JP2008310678A - Storage device, information apparatus, and content conversion method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a storage device, an information apparatus, and a content conversion method capable of sufficiently protecting content. <P>SOLUTION: The storage device 100 is provided with a DRM1 function part 104 decrypting first content, a DRM2 function part 105 encrypting the decrypted content by a second content protection method, a non-volatile memory 106 storing secrecy information to be used for content processing by the DRM1 function part 104 and the DRM2 function part 105, a storage part 103 storing temporary data generated during processing by the DRM1 function part 104 and the DRM2 function part 105, and a control part 101 controlling operation of the DRM1 function part 104 and the DRM2 function part 105 and at the same controlling permission/prohibition of reading access from an external bus 115 to the storage part 103. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a storage device, an information device, and a content conversion method.

  Conventionally, a computer system described in Patent Document 1 below is known as a technology in such a field. The computer system includes a storage device and an operating system, and access to at least a part of the storage device is restricted by the operating system. Further, in this kind of computer system, as shown in FIG. 13, it is possible to have a mechanism for transmitting encrypted data to an external device via a network.

In the information device 1300, the content encrypted by the first content protection method is stored in the external storage device 1303. Then, the information device 1300 decrypts the encrypted content by the DRM1 function unit 1306, encrypts the decrypted content again by the DRM2 function unit 1307 using the second content protection method, and passes the network content through the network control unit 1304. This is transmitted to the external device 1320. The above encryption / decryption operations are realized by the CPU 1301 executing the program stored in the program memory 1302 and controlling the DRM1 function unit 1306 and the DRM2 function unit 1307, and are used for encryption / decryption. Information is stored in advance in the nonvolatile memory unit.
JP 2005-517225 A

  During such computation processing related to encryption / decryption, information that is highly necessary to be protected, such as key information and decrypted content, is temporarily generated. Such information that is highly necessary to be protected enters and exits the main memory 1305 via the general-purpose external bus 1309, and may be illegally read by unauthorized access from the outside. If such information is read illegally, it may cause unauthorized copying of the content, and the content cannot be sufficiently protected.

  Therefore, an object of the present invention is to provide a storage device, an information device, and a content conversion method that can sufficiently protect content.

  The storage device of the present invention is connected to an external bus used for data transmission / reception in an information device, inputs content encrypted by the first encryption method from the external bus, and encrypts the input content A storage device that converts a method into a second encryption method different from the first encryption method and outputs the second encryption method to an external bus, wherein the content encrypted by the first encryption method is decrypted. A content processing operation unit, a second content processing operation unit that performs encryption processing by the second encryption method on the content decrypted by the first content processing operation unit, and the first and second content processing operation units A secret information storage unit that stores secret information used for processing by the content processing calculation unit, and a data storage unit that stores temporary data generated during processing by the first and second content processing calculation units It controls the operation of the first and second content processing arithmetic unit, characterized by comprising a control unit for controlling the propriety of read access to the data storage unit from the external bus, the.

  In addition, the storage device of the present invention disallows the normal mode in which read access to the data storage unit from the external bus is permitted and the read access to at least a part of the data storage unit from the external bus. You may further provide the mode switching means which selectively switches an operation mode to either of restriction | limiting modes.

  In addition, the data storage unit may be set in advance with an address of a non-readable area in which read access from the external bus is not permitted when operating in the restricted mode.

  In addition, when the control unit is operating in the restricted mode, if a read access request for the non-readable area of the data storage unit is received from the external bus, the control unit is stored in the non-readable area for the external bus. Data different from the data may be returned.

  The information device of the present invention is connected to an external bus used for data transmission / reception inside the device, a content storage unit connected to the external bus and storing content encrypted by the first encryption method, and the external bus The content encrypted by the first encryption method is input from the external bus, the input content encryption method is converted to a second encryption method different from the first encryption method, and the external bus is converted. A storage device that outputs the content encrypted by the first encryption method, and the storage device decrypts the content encrypted by the first encryption method by the first content processing operation unit and the first content processing operation unit. A second content processing calculation unit that performs encryption processing on the content that has been encrypted by the second encryption method, and secret information that is used for processing by the first and second content processing calculation units. The data storage unit controls the operations of the information storage unit, the data storage unit that stores temporary data generated during processing by the first and second content processing calculation units, and the data storage unit. And a control unit that controls whether or not read access from the external bus to the unit is possible.

  The content conversion method of the present invention uses a storage device connected to an external bus used for data transmission / reception in an information device to input content encrypted by the first encryption method from the external bus to the storage device. A content conversion method for converting an input content encryption method into a second encryption method different from the first encryption method and outputting the converted content to an external bus, the first content processing operation unit of the storage device However, the first operation processing step for decrypting the content encrypted by the first encryption method and the second content processing operation unit of the storage device are decrypted by the first content processing operation unit. A second calculation processing step for performing encryption processing on the content obtained by the second encryption method, and a secret information storage unit of the storage device is processed by the first and second content processing calculation units. A secret information storing step for storing secret information to be used, a data storage unit of the storage device, a temporary data storage step for storing temporary data generated during processing by the first and second content processing calculation units, and a storage device And a control step for controlling whether or not read access from the external bus to the data storage unit is performed while controlling the operations of the first and second content processing arithmetic units. .

  According to the present invention, it is possible to provide a storage device, an information device, and a content conversion method that can sufficiently protect content.

  Hereinafter, preferred embodiments of a storage device, an information device, and a content conversion method according to the present invention will be described in detail with reference to the drawings.

  The information device 1 shown in FIG. 1 is a device that can store content data and transmit the content data to the external device 120 via a network. The external storage device 113 of the information device 1 stores encrypted content encrypted by the first content protection method (hereinafter referred to as “DRM1 method”). The information device 1 has a function of encrypting the content stored in the external storage device 113 by the second content protection method (hereinafter referred to as “DRM2 method”) and transmitting the content to the external device 120. As the DRM1 system, for example, the CPRM system is used here. As the DRM2 system, for example, the DTCP-IP system is used here.

  The information device 1 includes a storage device 100. The storage device 100 is connected to an external bus 115 using a general-purpose interface, and a CPU 111, a program memory 112, an external storage device 113, and a network control unit 114 are connected to the external bus 115.

  The CPU 111 controls the storage device 100, the external storage device 113, and the network control unit 114 according to a control program stored in the program memory 112. The program memory 112 stores a main program, a DRM1 processing program, and a DRM2 processing program which will be described later.

  The external storage device 113 is for storing the encrypted content. As shown in FIG. 2, the data 700 stored in the external storage device 113 includes encrypted content 702 encrypted by the DRM1 method and a title key Kt1. The title key Kt1 is data used when the DRM1 function unit 104 generates the content key Kc1. The content key Kc1 is key data for encrypting or decrypting the content using the DRM1 method. The DRM1 encrypted content 702 is content data encrypted with the content key Kc1.

  The network control unit 114 in FIG. 1 is for communicating with the external device 120 on the network. The network control unit 114 is connected to the external device 120 via a network. The external device 120 is compatible with the DRM2 method, and can receive content protected by the DRM2 method from the counterpart device (in this case, the information device 1).

  The storage device 100 includes a storage unit 103, a DRM1 function unit 104, a DRM2 function unit 105, a nonvolatile memory 106, and a control unit 101 that controls these units 103 to 106. The units 101 and 103 to 106 are connected by an internal bus 102, and exchange data with each other through the internal bus 102. The external bus 115 described above is connected to the control unit 101, and all data exchange via the external bus 115 of the storage device 100 is performed via the control unit 101. The configuration of the storage device 100 is applied to, for example, a RAM, a FRAS ROM, an HDD, or the like.

  The storage unit 103 has a readable / writable mass storage capacity and corresponds to, for example, a disk unit of an HDD. The DRM1 function unit 104 is a calculation unit that performs content processing corresponding to the DRM1 method (hereinafter referred to as “DRM1 processing”). The DRM1 function unit 104 has functions such as encryption key generation processing and encryption decryption processing for protecting content stored in the external storage device 113. Although details will be described later, the DRM1 function unit 104 executes each process under the control of the control unit 101 when a command code for DRM1 is written in the control data area 211 of the storage unit 103.

  The DRM2 function unit 105 is a calculation unit that performs content processing corresponding to the DRM2 method (hereinafter referred to as “DRM2 processing”). The DRM2 function unit 105 has functions such as processing for performing authentication / key exchange with the external device 120, key generation processing, and encryption processing regarding content protection on the network. Although details will be described later, the DRM2 function unit 105 executes each process under the control of the control unit 101 when a command code for DRM2 is written in the control data area 211 of the storage unit 103. The method for realizing the DRM1 function unit 104 and the DRM2 function unit 105 may be hardware or software executed by the control unit 101 or the like. It is also possible to implement a combination of hardware and software.

  FIG. 3 shows an address map 300 of the nonvolatile memory 106. As shown in the figure, the non-volatile memory 106 is for storing secret information used for DRM1 processing and DRM2 processing. The device key Kd1 for DRM1 and the device key Kd2 for DRM2 are also non-volatile memory. 106. The DRM1 secret data 310 stores secret information used during the DRM1 process. The device key Kd1 in the DRM1 secret data is secret information used when generating the content key Kc1 for encrypting or decrypting the content encrypted by the DRM1 process. The content key Kc1 is generated by the DRM1 function unit 104 based on the device key Kd1 and the title key Kt1.

  The DRM2 secret data 320 stores secret information used in the DRM2 process. The device key Kd2 in the DRM2 secret data verifies the authentication data KsB (S901) or generates the authentication data KsA when communicating with the counterpart device (in this case, the external device 120) using the DRM2 method (S901). S903) This is secret information to be used. Here, the address map 300 of the nonvolatile memory 106 is mapped to a dedicated address space in the storage device 100 that cannot be accessed from the device on the external bus 115. In order to prevent the secret information stored in the non-volatile memory 106 from leaking outside, only the DRM1 function unit 104 and the DRM function unit 105 access the secret information via the internal bus 102.

  In such a storage device 100, two kinds of switchable operation modes such as “normal mode” and “DRM mode” are set, and the storage device 100 operates in one of the operation modes. When the storage device 100 operates in the “normal mode”, the control unit 101 assigns the entire area of the storage unit 103 as an area that is fully accessible from the CPU 111. That is, as shown in FIG. 4A, the address map 200 of the storage unit 103 is mapped as a free area where the entire address space can be freely read and written, and the storage device 100 functions as a simple storage medium. .

  On the other hand, when the storage device 100 operates in the “DRM mode (restricted mode)”, a part of the storage unit 103 is controlled by the control unit 101 according to the DRM1 method and the DRM2 method by the DRM1 function unit 104 and the DRM2 function unit 105. It is allocated as a work area used for arithmetic processing, and each temporary data generated during the arithmetic processing is written in this area. Specifically, as shown in FIG. 4B, in the address map 210 of the storage unit 103 during the DRM mode operation, a free area 216 that can be freely read and written, and areas 211 to 215 that are used during arithmetic processing. And are mapped.

  Among these, the control data area 211 is an area for writing various command codes for controlling the storage device 100. It is also used as an area for reading and writing data to be passed as an argument when executing a command. The private data area 212 is an area for storing secret information generated when a command related to DRM1 processing or DRM2 processing is executed. The intermediate content area 213 is an area for storing the decrypted content data. In the private data area 212 and the intermediate content area 213, secret information and decrypted content data are stored, so that the control unit 101 is placed in both areas in order to protect the content protection method and protect the content. Control is performed so that the stored data does not flow on the external bus 115. Specifically, read access to the above private data area (unreadable area) 212 or intermediate content area (unreadable area) 213 via the external bus 115 is prohibited, and the areas 212 and 213 are not allowed. When there is a read access via the external bus 115, the control unit 101 always returns “0” data as a fixed value.

  The DRM1 content area 214 is an area used when content protected by the DRM1 method is decrypted. The content area for DRM1 stores the encrypted content read from the external storage device 113 during the DRM1 decryption process. The DRM2 content area 215 is an area used when content is encrypted by the DRM2 method. In the content area for DRM2, content data encrypted by the DRM2 function unit 105 during the DRM2 encryption process is stored.

  Next, commands used for controlling the storage device 100 will be described. FIG. 5 is a table showing specifications of commands used when controlling the storage device 100. When the command code in this table is written to the command address in the control data area 211 of the storage unit 103, the control unit 101 executes processing corresponding to the command code.

  The DRM mode transition command 401 changes the operation mode of the storage device 100 from the normal mode to the DRM mode. This command is determined when the command code is written ten times in succession in order to distinguish between writing the command code for transitioning to the DRM mode and writing data in the normal mode. When the storage device 100 transitions to the DRM mode, the DRM1 function unit 104 and the DRM2 function unit 105, which are content protection functions inside the storage device 100, are activated, and the address map of the storage unit 103 becomes the DRM mode address map 210 (FIG. 4 (b)).

  The normal mode return command 402 returns the operation mode of the storage device from the DRM mode in which the content protection function can be used to the normal mode that can be used as a normal storage device. When returning to the normal mode, the DRM1 function unit 104 and the DRM2 function unit 105 having the content protection function inside the storage device 100 are invalidated, and the address map of the storage unit 103 is the address map 200 for the normal mode (FIG. )).

  That is, the control unit 101 switches from the normal mode to the DRM mode when the DRM mode transition command 401 is written to the corresponding command address, and when the normal mode return command 402 is written to the corresponding command address. Switch from mode to normal mode. The control unit 101 supports DRM1 commands 501 to 503 and DRM2 commands 601 to 607, which will be described later, in the DRM mode, and controls the DRM1 function unit 104 and the DRM2 function unit 105 according to the commands for content protection. Necessary arithmetic processing (DRM1 processing, DRM2 processing) is executed.

  Next, FIG. 6 is a table showing the specifications of commands used when the storage device 100 is controlled for DRM1 processing. When the command code in this table is written to the command address in the control data area 211, the control unit 101 and the DRM1 function unit 104 execute processing corresponding to the command code. The title key Kt1 set command 501 sets the title key Kt1 for DRM1. Command argument data for 20 bytes written following this command code is stored in the control data area 211 as the title key Kt1.

  The content key Kc1 generation command 502 generates a content key Kc1 for DRM1. The content key Kc1 is generated by the DRM1 function unit 104 based on the title key Kt1 and the device key Kd1 and stored in the private data area 212. The decryption start command 503 decrypts DRM1-encrypted content. The DRM1 functional unit 104 decrypts the encrypted content stored in the DRM1 content area 214 with the content key Kc1, and stores it in the intermediate content area 213.

  Next, FIG. 7 is a table showing specifications of commands used when the storage device 100 is controlled for DRM2. When the command code in the table is written to the command address in the control data area 211, the control unit 101 and the DRM2 function unit 105 execute processing corresponding to the command code. The authentication data KsB verification command 601 verifies the authentication data KsB received from the DRM2-compatible device. The argument data of the 40-byte command written following this command code is stored in the control data area 211 as authentication data KsB. The authentication data KsB is verified by the DRM2 function unit 105, and the verification result data output as a result of the verification process is stored in the private data area 212.

  The authentication key Ka2 generation command 602 generates an authentication key Ka2 for DRM2. The authentication key Ka2 is generated by the DRM2 function unit 105 based on the verification result data generated by the authentication data Ks verification command and the device key Kd2. The generated authentication key Ka2 is stored in the private data area 212. The authentication data KsA generation command 603 generates authentication data KsA to be transmitted to the DRM2-compatible device. The authentication data KsA is generated by the DRM2 function unit 105 based on the device key Kd2 and stored following the command address in the control data area 211. The exchange key Kx2 generation command 604 generates an exchange key Kx2 for DRM2. The arithmetic processing in the DRM2 function unit 105 generates the exchange key Kx2. The generated exchange key Kx2 is stored in the private data area 212.

  The exchange key Kx2 encryption command 605 encrypts the exchange key Kx2 for DRM2 with the authentication key Ka2. The DRM2 function unit 105 encrypts the exchange key Kx2 with the authentication key Ka2. The encrypted exchange key Kx2 is stored following the command address in the control data area 211. The content key Kc2 generation command 606 generates a content key Kc2 for DRM2. The content key Kc2 is generated by the DRM2 function unit 105 based on the exchange key Kx2. The generated content key Kc2 is stored in the private data area 212 and used for content encryption. The encryption start command 607 encrypts content using the DRM2 method. The DRM2 function unit 105 encrypts the content in the intermediate content area 213 with the content key Kc2, and stores it in the DRM2 content area 215.

  Next, the main program executed by the information device 1 will be described. The main program is a program for converting content stored in the external storage device 113 in a state encrypted by the DRM1 method into a state encrypted by the DRM2 method and transmitting the content to the external device 120.

  As shown in FIG. 8, when the storage device 100 is operating in the normal mode, the DRM mode transition command 401 is executed to change the operation mode of the storage device 100 to the DRM mode (S801). Thereafter, decryption processing of the content encrypted by the DRM1 method and stored in the external storage device 113 is performed, and the decrypted data is stored in the intermediate content area 213 (DRM1 processing; S802). Next, DRM2 content encryption processing is performed, and the content stored in the intermediate content area 213 is encrypted and transmitted to the external device 120 via the network control unit 114 (DRM2 processing; S803). ). Details of the processing in S802 and S803 will be described later. Thereafter, the normal mode return command 402 is executed, the storage device 100 is changed from the DRM mode to the normal mode, and the process is terminated.

  Next, the DRM1 process (S802) will be described in more detail with reference to FIG.

  First, the title key Kt1 portion of the content data 700 stored in the external storage device 113 is read (S901). Then, the title key Kt1 set command 501 is executed (S902), and the DRM1 function unit 104 stores the title key Kt1 in the control data area 211 of the storage unit 103. Next, the content key Kc1 generation command 502 is executed (S903), and the DRM1 function unit 104 stores the content key Kc1 in the private data area 212. Next, the DRM1 function unit 104 reads the DRM1 encrypted content 702 portion of the content data 700 stored in the external storage device 113 and stores it in the DRM1 content area 214 (S904). Next, a decryption start command 503 is executed (S905). As a result, the decrypted content is stored in the intermediate content area 213.

  Next, the DRM2 process (S803) will be described in more detail with reference to FIGS.

  First, when the information device 1 receives the authentication data KsB from the external device 120 via the network control unit 114 (S1001), the authentication data KsB verification command 601 is executed, and the DRM2 function unit 105 receives the received authentication data KsB. Verification is performed (S1002). The verification data output as a result is stored in the private data area 212 and used when generating the authentication key Ka2 in the next step. Next, an authentication key Ka2 generation command 602 is executed, and the DRM2 function unit 105 generates an authentication key Ka2. Here, the authentication key Ka2 is generated based on the verification data output in the previous step S1002 and the device key Kd2 in the DRM2 function unit 105, and stored in the private data area 212 (S1003).

  Next, an authentication data KsA generation command 603 is executed, and the DRM2 function unit 105 generates authentication data KsA based on the device key Kd2. The generated authentication data KsA is stored in the control data area 211 following the command address (S1004). Thereafter, the authentication data KsA is transmitted to the external device 120 via the network control unit 114 (S1005). Next, the exchange key Kx2 generation command 604 is executed, and the DRM2 function unit 105 generates the exchange key Kx2. The generated exchange key Kx2 is stored in the private data area 212 (S1006).

  Next, the exchange key Kx2 encryption command 605 is executed, and the DRM2 function unit 105 encrypts the exchange key Kx2 with the authentication key Ka2. The encrypted exchange key Kx2 is stored in the control data area 211 for transmission to the external device 120 in the next step (S1007). Thereafter, the exchange key Kx2 encrypted with the authentication key Ka2 is transmitted to the external device 120 via the network control unit 114 (S1008). Next, a content key Kc2 generation command 606 is executed, and the DRM2 function unit 105 generates a content key Kc2 based on the exchange key Kx2. The generated content key Kc2 is stored in the private data area 212 (S1009).

  Next, an encryption start command 607 is executed, and the DRM2 function unit 105 encrypts the content data using the DRM2 method. Here, the decrypted content stored in the intermediate content area 213 is encrypted by the DRM2 function unit 105 and stored in the DRM2 content area 215 (S1010). Thereafter, the content encrypted by the DRM2 method is transmitted to the external device 120 via the network control unit 114 (S1011). As shown in FIG. 12, the data 800 transmitted here includes DRM2 encrypted content 802 encrypted using the content key Kc2, and header information including content size information and copy control information. 801. In this way, the content flowing on the network is protected by the DRM 2, and secure content communication from the information device 1 to the external device 120 is realized.

  As described above, according to the information device 1 and the storage device 100, the secret information that is used or generated in the process of transmitting content to the external device 120 and the content data in the decrypted state are stored in the storage device 100. It will only appear inside. That is, the decrypted content and secret information do not appear on the external bus 115. In addition, since the secret process and data are mounted in the DRM1 function unit 104, the DRM2 function unit 105, and the nonvolatile memory 106 in the storage device 100, the secret process and data are stored outside the storage device 100 (for example, the program in the program memory 112). (Inside) there is no secret information related to the DRM1 process and the DRM2 process.

  During the content transmission process, secret information such as each encryption key and decrypted content appears as temporary data in the private data area 212 or the intermediate content area 213 of the storage unit 103. On the other hand, the control unit 101 performs read access from the external bus 115 to the private data area 212 or the intermediate content area 213 of the storage unit 103 during content transmission processing. Data “0” is always returned in a fixed manner. This prevents secret information that appears in the private data area 212 or the intermediate content area 213 during processing from flowing to the external bus 115.

  As described above, since the secret processing of the content protection function and the encryption / decryption processing can be performed while the secret information is enclosed in the storage device 100, the risk of leakage of the secret of the content protection function to the outside is reduced. can do. For example, since it is possible to prevent secret data such as a decrypted content and a key generated during the execution of the content protection function from appearing on the external bus 115, the data is illegally read and the content The risk of being used for unauthorized copying can be reduced. In addition, since there is no need to implement secret processing or data in the control program for controlling the storage device 100, there is no risk of leaking secret information even if the control program is analyzed. Therefore, the information device 1 does not need to implement a mechanism for protecting the program from an act of illegally analyzing the program.

In addition, the storage unit 103, the nonvolatile memory 106, the DRM2 function unit 105 having an encryption function, and the DRM1 function unit 104 having a decryption function, which are necessary elements for realizing the content protection function, are stored in the storage device 100. Since it is mounted, it has the effect of reducing the number of components and the mounting area.

  Further, the storage device 100 can operate as a normal storage device (normal mode) or operate as a content protection function device (DRM mode) by switching the operation mode. In recent years, with the spread of digital broadcasting and the like, opportunities to handle digital contents with a large-capacity storage device have increased, and large-capacity storage devices such as a RAM, a FRASH ROM, or an HDD have been increased in capacity and reduced in price. In such a situation, the storage device 100 has a built-in content protection function and can easily handle digital content, so that a storage device with great added value can be provided.

1 is a block diagram showing an embodiment of an information device and a storage device according to the present invention. It is a figure which shows the content accumulate | stored in the external storage device shown in FIG. It is a figure which shows the address map of the non-volatile memory shown in FIG. (A) is a memory | storage part address map in normal mode, (b) is a figure which shows the memory | storage part address map in DRM mode. 3 is a list of commands related to control of the storage device shown in FIG. 1. 3 is a list of commands related to control of the storage device shown in FIG. 1. 3 is a list of commands related to control of the storage device shown in FIG. 1. It is a flowchart of the main program in the information equipment of FIG. It is a flowchart of the DRM1 process in the information equipment of FIG. It is a flowchart of the DRM2 process in the information equipment of FIG. It is a sequence diagram of DRM2 processing in the information device of FIG. It is a figure which shows the transmission data from the information apparatus of FIG. 1 to an external device. It is a figure which shows an example of the conventional information apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Information apparatus, 100 ... Memory | storage device, 101 ... Control part, 103 ... Memory | storage part (data storage part), 104 ... DRM1 function part (1st content processing calculating part), 105 ... DRM2 function part (2nd content) Processing operation unit), 106 ... Non-volatile memory (secret information storage unit), 115 ... External bus, 212 ... Private data area (unreadable area), 213 ... Intermediate content area (unreadable area), 700 ... Content data , 800 ... transmission data.

Claims (6)

Connected to an external bus used for data transmission / reception in the information device, the content encrypted by the first encryption method is input from the external bus, and the encryption method of the input content is set to the first A storage device for converting to a second encryption method different from the encryption method and outputting to the external bus;
A first content processing operation unit for decrypting content encrypted by the first encryption method;
A second content processing arithmetic unit that performs encryption processing by the second encryption method on the content decrypted by the first content processing arithmetic unit;
A secret information storage unit that stores secret information used for processing by the first and second content processing calculation units;
A data storage unit for storing temporary data generated during processing by the first and second content processing arithmetic units;
And a control unit that controls operations of the first and second content processing arithmetic units and controls whether or not read access from the external bus to the data storage unit is possible. .   A normal mode in which read access from the external bus to the data storage unit is permitted, and a restriction mode in which read access from at least a part of the data storage unit from the external bus is not permitted. 2. The storage device according to claim 1, further comprising mode switching means for selectively switching the operation mode. In the data storage unit,
3. The storage device according to claim 2, wherein an address of a non-readable area in which the read access from the external bus is not permitted when operating in the restricted mode is set in advance. The controller is
When operating in the restricted mode, if there is a read access request for the non-readable area of the data storage unit from the external bus, it is stored in the non-readable area for the external bus. 4. The storage device according to claim 3, wherein data different from the data is returned. An external bus used to send and receive data inside the device;
A content storage unit connected to the external bus and storing content encrypted by the first encryption method;
Content that is connected to the external bus and encrypted by the first encryption method is input from the external bus, and an encryption method for the input content is different from the first encryption method. A storage device that converts the data into an encryption method and outputs it to the external bus,
The storage device
A first content processing operation unit for decrypting content encrypted by the first encryption method;
A second content processing arithmetic unit that performs encryption processing by the second encryption method on the content decrypted by the first content processing arithmetic unit;
A secret information storage unit that stores secret information used for processing by the first and second content processing calculation units;
A data storage unit for storing temporary data generated during processing by the first and second content processing arithmetic units;
An information device comprising: a control unit that controls operations of the first and second content processing arithmetic units and controls whether or not read access from the external bus to the data storage unit is possible. Using a storage device connected to an external bus used for data transmission / reception in the information device, the content encrypted by the first encryption method is input from the external bus to the storage device, and the input content is encrypted A content conversion method for converting a conversion method into a second encryption method different from the first encryption method and outputting the converted method to the external bus,
A first calculation processing step in which a first content processing calculation unit of the storage device decrypts the content encrypted by the first encryption method;
A second calculation processing step in which the second content processing calculation unit of the storage device performs an encryption process by the second encryption method on the content decrypted by the first content processing calculation unit; When,
A secret information storage unit in which the secret information storage unit of the storage device stores secret information used for processing by the first and second content processing calculation units;
A temporary data storage step in which a data storage unit of the storage device stores temporary data generated during processing by the first and second content processing arithmetic units;
A control unit for controlling the operation of the first and second content processing operation units and for controlling the read access from the external bus to the data storage unit. A content conversion method characterized by that.

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