HK1233405B - Condition access method, related device and system - Google Patents

Description

Conditional access method and related equipment and system

Technical Field

The present application relates to the field of digital television broadcasting technology, and in particular to a CA (Conventional Access) method and related equipment and systems.

Background Art

A CA system is a system used to control subscribers' access to broadcast services or programs, ensuring that only authorized broadcast services or programs are available. The CA system is key to delivering personalized services. Its primary purpose is to control and manage user authorization within a television station's system, thereby enabling paid data broadcasting services.

Specifically, Figure 1 illustrates the basic architecture of existing CA systems. As shown in Figure 1, a CA system employs a three-layer encryption approach: The TV program sender uses Ks (descrambling key) to scramble the program, which is then encrypted with Kw (working key), which is then encrypted with Kd (root key). At the TV program receiver, the user decrypts Kw using Kd, then uses Kw to decrypt Ks, and finally uses Ks to descramble the TV program back to a clean stream.

Ks and Kw can be sent to users via ECM (Entitlement Control Message) and EMM (Entitlement Management Message) along with the TV program stream (specifically, Ks can be sent via ECM, and Kw can be sent via EMM). However, Kd is not transmitted over the air. Specifically, Kd can only be distributed and updated in a confidential manner. For example, at the terminal device, Kd is typically written to the corresponding IC card by the terminal device manufacturer using dedicated equipment and cannot be dynamically changed.

That is to say, the current CA system adopts a fixed device key method. The device key (such as Kd) is stored in the IC card and cannot be dynamically changed. When the device key (such as Kd) is stolen or cracked, the device key (such as Kd) can only be updated by replacing the IC card or replacing the terminal device. As a result, when the user uses the corresponding CA system to receive programs, it takes a long time to update the device key to achieve program descrambling, which reduces the reception efficiency of the CA system and makes the user experience poor.

Summary of the Invention

The embodiments of the present application provide a conditional access method and related devices and systems to solve the problems of low reception efficiency in existing CA systems.

Specifically, an embodiment of the present application provides a conditional access method, including:

The terminal device receives the key update information including the set root key generation parameters sent by the television transmission center;

Generate a new root key according to the root key generation parameter and the set key generation algorithm stored locally on the terminal device;

A descrambling key is obtained according to the new root key, and the program stream sent by the television transmission center is descrambled according to the obtained descrambling key to obtain a clear program stream.

Accordingly, an embodiment of the present application further provides a terminal device, including:

A receiving module, configured to receive key update information including set root key generation parameters issued by a television transmission center;

An update module, configured to generate a new root key based on the root key generation parameters and a set key generation algorithm stored locally on the terminal device;

The descrambling module is used to obtain a descrambling key according to the new root key, and descramble the program stream sent by the television transmission center according to the obtained descrambling key to obtain a clear program stream.

Furthermore, an embodiment of the present application also provides a conditional access system, including a television transmission center and a terminal device, wherein:

The terminal device is used to receive key update information containing set root key generation parameters issued by the television transmission center; generate a new root key based on the root key generation parameters and a set key generation algorithm locally stored in the terminal device; and obtain a descrambling key based on the new root key, and descramble the program stream issued by the television transmission center based on the obtained descrambling key to obtain a clear program stream.

The beneficial effects of this application are as follows:

An embodiment of the present application provides a conditional reception method and related devices and systems, wherein a terminal device can generate a new root key based on the root key generation parameters in the key update information issued by the television transmission center and the set key generation algorithm locally stored in the terminal device, and obtain a descrambling key based on the new root key, and descramble the program stream issued by the television transmission center based on the obtained descrambling key to obtain a clear program stream, thereby solving the problem that when users use the existing CA system to receive programs, it takes a long time to update the device key to achieve program descrambling, thereby improving the reception efficiency of the CA system and enhancing the user's application experience.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

FIG1 shows a schematic diagram of the basic principle architecture of an existing CA system;

FIG2 is a flow chart showing the conditional access method described in Example 1 of the present application;

FIG3 is a schematic diagram showing a possible structure of the terminal device described in the second embodiment of the present application;

FIG4 is a schematic diagram showing a possible structure of the conditional access system described in the third embodiment of the present application.

DETAILED DESCRIPTION

To make the objectives, technical solutions, and advantages of this application more clear, this application will be further described in detail below with reference to the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

Example 1:

The first embodiment of the present application provides a conditional access method. As shown in FIG2 , which is a flow chart of the conditional access method in the first embodiment of the present application, the conditional access method may include the following steps:

Step 201: The terminal device receives key update information including set root key generation parameters sent by the television transmission center.

Optionally, the terminal device may receive the key update information including the set root key generation parameters issued by the television transmission center in the following manner:

Receiving EMM information sent by the television transmission center;

The original device identification of the terminal device is used to find information related to the terminal device itself from the EMM information, and the information related to the terminal device itself is decrypted based on the original root key of the terminal device to obtain key update information containing the set root key generation parameters.

That is to say, the key update information is usually sent by the television transmission center to the terminal device through EMM, and this embodiment of the application will not be described in detail.

Furthermore, the root key generation parameter (i.e., Kd generation parameter, which can be identified as Kr) is usually sent by the security server to the television transmission center via the key management center when it determines that the device key needs to be updated (such as when it is determined that the device key such as Kd authorized to be issued to the terminal device has been stolen or cracked), and then sent by the television transmission center to the terminal device.

Optionally, the process of transmitting the root key generation parameter between the security server, the key management center, the television transmission center and the terminal device can be as follows:

When the security server determines that the device key needs to be updated, it generates a new root key based on the set key generation algorithm and the set root key generation parameters, and sends the first key update information including the root key generation parameters and the new root key to the key management center through the set secure transmission tool;

After receiving the first key update information, the key management center updates the key database according to the first key update information, and sends the second key update information including the root key generation parameter but not including the new root key to the television transmission center;

After receiving the second key update information, the television transmission center sends the third key update information including the root key generation parameters but not the new root key to the corresponding terminal device, so as to send the root key generation parameters to the corresponding terminal device.

That is to say, during the transmission process of the root key generation parameters, the security server can use the set security transmission tool to point-to-point transmit the corresponding new root key and root key generation parameters to the key management center, that is, the key transmission is limited to between the security server and the key management center to prevent the leakage of the key and key generation parameters, thereby improving the security of the device key; wherein, the set security transmission tool can generally be provided by the key management center, and this embodiment of the present application will not elaborate on this.

Furthermore, it should be noted that when the security server generates a new root key, the key generation algorithm it uses can specifically be a proprietary algorithm pre-installed within the security server by the device manufacturer (i.e., this key generation algorithm runs on a secure computer with security measures). This key generation algorithm can generate a new Kd based on specific root key generation parameters (i.e., Kd generation parameters, denoted as Kr). This Kd generation parameter can be transmitted over the air, and even if intercepted by a third party, the corresponding Kd cannot be generated due to the lack of the corresponding key generation algorithm, thus ensuring the security of the device key.

In addition, it should be noted that when the security server generates a new root key, the set root key generation parameter (i.e., Kd generation parameter) is usually an M-bit random number (M is any positive integer), and the Kd generation parameter usually needs to meet the following conditions: the corresponding Kd can be uniquely generated based on the Kd generation parameter, including the unique generation of the Kd of the corresponding generation based on the Kd generation parameter of the historical generation.

Optionally, in the embodiment described in the present application, taking the Kd generation parameter as a 32-bit random number as an example, the security server may generate a new root key based on the set key generation algorithm and the set root key generation parameters in the following manner:

The 32-bit random number is shifted according to a set shift algorithm to obtain Y new 32-bit random numbers; for example, the 32-bit random number can be cyclically shifted left by 8 bits to obtain three new 32-bit random numbers;

Combine the obtained Y new 32-bit random numbers with the initial 32-bit random number to obtain a (Y+1)*32-bit random number; for example, combine the four 32-bit random numbers obtained in the above steps to obtain a 128-bit (16-byte) random number;

Based on a set matrix algorithm, the (Y+1)*32-bit random number is transformed to obtain a new (Y+1)*32-bit random number, and the obtained new (Y+1)*32-bit random number is used as a new root key;

Wherein, Y is a positive integer, and, similar to the set key generation algorithm, the set matrix algorithm can specifically be a private confidentiality algorithm pre-set by the corresponding device manufacturer in the security server, which is not elaborated in the embodiment of the present application.

Step 202: The terminal device generates a new root key according to the root key generation parameters and a set key generation algorithm stored locally on the terminal device.

Among them, when the terminal device generates a new root key according to the acquired root key generation parameters, the set key generation algorithm is based on the same algorithm as the key generation algorithm used by the security server to generate a new root key, and can usually be a private confidentiality algorithm pre-set by the device manufacturer related to the terminal device in the secure storage area (Trust zone) of the terminal device, that is, the key generation algorithm is not transmitted in the air, but is embedded in the terminal device to ensure the security of the device key.

Optionally, in the embodiment described in the present application, similar to the process of generating a new root key by the security server, taking the Kd generation parameter as a 32-bit random number as an example, the terminal device can specifically generate a new root key in the following manner:

The 32-bit random number is shifted according to a set shift algorithm to obtain Y new 32-bit random numbers; for example, the 32-bit random number can be cyclically shifted left by 8 bits to obtain three new 32-bit random numbers;

Combine the obtained Y new 32-bit random numbers with the initial 32-bit random number to obtain a (Y+1)*32-bit random number; for example, combine the four 32-bit random numbers obtained in the above steps to obtain a 128-bit (16-byte) random number;

Based on a set matrix algorithm, the (Y+1)*32-bit random number is transformed to obtain a new (Y+1)*32-bit random number, and the obtained new (Y+1)*32-bit random number is used as a new root key;

Wherein, Y is a positive integer; and, similar to the set key generation algorithm, the set matrix algorithm can specifically be a private confidentiality algorithm pre-set in the terminal device by the corresponding device manufacturer, which is not elaborated in the embodiment of the present application.

Step 203: The terminal device obtains a descrambling key according to the new root key, and descrambles the program stream sent by the television transmission center according to the obtained descrambling key to obtain a clear program stream.

It should be noted that, since Kd is updated, the Kw (working key) corresponding thereto also needs to be updated. That is, after receiving the updated Kd sent by the security server, the key management center needs to use the updated Kd to generate a corresponding new Kw (i.e., the updated Kw), and send the new Kw to the terminal device via the television transmission center (specifically, the television transmission center may carry the encrypted new Kw obtained by encrypting the updated Kd in the key update information and send it to the terminal device). Therefore, correspondingly, obtaining the descrambling key based on the new root key may include:

Decrypting the encrypted updated working key according to the new root key to obtain the updated working key;

The encrypted descrambling key carried in the ECM sent by the television transmission center is decrypted according to the updated working key to obtain the descrambling key.

That is to say, in the embodiment described in the present application, the terminal device can generate a new root key based on the root key generation parameters in the key update information issued by the television transmission center and the set key generation algorithm locally stored in the terminal device, and obtain the descrambling key based on the new root key, and descramble the program stream issued by the television transmission center based on the obtained descrambling key to obtain a clear program stream, thereby solving the problem that when users use the existing CA system to receive programs, it takes a long time to update the device key to achieve program descrambling, thereby improving the receiving efficiency of the CA system and improving the user's application experience.

Furthermore, it should be noted that, after the security server generates a new root key based on the set key generation algorithm and the set root key generation parameters, it can also generate a new root key generation number (i.e., an updated generation number) according to the historical sequence of the new root key, and replace the lower N bits of the original device identification (original device ID) of the corresponding terminal device with the new root key generation number to form a new device identification (i.e., an updated device identification, where N is a positive integer and its value is generally not less than the number of bits occupied by the root key generation number), and send the new root key generation number to the television transmission center via the key management center, and the television transmission center carries the new root key generation number in the key update information and sends it to the corresponding terminal device; therefore, in the embodiment of the present application, after the terminal device receives the key update information sent by the television transmission center, the method can also include the following steps:

According to the new root key generation number carried in the key update information, the lower N bits of the original device identification of the terminal device are replaced with the new root key generation number to form a new device identification; wherein, N is a positive integer and its value is not less than the number of bits occupied by the root key generation number.

Among them, it should be noted that, since the value range of the root key generation number can usually be 0 to 255, that is, it can usually occupy 8 digits (bits), therefore, replacing the lower N bits of the original device identification of the terminal device with the new root key generation number to form a new device identification can be specifically implemented as follows: replacing the lower 8 bits of the original device identification of the terminal device with the new root key generation number to form a new device identification. In addition, it should be noted that the device identification of the terminal device (including the original device identification and the updated device identification) can usually occupy 64 digits (bits), which will not be elaborated in the embodiments of this application.

Accordingly, from the above content, it can be seen that the process of transmitting the root key generation parameters between the security server, the key management center, the television transmission center and the terminal device can also be specifically described as follows:

When the security server determines that the device key needs to be updated, it generates a new root key based on the set key generation algorithm and the set root key generation parameters, generates a new root key generation number according to the historical sequence of the new root key, replaces the lower N bits of the original device identifier of the corresponding terminal device with the new root key generation number to form a new device identifier, and sends a first key update message including the root key generation parameters, the new root key, and the new root key generation number to the key management center via a set secure transmission tool;

After receiving the first key update information, the key management center updates the key database according to the first key update information, and sends the second key update information including the root key generation parameter and the new root key generation number but not including the new root key to the television transmission center;

After receiving the second key update information, the television transmission center sends the third key update information including the root key generation parameter and the new root key generation number but not including the new root key to the corresponding terminal device.

For example, taking a specific example, the process of transmitting the root key generation parameters between the security server, the key management center, the television transmission center, and the terminal device can be described as follows:

Once Kd is authorized and issued to the user, the user needs to ensure that it is not leaked. If Kd is accidentally leaked or stolen by hackers (this situation is usually unavoidable), the corresponding device manufacturer can generate new Kd update information through the corresponding security server, including: {updated generation number, Kr (root key generation parameter), updated root key Kd, updated device ID}, and transmit the above Kd update information to the key management center (i.e. RMP center) through a secure transmission tool; the RMP center enters the above Kd update information into a unified management database, and removes all information after Kd, including {updated generation number, Kr (root key generation parameter), updated root key Kd, updated device ID}. The television transmission center enters the corresponding information received into a unified management database, and after a set period of time (such as two days), sends the {updated generation number, Kr} to the user's terminal device through EMM information; after receiving the corresponding information, the terminal device can parse and decrypt the EMM information through the original device ID and the original Kd to obtain the corresponding Kd update information {updated generation number, Kr}, and start the Kd update process on the terminal side according to the obtained Kd update information {updated generation number, Kr} to realize the update of the device key.

It should be noted that after Kd is updated, Kw, which has a corresponding relationship with it, also needs to be updated. Therefore, after receiving the updated Kd sent by the security server, the key management center needs to use the Kd to generate a corresponding new Kw (i.e., the updated Kw), and send the new Kw together with the updated generation number, Kr, updated device ID, etc. to the TV transmission center, which sends the new Kw and Kr together to the terminal device, so that after the terminal device generates the updated Kd according to the corresponding Kr, it uses the updated Kd to obtain the new Kw, and then obtains the descrambling key Ks based on the new Kw, and realizes the descrambling of the program based on the obtained Ks.

Furthermore, in the embodiment of the present application, after the terminal device generates the corresponding new root key and new device identifier, the method may further include:

The generated new root key and the new device identification are stored in the secure storage area of the terminal device. That is, the device key can be encrypted and stored in the secure storage area to ensure the security of the device key.

Optionally, storing the generated new root key and the new device identifier in a secure storage area of the terminal device may include:

Using the new root key generation number as an index, a new file for storing the new root key and the new device identification is generated in the secure storage area of the terminal device; and the new root key and the new device identification are stored in the new file. After the new root key and the new device identification are stored in the new file, the attribute of the new file is set to read only (i.e., all updates are additional updates and cannot be replaced).

That is, in the embodiment described in this application, additional updates to Kd can be accomplished by creating an SFS (Secure File System) file indexed by a generation number. That is, all device key updates can be managed using an updated generation number. Correspondingly, Kd can also be retrieved by searching an SFS file indexed by a generation number. This embodiment of the application will not be described in detail.

Furthermore, it should be noted that since there is a one-to-one correspondence between the root key generation number and the root key, after the terminal device receives the key update information issued by the television transmission center, it can first determine whether the root key generation number in the key update information is stored on the terminal device side. If the judgment result is yes, the root key corresponding to the root key generation number can be directly obtained from the terminal device side based on the root key generation number, without the need to re-execute the operation of generating a new root key based on the root key generation parameters in the key update information and the locally saved set key generation algorithm, so as to reduce the system's processing delay and processing pressure, and the embodiments of the present application will not elaborate on this.

Embodiment 1 of the present application provides a conditional reception method, in which a terminal device can generate a new root key based on the root key generation parameters in the key update information issued by the television transmission center and the set key generation algorithm locally stored in the terminal device, and obtain a descrambling key based on the new root key, and descramble the program stream issued by the television transmission center based on the obtained descrambling key to obtain a clear program stream, thereby solving the problem that when users use the existing CA system to receive programs, it takes a long time to update the device key to achieve program descrambling, thereby improving the reception efficiency of the CA system and improving the user's application experience.

Example 2:

Based on the same inventive concept, the second embodiment of the present application provides a terminal device. The specific implementation of the terminal device can refer to the relevant description in the first embodiment of the method above, and the repeated parts are not repeated here. As shown in FIG3 , the terminal device mainly includes:

The receiving module 31 is configured to receive key update information including set root key generation parameters sent by the television transmission center;

An update module 32 is configured to generate a new root key based on the root key generation parameter and a set key generation algorithm stored locally on the terminal device; wherein the set key generation algorithm is a private confidentiality algorithm pre-set by a device manufacturer associated with the terminal device in a secure storage area of the terminal device; the root key generation parameter is an M-bit random number, where M is any positive integer, and the corresponding root key can be uniquely generated based on the root key generation parameter;

The descrambling module 33 may be configured to obtain a descrambling key according to the new root key, and descramble the program stream sent by the television transmission center according to the obtained descrambling key to obtain a clear program stream.

Furthermore, the key update information may also carry an encrypted updated working key;

The descrambling module 33 can be specifically configured to decrypt the encrypted updated working key according to the new root key to obtain the updated working key, and decrypt the encrypted descrambling key carried in the ECM issued by the television transmission center according to the updated working key to obtain the descrambling key.

Furthermore, the key update information may also carry a new root key generation number;

The update module 32 can also be used to replace the lower N bits of the original device identification of the terminal device with the new root key generation number according to the new root key generation number to form a new device identification; wherein, N is a positive integer and its value is not less than the number of bits occupied by the root key generation number.

Furthermore, the terminal device may further include a storage module 34:

The storage module 34 may be configured to store the generated new root key and the new device identification in a secure storage area of the terminal device.

Optionally, the storage module 34 can be specifically used to generate a new file for storing the new root key and the new device identification in the secure storage area of the terminal device using the new root key generation number as an index; and, save the new root key and the new device identification in the file, and after saving the new root key and the new device identification in the file, set the file attribute to read-only.

In addition, it should be noted that the storage module 34 can also be used to store parameters such as the original device identification and original root key of the terminal device; and, specifically, the original generation number of the terminal device can be used as an index to store the original device identification and original root key of the terminal device and other parameters, which will not be elaborated in the embodiments of the present application.

Furthermore, it should be noted that since the key update information containing the set root key generation parameters is usually sent to the terminal device by the television transmission center through EMM information, the receiving module 31 can be specifically used to receive the EMM information carrying the key update information issued by the television transmission center, and use the original device identification of the terminal device to find information related to itself from the EMM information, and decrypt the information related to itself found based on the original root key of the terminal device to obtain the key update information containing the set root key generation parameters.

In addition, it should be noted that the receiving module 31 can also be used to receive ECMs and program streams sent by the television transmission center, which will not be described in detail in this embodiment of the present application.

Based on the same inventive concept, the second embodiment of the present application further provides a conditional access system. The specific implementation of the conditional access system can refer to the relevant description in the first embodiment of the method above, and the repeated parts will not be repeated. As shown in FIG4 , the conditional access system mainly includes a television transmission center 41 and a terminal device 42, wherein:

The television transmission center 41 may be configured to send key update information including set root key generation parameters to the terminal device 42;

The terminal device 42 can be used to receive key update information containing set root key generation parameters issued by the television transmission center 41; and generate a new root key based on the root key generation parameters and the set key generation algorithm locally stored in the terminal device 42; and obtain a descrambling key based on the new root key, and descramble the program stream issued by the television transmission center 41 based on the obtained descrambling key to obtain a clear program stream.

Furthermore, it should be noted that, in addition to the television transmission center 41 and the terminal device 42, the conditional access system may also include a security server 43, a key management center 44 and other devices, wherein: the security server 43 can be used to generate a new root key based on the set key generation algorithm and the set root key generation parameters when it is determined that the device key needs to be updated, and send the root key generation parameters to the key management center 44; the key management center 44 can be used to send the root key generation parameters sent by the security server 43 to the television transmission center 41, which is not elaborated in the embodiments of the present application.

Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, devices (equipment), or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

The present application is described with reference to the flowcharts and/or block diagrams of the methods, devices (equipment) and computer program products according to the embodiments of the present application. It should be understood that each process and/or box in the flowchart and/or block diagram, as well as the combination of the processes and/or boxes in the flowchart and/or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for implementing the function specified in one process or multiple processes in the flowchart and/or one box or multiple boxes in the block diagram.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims (11)

1. A conditional access method, comprising: The terminal device receives the key update information including the set root key generation parameters sent by the television transmission center; Generate a new root key according to the root key generation parameter and the set key generation algorithm stored locally on the terminal device; Obtaining a descrambling key according to the new root key, and descrambling the program stream sent by the television transmission center according to the obtained descrambling key to obtain a clear program stream; The key update information is sent by the television transmission center to the terminal device through the authorization management message EMM; Using the original device identifier of the terminal device, searching for information related to the terminal device itself from the authorization management information EMM; Decrypting the found information related to the terminal device itself using the original root key of the terminal device to obtain key update information containing the set root key generation parameters; The root key generation parameter is an M-bit random number, where M is any positive integer; and the corresponding root key can be uniquely generated according to the root key generation parameter; The key update information also carries a new root key generation number; according to the new root key generation number, the lower N bits of the original device identification of the terminal device are replaced with the new root key generation number to form a new device identification; wherein, N is a positive integer and its value is not less than the number of bits occupied by the root key generation number. 2. The method according to claim 1, wherein the key update information further carries an encrypted updated working key; obtaining a descrambling key based on the new root key comprises: Decrypting the encrypted updated working key according to the new root key to obtain an updated working key; The encrypted descrambling key carried in the entitlement control message ECM sent by the television transmission center is decrypted according to the updated working key to obtain the descrambling key. 3. The method according to claim 1, further comprising: The generated new root key and new device identification are stored in the secure storage area of the terminal device. 4. The method according to claim 3, wherein storing the generated new root key and new device identification in a secure storage area of the terminal device comprises: Using the new root key generation number as an index, a new file for storing the new root key and the new device identification is generated in the secure storage area of the terminal device; and the new root key and the new device identification are stored in the file. After the new root key and the new device identification are stored in the file, the attribute of the file is set to read-only. 5. The method according to claim 1, wherein the set key generation algorithm is a private confidentiality algorithm pre-set by a device manufacturer related to the terminal device in a secure storage area of the terminal device. 6. A terminal device, comprising: A receiving module, configured to receive key update information including set root key generation parameters issued by a television transmission center; use the original device identifier of the terminal device to retrieve information related to the terminal device from the authorization management information (EMM) issued by the television transmission center; decrypt the retrieved information related to the terminal device using the original root key of the terminal device to obtain key update information including the set root key generation parameters; the root key generation parameters are an M-bit random number, where M is an arbitrary positive integer; and a corresponding root key can be uniquely generated based on the root key generation parameters; an update module, configured to generate a new root key based on the root key generation parameters and a set key generation algorithm locally stored on the terminal device; the key update information also carries a new root key generation number; the update module is further configured to replace the lower N bits of the original device identifier of the terminal device with the new root key generation number based on the new root key generation number to form a new device identifier; wherein N is a positive integer and its value is not less than the number of bits occupied by the root key generation number; The descrambling module is used to obtain a descrambling key according to the new root key, and descramble the program stream sent by the television transmission center according to the obtained descrambling key to obtain a clear program stream. 7. The terminal device according to claim 6, wherein the key update information also carries an encrypted updated working key; The descrambling module is specifically configured to decrypt the encrypted updated working key according to the new root key to obtain the updated working key, and decrypt the encrypted descrambling key carried in the authorization control information ECM issued by the television transmission center according to the updated working key to obtain the descrambling key. 8. The terminal device according to claim 6, further comprising a storage module: The storage module is used to store the generated new root key and new device identification in the secure storage area of the terminal device. 9. The terminal device according to claim 8, wherein: The storage module is specifically used to generate a new file for storing the new root key and the new device identification in the secure storage area of the terminal device using the new root key generation number as an index; and to store the new root key and the new device identification in the file, and after saving the new root key and the new device identification in the file, set the attribute of the file to read-only. 10. The terminal device according to claim 6, wherein the set key generation algorithm is a private confidentiality algorithm pre-set by a device manufacturer related to the terminal device in a secure storage area of the terminal device. 11. A conditional access system, comprising a television transmission center and terminal equipment, wherein: The terminal device is used to receive key update information containing set root key generation parameters issued by the television transmission center; use the original device identifier of the terminal device to find information related to the terminal device itself from the authorization management information EMM issued by the television transmission center; decrypt the found information related to the terminal device itself according to the original root key of the terminal device to obtain key update information containing set root key generation parameters; and generate a new root key according to the root key generation parameters and the set key generation algorithm locally stored in the terminal device; and according to the new The root key is used to obtain a descrambling key, and the program stream sent by the television transmission center is descrambled according to the obtained descrambling key to obtain a clear program stream; the root key generation parameter is an M-bit random number, and M is an arbitrary positive integer; and the corresponding root key can be uniquely determined to be generated according to the root key generation parameter; the key update information also carries a new root key generation number; according to the new root key generation number, the lower N bits of the original device identification of the terminal device are replaced with the new root key generation number to form a new device identification; wherein, N is a positive integer and its value is not less than the number of bits occupied by the root key generation number.