JP2006217218A - Method of managing copyright key - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a storage area from being wasted by efficiently leaving only an effective key for copyright management recorded in a secret area of a recording medium as to a managing method for a key effective in protecting the copyright of contents. <P>SOLUTION: When key management information is not present in a normal area 20 and a title key 25 is present in the secret area 21 while the recording medium is inserted into a device managing a copyright key, the title key 25 in the secret area 21 and a key use flag indicating whether the title key 25 is used or not are all erased even if the key use flag indicates a use state. When key management information is present in the normal area 20 and the title key 25 is present in the secret area 21, the title key 25 in the secret area 21 that the key management information in the normal area 20 does not refer to is erased even if the key use flag indicates the use state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an effective key management method for storing contents such as music and movies on a recording medium having a secret area and protecting the copyright of the contents.

  In recent years, video and audio equipment has been digitized and miniaturized, and apparatuses for recording content on a small recording medium such as a semiconductor memory card are becoming widespread. When recording copyrighted video or audio digital content with such a digital device, copyright protection technology for encrypting the content has been introduced in order to restrict copying and distribution of the content. For example, in a semiconductor memory card, a copyright control function is incorporated in a semiconductor memory card such as an SD card (trademark) or a memory stick (trademark) for the purpose of protecting these copyrights. A device having a secret area that can be written and read only when it is recognized as a device has been widely used.

  A recording / reproducing apparatus using a recording medium having such a copyright protection function will be described below.

  FIG. 14 shows an example of a conventional recording / reproducing apparatus using a semiconductor memory card as a recording medium.

  In FIG. 14, 2 is a semiconductor memory card (recording medium) such as an SD card, 6 is a recording / reproducing device, 61 is an encoding unit that digitally compresses and encodes a video signal and an audio signal, 62 is a content encryption unit, 63 Is a media interface unit, 64 is a content encryption restoration unit, and 65 is a decoding unit that decodes the compression-encoded signal and outputs a video signal and an audio signal.

  When the semiconductor memory card 2 is inserted into the recording / reproducing device 6, first, it is confirmed from the recording / reproducing device 6 whether or not the semiconductor memory card 2 is a legitimate memory card, and recording from the semiconductor memory card 2. In order to confirm whether or not the playback device 6 is a legitimate device, the media interface unit 63 performs mutual authentication. Mutual authentication is performed using information unique to each medium for each semiconductor memory card 2, and information such as the title key 25 in the secret area 21 (see FIG. 15) of the semiconductor memory card 2 is stored and read out by successful mutual authentication. It becomes possible. At least each time a new semiconductor memory card 2 is inserted, mutual authentication is performed.

  First, the recording operation will be described. The input video signal and audio signal are compression encoded by the encoding unit 61. The content encryption unit 62 encrypts the encoded signal using the title key 25 that is randomly generated for each content, and outputs the encrypted content 26. The media interface unit 63 records the encrypted content 26 in the normal area 20 of the semiconductor memory card 2 and records the title key 25 in the secret area 21. The corresponding use key number 27 is written in the table in the normal area 20 so that it can be seen which title key 25 is used. A key use flag 28 is set on the title key 25 of the secret area 21 so that the key is used. In the second and subsequent recordings, a new additional recording is performed by searching for a free space (0) in the table of the used key number 27 in the normal area 20 and a free space (0) in the key use flag 28 in the secret area 21. .

  FIG. 15 shows an example of recording on the semiconductor memory card 2 by the conventional recording / reproducing apparatus 6.

  In the example of FIG. 15, there are vacancies after the sixth in a state where five encrypted contents 26 are recorded. In FIG. 15, in order to facilitate understanding, the used key number 27 and the title key 25 all correspond to the numerical order. However, the order may be disturbed by partially deleting or editing the content. For this association, a table of used key numbers 27 is required. Further, the key use flag 28 is effective for easily searching for the title key 25 that is not referenced from the table of the use key number 27.

  Next, the reproduction operation will be described. The media interface unit 63 selects content to be reproduced, performs mutual authentication in advance, accesses the secret area 21, and reads the title key 25 of the selected content. The content encryption restoration unit 64 uses the read title key 25 to decrypt the encryption. The decoding unit 65 decodes the compressed signal and outputs a video signal and an audio signal.

  Since the media unique information of the semiconductor memory card 2 cannot be rewritten from the outside, even if the encrypted content 26 in the normal area 20 is illegally copied to another recording medium, it cannot be decrypted normally. .

As described above, in the conventional system, when recording copyrighted video or audio digital content, it is possible to realize copyright protection by restricting content duplication by encrypting the content ( For example, see Patent Document 1).
Japanese Patent Laid-Open No. 2002-15147 (paragraphs 0044 to 0088, FIGS. 12 to 29)

  However, in the above-described conventional copyright key management method, the semiconductor memory card 2 can also be used in an ordinary digital still camera or the like that does not require copyright protection, and the semiconductor memory card 2 is shared by such devices. There were cases where problems occurred when using the

  In a device that handles only images that do not require copyright protection, such as images taken by the user, there is no need to access the secret area 21 of the semiconductor memory card 2, so only the normal area 20 is used. For example, when the semiconductor memory card 2 is used for the first time, a function for initializing (formatting) information of the semiconductor memory card 2 is generally installed, but the secret area 21 is left as it is and only the normal area 20 is initialized. There are many devices that will be converted. The same applies to initialization not only with digital still cameras but also with personal computers.

  In that case, if the title key 25 for content management has already been recorded in the secret area 21 by a device having a copyright protection function, the title of the secret area 21 is initialized by initializing only the normal area 20. The key 25 is left as it is, and the storage area of the secret area 21 is wasted.

  Thereafter, when the additional recording is performed again by a conventional device having a copyright protection function without initializing the secret area 21 in the semiconductor memory card 2, a part of the title key 25 remains used. Therefore, the additional recordable area is reduced. In some cases, the title key 25 for content management is used up to the recordable upper limit in the secret area 21, and the recordable area of the normal area 20 is sufficiently vacant but cannot be recorded. Will occur.

  The copyright key management method of the present invention uses a recording medium having a normal area that can be freely accessed and a secret area that can be accessed only by performing authentication. Copyright key for storing key management information for associating the encrypted title key and storing the title key of the content and key management information for managing the validity of the title key in the secret area In the management method, a key use flag for indicating whether the title key is used or not used in the normal area is recorded as key management information for the secret area, and the recording medium is a copyrighted work. When the key management information does not exist in the normal area and the title key exists in the secret area when inserted in a device that manages the right key, the type of the secret area The key key and the key usage flag for indicating the status of non-use of the title key are all deleted even if the key usage flag is in use, and key management information exists in the normal area, When the title key exists in the secret area, the title key in the secret area that is not referred to by the key management information in the normal area is deleted even if the key use flag is in use. Features.

  According to the copyright key management method of the present invention, when a recording medium is used, even if the key usage flag of the secret area is a title key indicating the use state, the secret area is not consumed unnecessarily. Even if a device that does not handle a secret area is used together, there is no problem that recording cannot be performed even though the capacity remains in the normal area.

  The copyright key management method of the present invention uses a recording medium having a normal area that can be freely accessed and a secret area that can be accessed only by performing authentication. Copyright key for storing key management information for associating the encrypted title key and storing the title key of the content and key management information for managing the validity of the title key in the secret area In the management method, a key use flag for indicating whether the title key is used or not used in the normal area is recorded as key management information of the secret area, and a copyright is recorded on the recording medium. When content is recorded by a device that manages a right key, there is a space in the title key area of the secret area on the key management information of the normal area, and the secret area When the number of title keys that cannot be recorded any more is used, the key use flag for indicating the state of non-use of the title key in the secret area, Even if the key use flag is in use, at least one title key area that has been erased and used is used.

  According to the copyright key management method of the present invention, when content is recorded, an unnecessary title is used even if the secret key is used in the secret area when the title key storage area is insufficient. By initializing the key and using the area, the secret area is prevented from being consumed unnecessarily while leaving the title key as much as possible. In addition, even if the recording medium is mixed with a device that does not handle the secret area or the conventional recording / reproducing apparatus, there is no problem that the recording cannot be performed even though the capacity remains in the normal area, and Since it is possible to leave the key to the maximum extent, it is possible to minimize the key erasure when the key is intentionally left for some reason.

  The copyright key management method of the present invention uses a recording medium having a normal area that can be freely accessed and a secret area that can be accessed only by performing authentication. Copyright key for storing key management information for associating the encrypted title key and storing the title key of the content and key management information for managing the validity of the title key in the secret area The key management information for the secret area is a key usage flag for indicating whether the title key is used or not used in the normal area, and the title key is deleted. When the content is recorded by a device that manages a copyright key on the recording medium, the key management of the normal area is recorded. In the report, when there is a space in the title key area of the secret area, and the key management information of the secret area is in a state where the number of title keys that cannot be recorded any more is used, The key use flag for indicating the non-use state of the title key in the secret area can be deleted even if the key use flag is in use. It is characterized in that at least one title key area that has been erased from the inside is used.

  According to the copyright key management method of the present invention, when content is recorded, if the title key storage area of the secret area is insufficient, a range in which the key deletion disable flag indicating that the title key is intentionally left is not raised Therefore, even if the key usage flag of the secret area is a title key indicating the use state, an unnecessary title key is initialized and used so that it can be used in the secret area of the recording medium. It is possible to prevent an unnecessary title key from being inadvertently deleted.

  According to the copyright key management method of the present invention, the effective use of the copyright management key to be recorded in the secret area of the recording medium efficiently leaves the storage area unnecessarily consumed. Can be prevented.

(Embodiment 1)
A first embodiment of the present invention will be described with reference to FIGS.

  1 is a block diagram of a recording / reproducing apparatus, FIG. 2 is a block diagram of a recording medium, FIGS. 3 to 6 are explanatory diagrams of recording of the recording medium, and FIG. 7 is a flowchart of a copyright key management method.

  In FIG. 1, 1 is a recording / reproducing apparatus, 2 is a semiconductor memory card (recording medium), 11 is an encoding unit that digitally compresses and encodes a video signal and an audio signal, 12 is a content encryption unit, and 13 is a media interface unit. , 14 is a content encryption restoration unit, and 15 is a decoding unit that decodes the compression-encoded signal and outputs a video signal and an audio signal.

  Note that the recording / reproducing apparatus 1 is configured in the same manner as the recording / reproducing apparatus 6 shown in FIG. However, the operation of the media interface unit 13 is different from that of the media interface unit 63.

  FIG. 2 shows a configuration example of a semiconductor memory card 2 which is an example of a recording medium.

  The storage area inside the semiconductor memory card 2 is roughly divided into two areas, and comprises a secret area 21 that can be accessed only through a specific procedure and a normal area 20 that can be accessed by a normal procedure. A read-only MKB (media key block) 23 and a media ID 24 are written in the secret area 21. The media ID 24 is a unique ID for each medium and is recorded in advance when the memory card is manufactured. In addition, a title key (copyright key) 25 and key management information for encrypting content can be stored in a readable / writable area of the secret area 21. The normal area 20 is freely readable and writable by the user using a normal access method, and can store the encrypted content 26 and key management information. In this example, the semiconductor memory card 2 has an AKE (Authentication and Key Exchange) processing unit 22 for performing mutual authentication and key exchange.

  The recording media are not necessarily all semiconductors, and for example, a recording medium such as a small hard disk using magnetic recording may be used.

  When the semiconductor memory card 2 is inserted into the recording / reproducing apparatus 1, the media interface unit 13 first checks whether the semiconductor memory card 2 is a regular memory card as viewed from the recording / reproducing apparatus 1. Mutual authentication is performed to confirm whether the recording / reproducing apparatus 1 is a legitimate apparatus when viewed from the card 2. In the mutual authentication, the media interface unit 13 first reads the MKB 23 and the media ID 24 from the semiconductor memory card 2 by a predetermined procedure, and performs a predetermined calculation process using these and a device-specific key owned by the media interface unit 13. Then, the media unique key Kmu is calculated. Next, a predetermined calculation is performed using a random number generated by the media interface unit 13 to confirm that the media unique keys Kmu possessed by each other match, thereby completing mutual authentication. When this mutual authentication is successful, the secret area 21 can be accessed. In addition, information such as the title key 25 in the secret area 21 can be stored and read by the session key Ks obtained by a predetermined calculation at the time of mutual authentication. The mutual authentication is performed at least every time a new semiconductor memory card 2 is inserted.

  Next, the recording operation will be described. The input video signal and audio signal are compression encoded by the encoding unit 11. The content encryption unit 12 encrypts the encoded signal using a title key 25 that is randomly generated for each content, and outputs the encrypted content 26. The media interface unit 13 records the encrypted content 26 in the normal area 20 of the semiconductor memory card 2 and records the title key 25 in the secret area 21. The used key number 27 is entered in a table in the normal area 20 so that it can be seen which title key 25 is used. A key use flag 28 is set up so that the title key 25 in the secret area 21 can be seen as being used. In the second and subsequent recordings, a new recording is performed by searching for a free space (0) in the table of the used key number 27 in the normal area 20 and a free space (0) in the key use flag 28 in the secret area 21.

  Next, a copyright key management method will be described with reference to FIGS.

  Here, as an example, it is assumed that there is the semiconductor memory card 2 (FIG. 15) in the recording state described in the conventional recording / reproducing apparatus. In the example of FIG. 15, there is a sixth free space in a state where five encrypted contents 26 are recorded, and the used key number 27 and the title key 25 all correspond to the numerical order.

  When only the normal area 20 is initialized in the semiconductor memory card 2 in such a state, the list corresponding to the key number 27 used in the normal area 20 and the encrypted content 26 do not exist, and the state corresponds to FIG. When such a semiconductor memory card 2 is inserted into the recording / reproducing apparatus 1, the media interface unit 13 determines whether there is a list of used key numbers (normal area key management information) 27 in the normal area 20 (see FIG. 7 (S31), since the list of the used key number 27 does not exist, the media interface unit 13 deletes all the title key 25 and the key use flag 28 in the secret area 21 (S32 of the same), and makes the state shown in FIG.

  When the semiconductor memory card 2 in the state shown in FIG. 3 is recorded by the conventional recording / reproducing apparatus 6, since five title keys 25 are already used, the state shown in FIG. 5 is obtained. . When such a semiconductor memory card 2 is inserted into the recording / reproducing apparatus 1, the media interface unit 13 determines whether there is a list of used key numbers 27 in the normal area 20 (S31). Since the list exists, it is next determined whether or not the list of the key use flag (the secret area key management information) 28 exists in the secret area 21 (S33). If the list of key usage flags 28 does not exist, the process ends. If the list of key usage flags 28 exists, the media interface unit 13 erases all the title keys # 1 to # 5 in which the usage key numbers are not used. (S34), these key use flags are set to (0), and the state shown in FIG. 6 is obtained.

  According to the copyright key management method configured as described above, when the semiconductor memory card 2 is inserted, even if the key use flag 28 of the secret area 21 is the title key 25 indicating the use state, the initialization is performed. Thus, the unused title key 25 and the key use flag 28 are deleted to prevent the secret area 21 from being wasted, and the area that can be added by the unused title key 25 is reduced. Can be prevented.

  Further, even if a mixed use with a device that does not handle the secret area 21 is performed, the unused title key 25 and the key use flag 28 are deleted, so that the capacity of the normal area 20 remains. It is possible to prevent the problem that the recording cannot be performed.

(Embodiment 2)
A second embodiment of the present invention will be described with reference to FIGS.

  1 is a block diagram of a recording / reproducing apparatus, FIG. 2 is a block diagram of a recording medium, FIGS. 8 and 9 are explanatory diagrams of recording of the recording medium, and FIG. 10 is a flowchart of a copyright key management method.

  Note that the configurations of the recording / reproducing apparatus 1 and the semiconductor memory card 2 are the same as those in the first embodiment, and a description of each part is omitted. However, the operation of the media interface unit 13 is different from that of the first embodiment.

  The copyright key management method will be described with reference to FIGS.

  Here, as an example, there is a semiconductor memory card 2 in a recording state as described in FIG. 3 of the first embodiment, in which encrypted contents 1 to 3 are recorded by the conventional recording / reproducing apparatus 6. To do. This semiconductor memory card 2 is shown in FIG. In the example of FIG. 8, the five title keys 25 are in use in a state where they are not referenced from the list of use key numbers 27.

  When the semiconductor memory card 2 in such a state is inserted into the recording / reproducing apparatus 1 and recording is started, the media interface unit 13 first reads the list of the used key numbers 27 from the normal area 20 (S41 in FIG. 10). ), It is confirmed that the used key number 27 is empty (S42). In the example of FIG. 8, since the fourth and subsequent spaces are vacant, it is decided to perform the fourth recording. Next, mutual authentication is performed if necessary, and a list of the key use flag 28 is read from the secret area 21 (S43), and it is confirmed whether there is a space in the key use flag 28 (S44). If there is no available space, it is checked in turn whether there is a title key 25 that is not referenced from the list of used key numbers 27 (S45). Since the title key # 1 is not referenced, it is determined that the title key # 1 is not used, and a new title key 25 is generated using the key area of the # 1 (S46), and the title key 25 is encrypted. Recording is performed (S48). If the key use flag 28 is empty in S44, a new title key 25 is generated with the key use flag 28 set to (1) (S47), and the title key 25 is encrypted and recorded. (S48). The state of the semiconductor memory card 2 after recording is shown in FIG.

  According to the copyright key management method configured as described above, the title key 25 in which the key use flag 28 of the secret area 21 indicates the use state when the key storage area of the secret area 21 is insufficient at the time of content recording. Even so, by initializing the unnecessary title key 25 and using the area, it is possible to prevent the secret area 21 from being consumed unnecessarily while leaving the title key 25 as much as possible.

  In addition, even when the semiconductor memory card 2 is used together with a device that does not handle the secret area 21 or the conventional recording / reproducing apparatus 6, there is a problem that recording cannot be performed even though the capacity remains in the normal area 20. Since the title key 25 can be left as much as possible without being generated, the deletion of the title key 25 can be minimized when the title key 25 is intentionally left for some reason. .

(Embodiment 3)
A second embodiment of the present invention will be described with reference to FIGS.

  1 is a block diagram of a recording / reproducing apparatus, FIG. 2 is a block diagram of a recording medium, FIGS. 11 and 12 are explanatory diagrams of recording on the recording medium, and FIG. 13 is a flowchart of a copyright key management method.

  Note that the configurations of the recording / reproducing apparatus 1 and the semiconductor memory card 2 are the same as those in the first embodiment, and a description of each part is omitted. However, the operation of the media interface unit 13 is different from that of the first embodiment.

  Here, as an example, there is a semiconductor memory card 2 in a recording state as described in FIG. 3 of the first embodiment, in which encrypted contents 1 to 3 are recorded by the conventional recording / reproducing apparatus 6. To do. This semiconductor memory card 2 is shown in FIG. In the example of FIG. 11, the five title keys 25 are in use in a state where they are not referenced from the list of use key numbers 27. The secret area 21 is newly provided with a key deletion impossible flag (secret area key management information) 29 indicating whether or not the title key 25 may be deleted. In this example, the title key # 1 is deleted. It shall be impossible. For example, when the semiconductor memory card 2 is used as a key bundle and this card is inserted into a specific device different from the recording / reproducing device 1, the key deletion impossible flag 29 refers to the key and refers to the key inside the device. It is used for purposes such as decrypting content using this key.

  When the semiconductor memory card 2 in such a state is inserted into the recording / reproducing apparatus 1 and recording is started, the media interface unit 13 first reads the list of the used key numbers 27 from the normal area 20 (S51 in FIG. 13). ), It is confirmed that there is a vacancy in the used key number 27 (S52). In the example of FIG. 11, since the fourth and subsequent spaces are vacant, it is determined to perform the fourth recording. Next, mutual authentication is performed if necessary, and a list of key use flags 28 is read from the secret area 21 (S53), and it is confirmed whether there is an empty key use flag 28 (S54). If there is no available space, it is checked in turn whether there is a title key 25 that is not referenced from the list of used key numbers 27 (S55). It is determined that the title key # 1 cannot be used because the key deletion disable flag 29 is set, and the next title key # 2 is investigated. Since the title key # 2 is not referenced from the list of the used key number 27, it is determined that it is not used, and it is determined that it can be used because the key deletion disable flag 29 is not set. The title key 25 is newly generated using the same (S56), and the title key 25 is encrypted and recorded (S58). If the key use flag 28 is empty in S54, a new title key 25 is generated with the key use flag 28 set to (1) (S57), and the title key 25 is encrypted and recorded. (S58). The state of the semiconductor memory card 2 after recording is shown in FIG.

  According to the copyright key management method configured as described above, when content is recorded, if the storage area of the title key 25 in the secret area 21 is insufficient, the key cannot be deleted indicating that the title key 25 is intentionally left. Even if the key use flag 28 of the secret area 21 indicates the use state within the range where the flag 29 is not set, the unnecessary title key 25 is initialized and the area is used. Thus, it is possible to prevent the secret area 21 from being consumed unnecessarily while leaving the necessary title key 25.

  In addition, even when the semiconductor memory card 2 is used together with a device that does not handle the secret area 21 or the conventional recording / reproducing apparatus 6, there is a problem that recording cannot be performed even though the capacity remains in the normal area 20. Since the necessary title key 25 in the secret area 21 that does not occur and is not used in the semiconductor memory card 2 can be left by the key deletion impossible flag 29, only the title key 25 is intentionally used for some reason. It is possible to prevent the necessary title key 25 from being erased accidentally when it is used to leave

  The present invention is useful as a copyright key management method in a digital device that records video and audio digital contents on a small recording medium such as a semiconductor memory card.

The block diagram of the recording / reproducing apparatus in embodiment of this invention The block diagram of the recording medium in embodiment of this invention Recording explanatory diagram of a recording medium in Embodiment 1 of the present invention Recording explanatory diagram of a recording medium in Embodiment 1 of the present invention Recording explanatory diagram of a recording medium in Embodiment 1 of the present invention Recording explanatory diagram of a recording medium in Embodiment 1 of the present invention Flowchart of copyright key management method in Embodiment 1 of the present invention Recording explanatory diagram of a recording medium in Embodiment 2 of the present invention Recording explanatory diagram of a recording medium in Embodiment 2 of the present invention Flowchart of copyright key management method in Embodiment 2 of the present invention Recording explanatory diagram of a recording medium in Embodiment 3 of the present invention Recording explanatory diagram of a recording medium in Embodiment 3 of the present invention Flowchart of copyright key management method in Embodiment 3 of the present invention Block diagram of a recording / reproducing apparatus in a conventional example Recording explanatory diagram of a recording medium in a conventional example

Explanation of symbols

1 Recording / Reproducing Device 2 Semiconductor Memory Card (Recording Medium)
DESCRIPTION OF SYMBOLS 11 Encoding part 12 Content encryption part 13 Media interface part 14 Content encryption decompression | restoration part 15 Decryption part 20 Normal area | region 21 Secret area 22 AKE process part 23 MKB
24 Media ID
25 Title key (copyright key)
26 Encrypted Content 27 Key Number Used (Normal Area Key Management Information)
28 Key usage flag (key management information for the secret area)
29 Key deletion impossible flag (secret area key management information)

Claims (3)

Using a recording medium having a normal area that can be freely accessed and a secret area that can be accessed only after authentication, the encrypted content is associated with the title key obtained by encrypting the encrypted content in the normal area And a key management information for storing the title key of the content and key management information for managing the validity of the title key in the secret area,
As the key management information of the secret area, record a key use flag for indicating whether the title key is used or not used in the normal area,
When the recording medium is inserted into a device that manages a copyright key, if there is no key management information in the normal area and the title key exists in the secret area, the title key of the secret area And the key use flag for indicating the non-use state of the title key are deleted even if the key use flag is in use,
When the key management information exists in the normal area and the title key exists in the secret area, the title key of the secret area that is not referred to by the key management information of the normal area is used even if the key is used. A copyright key management method characterized by erasing a flag even when it is in use. Using a recording medium having a normal area that can be freely accessed and a secret area that can be accessed only after authentication, the encrypted content is associated with the title key obtained by encrypting the encrypted content in the normal area And a key management information for storing the title key of the content and key management information for managing the validity of the title key in the secret area,
As the key management information of the secret area, record a key use flag for indicating whether the title key is used or not used in the normal area,
When content is recorded by a device that manages a copyright key on the recording medium, there is a space in the title key area of the secret area on the key management information of the normal area, and the key of the secret area When the management information is in a state where the number of title keys that cannot be recorded any more is used, the key use flag for indicating the state of non-use of the title key in the secret area is indicated, for example A copyright key management method characterized by using at least one empty title key area after erasing at least one of the key usage flags. Using a recording medium having a normal area that can be freely accessed and a secret area that can be accessed only after authentication, the encrypted content is associated with the title key obtained by encrypting the encrypted content in the normal area And a key management information for storing the title key of the content and key management information for managing the validity of the title key in the secret area,
As the secret area key management information, it indicates a key use flag for indicating whether the title key is used or not used in the normal area, and whether the title key may be deleted. A key deletion impossible flag for
When content is recorded by a device that manages a copyright key on the recording medium, there is a space in the title key area of the secret area on the key management information of the normal area, and the key of the secret area When the management information is in a state where the number of title keys that cannot be recorded any more is used, the key use flag for indicating the state of non-use of the title key in the secret area is indicated, for example Even if the key use flag is in use, a title key area that is freed by erasing at least one of the key deletion impossible flags in the secret area can be used. Rights key management method.

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