JP4580024B2 - Content playback method - Google Patents

Description

  The present invention belongs to a technique for improving security in a semiconductor device such as an LSI used in a key mounting system.

  In Japanese Patent Application No. 2001-286881 by the same applicant as the present application, a technique for improving the confidentiality and confidentiality of a key in a key mounting system is shown.

  However, since this prior art does not relate to a known literature invention, there is no prior art document information to be described.

  An object of the present invention is to provide a semiconductor device with a high security level. It is another object of the present invention to provide a content reproduction method with a high security level.

The solution provided by the present invention is a content playback method for playing back content stored in an external memory using an LSI. The external memory has a first area for storing plaintext content, and is unique to the LSI. And a second area for storing content encrypted using the data unique key, and the content reproduction method is executed when the CPU of the LSI executes an application program, Inputting plaintext content stored in the first area of the external memory to the LSI; generating a data unique key using a unique ID stored in the internal memory of the LSI; and storing input the plaintext content was, encrypted using the data inherent key, the second region of the external memory A step that was stored in the second area, the content encrypted using the data inherent key, the enter to the LSI, and a step of reproducing and decoding using the data inherent key It is a thing.

According to the present invention, the plaintext content stored in the first area of the external memory is encrypted in the LSI using the data unique key generated using the unique ID stored in the internal memory. The encrypted content is stored in a second area of the external memory, when the reproduction is decrypted using the data inherent key. For this reason, since the content encrypted using the data unique key generated from the unique ID is stored in the second area of the external memory, depending on other LSIs that do not have the same data unique key, Playback becomes impossible. This prevents unauthorized execution of the content and improves the security level.

The solution provided by the present invention is a content playback method for playing back content stored in an external memory using an LSI. The external memory stores content encrypted using a shared key. 1 area and a second area for storing content encrypted using a data unique key unique to the LSI, and the content reproduction method is performed by the LSI CPU executing an application program. The content encrypted by the shared key stored in the first area of the external memory is input to the LSI, and stored in the internal memory of the LSI Decrypting the content encrypted with the shared key using the shared key to obtain plaintext content; Generating a data unique key using the unique ID stored in the memory; and encrypting the decrypted plaintext content using the data unique key and storing the encrypted data in the second area of the external memory And inputting the content stored in the second area and encrypted using the data unique key to the LSI, decrypting the content using the data unique key, and reproducing the content. It is a thing.

As described above, according to the present invention, since the content encrypted using the data unique key generated from the unique ID is stored in the second area of the external memory, it does not have the same data unique key. Some other LSIs cannot be played back. For this reason, illegal execution of content is prevented. Therefore, the security level is improved.

1 is a block diagram showing a configuration of a secure LSI as a semiconductor device according to an embodiment of the present invention. It is a figure showing the whole flow of development and commercialization using the secure LSI of FIG. It is a flowchart which shows the flow of the whole process of a boot program. It is a flowchart of initial value setting processing SZ1. FIG. 2 is a diagram illustrating a configuration of an encryption unit and its periphery in the secure LSI of FIG. 1. It is a figure which shows the setting method of the common bus and private bus in the secure LSI of FIG. FIG. 2 is a diagram illustrating a configuration of an external host I / F and its periphery in the secure LSI of FIG. 1. It is a figure which shows operation | movement of the external host I / F in goods operation mode. It is a figure which shows access control of a secure memory. It is the data flow 1 of the normal boot process in goods operation mode. It is the data flow 2 of the normal boot process in goods operation mode.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an internal configuration of a secure LSI as a semiconductor device according to the present embodiment. In FIG. 1, the secure LSI 1 is configured to be connectable to an external memory 100 (flash memory 101 and RAM 102) via an external bus 120. In addition, the operation mode can be set by giving the mode ID.

  The main components related to this embodiment will be briefly described.

  First, the secure LSI 1 includes a secure memory (secure flash) 10 including a non-rewritable area 11. In this non-rewritable area 11, a non-rewritable area write flag 12 is provided. The non-rewritable area write flag 12 changes its flag value from “permitted” to “done” once the mode ID is written in the secure memory 10 and disables subsequent writing to the non-rewritable area 11. In the present embodiment, the secure memory 10 is constituted by a flash memory. However, the present invention is not limited to this, and any type of non-volatile memory may be used.

  The encryption unit 2 encrypts and decrypts a program. The secret key calculation processing unit 20 as an encryption calculation unit, a key generation / update sequencer 30 as an encryption control unit, and a program encryption And a storage unit 35 for storing seeds. The secret key calculation processing unit 20 includes a register for storing various keys and the like, and can execute a plurality of sequences including program encryption processing or decryption processing. The key generation / update sequencer 30 determines whether to execute each sequence that can be executed by the secret key calculation processing unit 20, and prohibits the operation of the secret key calculation processing unit 20 for the sequence that is determined not to be executed. The key generation / update sequencer 30 has a mode ID storage register 31, and determines whether to execute each sequence based on the value of the mode ID stored in the mode ID storage register 31. Also, an encryption type identifier storage register 32 for storing an encryption type identifier indicating what algorithm and key length the key or program is encrypted with is provided. Details of the configuration and operation of the encryption unit 2 will be described later.

  The mode sequencer 40 also includes a mode ID storage register 41, and the operation of the external interface (I / F) 50 according to the mode ID stored in the mode ID storage register 41 and the value of the jumper 43, that is, The I / F through which the program or data stored in the external memory 100 is read is controlled. Thereby, it is possible to control whether or not the plaintext program stored in the external memory 100 can be executed. Furthermore, the mode sequencer 40 includes an encryption type identifier storage register 42 that stores an encryption type identifier indicating which method is used to encrypt the key.

  Under the control of the mode sequencer 40, the external I / F 50 includes a through unit 52 and a program decryption cryptographic engine 53 included in the program processing unit 51, and a through unit 56 and a data encryption / decryption cryptographic engine 58 included in the data processing unit 55. A program and data are input / output to / from the external memory 100 via any of them.

  Here, except for an administrator mode and application program development which will be described later, the program input via the through unit 52 is not executed inside the secure LSI 1. In other words, the through unit 52 is effective when encrypting a plain text program or re-encrypting an already encrypted program using another key. The secure LSI 1 has an administrator mode described later. Except for application program development, the operation is not shifted to the program input via the through unit 52. Therefore, for example, even if the secure LSI 1 that has become a product takes in the plain text program via the through unit 52, it cannot be executed.

  The boot ROM 60 stores a boot program that controls the startup operation of the secure LSI 1. The HASH calculation unit 70 calculates a HASH value in order to verify the validity of the program read into the secure LSI 1.

  In the external memory 100, the program is stored in the flash memory 101, and the data (content) is stored in the RAM 102. The external tool 110 stores various initial values stored in the secure memory 10 when the secure LSI 1 is first activated. The type of the initial value varies depending on the set operation mode.

  FIG. 2 is a diagram showing the overall flow of development and commercialization using the secure LSI 1 of FIG. As shown in FIG. 2, the secure LSI 1 has four modes: an administrator mode (mode ID: 00), a key generation mode (mode ID: 01), a development mode (mode ID: 10), and a product operation mode (mode ID: 11). Operates in various operation modes.

  First, the secure LSI 1 set to the administrator mode operates as an administrator LSI. In the administrator LSI, a key generation program is developed (PA1), and the key generation program is encrypted using an arbitrary key generation key (PA2).

  The secure LSI 1 set to the key generation mode operates as a key generation LSI. In the key generation LSI, an encrypted key generation program generated in the administrator LSI is mounted (PB1), and various keys are generated by executing this key generation program (PB2).

  The secure LSI 1 set to the development mode operates as a development LSI. In the development LSI, an application program to be executed by an actual product is developed (PC1). Then, the application program is encrypted using the program shared key (PC2).

  The secure LSI 1 set in the product operation mode operates as an actual product LSI. In the product LSI, the application program generated by the development LSI and encrypted with the program shared key is installed and converted into the application program encrypted with the program unique key (PD1). . The application program encrypted with the program unique key is executed in normal product operation. This conversion process can be executed in the development LSI (PC3) for debugging the application program (PC4).

  The secure LSI 1 performs the following operation by executing the boot program stored in the boot ROM 60.

  FIG. 3 is a flowchart showing the overall processing flow of the boot program. When the secure LSI 1 is turned on, the boot program stored in the boot ROM 60 is executed by the CPU 65. As shown in FIG. 3, first, each hardware is initialized (SZ0). Then, various initial values are read from the external tool 110 and set in the secure memory 10 (SZ1).

  FIG. 4 is a flowchart of the initial value setting process SZ1. First, the jumper 44 determines whether or not the secure memory 10 is mounted in the LSI (SZ11). Next, it is determined whether or not the non-rewritable area write flag 12 is “completed” (SZ12). If it is “completed” (Yes in SZ12), an initial value has already been set in the secure memory 10. Then, the process SZ1 is terminated. When the non-rewritable area write flag 12 is “permitted” (No in SZ12), the initial value is written into the secure memory 10. In addition to the mode ID, the encrypted program unique key, address management information, and data unique key are written in the non-rewritable area 11 of the secure memory 10 (SZ13, SZ16 to SZ18). As a result of the initial determination, when it is determined that the secure memory 10 is outside the LSI (No in SZ14), the mode ID is overwritten with a value representing the product operation mode (SZ15). Thereby, a product in which the secure memory 10 is outside the LSI package can operate only in the product operation mode.

  Next, the unwritable area write flag 12 is set to “completed” (SZ19). This makes it impossible to rewrite the non-rewritable area 11 thereafter. Further, the encryption type identifier and the implementation mode flag are written in the normal areas 13 and 14 (SZ1A). When the mode ID indicates a mode other than the administrator mode (No in SZ1B), in addition to these, the encrypted shared key / key generation key is also written in the normal areas 13 and 14 (SZ1C).

  Thereafter, returning to FIG. 3, the preprocessing SZ2 is executed. Here, the mode ID set in the non-writable area 11 of the secure memory 10 is set in the mode ID storage register 31 of the key generation / update sequencer 30 and the mode ID storage register 41 of the mode sequencer 40. In addition, the encryption type identifier set in the first normal area 13 of the secure memory 10 is set in the encryption type identifier storage register 32 of the key generation / update sequencer 30 and the encryption type identifier storage register 42 of the mode sequencer 40. The Further, the address management information stored in the non-rewritable area 11 of the secure memory 10 is set in the address division storage register 81 of the MEMC 80. The operations so far correspond to the initial value setting phases PA0, PB0, PC0, PD0 in FIG.

  Thereafter, the operation in each mode is performed according to the value of the mode ID (SZ3).

  When the mode ID is “00”, the secure LSI 1 enters the administrator mode, and executes the plaintext program execution process SA1 or the program encryption process SA2 according to the value of the jumper 43 (SA0). In the key generation program development phase PA1, a plain text program execution process SA1 is performed, where a key generation program is generated. This key generation program is stored in the external memory 100. In the key generation program encryption phase PA2, the key generation program is encrypted with an arbitrary key generation key.

  When the mode ID is “01”, the secure LSI 1 enters the key generation mode, and executes the key generator manufacturing process SB1 or the key management / issue process SB2 according to the value of the mounting mode flag (SB0). In the key generator manufacturing phase PB1, the key generator manufacturing process SB1 is executed, and the key generation program encrypted with an arbitrary key generation key is re-encrypted with the program unique key. In the key management / issue phase PB2, by executing the key generation program encrypted with the program unique key, the key management / issue process SB2 executes to generate a key.

When the mode ID is “10”, the secure LSI 1 is in the development mode, and depending on the value of the jumper 43 (SC0), the program encryption process SC1, the plaintext program execution process SC2, the program implementation process SC3, or the encryption program execution Process SC4 is executed. In the application program development phase PC1, a plain text program execution process SC2 is performed to develop an application program. The developed application program is stored in the external memory 100. In the application program encryption phase PC2, program encryption processing SC1 is executed. In the application program implementation phase PC3, the program implementation process SC3 is executed, and in the application program debug phase PC4, the encrypted program execution process SC4 is executed. These processes are the same as the processes SD1 and SD2 in the product operation mode. When the mode ID is “11”, the secure LSI 1 enters the product operation mode, and the program implementation is performed according to the value of the implementation mode flag (SD0). The process SD1 or the normal boot process SD2 is executed. In the product mounting phase PD1, program mounting processing SD1 is executed. In the product operation phase PD2, the normal boot process SD2 is executed.

  FIG. 5 is a diagram showing the configuration of the encryption unit 2 and its surroundings. As shown in FIG. 5, in addition to the mode ID storage register 31 and the encryption type identifier storage register 32, the key generation / update sequencer 30 is provided corresponding to each sequence executed using the secret arithmetic processing unit 20, Referring to register 33 for storing the number of times of issuance and registers 31 and 33, whether or not each sequence can be executed (whether or not each program in boot ROM 60 and an external program can be executed) ) And a control unit 34 for controlling the operation of the secret key calculation processing unit 20. In the secure LSI 1, when each sequence is issued once, 1 is added to the register 33 corresponding thereto.

  The program encryption type 35 is used when a key is decrypted or a key is generated, and a shared key and a unique key are prepared.

  In the product operation mode and development mode described above, a sequence (secure flash loader) for setting values stored in the secure memory 10 in each register of the encryption unit 2 and a sequence for generating / decrypting a key (key sequencer) Are restricted by the control unit 34 so that each can be issued only once. For example, once the mode ID stored in the secure memory by the boot program is stored in the mode ID storage register 31 once the secure LSI 1 is started, the mode ID cannot be rewritten again. Also, if the shared key and the unique key are decrypted when the secure LSI is activated and stored in the register inside the secret key calculation processing unit 20, the key cannot be generated / decrypted again. Therefore, even if a key generation program is installed in the external memory 100, a key cannot be generated. The unique key once decrypted is stored in a unique key storage register in the external I / F 50, and the encryption program is executed using this unique key. The program is updated using a shared key or unique key stored in a register inside the secret key calculation processing unit 20.

  In the key generation mode and the administrator mode described above, the key sequencer is not restricted, so that a key can be generated.

  Here, instead of the sequence issuance count storage register 33, a program cipher type use count storage register that is provided corresponding to the program cipher type and stores the use count may be provided. Since the program encryption type is used when generating / decrypting the key, for example, if the number of uses is limited by the mode ID, the key generation / decryption is also limited by counting the number of times the program encryption type is used. can do.

  Further, it is not always necessary to prepare a shared key and a unique key for the program encryption type.

  FIG. 6 is a diagram showing a method for setting a common bus and a private bus. Here, the “private bus” refers to a bus that cannot be accessed from the outside (external access), and is not necessarily physically independent from the external I / F 50. That is, a register or the like set as being connected to the private bus 91 cannot be read / written by external access.

  An address is given to each register in the secure LSI 1. Among the addresses, the common bus address storage unit 82 stores addresses of registers and the like connected to the common bus 92 ("0X00000" to "0X10000" in FIG. 6). When there is an external access, the external access address determination unit 83 refers to the common bus address storage unit 82 to determine whether the access is to the common bus 92, and if so, accepts this. On the other hand, when the external access is not an access to the common bus 92, the access is denied because the access is to the private bus 91.

  In the case of access from the CPU 65 (internal access), such a determination is not performed and the internal access is accepted.

  FIG. 7 is a diagram showing the configuration of the external I / F 50 and its periphery. In FIG. 7, the address division storage register 81 stores address management information indicating the correspondence between each area in the external memory 100 and the address. Here, the external memory 100 includes a first area (program within the setting range), a second area (program outside the setting range), a third area (data within the setting range), and a fourth area (setting). The addresses are stored in four areas (data outside the range).

  The comparator 85 refers to the address management information stored in the address division storage register 81, determines which of the first to fourth areas the address of the information to be input / output corresponds to, and The determination result is sent to the input / output control signal generator 84.

  The input / output control signal generation unit 84 determines which interface of the external I / F 50 is enabled based on the mode ID and jumper determination result output from the mode sequencer 40 and the output of the comparator 85. The determination result is sent to the external input / output mode control unit 54 as an input / output control signal. The external input / output mode control unit 54 enables one of the interfaces according to the received input / output control signal. In addition, when the mode ID indicates the product operation mode, the execution through unit 52b is not necessarily enabled. As a result, the plaintext program stored in the external memory 100 is restricted from being executed.

  The program stored in the first area is fetched through the execution through unit 52b of the program processing unit 51 and debugged in the key generation mode, the product operation mode, or the development mode when debugging in the administrator mode or the development mode. At other times, the program is taken in via the program decryption cryptographic engine 53. These programs are executable. On the other hand, the program stored in the second area is taken in via the encryption through unit 52a of the program processing unit 51, supplied to the encryption unit 2, and encrypted or re-encrypted. These programs are not executable.

  Further, the data stored in the third area is taken in via the data encryption / decryption encryption engine 58 of the data processing section 55, and the data stored in the fourth area is stored in the through section 56 of the data processing section 55. Is taken in through.

  The program taken in through the encryption through unit 52a is encrypted or re-encrypted in the secret key calculation processing unit 20 of the encryption unit 2, and then again in the external memory 100 through the encryption through unit 52a. Are written in the first area. As a result, the program is executable thereafter.

  Note that data is set in the address classification storage register 81 and the mode ID storage register 41 via the private bus 91. That is, data is set by access from the inside. This data setting can be executed only once after the secure LSI 1 is reset.

  FIG. 8 is a diagram showing the operation of the external I / F 50 and assumes a product operation mode. As shown in FIG. 8, before implementation, the application program encrypted with the shared key is stored in the second area (outside the setting range) of the external memory 100, and therefore cannot be executed as it is. . That is, the application program stored in the second area and encrypted with the shared key is taken into the secure LSI 1 through the encryption through unit 52a at the time of mounting, and is decrypted with the shared key and then unique. The data is re-encrypted with the key and stored again in the first area (within the set range) of the external memory 100 via the encryption through unit 52a. Then, the application program encrypted with the unique key stored in the first area is taken into the secure LSI 1 via the program decryption cryptographic engine 53 and executed.

  In the development mode, the following operation is performed. First, at the time of debugging, a program to be executed is written in the first area (within the set range). As a result, even a plain text program is fetched and executed through the execution through unit 52b. At the time of encryption, the program to be encrypted is written in the second area (outside the setting range). Thus, when the secure LSI 1 is activated, an encryption sequence is executed, encrypted with the shared key, and stored in the external memory 100. At the time of debugging, a program to be re-encrypted is written in the second area (outside the setting range). Furthermore, at the time of encryption debugging, the encryption program to be debugged is written in the first area (within the set range). Thereby, it is decoded and executed.

  FIG. 9 is a diagram showing access control of the secure memory 10. As shown in FIG. 9, the access control unit 95 includes a register 96 that stores the address of the non-rewritable area 11, a register 97 that stores the address of the non-rewritable area write flag 12, and a writable / unusable determination unit 98. I have. The registers 96 and 97 are configured such that once data is written, further writing cannot be performed by flag management or the like.

Access control is performed as follows. Access from the CPU 65 to the secure memory 10 is always executed via the access control unit 95. When the command is “read”, the data in the secure memory 10 is output to the private bus 91 regardless of whether the access destination address is a non-rewritable area or a normal area. On the other hand, when the command is “write”, the write enable / disable determining unit 98 performs writing with reference to the access destination address, the address stored in the register 96, and the value of the non-rewritable area write flag 12. It is determined whether or not. Specifically, the following determination is made.
(Flag “Done” and write-disabled area)… Writable (Flag “Done” and normal area)… Writable (Flag “Not” and write-disabled area)… Writable (Flag “Not” and normal area)… Writable

  Note that commands such as “sector erase” and “chip erase” are also prepared in the secure memory 10. When the non-rewritable area write flag 12 is “completed”, “sector erase” is accepted for the normal area but not for the non-writable area. Also, “chip erase” is not accepted.

  Also in the reproduction of content (data), security is improved by adopting the following method.

  Data is initially placed in the fourth area (outside the set range) in the external RAM 102. When placed in the fourth area, the data is either encrypted with a data shared key (different from the program shared key) or in plain text. For this reason, there is a possibility of unauthorized use by other LSIs, and there is a problem in terms of security.

  In order to solve this problem, for content such as video and music for which unauthorized use is particularly prevented, only the content stored in the third area (within the setting range) of the external RAM 102 can be played back. Create as follows. The data placed in the third area is decrypted by the data encryption / decryption encryption engine 58 when taken into the secure LSI. Since the data unique key used in this decryption is created by a unique ID and a random number, it differs not only for each secure LSI 1 but also for each activation. Therefore, the data is less likely to be illegally used, and security is improved. Since the program for reproducing the content is also encrypted with the unique key, it is considered that the program is difficult to be tampered with.

  10 and 11 are data flows of the normal boot process in the product operation mode. In FIG. 10, first, the encrypted program unique key Enc (program unique key, MK0), Enc (MK0, CK) stored in the non-writable area 11 of the secure memory 10 is stored in the secret key calculation processing unit 20. Set in the encryption key storage register. Then, the encrypted program unique key is decrypted using the installed program encryption type to obtain the program unique key. The obtained program unique key is set in the program unique key storage register of the program decryption cryptographic engine 53 of the external I / F 50. Thereafter, the data unique ID stored in the unwritable area 11 of the secure memory 10 is set in the unique ID storage register of the secret key calculation processing unit 20. In addition, a random number is generated by the CPU 65 and set in a random number storage register of the secret key calculation processing unit 20. Then, the secret key calculation processing unit 20 generates a data unique key from the data unique ID and the random number. The generated data unique key is set in the data unique key storage register of the data encryption / decryption encryption engine 58 of the external I / F 50.

  Thereafter, in FIG. 11, the application program Enc (application program, program unique key) encrypted with the program unique key stored in the external memory 100 is decrypted by the program processing unit 51 of the external I / F 50. The decryption is performed via the cryptographic engine 53, the data is taken into the HASH calculation unit 70, and the HASH value is calculated. Then, the calculated HASH value is compared with the HASH value stored in the normal area 13 of the secure memory 10 to check whether the application program has been tampered with. When the HASH values match, the process is shifted to the application program Enc (application program, program unique key) stored in the external memory 100, and the application is executed. If the HASH values do not match, it is estimated that some kind of fraud has been performed, and processing by the unauthorized access time control is executed.

  The application program is executed by the CPU 65. That is, since the CPU 65 in the secure LSI 1 performs access control as a master, the subsequent operation is internal access, and therefore the external access address determination unit 83 is not involved. The content (original content) encrypted with the data sharing key is taken into the secure LSI 1 from the fourth area (non-reproducible area) of the external RAM 102 by the application program. The captured content is decrypted by the secret key calculation processing unit 20 using the data shared key written in the secure memory 10. Thereafter, the data is encrypted with the data unique key via the data encryption / decryption encryption engine 58 in the data processing unit 55 of the external I / F 50 and written to the third area (reproducible area) of the external RAM 102. Thereafter, the content encrypted with this data unique key can be played back, and when played back, it is decrypted with the data unique key via the data encryption / decryption encryption engine 58 in the data processing unit 55 of the external I / F 50. The

1 Secure LSI (semiconductor device)
2 Encryption unit 10 Secure memory 11 Non-rewritable area 20 Secret key operation processing unit (encryption operation unit)
30 Key generation / update sequencer (encryption controller)
31 Mode ID storage register 33 Sequence issue count storage register 35 Storage unit 40 Mode sequencer 41 Mode ID storage register 45 Jumper value determination unit 50 External interface 51 Program processing unit 52 Through unit 52a Execution through unit 52b Encryption through unit 53 Program Decryption encryption engine 55 Data processing unit 56 Through unit 58 Data encryption / decryption encryption engine 60 Boot ROM
81 Address division storage register 82 Common bus address storage unit 83 External access address determination unit 100 External memory

Claims (2)

A content playback method for playing back content stored in an external memory using an LSI,
The external memory includes a first area for storing plaintext content and a second area for storing content encrypted using a data unique key unique to the LSI,
The content reproduction method is executed by the CPU of the LSI executing an application program,
Inputting plaintext content stored in the first area of the external memory into the LSI;
Generating a data unique key using a unique ID stored in an internal memory of the LSI;
Encrypting the plaintext content input to the LSI using the data unique key and storing it in the second area of the external memory ;
The content encrypted using the data unique key stored in the second area is input to the LSI, decrypted using the data unique key, and reproduced. Content playback method. A content playback method for playing back content stored in an external memory using an LSI,
The external memory includes a first area for storing content encrypted using a shared key and a second area for storing content encrypted using a data unique key unique to the LSI. ,
The content reproduction method is executed by the CPU of the LSI executing an application program,
Inputting the content encrypted by the shared key stored in the first area of the external memory into the LSI;
Decrypting the content encrypted with the shared key using the shared key stored in the internal memory of the LSI to obtain plaintext content;
Generating a data unique key using a unique ID stored in the internal memory;
Encrypting the decrypted plaintext content using the data unique key and storing the encrypted content in the second area of the external memory;
The content encrypted using the data unique key stored in the second area is input to the LSI, decrypted using the data unique key, and reproduced.
A content reproduction method characterized by the above.

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