, and the present invention should of course not be limited to the recording device described in the above embodiment. 
     (1) Although the playback device is described as not being able to read information from the Initial Zone in the above embodiment, the present invention is not limited to this. The playback device may be able to read information from the Initial Zone. 
     In this case, the playback device may, as in a playback device  3100  shown in  FIG. 6 , further include a check unit  306  that reads an MKB etc. from the Initial Zone and the buffer zone  2  and verifies the validity of the read MKB etc. The check unit  306  calculates a hash value for the MKB recorded in the buffer zone  2 , and verifies the validity of the MKB by comparing the calculated hash value to the MKB validation data recorded in the BCA. The check unit  306  also verifies the validity of the media ID recorded in the buffer zone  2  by performing a comparison with the media ID recorded in the BCA. 
     This enables the playback device  3100  to verify the validity of the MKB and media ID recorded in the buffer zone  2  of the recording medium  2000 . 
     Furthermore, the playback device  3100  may end processing such as decoding if a result of the verification is negative.  FIG. 7  is a flowchart showing processing performed by the playback device  3100 . 
     As shown in  FIG. 7 , the playback device  3100  judges whether the MKB and media ID are recorded in the buffer zone  2  (step S 71 ). If the judgment is negative (step S 71 :NO), the playback device  3100  acquires the MKB and media ID from the Initial Zone (step S 74 ), and decrypts the AV data with use of the acquired MKB and media ID (step S 75 ). 
     If the playback device  3100  judges in step S 71  that the MKB and media ID are recorded in the buffer zone  2  (step S 71 :YES), the check unit  306  verifies the validity of the MKB recorded in the buffer zone  2  (step S 72 ). If the MKB recorded in the buffer zone  2  is valid, that is, if the MKB recorded in the buffer zone  2  is the same as the MKB recorded in the Initial Zone (step S 72 :YES), the check unit  306  similarly verifies the validity of the media ID recorded in the buffer zone  2  (step S 73 ). If the media ID recorded in the buffer zone  2  is valid (step S 73 :YES), the playback device  3100  acquires the MKB and media ID from the buffer zone  2  or the Initial Zone (step S 74 ), and decrypts the AV data with use of the acquired MKB and media ID (step S 75 ). 
     Also, if the MKB or media ID recorded in the buffer zone  2  are not valid (step S 72 :NO or step S 73 :NO), processing ends without the AV data being decrypted. 
     Note that if the MKB or media ID recorded in the buffer zone  2  are not valid (step S 72 :NO or step S 73 :NO), processing such as decryption may be performed with use of the MKB etc. recorded in the Initial Zone. 
     (2) Although the recording device  1000  reads information from the Initial Zone and records the read information in the buffer zone  2  in the above embodiment, the present invention is not limited to this. Instead of the buffer zone  2 , the recording device  1000  may record the read information in another area such as the data area. 
     Also, the information to be recorded in the buffer zone  2  may be an ADIP (Address In Pre-groove). 
     Also, information recorded in an area other than the Initial Zone may be recorded in the buffer zone  2  etc. 
     (3) Although a media ID is read and recorded in the above embodiment, the present invention is not limited to this. A media ID seed may be read and recorded. A media ID is generated by processing the media ID seed using a random number generating function. 
     (4) Although an exemplary case of using a DVD+RW disk compatible with CPRM is described in the above embodiment, the present invention is not limited to this. The present invention also includes cases of recording to any optical disk or other recording medium. 
     (5) The devices of the above embodiment and variations may be computer systems structured specifically from a microprocessor, a ROM, a RAM, a hard disk unit, a display unit, a keyboard, a mouse, etc. A computer program is stored in the RAM or the hard disk unit. The devices achieve their functions as the microprocessor operates in accordance with the computer program. Instruction code which indicates commands to the computer is structured as a combination of multiple instruction codes in order for the computer program to achieve predetermined functions. 
     (6) A portion or all of the constituent elements of the devices of the above embodiment and variations may be structured as a single system LSI (Large Scale Integration). A system LSI is a super multifunctional LSI manufactured by integrating a plurality of structural units onto a single chip. Specifically, it is a computer system including a microprocessor, a ROM, a RAM, and the like. A computer program is stored in the RAM. The system LSI achieves its functions as the microprocessor operates in accordance with the computer program. 
     (7) A portion or all of the constituent elements of the devices of the above embodiment and variations may be structured as a removable IC card or stand-alone module. The IC card or the module is a computer system including a microprocessor, a ROM, and a RAM. The IC card and the module may include the above super multifunctional LSI. The IC card and the module achieve their functions as the microprocessor operates in accordance with the computer program. This IC card or module may be tamper resistant. 
     (8) The present invention may be the methods shown above. Also, the present invention may be computer programs for causing computers to realize the methods, or may be digital signals representing the computer programs. 
     Also, the present invention may be a computer-readable recording medium such as a flexible disk, a hard disk, a CD-ROM, an MO, a DVD, a DVD-ROM, a DVD-RAM, a BD (Blu-ray Disc), or a semiconductor memory on which the computer programs or the digital signals are recorded. The present invention may be the computer programs or the digital signals which are recorded on these recording media. 
     Also, the present invention may be the computer programs or digital signals which are transmitted via an electronic communications circuit, a wireless or fixed-line communications circuit, a network such as the Internet, a data broadcast, etc. 
     Also, the present invention may be a computer system including a microprocessor and a memory, whereby the memory stores the computer programs, and the microprocessor operates in accordance with the computer programs. 
     Also, the present invention may be carried out by another independent computer system by transferring the programs or the digital signals which have been recorded on the recording media, or by transferring the programs or the digital signals via the network, etc. 
     (9) The present invention may be any combination of the above embodiment and variations. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be used in a recording device that records data such as content to a recording medium such as a DVD, for which more than one standard has been established.