JP2003066837A - Address generating method and data deciphering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adequately protect data of high secrecy which are being processed by firmware. SOLUTION: In a deciphering device 1, an address generation part 11 generates a 1st random number as a base address and a 2nd random number as an offset address and stores parameters, etc., used to decipher contents data in the address indicated by the 1st and 2nd random numbers. The 1st random number is deciphered by a deciphering part 12 and the ciphered 1st random number and the 2nd random number are stored in other addresses; and information on the addresses is also ciphered and stored in another address. The addresses where the 1st and 2nd random numbers are stored are moved through the timer processing of a timer processing part 13. When the contents data are deciphered, the parameters are read out and a deciphering key is generated according to the information and parameters sent together with the contents data and used to decipher the contents data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an address generation method for generating an address for storing data that appears during processing in firmware processing that requires high confidentiality.
And a data decryption method for decrypting encrypted data using the address generation method.

[0002]

2. Description of the Related Art In recent years, data distribution has been performed in which content data (for example, music data, video data, document data such as books, still image data, etc.) is provided to users by electronic distribution using satellite broadcasting or the Internet. ing. At this time, since there is a risk that the transmitted data may be intercepted or tampered with by a third party, the information to be kept secret is transmitted after being encrypted.

Various encryption techniques have been proposed, developed, and realized, but basically, the data is different from the original state depending on the calculation method determined for each encryption method. It is encrypted by being performed.

By the way, for example, in a method in which the calculation method is kept secret and all information is encrypted by the same calculation method, when the calculation method is specified by a third party, all information is There is a risk of eavesdropping and falsification by the third party. Therefore, there is an encryption method in which a calculation for encrypting data is performed using a numerical sequence called an encryption key, and different encryption results can be obtained if the encryption key is different even if the data is the same.

In this case, even if the calculation method is specified by a third party, the information cannot be decrypted without knowing the decryption key for the encryption key, and is identified by the leakage of the encryption key or the decryption key. In such a case, by performing encryption using a new encryption key, it is possible to prevent subsequent wiretapping and tampering of data by a third party without changing the calculation method.

As a calculation method used for encryption,
Generally, even if the calculation method for decryption is published, it is desirable that the original data cannot be decrypted unless the decryption key for the encryption key for the decryption is specified. , Such a calculation method is generally adopted.

The encryption and decryption methods are roughly classified into two types depending on whether the encryption key used for encryption and the decryption key used for decryption are the same. The same encryption key and decryption key are called a symmetric key method, and different ones are called an asymmetric key method.

In the symmetric key system, since the encryption key and the decryption key are the same, the data can be decrypted if any one of them is specified. Therefore, both the encryption key and the decryption key must be private keys. There is also a secret key method.

According to this symmetric key system, as described above,
When the encryption key or the decryption key is specified, the data can be decrypted, and it is necessary to have the keys as many as the number of communication partners. However, the symmetric key system has a relatively light processing load for encryption and decryption, and is therefore suitable for transmitting a large amount of information in real time.

On the other hand, in the asymmetric key system, since the encryption key and the decryption key are different, it is possible to make the other key a public key by setting one key as a secret key, which is also called a public key encryption system. .

In the asymmetric key system, one of the two keys serving as an encryption key and a decryption key is held by itself as a secret key, and the other is distributed as a public key to many parties. . Then, when transmitting data to the other party, the user performs encryption using his / her own private key. In this case, the other party receiving the encrypted data decrypts the data using the public key. If the data cannot be decrypted, it means that the data has been tampered with, or the received data has been encrypted with a key that is not the user's private key. In this case, the private key becomes the encryption key and the public key becomes the decryption key.

When the other party sends data, the other party uses the distributed public key for encryption. In this case, the encrypted data can be decrypted only by using the user's private key. Therefore, when the decryption cannot be performed by using the user's private key, whether the data has been tampered with, Alternatively, the received data is encrypted with a key that is not the public key corresponding to the user's private key. In this case, the public key becomes the encryption key and the secret key becomes the decryption key.

According to this asymmetric key system, the processing load for encryption and decryption is relatively heavy, but decryption cannot be performed unless the secret key is specified. Therefore, the asymmetric key method is suitable for transmitting a small amount of data with high confidentiality.

[0014]

By the way, when the information used for decryption is transmitted together with the content data, the user generates a decryption key from the information and the parameters possessed by the user, and decrypts the encrypted content data. There is.

Here, the data during the decoding process including the above-mentioned parameters is, for example, ma which is a standard library of C language.
It is stored in the memory area secured by using the lloc function.
However, since the same system resources are generally used when the same program is executed, malloc
If a memory area is to be secured by using a function, the same memory area is always secured. Therefore, there is a demand for a method of storing data during decoding processing more strictly.

The present invention has been proposed in view of such conventional circumstances, and in firmware processing that requires high confidentiality, data is generated by generating an address for storing data that appears during processing. An object of the present invention is to provide an address generation method for protection and a data decryption method for decrypting encrypted data using the address generation method.

[0017]

In order to achieve the above-mentioned object, an address generating method according to the present invention is an address generating method for generating a storage address for storing data, which is a first address indicating a base address. A random number generating step of generating a random number and a second random number indicating an offset address; an encryption step of encrypting the first random number with an encryption key;
And an address generating step of generating a storage address using the second random number.

In the random number generating step, the first random number is generated based on the first input value and the second input value, and the second random number is the third input value and the fourth input value. Of the first input value and the second input value, and / or one of the third input value and the fourth input value is generated at the time of random number generation. Determined based on information.

Further, the address generating method includes a random number storing step of storing the first random number and the second random number encrypted in the encrypting step in random number storing addresses different from the storing addresses in the storing means, and An address information storing step of encrypting information indicating a random number storage address with an encryption key and storing the information in a different address information storage address in the storage means.

Further, the address generating method includes a changing step of changing the random number storage addresses of the first random number and the second random number, and an address changed in the changing step of the address information stored in the address information storing step. And an updating step of updating the information to indicate. Here, the changing process and the updating process are performed at regular intervals by, for example, a timer process.

In the address generating method according to the present invention, the first random number indicating the base address and the second random number indicating the offset address are generated, and the data is generated by the first random number and the second random number. Generate a storage address to store. Further, the random number storage addresses of the first random number and the second random number are moved in a fixed cycle by the timer process.

In order to achieve the above-mentioned object, the data decryption method according to the present invention is a data decryption method for decrypting encrypted data, which comprises a first random number indicating a base address and an offset address. A random number generating step for generating the second random number shown, an encryption step for encrypting the first random number with an encryption key, and an address generating step for generating a storage address by the first random number and the second random number. Have
When decoding the data, the storage address generated in the address generation step is used for processing.

Here, the data decoding method includes a storage step of storing a parameter used for data decoding in a storage address, a parameter reading step of reading a parameter from the storage address, and a decoding step of decoding data using the parameter. , And an output step of outputting the data decoded in the decoding step to the outside.

Further, in the parameter reading step, the first random number address regarding the first random number address in which the first random number is encrypted and stored and the second random number address in which the second random number is stored. Second address information regarding the first random number and the second random number read from the first address and the second address, respectively, and encrypted based on the first address information and the second address information. Is read, the storage address storing the parameter is generated by the first random number and the second random number obtained by decrypting the encrypted first random number, and the parameter is stored from the storage address based on the storage address. Read out.

The first random number address and the second random number address are changed, and the first address information and the second address information are updated according to the change. Here, the change and the update are performed in a constant cycle by, for example, a timer process.

When the parameters are read in the parameter reading step, the timer processing cycle is changed.

In the data decoding method according to the present invention as described above, the first random number indicating the base address and the second random number indicating the offset address are generated, and the data is decoded by the first random number and the second random number. The input data is decoded by generating a storage address for storing the parameter used for decoding and processing using this storage address.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described below in detail with reference to the drawings. First, FIG. 1 shows a principle diagram of an address generation method according to the present embodiment. This address generation method is
By generating a random number, an address indicating a memory area for storing data being processed is generated. Specifically, as shown in FIG. 1, the entire memory area is divided into an address generation area and a variable size area. A first random number is generated at an address in the address generation area, and a second random number is generated at an address in the variable size area. Generation of this random number is performed as follows. That is, as shown in FIG. 2, by inputting the input A and the input B, the output C as a random number is obtained. This process is the same whether the first random number is generated or the second random number is generated. Here, the input A and the input B are
Although given based on predetermined rules, time information at the time of random number generation is used as an initial value for either input A or input B in order to obtain a different random value each time. The initial value is not limited to the time information, and for example, a temperature sensor may be provided and the temperature information sensed by the temperature sensor may be used. Here, the first random number and the second random number indicate a base address and an offset address, respectively, and a storage address is generated by the first random number and the second random number. When decrypting encrypted content data, which will be described later, this storage address is used for processing. The reason why the variable size area is prepared in addition to the address generation area is to secure a data area for calculation when the first random number is generated at the end of the address generation area.

Although not shown here, as will be described later, the first random number is stored in the memory after being encrypted, and the second random number is also stored in an address different from the first random number in the memory. To be done. Further, the address information indicating the address where the first random number and the second random number are stored is
It is stored in memory after being encrypted.

A case will be described below in which the above-described address generation method is applied to a decryption device for decrypting encrypted content data (eg, music data, video data, document data such as books, still image data, etc.). . It should be noted that in the decryption device, all the data that appears during the decryption process such as content data and data obtained in the other process are stored in the storage address generated by the above-mentioned method when temporarily stored in the memory. However, for convenience of description, a case where a decryption key is generated by using a parameter stored at a storage address and information transmitted together with the content data to decrypt the content data will be described here.

The decryption apparatus 1 according to the present embodiment whose schematic configuration is shown in FIG. 3 includes a control section 10 for controlling each section of the decryption apparatus 1 and a decryption process for parameters and the like used to decrypt encrypted content data. An address generation unit 11 that generates an address for storing internal data, an encryption unit 12 that performs various types of encryption, and a timer processing unit 13 that performs timer processing are provided. Here, the control unit 10, the address generation unit 11, the encryption unit 12, and the timer processing unit 13
Is a CPU (Central
Processing Unit) and, if necessary, DSP (Digital S
It can also be configured by a computing auxiliary device such as an ignal processor). Further, although detailed description is omitted, the decoding device 1 is a ROM (Read O
nly Memory) 14 and RA, which is a volatile memory that stores various data being processed by expanding the decoding program and the like.
An M (Random Access Memory) 15 and a bus 16 that connects each unit are further provided.

The control unit 10 controls each unit in the decryption device 1 to control the decryption of the encrypted content data.

The address generation unit 11 generates an address for storing a parameter used for decrypting encrypted content data, a calculation value for generating a decryption key, and the like, based on the address generation method described above. . Specifically, as described above, the address generator 11 uses the first random number as the base address and the second random number as the offset address.
And the storage address in the RAM 15 for storing the data appearing during the decryption process such as the parameters used for decrypting the above-mentioned encrypted content data by using the first random number and the second random number. Is generated. That is, the parameter, the calculated value generated when generating the decryption key, and the like are stored in the RAM 15 at the storage address defined by the first random number and the second random number.

The first random number and the second random number are stored in different addresses. This address can be secured by the malloc function, which is a standard library of C language, for example. At this time, the first random number is stored after being encrypted by the key in the encryption unit 12 described later. This key is a random number generated from a certain value by a predetermined generation method, and any encryption method may be used. The information about the address in which the first random number and the second random number are stored is encrypted and then stored in another address in the RAM 15. This address can also be secured by the malloc function, for example.

As described above, by generating the address for storing the parameter and the like using the random number, it is difficult to specify the storage location of the parameter and it is possible to appropriately protect highly confidential data. Further, by encrypting the address information and storing it in another address, it is possible to further protect the data.

The addresses stored in the first random number and the second random number described above are changed in a constant cycle by the timer processing of the timer processing unit 13 described later. Each time the address in which the first random number and the second random number are stored is changed, the above-mentioned address information is updated to information indicating a new address after the change.

The encryption unit 12 performs various types of encryption in the decryption device 1. Specifically, the encryption unit 12 encrypts the above-mentioned first random number with a key. This key is a random number generated from a certain value by the predetermined generation method as described above. The principle of this encryption can be explained using FIG. 2 described above. That is, in FIG. 2, by inputting the key as the input A and the first random number as the input B, the encrypted first random number is obtained as the output C. The encryption unit 12 also encrypts the address information indicating the address in which the first random number and the second random number described above are stored. Further, when the address in which the first random number and the second random number are stored is changed by the timer processing in the timer processing unit 13, the encryption unit 12 encrypts the new address information and overwrites the original address. Update by that.

The timer processing unit 13 performs timer processing executed by interruption. The timer processing unit 13 has a counter (not shown) and counts the time after the first random number and the second random number are stored. When the count value of the counter reaches a predetermined value, the address storing the first random number and the second random number is changed to another address. As a result, the addresses at which the first random number and the second random number are stored will continue to be changed in a predetermined cycle. It should be noted that the change destination address can be secured by the malloc function, for example, as described above. Further, the timer processing unit 13 stores the first random number and the second random number when the address information in which the first random number and the second random number are stored to read the content data is read. The predetermined value of the counter for changing the address is changed. As a result, the next time the parameters are stored, the first random number and the second random number are stored.
The address in which the random number is stored will be changed in different cycles.

The decoding device 1 according to the present embodiment is configured as described above to generate a storage address for storing a parameter or the like used when decoding content data, and read the parameter to decode the content data. I do. That is, when the encrypted content data is input to the decryption device 1, the address information of the first random number and the second random number is changed from the address where the address information of the first random number and the second random number is stored. It is read and the first random number and the second random number are read based on the address information. At this time, since the first random number is encrypted with the key, it is decrypted. Then, the storage address in which the parameter is stored is generated by the read first random number and the second random number, and the parameter is read from the storage address. A decryption key for decrypting the content data is generated by the information and the parameter sent together with the encrypted content data. As described above, the calculated value and the like generated when generating the decryption key are also stored in the storage address generated by the first random number and the second random number. The content data is decrypted by this decryption key and output to the outside.

Next, FIG. 4 is a flowchart for decrypting the encrypted content data in the decryption apparatus 1.
Shown in. First, in step S1, the encrypted content data is input to the decryption device 1. Information for decrypting the content data is input together with the content data.

Next, in step S2, the parameters for decoding the content data are read. In step S2, as described above, the address information of the first random number and the second random number is read from the address where the address information of the first random number and the second random number is stored, and the address information is read. The first random number and the second random number are read out based on At this time, since the first random number is encrypted with the key, it is decrypted. Then, the storage address in which the parameter is stored is generated by the read first random number and the second random number, and the parameter is read from the storage address.

Then, in step S3, a decryption key for decrypting the encrypted content data is generated. That is, the decryption key is generated by the information for decrypting the content data input in step S1 and the parameter read in step S2. As described above, the calculated value generated when generating the decryption key is also stored in the storage address generated by the first random number and the second random number.

Subsequently, in step S4, the content data is decrypted by the generated decryption key. The decrypted content data is output to the outside in the subsequent step S5. The content data encrypted as described above is decrypted.

As described above, in the decoding device 1 according to this embodiment, the first random number and the second random number are stored, and the first random number and the second random number are stored. The address information is also stored in another address, and the address is changed by the timer processing unit 13 at regular intervals.

Therefore, FIG. 5 shows a flowchart of the operation from the generation of the first random number and the second random number to the execution of the timer process.

First, in step S10, a first random number indicating a base address and a second random number indicating an offset address are generated. Next, in step S11, the first
The random number of is encrypted with the key. This encryption is performed by the encryption unit 12.

Subsequently, in step S12, the parameters are stored in the RAM 15. That is, as described above, the parameter is stored in the storage address defined by the first random number and the second random number.

Subsequently, in step S13, the first random number and the second random number are stored in the RAM 15. here,
The first random number is encrypted. This storage location can be secured by the malloc function, for example.
It should be noted that when the first random number and the second random number are stored, the timer processing unit 13 starts counting the time after being stored.

Then, in step S14, the information indicating the address where the first random number and the second random number are stored is encrypted.

The encrypted address information is obtained in step S
It is stored in the RAM 15 at 15. This storage location can also be secured by the malloc function, for example.

Subsequently, in step S16, it is determined whether or not the count value of the counter exceeds a predetermined value N.
If the count value is less than N (Yes), it means that the period for moving the first random number and the second random number has not been reached, and step S1 is performed until the count value reaches N.
The determination in 6 is repeated. In step S16,
If the count value has reached N (No), step S
Proceeding to 17, the first random number and the second random number are moved.

In step S17, the first random number and the second random number
Change the address where the random number of is stored. The address after this change can be secured by the malloc function, for example.

Subsequently, in step S18, the information indicating the address in which the first random number and the second random number are stored after the change is encrypted.

In step S19, the original address information is updated based on the address information encrypted in step S18.

Subsequently, in step S20, it is judged whether or not the processing is to be ended. Here, when the information indicating the address where the first random number and the second random number are stored is read, it is determined that the process ends (Yes), and the process proceeds to step S21. In step S20, when it is not finished (No),
That is, when the address information in which the first random number and the second random number are stored is not read, step S
In step 16, the address in which the first random number and the second random number are stored is changed again at regular intervals.

In step S21, the predetermined value N of the counter for changing the address is changed and the process ends.
By doing this, the next time you store parameters,
The addresses where the first random number and the second random number are stored are changed in different cycles.

As described above, in the decoding device 1 according to the present embodiment, the first random number indicating the base address and the second random number indicating the offset address are generated to generate the first random number and the second random number. Generates a storage address for storing the parameter used for decoding the data, and stores the parameter at this storage address. This makes it difficult to illegally monitor the data, and when decoding the data,
The input data can be decrypted by reading the parameter from the storage address and generating the decryption key using this parameter.

Further, the address at which the first random number and the second random number are stored is changed at a constant cycle by a timer process,
By changing the cycle of the timer processing when the parameters are read for the data decoding, the data protection can be further increased.

The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

For example, in the above-mentioned embodiment, the description was made assuming that a decryption key is generated by the information transmitted together with the content data and the parameters of the decryption device to decrypt the content data, but the present invention is not limited to this. Instead, for example, the decryption key of the content data may be transmitted and the decryption key may be stored in the generated storage address. That is, the present invention can be applied if the data can be protected strictly by storing it in the generated storage address.

[0061]

As described in detail above, the address generating method according to the present invention is an address generating method for generating a storage address for storing data, and shows a first random number indicating a base address and an offset address. A random number generating step for generating a second random number, an encryption step for encrypting the first random number with an encryption key, and an address generating step for generating a storage address by the first random number and the second random number. It is characterized by having.

In the random number generating step, the first random number is generated based on the first input value and the second input value, and the second random number is the third input value and the fourth input value. Of the first input value and the second input value, and / or one of the third input value and the fourth input value is generated at the time of random number generation. Determined based on information.

Further, the address generating method includes a random number storing step of storing the first random number and the second random number encrypted in the encrypting step in random number storage addresses different from the storage addresses in the storage means. An address information storing step of encrypting information of a random number storage address with an encryption key and storing it in a further different address information storage address in the storage means.

In addition, the address generation method includes a changing step of changing the random number storage addresses of the first random number and the second random number, and an address changed in the changing step of the address information stored in the address information storing step. And an updating step of updating the information to indicate. Here, the changing process and the updating process are performed at regular intervals by, for example, a timer process.

According to the address generating method according to the present invention, the first random number indicating the base address and the second random number indicating the offset address are generated, and the data is generated by the first random number and the second random number. By generating the storage address for storing the data, it becomes difficult to illegally monitor the data, and the data can be appropriately protected in the highly confidential firmware processing.

The first random number and the second random number encrypted in the encryption step are stored in random number storage addresses different from the storage address in the storage means, and the information of the random number storage address is stored by the encryption key. Data can be protected more strictly by encrypting and storing it in a different address information storage address in the storage means and changing the random number storage address of the first random number and the second random number.

The data decryption method according to the present invention is a data decryption method for decrypting encrypted data.
A random number generating step of generating a first random number indicating a base address and a second random number indicating an offset address, an encryption step of encrypting the first random number with an encryption key, a first random number and a second random number. The present invention is characterized in that it has an address generation step of generating a storage address by using a random number, and when decoding data, processing is performed using the storage address generated in the address generation step.

Here, the data decoding method includes a storage step of storing a parameter used for data decoding in a storage address, a parameter reading step of reading a parameter from the storage address, and a decoding step of decoding data using the parameter. , And an output step of outputting the data decoded in the decoding step to the outside.

In the parameter reading step, the first address information regarding the first random number address in which the first random number is encrypted and stored and the second random number address in which the second random number is stored. Second address information regarding the first random number and the second random number read from the first address and the second address, respectively, and encrypted based on the first address information and the second address information. Is read, the storage address storing the parameter is generated by the first random number and the second random number obtained by decrypting the encrypted first random number, and the parameter is stored from the storage address based on the storage address. Read out.

The first random number address and the second random number address are changed, and the first address information and the second address information are updated according to the change. Here, the change and the update are performed in a constant cycle by, for example, a timer process.

When the parameter is read in the parameter reading step, the timer processing cycle is changed.

According to the data decoding method according to the present invention, the first random number indicating the base address and the second random number indicating the offset address are generated, and the data is generated by the first random number and the second random number. It is possible to make illegal monitoring of data, etc., difficult by generating a storage address that stores the data during the decoding process such as parameters used for decoding the data and performing the decoding process using this storage address. .

Further, by protecting the data by changing the first random number address and the second random number address by the timer process at a constant cycle and changing the cycle of the timer process when the parameters are read for the decoding of the data. Can be made more stringent.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of address generation in this embodiment.

FIG. 2 is a diagram for explaining the principle of random number generation and encryption in this embodiment.

FIG. 3 is a diagram illustrating a schematic configuration of a decoding device according to the present embodiment.

FIG. 4 is a flowchart illustrating a decryption process of encrypted content data in the decryption apparatus.

FIG. 5 is a flowchart illustrating a process from generation of the first random number and the second random number to execution of a timer process in the decoding device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 decryption device, 10 control unit, 11 address generation unit, 12 encryption unit, 13 timer processing unit, 1
4 ROM, 15 RAM, 16 bus

Claims (11)

[Claims] 1. An address generating method for generating a storage address for storing data, the random number generating step of generating a first random number indicating a base address and a second random number indicating an offset address, the first random number generating step. An address generation method comprising: an encryption step of encrypting the random number of 1. by an encryption key; and an address generation step of generating the storage address by the first random number and the second random number. 2. The random number generating step, wherein the first random number is generated based on a first input value and a second input value, and the second random number is a third input value and Fourth
Generated based on the input value of, one of the first input value and the second input value,
2. The address generating method according to claim 1, wherein one of the third input value and the fourth input value is determined based on time information when a random number is generated. 3. A random number storing step of storing the first random number and the second random number encrypted in the encrypting step in a random number storage address different from the storage address in the storage means, and the random number. An address information storage step of encrypting information indicating a random number storage address stored in the storage means in the storage step with an encryption key and storing the encrypted information in a different address information storage address in the storage means. The address generation method according to Item 1. 4. The changing step of changing the random number storage addresses of the first random number and the second random number, and the address information stored in the address information storing step is changed to the address changed in the changing step. 4. The address generating method according to claim 3, further comprising an updating step of updating to the information shown. 5. The address generating method according to claim 4, wherein the changing step and the updating step are performed in a constant cycle by a timer process. 6. A data decryption method for decrypting encrypted data, comprising a random number generating step of generating a first random number indicating a base address and a second random number indicating an offset address, and the first random number generating step. There is an encryption step of encrypting a random number with an encryption key, and an address generation step of generating a storage address by the first random number and the second random number. When decrypting the data, the address generation is performed. A data decoding method characterized in that processing is performed using the storage address generated in the step. 7. A storage step of storing a parameter used for decoding the data in the storage address, a parameter reading step of reading the parameter from the storage address, and a decoding step of decoding the data using the parameter. 7. The data decoding method according to claim 6, further comprising an output step of outputting the data decoded in the decoding step to the outside. 8. In the parameter reading step, first address information relating to a first random number address in which the first random number is encrypted and stored, and second address information in which the second random number is stored. The second address information regarding the random number address and the first random number read from the first address and the second address, respectively, and encrypted based on the first address information and the second address information. And the second random number is read, and the storage address in which the parameter is stored is generated by the first random number obtained by decoding the encrypted first random number and the second random number, and the storage address 7. The parameter is read from the storage address based on the above.
The described data decryption method. 9. The first random number address and the second random number address are changed, and the first address information and the second address information are updated according to the change. Item 8. The data decoding method according to Item 8. 10. The change and the update are performed at regular intervals by a timer process.
The described data decryption method. 11. The data decoding method according to claim 10, wherein the cycle of the timer processing is changed when the parameter is read in the parameter reading step.