KR20040050561A - Conversion method of entitlement message for public key infrastructure based on conditional access system - Google Patents

Abstract

PURPOSE: A method for converting an EMM(Entitlement Management Message) in a CAS(Conditional Access System) with a PKI(Public Key Infrastructure) is provided to solve problems of a CAS with a symmetric key scheme. CONSTITUTION: A CAS(207) connects to a subscriber management system(206), reads each subscriber information from a database through the subscriber management system(206), and transmits subscriber information to a CA(Certificate Authority) server(202) according to a certificate policy. The CAS(207) transmits a certificate request form including a public key of electronic signature keys stored in the database to the CA server(202). The subscriber management system(206) records a certificate issued from the CA server(202) and a subscriber's private key stored in the database in a conditional access module through a recording device(204).

Description

Restriction of public key infrastructure {Conversion method of entitlement message for public key infrastructure based on conditional access system}

The present invention relates to a credential management message conversion method in a public key infrastructure limited reception system and a computer readable recording medium recording a program for realizing the method. In the case of the service, the symmetric key type restricted reception system can read the credential management message conversion method to solve the problem of key sharing, secure key transmission, and non repudiation of the key, and the program for realizing the method can be read by a computer. To a recording medium.

By utilizing this, a broadcast service provider who is paying with a symmetric key type limited reception system can perform a secure two-way service even without introducing a separate public key based restricted reception system.

1 is a conceptual diagram of a general digital cable TV broadcasting system.

As shown in FIG. 1, a general digital cable TV broadcasting system includes an encoder system of audio, video, data, subscriber management system, a conditional access system, an application server that provides two-way service, and a system that configures such information as a broadcast signal. A headend 101 covering the network, an in-band channel network 105 for transmitting a broadcast signal, an out-of-band channel network 106 for providing additional information and bidirectional service information, and a broadcast signal and bidirectional service information. It consists of a receiving host (102), a conditional receiving module (103) for analyzing data received on out-of-band channels and limited reception data, and a TV (104) for viewing applications and broadcast programs of the host (102). do.

In particular, if the conditional reception module 103 is inserted into the host 102 in order to watch a paid service, and normally exchanges data with the host 102, the cable broadcaster may use an emergency alert system (EAS) or an interactive program guide. , Implement Impulse Pay Per View (IPPV), Video On Demand (VOD), and Interactive services. Recently, as the interactive service is enabled, data broadcasting service is available, and as a result, various services such as home shopping, home banking, mail transmission, interactive advertisement, and online game are expected to expand further. Accordingly, the broadcaster is forced to introduce a limited reception system having a public key infrastructure that guarantees fraud prevention of purchase behavior.

The conditional access system generates an EMM that manages the subscriber's entitlement and an Entitlement Control Message (ECM) that controls the subscriber's entitlement. The ECM is used as an in-band channel and an out-of-band channel (Out Of). Band) transmits the EMM to the host 102 of the subscriber. The EMM and ECM transmitted to the subscriber's host 102 go through a Quadrature Phase Shift Keying (QPSK) demodulator of the host 102 and then pass through a filter that distinguishes between the EMM and ECM of the CA. Specifically, the conditional access module 103 should be able to acquire a CW (Control Word, hereinafter referred to as CW) included in the message scrambled broadcast signal.

Therefore, the headend restricted reception system broadcasts the ECM encrypted CW for each channel, and transmits the EMM capable of unlocking the key of the CW encrypted channel to the host of the subscriber. The encryption key management structure in the symmetric key structure and public key infrastructure related to this is shown in FIG. 4. The limited reception system has a difference in the composition of the broadcast system and the composition of the message depending on the encryption method and the authentication problem. In particular, the public key infrastructure restricted reception system configuration communicates with the subscriber management system, downloads a certificate received from a certification authority, and records the certificate in the conditional access module 103 through a recording device. The encryption of the message with the public key in the issued certificate can be referred to as a difference from the symmetric key type limited reception system.

The EMM generated from the conditional access system is an EMM (hereinafter referred to as EMM_ps) containing paid service information (package service, IPPV service, etc.), and an EMM transmitted to receive different services for each subscriber. (Hereinafter referred to as EMM_su).

Generally, public key cryptography takes longer to encrypt and decrypt than symmetric key. Therefore, if the message is to be sent to all subscribers at regular intervals, it is preferable to use the symmetric key method, and to use the public key infrastructure to distribute encryption keys to subscribers at random intervals and to ensure subscribers' buying behavior. It is desirable to.

Therefore, the ECM transmitted in the in-band channel and the EMM_ps transmitted in the out-of-band channel at regular intervals are encrypted and transmitted using a symmetric key method. On the other hand, in order to be transmitted per subscriber and not to deny the purchase from the return channel, a method of performing public key infrastructure encryption is required.

The present invention has been proposed to meet the above-described needs, so that the public key infrastructure limited reception system, which must be introduced inevitably due to the expansion of the interactive service, can be easily switched from the symmetric key type restricted reception system. It is an object of the present invention to provide a method for converting a qualification management message and a computer-readable recording medium recording a program for realizing the method.

1 is a conceptual diagram of a general digital cable TV broadcasting system.

2 is an exemplary configuration diagram of a system for receiving a restriction of a public key infrastructure in digital cable TV broadcasting to which the present invention is applied.

3 is an explanatory diagram showing a structure of a subscriber identity management message encrypted with a public key scheme according to the present invention;

4 is an exemplary diagram of an encryption key management method of a symmetric key and public key type limited reception system used in the present invention.

5 is an exemplary detailed configuration diagram of a credential management message conversion apparatus in a system for receiving a public key infrastructure according to the present invention.

6 is a flowchart illustrating a method for translating a credential management message in a system for receiving a public key infrastructure according to the present invention.

7 is an exemplary diagram illustrating a changed database schema structure in a method for transforming a credential management message according to the present invention.

* Explanation of symbols for the main parts of the drawings

501: database processing unit 502: database

503: main memory 504: message generator

505: symmetric key encryption processing unit 506: message synchronization and transmission unit

507: Message division unit 508: EMM_su message regeneration unit

509: public key encryption processing unit

510: database schema change

The present invention for achieving the above object, in the credential management message conversion method applied to the public key infrastructure limited reception system, connected to the subscriber management system in charge of the function of the registration authority (RA), the subscriber management A first step of reading each subscriber information from a database through a system and transmitting it to a certification authority according to a certificate policy; A second step of transmitting a certificate request form including a public key of an electronic signature generation key (composed of a public key and a private key) generated in the database to a certification authority; And a third step in which the subscriber management system records the certificate issued from the certification authority and the subscriber's private key generated in the database to the conditional access module through a recording device. In addition, the present invention, when subscribing to a subscriber pay service, converts the message of the limited reception system every time it is registered in the subscriber management system, or whenever the content of the subscriber pay service reception is changed in the subscriber management system, the message of the limited reception system is transmitted. And further comprising a fourth step of converting.

In addition, the present invention is connected to a subscriber management system in charge of the function of the registration authority (RA) in the public key infrastructure limited reception system having a processor, and through the subscriber management system, each subscriber information is stored in a database. A first function of reading and sending to a certification authority in accordance with a certificate policy; A second function of transmitting a certificate request form including a public key of a digital signature generation key (composed of a public key and a private key) generated in the database to a certification authority; And a program for realizing a third function for the subscriber management system to record a certificate issued from the certification authority and a subscriber's private key generated in the database to a conditional access module through a recording device. Provide the medium.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is an exemplary configuration diagram of a system for receiving a restriction of a public key infrastructure in a digital cable TV broadcast to which the present invention is applied.

As shown in FIG. 2, when a new subscriber is registered by a subscriber management system operator 201, a certificate authority server is stored to store subscriber information in a database 208 and issue a certificate. The subscriber's application information is sent to 202. Accordingly, the reference number and the authorization code are transmitted from the CA server 202 to the subscriber management system 206, and then a certificate issuance is requested through the subscriber's reference number and the authorization code. The subscriber management system automatically generates a pair of digital signature keys (public key and private key) upon request for certificate issuance. The certificate request form with the public key is then sent to the authorized CA. Therefore, the CA checks the certificate issuing information of the subscriber and issues the certificate. The CA stores the certificate and the private key of the subscriber through the recording device 204 in the limited reception module. Further, the digital signature generation key is stored in the database 208 and the issued certificate is published in the directory.

As described above, a message transmitted at regular intervals by the encryption rate is encrypted in a symmetric key manner, and it is efficient to construct a message in a public key infrastructure for a message changed at random intervals. Therefore, after reading the EMM_su stored before being encrypted in memory to generate the EMM_su message in the symmetric-keyed restricted reception system, the public key of the subscriber is encrypted to the subscriber who has changed the application for the paid service along with the certificate of the headend restricted reception system. Send one EMM_su. Receiving the EMM_su, the subscriber may obtain the encryption key of EMM_ps by decrypting the EMM_su encrypted with the public key using the private key previously stored in the conditional access module. That is, descramble is possible by acquiring the CW-encrypted channel key.

In the public key encryption algorithm, since the length of the key is longer than that of the secret key, the encryption and decryption takes a long time, and thus the message is encrypted by the session key 301. In addition, the session key 301 is transmitted to the out-of-band channel after performing encryption with the subscriber's public key (302). At this time, even if the original message is encrypted with the session key, since the session key is a result of performing the hash function of the subscriber, it is difficult to trace back and the secret key is transmitted in the encrypted state by the secure public key.

5 is an exemplary detailed configuration diagram of a credential management message conversion apparatus in a system for receiving a public key infrastructure according to the present invention.

As shown in FIG. 5, the apparatus for converting a credential management message to which the present invention is applied performs a query for generating a message from the database 502 to construct a symmetric key based restricted reception message (ECM, EMM). There is a database processing unit 501 for this purpose. That is, through the user interface 206, the paid service information is stored in the database 502 via the database processor 501 due to the generation of the paid channel or package service and the addition of the paid service by the subscriber.

The message information and encryption key information stored in the database 502 by the database processing unit 501 must be read periodically to be transmitted to the CA. Accordingly, the message generation information is read in the main memory 503 in advance without accessing the database 502 whenever the message is generated and transmitted.

As the paid service information is stored in the database 502 by the database processing unit 501, the symmetric key type encryption processing unit 505 performs a random function to generate a key descriptor value and generates a key in the database 502. Save the descriptor value.

Then, the database processing unit 501 reads the key descriptor stored in the database 502 and passes the result to the symmetric key type encryption processing unit 505. Then, the symmetric key type encryption processing unit 505 is a private key (hereinafter, referred to as PK) capable of decrypting EMM_su, a group key (hereinafter referred to as GK) capable of decrypting EMM_ps, a broadcast key (hereinafter referred to as BK), and a channel. Generates a Directentitmenet Key (DEK) that can decrypt. These key values change at random intervals.

Thus, the information necessary for generating the message stored in the main memory 503 and the encryption key stored in the database 502 are encrypted using a symmetric key encryption algorithm. The encrypted message is loaded back into the memory. It consists of IP packets for transmission over the cable network.

The message to be transmitted is through the message synchronization and transmission unit 506. This allows the receiver to receive the encryption key first so that the receiver can receive CW from the scrambled A / V data so that the CW, ECM, and EMM can be synchronized and transmitted for each channel during transmission. . That is, the subscriber receives the EMM_su first, decrypts it with a private key (PK) recorded in the CA module 103, obtains the DEK through the GK or BK, and then obtains the CW encrypted with the DEK to finally scramble the A / V data. To watch.

Here, in order to switch to the public key type limited reception system, in order to store the reference number, the authorization code, and the digital signature generation key pair in the existing subscriber information in the database, the database schema changer 510 may be configured as a message conversion device of the limited reception system. It should work on the initial run. In other words, in order to store data generated in a public key type restricted reception system, a field is added to a database table that stores personal information of a subscriber, and a reference number, authorization code, and digital signature generation key pair are added. Change the schema to correspond to the Subscriber ID. The changed database schema is shown in FIG.

In addition, if information necessary for generating a message is loaded into the main memory 503 by the message generating unit 504 through the database processing unit 501, the message code of FIG. 3 by the message separating unit 907. The EMM_su must be processed by the EMM_su message regenerator 508 to generate a message encrypted by the public key method of FIG. That is, the message structure of FIG. 3 adds a session key field to an existing symmetric key type message structure, executes this session key by the public key type encryption processing unit 509, and loads it into the main memory 503. After the public key algorithm is performed by the public key encryption processing unit 509, the message synchronization and transmission unit 506 transmits the ECM to Remux and the EMM_su together with the EMM_ps.

The operation of FIG. 5 having the structure as described above will be described in detail as follows.

The database schema change unit 510 needs to be changed to store the authorization number and reference number received after transmitting the subscriber's application information to the CA server, and the digital signature generation key generated when the certificate issuance request is made. This is to change the database schema structure that can create the database used in the existing symmetric key based CA system or create a new database to store the information generated in the public key based CA system.

Messages generated in the CA system are generated by transmitting CWs which are different for each channel at regular intervals and then encrypted by the encryption keys of the corresponding channels. This message is ECM, and the information set in the paid channel is read from the database and loaded into memory when the restricted system is initialized.

In the same manner as the ECM PID value defined in the CA descriptor of the PMT (Program Map Table) table of the MPEG-2 system, the data is generated in the form of MPEG2-TS packet, and then encapsulated into an IP packet to encapsulate the in-band channel. Send it at regular intervals. The EMM (EMM_ps, EMM_su) for decrypting the transmitted ECM encrypts the encryption key information (EMM INSIDE DATA) 301 that can decrypt the encrypted channel with the session key, and the session key corresponds to the subscriber's private key again. Encrypt with a public key.

This operation shows a part and a function where the conversion device is located in the symmetric key type limited reception system as shown in FIG. Messages generated in the symmetric key type limited reception system are loaded into the main memory 503 by selecting information for generating a message from the database 501. The information stored in the memory passes through the message generator 504. At this time, the message is generated through the message separator 507 to distinguish the message to be generated and distinguished that the message is to be transmitted for each subscriber. The public key encryption processing section 509 is passed.

Then, the message is transmitted to the Remux 210 and the OOB NC 209 of FIG. 2 through the message synchronization and transmitter 506. At this time, the generated out-of-band message is transmitted to the MPEG2 Private Section or IP packet. In particular, when transmitting to the "MPEG2 Private Section", the "table_id" value between the receiver and the headend restricted reception system must be promised in order for the receiver to filter the EMM message. The present invention having such a configuration will now be described in more detail with reference to a method of converting a message generated in a restricted reception system of a public key infrastructure.

6 is a flowchart illustrating a method for converting a credential management message in a system for receiving a public key infrastructure according to the present invention.

As illustrated in FIG. 6, the message conversion method of the public key infrastructure first changes the database schema in order to store the reference code, the authorization code, and the electronic signature key (615). In addition, the subscriber's PK (Private Key) of the subscriber encrypted with the symmetric key is expired (or deleted) (616) and the subscriber information is sent to the CA server according to the certificate application information form of the existing subscriber who was receiving the symmetric key service. (617).

If a new subscriber other than the existing subscriber is registered at the time of initialization, if a change notification message indicating that the new subscriber is registered without passing through steps 615 to 617 is received (602), the subscriber's application information is transmitted to the CA server. (603).

Accordingly, the reference number and authorization code issued from the CA server are stored according to the changed database schema structure (604), and the subscriber management system requests a certificate from the CA server based on the reference number and authorization code stored in the database. At this time, the generated digital signature generation key is also stored in the database (605). The certificate request form including the public key is sent to a public CA, and the downloaded certificate is posted in the directory (606), and the certificate and private key are recorded in the CA module (607).

When a certificate and a private key are stored in the subscriber's limited reception module through this series of procedures, when a user tries to purchase a product using a return channel, the purchase cannot be denied through an electronic signature. In addition, for key distribution and digital signature in the headend CA system, the message generation unit 504 of the CA system of the conventional symmetric key system should read and distinguish the message information to be generated loaded in the main memory 503. (608). This can be distinguished through a field for distinguishing a message code of an EMM message (609), and if it is EMM_su which should be transmitted to a specific subscriber, it should be able to be encrypted and transmitted with a public key (613, 614).

That is, in order to regenerate the EMM_su with the message as shown in FIG. 3, the EMM_su is distinguished by a message code (a message separator is used as a table_id value if the message follows the MPEG2 Private Section format). The separated message generates a session key by performing a hash function on the subscriber's password (610). Therefore, the data 301 constituting the EMM_su is encrypted using the session key of FIG. 3 (611). The data 301 constituting the EMM_su is composed of a value capable of producing a key that encrypts the actual CW. In addition, the generated session key is encrypted with the public key (612) and transmits a message to the subscriber (614).

7 is an exemplary view showing a modified database schema structure in the method for converting a qualification management message according to the present invention.

As shown in FIG. 7, the PUBK_info table of FIG. 7 is an additional modified table, which has a 1: 1 relationship with a subscriber table. In addition, description of the main fields of a subscriber table is as follows [Table 1]-[Table 7].

The method of the present invention as described above may be implemented as a program and stored in a computer-readable recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.).

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

According to the present invention as described above, even if a broadcaster who wants to perform a bidirectional service does not introduce another restriction reception system, the apparatus for converting a message reception system to a restriction reception system message according to the present invention is used on the existing restriction reception system based on the existing symmetric key method. There is an effect that it is possible to implement a high value-added pay broadcasting service without introducing another public key infrastructure limited reception system.

Claims (4)

In the credential management message conversion method applied to the restricted receiving system of the public key infrastructure, A first step of connecting to a subscriber management system in charge of a registration authority (RA) and reading each subscriber information from a database through the subscriber management system to a certification authority according to a certificate policy; A second step of transmitting a certificate request form including a public key of an electronic signature generation key (composed of a public key and a private key) generated in the database to a certification authority; And A third step in which the subscriber management system records the certificate issued from the certification authority and the subscriber's secret key generated in the database to the conditional access module through a recording device; Credential management message conversion method in the limited receiving system of the public key infrastructure comprising a. The method of claim 1, A fourth step of converting the message of the limited reception system each time it is registered in the subscriber management system when the subscriber pay service is subscribed, or converting the message of the limited reception system whenever the content of the subscriber pay service reception is changed in the subscriber management system. Credential management message conversion method in the limited receiving system of the public key infrastructure further comprising a. The method of claim 2, The fourth step, A fifth step of classifying symmetric key-based restricted reception messages (ECM, EMM) and determining that the message includes channel key information obtained by encrypting CW (Control Word) for each subscriber; A sixth step of generating a session key using a hash function by reading the password of the subscriber according to the determination result of the fifth step; A seventh step of encrypting data constituting the EMM through the session key after generating the session key; And An eighth step of encrypting the session key with a public key and transmitting it to the host of the subscriber after performing the encryption; Credential management message conversion method in the limited receiving system of the public key infrastructure comprising a. In a public key infrastructure limited reception system having a processor, A first function connected with a subscriber management system in charge of a function of a registration authority (RA), and reading each subscriber information from a database through the subscriber management system and transmitting it to a certification authority according to a certificate policy; A second function of transmitting a certificate request form including a public key of a digital signature generation key (composed of a public key and a private key) generated in the database to a certification authority; And A third function of the subscriber management system recording a certificate issued from the certification authority and a subscriber's private key generated in the database to a conditional access module through a recording device; A computer-readable recording medium having recorded thereon a program for realizing this.