KR20090129610A - Service method for conditional access system with public key infrastructure and efficient secure protocol - Google Patents

Abstract

PURPOSE: A service method for conditional access system with public key infrastructure and efficient secure protocol are provided to apply the conditional access system of the digital data broadcasting by transmitting the EMM require-message with the out-of-band channel. CONSTITUTION: The server part(20) comprises the CAS server(22) and PKI server(24). The CAS client(30) transmits the EMM require-message with the server part. The original copy comprises the caller identifier, and the PKI server information and purchasing information. The integrity key is inserted in HMAC. The electronic signature is signed to the private key of the CAS client. By using the random number, the integrity key is generated in the CAS client and PKI server according to the same key production rule.

Description

SERVICE METHOD FOR CONDITIONAL ACCESS SYSTEM WITH PUBLIC KEY INFRASTRUCTURE AND EFFICIENT SECURE PROTOCOL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital data broadcasting systems, and more particularly, to a service method and a protocol therefor for a reception restriction system of digital data broadcasting.

As digitalization of broadcasting has recently progressed, digital data broadcasting services such as digital video broadcasting (DVB) and digital audio broadcasting (Digital Audio Broadcasting) have been in the spotlight. A key technology in digital data broadcasting service is a conditional access system (CAS). CAS is a system that allows only authorized subscribers to use a broadcast service, and means a series of processes that allow each digital broadcast receiver to determine whether or not reception is possible.

The CAS consists of a sender (CAS server) that encrypts and transmits a signal, and a receiver (CAS client) that receives and decrypts the encrypted signal. The sender delivers the Entitlement Management Mesaage (EMM) and Entitlement Control Message (ECM), which are the core message protocols of CAS, to the receiver. The EMM includes a broadcast right and a user key, and the ECM includes an encryption key used to decrypt an encrypted broadcast. In the conventional CAS, a system based on a secret key cryptography is mainly used. In order to obtain a key required for a broadcast subscription, a symmetric key for receiving and decrypting an encrypted message from a CAS client is issued in advance in a mobile terminal production step. It is. Such a structure requires a hardware such as a secure chip or a smart card for secure key management on a mobile terminal, so it is difficult to update in real time. In addition, in the conventional PKI infrastructure, the certification authority generates a public key pair, generates a certificate, and transmits the certificate to each subscriber. In addition, since the conventional unidirectional CAS client needs to receive the EMM as an in-band channel, the conventional one-way CAS client consumes the bandwidth of the in-band channel unnecessarily to receive a service at the time of the subscriber's request.

An object of the present invention is to provide a service method of a reception restriction system having a public key infrastructure. Another object of the present invention is to provide a service method of a reception limiting system capable of receiving a service at a desired time for a broadcast subscriber. It is still another object of the present invention to provide a method for supporting a bidirectional service in a unidirectional reception control system client. It is still another object of the present invention to provide an enhanced EMM transmit / receive security protocol of a reception restriction system having a public key infrastructure.

According to an aspect of the present invention, a service method of a reception restriction system including a server unit having a CAS server and a PKI server and a two-way CAS client, wherein the CAS client sends an EMM request message to the server through an out-of-band channel. And a step of transmitting, and the CAS client receiving an EMM response message through the out-of-band channel from the server unit.

According to another aspect of the present invention, a service method of a reception restriction system including a server unit having a CAS server and a PKI server and a two-way CAS client, wherein the CAS client includes a key pair consisting of a public key and a private key for receiving an EMM. And generating a certificate, and transmitting a public key of the key pair to the PKI server to request for issuance of a certificate.

According to still another aspect of the present invention, there is provided a service method of a reception limiting system including a server unit having a CAS server and a PKI server and a unidirectional CAS client, the relay method capable of bidirectional communication with the server unit and the unidirectional CAS client. Connecting to a communicable means, requesting an EMM from the CAS client by the CAS client, requesting an EMM from the server at the repeater, and receiving a EMM response message from the server at the repeater And receiving, by the CAS client, the EMM from the repeater.

According to another aspect of the present invention, as a protocol for the EMM request message transmitted by the CAS client to the server unit in the service method of the receiving system including a server server having a CAS server and a PKI server, and a two-way CAS client, Includes a source consisting of subscriber information, PKI server information, purchase information, a key-based hash message authentication code (HMAC) for the source into which the integrity key value is inserted, and an electronic signature signed with the CAS client's private key; In addition, the integrity key is a random value generated by the CAS client, and a protocol for an EMM request message, which is a value generated by using the same key generation rule in the CAS client and the PKI server, is provided.

According to another aspect of the present invention, in the service method of a receiving system including a server unit having a CAS server and a PKI server, and a two-way CAS client, as a protocol for an EMM response message transmitted by the server unit to the CAS client, Information, a PKI server information, a source consisting of an EMM, a key-based HMAC for the source into which the integrity key value has been inserted, and an electronic signature signed with a PKI server private key, the integrity key being generated at the PKI server. One random number provides a protocol for EMM response messages, which is a value generated using the same key generation rule on the CAS client and PKI server.

According to the configuration of the present invention can achieve all the objects of the present invention described above. Specifically, since the EMM is transmitted to the out-of-band channel at the time of the subscriber's request, the in-band channel and the out-of-band channel may have a margin in bandwidth. Accordingly, more content can be transmitted or the content purchasing method can be configured centering on the broadcast receiver using the free bandwidth, and various business models can be applied away from the conventional broadcaster center business model. In addition, since the CAS client generates a public key pair and requests for issuing a certificate to the PKI server, the user can receive the certificate again whenever he / she wants it. Because it is encrypted and stored, efficient and secure key management is possible without hardware devices such as security chips or smart cards. In addition, since the repeater is connected to support the bidirectional service in the unidirectional CAS client, bidirectional communication is possible in the unidirectional CAS client. In addition, since the EMM transmit and receive security protocol suitable for the service of the PKI-based reception restriction system is provided, security is further enhanced.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, the public key based reception restriction system 10 includes a server unit 20 and a CAS client 30. The server unit 20 includes a CAS server 22 and a PKI server 24. The CAS server 22 and the PKI server 24 are connected to each other to form a server unit 20. The server unit 20 delivers the ECM 50 to the CAS client 30 in the in-band channel, receives the EMM request message 60 from the CAS client 30 through the out-of-band channel, and sends the CAS client 30 to the CAS client 30. Deliver the EMM response message 70. The CAS client 30 is a bidirectional CAS client provided in the mobile terminal 40 capable of bidirectional communication. The CAS client 30 receives the ECM 50 from the server unit 20 through an in-band channel and the server unit 20 through an out-of-band channel. ) Sends an EMM request message 60 requesting EMM transmission, and receives an EMM response message 70 including the EMM sent by the server unit 20.

Conventional CAS takes the form of guaranteeing the integrity of the message through the HASH function during EMM transmission, but may be vulnerable to security. Thus, the EMM request message 60 and the EMM response message 70 have a security-enhanced protocol structure as described below.

Referring to Fig. 2, the EMM request message 60 includes subscriber information 62, PKI server information 64, purchase information 66, HMAC 68, and electronic signature 69. The original request is made from the subscriber information 62, the PKI server information 64, and the purchase information 65, and an integrity key (IK) value is inserted into the key-based HMAC 68 for it. At this time, the integrity key (IK) is a random value generated by the CAS client and is a key value generated by using the same key generation rule in the CAS client (30 in FIG. 1) and the PKI server (24 in FIG. 1). Next, by electronically signing and attaching the entire message with the CAS client's private key, the server supports a strong security function that enables message authentication for the CAS client.

Referring to Fig. 3, the EMM response message 70 includes subscriber information 72, PKI server information 74, EMM 76, HMAC 78, and electronic signature 79. The response source is created from the subscriber information 72, the PKI server information 74, and the EMM 76, and inserts an integrity key (IK) value into the key-based HMAC 78 for it. Next, if the entire message is attached and sent electronically (79) with the private key of the PKI server (24 in FIG. 1), the CAS client verifies the message using the PKI server's public key and checks the HMAC information for final purposes. Acquire a broadcast key.

4 shows a service method step by step using the system of FIG. Referring to FIG. 4, the service method includes a step S1 of transmitting an EMM request message, a mutual authentication step S2, and a step S2 of receiving an EMM response message. The step S1 of sending the EMM request message is made by the bidirectional CAS client (30 in FIG. 1) sending the EMM request message (60 in FIG. 1) to the PKI server 24 via the out-of-band channel. The mutual authentication process (S2) is performed using a PKI certificate between the PKI server (24 in FIG. 1) and the CAS client (30 in FIG. 1). Through this process, the CAS client secures the trust between devices and synchronizes encryption keys. The PKI server securely receives the EMM response message (70 in FIG. 1). As such, when the PKI security technology is used based on the bidirectional CAS client, the EMM information can be safely transmitted and received between devices trusted by the subscriber. In addition, PKI-based security technology is used to solve the problems caused by the passive method of the conventional one-way CAS, which is a secret key method. , WSP, etc.) provides the following advantages.

If the broadcast receiver purchased the service, the broadcast receiver had to wait for a certain time to receive the EMM transmitted through the in-band channel in the one-way CAS, but the broadcast receiver used the EMM using the out-of-band channel. In the structure of requesting the EMM, the EMM does not need to be delivered to the in-band channel, and the EMM is received through the out-of-band channel immediately so that the viewer can watch the broadcast. This increases the proportion of broadcast content that can be allocated to in-band channels.

Since broadcasters do not have to use in-band channels to process EMM transmissions, they can more easily respond to bandwidth utilization, and broadcast receivers can receive active EMMs upon request, enabling active purchase. In addition, since the time taken to receive the EMM after purchase is very short, it is not necessary to purchase a few days before the broadcast schedule, and even if the schedule is changed, the service provider for the refund is greatly reduced. In addition, the broadcast receiver can actively subscribe and unsubscribe at the desired time, thereby creating various business models.

Referring to Fig. 5, the CAS client 30a of the public key based reception restriction system 10a includes a user interface (UI) 32a, a core security engine 34a, and a security I / F (interface). A driver 36a and a storage device 38a are provided. Through the UI 32a, the subscriber requests generation of a public key pair, and inputs a password for encrypting a private key among the public key pairs. The security I / F driver 36a generates a public key pair by calling a key pair generation module from a PKI crypto code engine. The core security engine 34a has a security rule set 341a and a cryptographic API I / F 342a. The private key of the key pair generated by the security rule set 341a is encoded, and then encrypted using the password key input by the subscriber and the encryption API I / F 342a. The storage device 38a stores a private key 381a and a public key 382a. When the subscriber wants to use the private key 381a stored in the storage device 38a, the subscriber decodes the password using the password key and the crypto API I / F 342a and then decodes it into the security rule set 341a. Used for data decryption and digital signature. The CAS client 30a sends the public key 382a and the certificate request message to the PKI server 24a, and receives the certificate sent from the PKI server 24a.

6 shows a service method step by step using the system of FIG. 6, the key pair request and password input step S10, the key pair generation step S20, the private key encryption step S30, the key pair storage step S40, and the certificate request step S50. ) And a certificate accepting step (S60). The key pair request and password input step S10 is performed through the UI (32a in FIG. 5). The key pair generation step S20 is performed by the secure I / F driver (36a in FIG. 5) calling the key pair generation module in the PKI cryptographic code engine to generate a key pair. The private key encryption step (S30) is performed by encoding the private key of the generated key pair into a security rule set (341a in FIG. 5) and then encrypting it using a password key and encryption API I / F (342a in FIG. 5). The key pair storage step S40 is performed by storing the public key and the encrypted private key in the storage device (38a in Fig. 5). The certificate request step S50 is performed by the CAS client 30a of FIG. 5 by sending a public key and certificate request message. The certificate accepting step (S60) is to issue a certificate signed electronically by the PKI server (24a of FIG. 5) to the CAS client (30a of FIG. 5) by issuing a digitally signed certificate as the private key of the certification authority, and the CAS client receives it. Is done. By using the issued certificate, users can subscribe to the broadcast and purchase contents, so that the user can receive the certificate again whenever he / she wants it, and the subscriber's private key is encrypted and stored in the key pair generation step. Efficient and secure key management is possible without hardware equipment such as smart cards.

Referring to Fig. 7, the reception restriction system 10b includes a server unit 20b including a CAS server 22b and a PKI server 24, a CAS client 30b provided in the one-way mobile terminal 40b, and a server. A repeater 90b for connecting the unit 20b and the one-way CAS client 30b is provided.

Since the one-way mobile terminal 40b is a one-way-based broadcast reception-only terminal device, the one-way mobile terminal 40b cannot directly support a PKI-based two-way service. The repeater 90b is used to support a bidirectional service in such a unidirectional CAS client 30b. The repeater 90b is connected to the unidirectional CAS client 30b by means such as, for example, USB. As a repeater 90b, a device equipped with a bidirectional mobile terminal 40 such as a personal computer (PC), a mobile phone, and a set-top box may be used. The repeater 90b has a defined communication method with the one-way CAS client 30b and a communication with the server unit 20b, and transmits the EMM request packet generated by the one-way CAS client to the server unit 20b and from the server unit 20b. The received EMM data is transferred to the one-way CAS client 30b.

8 shows a service method using the reception restriction system of FIG. 7 step by step. Referring to FIG. 7, the service method includes a step (S100) of connecting the one-way CAS client 30b and the repeater 90b, a request for an EMM from the repeater 90b (S200), and a server unit 20b. Requesting an EMM (S300), receiving a EMM response message from the server unit 20b by the relay 90b (S400), and receiving the EMM from the relay 90b by the CAS client 30b ( S500) is provided.

When the broadcast terminal does not have a channel to communicate with the server, communication is possible through a terminal device equipped with a self-provided software-based repeater. When requesting an EMM to a broadcast server (CAS server) through a device in which a repeater is installed, the mobile terminal device may transmit an EMM request packet to the repeater, and the repeater forwards the packet received from the one-way CAS client device to the server to transmit the one-way CAS client. It substitutes the device's EMM request and forwards the EMM response received from the server to the one-way CAS client device. If the broadcast terminal can also be connected to a device having an intercommunication channel such as a mobile phone, a repeater can be mounted on the mobile phone and the EMM can be obtained when desired using the mobile phone anywhere.

Although the present invention has been described with reference to the above embodiments, the present invention is not limited thereto. Those skilled in the art will appreciate that modifications and variations can be made without departing from the spirit and scope of the present invention and that such modifications and variations also fall within the present invention.

1 is a block diagram schematically illustrating a structure of a public key based reception restriction system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a structure of a security protocol of the EMM request message of FIG. 1.

FIG. 3 is a diagram illustrating a structure of a security protocol of the EMM response message of FIG. 1.

FIG. 4 is a flowchart illustrating a method of service of a reception restriction system using the system of FIG.

5 is a block diagram schematically illustrating a structure of a public key based reception restriction system according to another embodiment of the present invention.

6 is a flowchart illustrating a service method of a reception restriction system using the system of FIG.

7 is a block diagram schematically illustrating a structure of a public key based reception restriction system according to another embodiment of the present invention.

FIG. 8 is a flowchart illustrating a service method of a reception limit system using the system of FIG.

Claims (9)

In the service method of the receiving system including a server unit having a CAS server and a PKI server and a two-way CAS client, Transmitting, by the CAS client, an EMM request message to the server through an out-of-band channel; And receiving, by the CAS client, an EMM response message from the server unit through an out-of-band channel. The method of claim 1, further comprising the step of mutually authenticating using a PKI certificate between the PKI server and the CAS client. In the service method of the receiving system including a server unit having a CAS server and a PKI server and a two-way CAS client, Generating, by the CAS client, a key pair consisting of a public key and a private key for receiving an EMM; Requesting issuance of a certificate by transmitting a public key of the key pair to the PKI server. 4. The service method of claim 3, wherein the CAS client further comprises encrypting a private key of the key pair. The service method of claim 4, wherein the CAS client further comprises receiving a password from a subscriber. The service method of claim 5, wherein the private key is encrypted using the password key and cryptographic API I / F after encoding the private key into a security rule set. A service method of a reception control system including a server unit having a CAS server and a PKI server and a unidirectional CAS client, Connecting a repeater capable of bidirectional communication with the server unit and the one-way CAS client by means of communication means; Requesting, by the CAS client, the EMM from the repeater; Requesting, by the repeater, the EMM from the server; Receiving, by the repeater, an EMM response message from the server unit; Receiving, by the CAS client, the EMM from the repeater. A protocol for an EMM request message transmitted by the CAS client to the server in a service method of a reception system including a server unit having a CAS server and a PKI server and a bidirectional CAS client, An original consisting of subscriber information, PKI server information, purchase information, A key-based HMAC for the original with an integrity key value inserted, Contains an electronic signature signed with the CAS client's private key, The integrity key is a random value generated by a CAS client and is a value generated by using the same key generation rule on a CAS client and a PKI server. A protocol for an EMM response message transmitted from a server unit to a CAS client in a service method of a reception system including a server unit having a CAS server and a PKI server and a bidirectional CAS client, A source consisting of subscriber information, PKI server information, EMM, A key-based HMAC for the original with an integrity key value inserted, Contains an electronic signature signed with a PKI server private key, The integrity key is a random number generated by the PKI server and a value generated using the same key generation rule on the CAS client and the PKI server.

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