KR20070097611A - An efficient key distribution method for digital contents distribution - Google Patents

Abstract

A method for efficiently distributing keys for digital content distribution is provided to transfer an encryption right key, a domain key, and a message affirmation key by using a symmetrical key mode requiring less computation, and enable an RI(Right Issuer) device to safely transfer a master key used for key transmission by including the master key to a registration response message transferred to a customer terminal. A customer terminal sends a hello message including a terminal ID to the RI device. The RI device sends a hello message including an RI ID, and a random number and a session ID of the RI device in response to the hello message received from the customer terminal. The customer terminal sends a message and a signature for requesting registration to the RI device. The registration request of the customer terminal includes the session ID, and the random number, request time information, and the signature of the customer terminal. If the RI device confirms validity of a public key authentication of the customer terminal, the RI device transmits a registration response message including the master key encrypted by the public key of the customer terminal, the session ID, a URL(Uniform Resource Locator) of the RI device, and the signature for the registration request message.

Description

Effective Key Distribution Method for Digital Content Distribution {AN EFFICIENT KEY DISTRIBUTION METHOD FOR DIGITAL CONTENTS DISTRIBUTION}

1 is a key distribution method for digital content distribution showing a conventional OMA DRM standard version 2.0 system.

2 is the main process of packaging.

3 is important information included in a license as described above.

4 is a conventional four-step registration protocol.

5 is a two-step license (authorization object) acquisition protocol.

6 is a one-step license (authorization object) acquisition protocol.

7 is a two stage domain join protocol.

FIG. 8 is a conceptual diagram illustrating a process in which an authorization key included in a license response message of FIGS. 5 and 6 is securely encrypted and transferred from an authorization issuer device to a consumer terminal device.

9 is a conceptual diagram illustrating a modification of a registration response message of a 4-step registration protocol of an existing ROAP for transmission of an encrypted master key (MK) according to the present invention.

FIG. 10 is a conceptual diagram illustrating a process in which a Mas Turkey (MK) transmitted by being included in a license response message applied to the present invention is securely encrypted and transferred from an authority issuer device to a consumer terminal device. FIG.

11 is a two-step license (authorized object) acquisition protocol including a right key encryption key (REK) and a message authentication key (MAK) encrypted with a master key (MK) according to the present invention.

12 is a one-step license (authorized object) acquisition protocol including an authorization key (REK) and a message confirmation key (MAK) encrypted with a master key (MK) according to the present invention.

13 is a two-step domain join protocol including a domain key (DK) and a message verification key (MAK) encrypted with a master key (MK) according to the present invention.

14 is a key distribution mechanism using a symmetric key certificate in the authority issuer device according to the present invention.

15 is a conceptual diagram illustrating a process of extracting sensitive information by decrypting a symmetric key certificate using a master key (MK) in a consumer terminal device according to the present invention.

FIG. 16 illustrates a process of comparing an issuer device identifier 'and a consumer terminal device identifier' extracted from a symmetric key certificate with an authority issuer device identifier and a consumer terminal device identifier stored in the consumer terminal in the consumer terminal device according to the present invention. Conceptual diagram representing.

The present invention relates to an effective key distribution method for digital content distribution, and more particularly, to a key distribution method that reduces the protocol by replacing an existing key transmission mechanism with a key transmission mechanism using a symmetric key certificate.

In general, Digital Rights Management (DRM) protects the rights and interests of digital content providers, which are essential to building the foundation of the content industry that is emerging as a new industry in the 21st century. It is an essential technology to collectively build the infrastructure from generation of contents to distribution and management such as payment agency.

Unlike the initial network environment, current consumers want to use the contents in various terminals such as desktop PCs, laptops, MP3 players, PDAs, and mobile phones.

DRM is a system technology that securely delivers various contents in a network from a content provider (CP) to a client and prevents the customer from illegally distributing the content.

The most important technology in the DRM system is encryption technology, which encrypts the content using the customer's password or the unique number of the customer's computer as the encryption key. . Of course, the DRM requires additional technologies such as content usage rule control technology and billing technology.

Among them, encryption / decryption technology is a core technology for preventing illegal distribution or illegal copying in the distribution of multimedia contents, and encrypts the contents using a specific encryption key so that only legitimate users can decrypt and use the contents. . Existing content delivery system uses only user ID and password. In this case, there is a problem that it is easy to illegally use content by sharing ID and password. In order to solve this problem, there is a method of (1) using a unique ID of a customer's computer and (2) using a customer's PKI key or a secret private key.

Content may be encrypted using a unique number of the customer's computer, for example, a hard disk number or a CPU number. However, the unique number of the computer has a disadvantage in that it is inferior in security because anyone can easily access it. . Therefore, the most common DRM encryption method is to embed a private secret key in the computer and use it like a public / secret key. The advantage of encrypting with the customer's unique key is that even if the downloaded content is delivered to a third party, it cannot be operated on the third party's computer. By using this, the DRM system can prevent illegal copying and distribution of content.

On the other hand, in the existing DRM system using the unique ID of the terminal in the central server to provide the DRM packaged content to be available only to the terminal and to use it. This procedure is inconvenient for the consumer and has an inefficiency that must be transmitted separately when the same content is to be used in multiple terminals.

Prior to describing such a prior art, an encryption algorithm will be briefly described to help understand the contents described below.

The encryption algorithm is classified into a symmetric key encryption algorithm having the same encryption key and decryption key and an asymmetric key encryption algorithm having different encryption / decryption keys according to the characteristics of the key used for encryption and decryption. .

Symmetric key encryption algorithm can be divided into stream encryption algorithm and block encryption algorithm according to data processing type. Symmetric key encryption method requires fast distribution while secure encryption of key.

The public key algorithm uses two keys, a public key and a private key. The public key is open on an open network and the private key is kept private. Therefore, in case of using the public key method, if the plain text is encrypted and transmitted, the plain text is transmitted by encrypting the plain text with the public key of the other party, and the other party decrypts it with its own secret key.

In such a public key infrastructure (PKI), when a sender encrypts his or her ID with a private key and sends it to the receiver, the receiver can verify that the signature has been transmitted from the receiver by decrypting the signature with the public key of the sender. This is called digital signature or digital signature and can be used to verify sender's identity and message integrity.

Recently, the Open Mobile Alliance ^TM (OMA DRM Spec. V2: 0pen Mobile Alliance ^TM , DRM Specification, candidate Version 2.0) introduced the concept of domain. It is possible to freely move content between terminals registered in an arbitrary domain.

For example, if a consumer purchases MP3 music and its license on a mobile phone and registers PDAs and notebook computers in the consumer domain, the licensed MP3 music can be played on these two consumer terminal devices.

1 is a conventional OMA DRM specification version 2.0 system, and FIG. 2 shows the main process of packaging.

1 and 2, in the OMA DRM standard version 2.0 system, the content issuer (CI) 10 encrypts and packages the content (S1).

That is, the content is symmetrically encrypted with the content key. The key used for encryption is called a Contents Encryption Key (CEK).

The content issuer 10 registers the content key and the packaged content (S2).

The consumer requests registration of his terminal device 30 to the authority issuer device 20, and the authority issuer device 20 confirms the consumer terminal device 30 and then permits registration (S3).

The packaged content is freely distributed to the consumer terminal device 30 to be played (a) (b) (c).

The consumer terminal device 30 that will use the content has the permission or restriction (eg, expiration date, remaining play count, etc.) related to the content from the rights issuer (RI) device 20 and the content key (CEK). When the license including the license (OMA DRM Spec v2.0 is called "rights object (RO)") is purchased, the authority issuer device 20 issues a license (S4-1, S4-2, S4-3).

In addition, the user device 30 may register a domain (S5-1, S5-2, S5-3).

At this time, the license includes important information such as license identifier, license authority, digital signature, expiration date, packed content key (encrypted content key), ROAP version, consumer terminal device ID, domain license status, license issuer URL, and the like.

3 shows important information included in the license as described above. In particular, the content information (CEK), the authorization key (REK) applied to CEK encryption, and the message confirmation key (MAK), which are sensitive information included in the license, must be encrypted and transmitted securely.

The consumer terminal device 30 implements a DRM agent program certified by the authority issuer (RI) 20 at the shipping stage. This DRM agent is responsible for enforcing permissions and regulations with respect to the content and controlling access to the content. The DRM agent checks the license, decrypts the content key, decrypts the content using the same, and then plays it on the consumer terminal device 30. The content cannot be played on the terminal without an associated license.

As described above, in the OMA DRM, the DRM content is logically separated from the license, and the license can be freely distributed by cryptographically combining the license with the consumer terminal device 30.

The consumer can register multiple devices that he owns in the domain. The content that has obtained the domain license may be played on all the consumer terminal devices 30 registered in the same domain.

The OMA DRM specification version 2.0 defines a Rights Object Acquisition Protocol (ROAP) suite. The authority object acquisition protocol is a protocol between the DRM agent program installed in the consumer terminal device 30 and the authority issuer (RI) device 20.

The conventional ROAP protocol includes a four-stage registration protocol, a two-stage license (authorized object) acquisition protocol, a one-stage license (authorized object) acquisition protocol, a two-stage domain join protocol, and a two-stage domain leave protocol.

Figure 4 shows a conventional four-step registration protocol, Figure 5 shows a two-step license (authorized object) acquisition protocol, Figure 6 shows a one-step license (authorized object) acquisition protocol, and Figure 7 shows a two-step domain join protocol.

In the license response message of FIGS. 5 and 6, the content key CEK, the authorization key REK, and the message confirmation key MAK are encrypted and then transmitted to the consumer terminal device 30.

In addition, the domain join response message of FIG. 7 includes a domain key DK and a message confirmation key MAK. At this time, the domain key is an encryption key of the symmetric key encryption method. 5 and 6, if the license is for a domain, the encryption authorization key REK and the message confirmation key MAK are encrypted with the corresponding domain key DK and transmitted to the consumer terminal device 30.

8 illustrates a process in which an encryption authority key (REK) included in the license response message of FIGS. 5 and 6 is securely encrypted and transferred from the authority issuer (RI) device 20 to the consumer terminal device 30.

That is, the authorization issuer device 20 encrypts the authorization key (REK), message confirmation key (MAK) or domain key (DK), and message confirmation key (MAK) using the public key of the consumer terminal device 30. Transfer to the terminal device 30. The consumer terminal device 30 decrypts the keys that have been transmitted using its private key. The consumer terminal device 30 can decrypt the content key CEK using the encryption authority key REK, and can decrypt and play the content using this. The message acknowledgment key (MAK) is used to verify received protocol messages.

As shown above, in the OMA DRM specification version 2.0, a cryptographic authorization key (REK), a domain key (DK), and a message verification key (MAK) are delivered by using a large computational public key infrastructure (PKI). Receive. This method has a problem of increasing battery usage and long processing time in a mobile terminal having low computational power.

Accordingly, the present invention has been made to solve the above problems, and uses a symmetric key method with a small amount of computation to transmit an encryption authority key (REK), a domain key (DK), and a message confirmation key (MAK). An object of the present invention is to provide an effective key distribution method for content distribution.

In addition, another object of the present invention is to securely deliver the master key (symmetric key) to be used for key transmission in the registration response message of the 4-step registration protocol of the authority object acquisition protocol (ROAP) that the authority issuer device sends to the consumer terminal device. Another object is to provide an effective key distribution method for digital content distribution.

In addition, another object of the present invention is maintained until the master key (MK) is renewed, the consumer terminal device is lost if there is a risk of key exposure, discarded, and expired for digital content distribution It is another object to provide an effective key distribution method.

In order to achieve the above object, an effective key distribution method for digital content distribution in accordance with a preferred embodiment of the present invention is a key distribution method for digital content distribution, in which a consumer terminal device includes an identifier of a terminal device. Transmitting a Hello message to the authority issuer device at step S100; The authority issuer device transmits a hello message of the authority issuer device including the authority issuer identifier, a random number of the authority issuer device, and a session identifier in response to the hello message from the consumer terminal device (S200). )Wow; Wherein the consumer terminal device transmits a message relating to a registration request to the authority issuer device, wherein the registration request of the consumer terminal device comprises a registration request message including a session identifier, a random number of the consumer terminal device, request time information, and a signature; Transmitting (S300); And when the authority issuer device is verified that the public key certificate of the consumer terminal device is valid during registration, a master key (MK) encrypted with the public key of the consumer terminal device, a session identifier, a web address (URL) of the authority issuer device, And transmitting a registration response message including a signature regarding these messages and a registration request message (S400).

Preferably, the signature of the step (S300), the session identifier, the random number of the consumer terminal device, the request time information; And a Hello message of the consumer terminal device and a Hello message of the authority issuer device.

In addition, according to another exemplary embodiment of the present invention, in an effective key distribution method for digital content distribution, an issuer device masters an authorization key (REK) and a message confirmation key (MAK) in response to a license request of a consumer terminal device. And encrypting and transmitting with a key (MK) (S500).

In addition, in an effective key distribution method for digital content distribution according to another preferred embodiment of the present invention, in response to a request for a domain subscription of a consumer terminal device, the authority issuer device receives a domain key (DK) and a message confirmation key (MAK). And encrypting and transmitting the master key (MK) (S600).

On the other hand, the key distribution method for distributing digital content according to another embodiment of the present invention, the consumer terminal device transmits a Hello message including the identifier of the terminal device to the authority issuer device (S100); Transmitting, by the authority issuer device, a hello message of the authority issuer device including the authority issuer identifier, a random number of the authority issuer device, and a session identifier in response to the hello message from the consumer terminal device (S200). )Wow; Wherein the consumer terminal device transmits a message and a signature relating to a registration request to the authority issuer device, wherein the registration request of the consumer terminal device includes a registration including a session identifier, a random number of the consumer terminal device, request time information, and a signature; Transmitting a request message (S300); If the authority issuer device confirms that the public key certificate of the consumer terminal device is valid during registration, the master key (MK) encrypted with the public key of the consumer terminal device, a session identifier, a web address (URL) of the authority issuer device, and Transmitting a registration response message including a signature relating to the registration request message (S400); In step S500, in response to the license request of the consumer terminal device, the authority issuer device encrypting the authorization key REK and the message confirmation key MAK with the master key MK; And encrypting and transmitting, by the authority issuer device, the domain key (DK) and the message confirmation key (MAK) with the master key (MK) in response to the domain join request of the consumer terminal device (S600). do.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

An effective key distribution method for digital content distribution according to the present invention is based on a symmetric key encryption algorithm structure as shown in FIGS. 9 to 16.

As is conventional, the content issuer (CI) 10 encrypts and packages the content. In other words, the content is symmetrically encrypted. The key used for encryption is called a content key (CEK).

The packaged content is also freely distributed to the consumer terminal device 30 to be played.

The content issuer 10 registers the content key CEK with the authority issuer device 20.

9 is a conceptual diagram illustrating a modification of a registration response message of a four-step registration protocol of an existing ROAP for transmission of an encrypted master key (MK) according to the present invention, which is modified in step S-3 of FIG. The contents are described in detail.

First, the consumer terminal device 30 transmits a Hello message including the identifier of the terminal device to the authority issuer device 20 (S100).

The authority issuer device 20 may include an authority issuer identifier, a random number of the authority issuer device 20, and a session identifier in response to a Hello message from the consumer terminal device 30. Transmits a hello message (S200).

Subsequently, the consumer terminal device 30 transmits a message relating to a registration request to the authority issuer device 20 (S300). That is, the registration request of the consumer terminal device 30 transmits a registration request message including a session identifier, a random number of the consumer terminal device 30, request time information, and a signature.

Here, the signature includes [session identifier, random number of the consumer terminal device 30, request time information], [hello message of the consumer terminal device 30 and hello of the authority issuer device 20]. Message].

10 is a main conceptual diagram illustrating a process in which the master key (MK) included in the registration response message applied to the present invention is securely encrypted and transferred from the authority issuer device 20 to the consumer terminal device 30.

As shown in FIG. 10, if the authority issuer device 20 confirms that the public key certificate of the consumer terminal device 30 is valid during the registration process, the master key (MK) encrypted with the public key of the consumer device device 30. And a registration response message including a session identifier, a web address (URL) of the authority issuer device 20, and a signature for these messages and a registration request message (S400).

Then, the consumer terminal device 30 decrypts the master key (MK) received by its secret key and stores it in the secret storage means.

Therefore, preparation for key distribution using the symmetric key method is completed between the authority issuer device 20 and the consumer terminal device 30.

Next, as shown in FIG. 11, the consumer terminal device 30 transmits a request for a license (authorized object) to an encrypted content item to the authority issuer device 20.

Accordingly, the authority issuer device 20 receives the license key of the consumer terminal device 30, that is, the authorization object RO request once as shown in FIG. 11 or at regular intervals as shown in FIG. A license (authorized object) response message including a content key (CEK) encrypted with (REK), an authorization key (REK) encrypted with a master key (MK), and a message confirmation key (MAK) is transmitted (S500).

Here, the message acknowledgment key (MAK) is used to verify the received protocol message.

In addition, the consumer terminal device 30 may transmit a domain join request message to the authority issuer device 20 as illustrated in FIG. 13.

In contrast, the authority issuer device 20 receives a domain subscription response message including a domain key (DK) and a message confirmation key (MAK) encrypted using the master key (MK) of the consumer terminal device (30). Transfer to the terminal device 30.

FIG. 14 shows that the authority issuer device 20 generates a symmetric key certificate with a master key MK and transmits the authority key REK or domain key DK to the consumer terminal device 30. It is a block diagram.

That is, as shown in FIG. 14, the authority issuer device 20 encrypts the authority key (REK) or domain key (DK) and the authority issuer device identifier and the consumer terminal device identifier with a master key (MK) to form a symmetric key. Create a certificate.

As such, a symmetric key certificate is a technique for realizing a fast secret key cryptography while providing authentication and accountability like a public key certificate.

Hereinafter, a method of generating a symmetric key certificate according to the present invention will be described in detail.

The symmetric key certificate cryptographically combines a key and a key owner like a public key certificate.

In particular, the symmetric key certificate c _i encrypts these two values with a secret master key (MK) to combine an entity's data encryption key k and its identifier i .

That is, a symmetric key certificate can be written as c _i = E _MK (k∥i) .

Here, '∥' is an operation symbol that concatenates the left and right data. ' E _MK ()' indicates the encryption using the symmetric key master key (MK).

Symmetric key certificates can be created and distributed by third parties that they create and exchange with other entities, or by trusted third parties, similar to a Certificate Authority (CA). The symmetric key certificate of the data encryption key can be used for authentication and data authenticity of the data sender with confidence in its owner.

In order to apply the encryption key distribution mechanism using the symmetric key certificate, the master key (MK) must be shared in advance between the authority issuer device 20 and the consumer terminal device 30. That is, as described above with reference to FIG. 10, the process in which the master key MK, which is included in the registration response message transmitted from the authority issuer device 20 to the consumer terminal device 30, is transmitted in a secure manner has been described. .

Referring to FIG. 15, the user terminal device 30 decrypts a symmetric key certificate received from the authority issuer device 20 with a master key MK to receive an authorization key REK or a domain key DK.

Thereafter, as shown in FIG. 16, the consumer terminal device 30 is the [authority issuer device identifier] extracted from the symmetric key certificate by the [authority issuer device identifier] and the [consumer terminal device identifier]. And [consumer terminal device identifier] '. If these pairs are the same, the consumer terminal device 30 assures that the received keys are sent by the authority issuer device 20.

Therefore, the consumer terminal device 30 is able to decrypt and play the content downloaded from the content publisher 10 using the encryption master key (MK).

As such, a comparison of the speeds of symmetric key encryption and conventional asymmetric key encryption according to an effective key distribution method for digital content distribution of the present invention is shown in the following table.

Cryptographic algorithm encryption Decrypt Sum 1024bit RSA 0.18 ms 4.78 ms 4.92 ms 128bit AES 1.6 μsec 1.6 μsec 3.2 μsec

Here, this comparison compared the time required for encrypting and decrypting 1024-bit information on a Pentium 4 2.1GHz CPU Windows XP. See also Crypto ++ 5.2.1 Cryptographic Library Benchmarks.

The symmetric key encryption algorithm used in the conventional key transmission is 1024 bit RSA, and the symmetric key encryption algorithm used in the key transmission of the present invention is 128 bit AES as a representative example.

Table 1 compares the time taken to encrypt and decrypt the two algorithms. As can be seen from the results shown in Table 1, the present invention can reduce the computation amount and the computation time according to encryption and decryption by the lightweight key management protocol compatible with OAM DRM, compared to the conventional asymmetric key encryption algorithm. It was confirmed that there is.

On the other hand, the master key (MK) sent from the authority issuer device 20 to the user terminal device 30 during the registration process used the RSAES-KEM-KWS standard, which is a key distribution protocol defined in X9.44, which proves safety. Since the standard is used, master key (MK) transmission is secure.

In addition, the authority issuer device 20 and the user terminal device 30 transmit the symmetric key certificate using the master key MK shared during the registration process. At this time, since the transmitted key uses the key wrapping algorithm defined in the IETF RFC standard document, the transmitted message is not a finite element, so it is safe against a partition attack, which is a kind of offline dictionary attack. This is the same as a key transmission mechanism for distributing a domain key (DK) to a terminal in an existing OMA RDM and distributing a session identifier under this domain key (DK).

The present invention has been described with reference to specific embodiments of the present invention, but it is apparent that various modifications and changes can be made as described above without departing from the technical spirit described in the claims of the present invention. Accordingly, the detailed description of the invention and the accompanying drawings should be construed as illustrative rather than limiting to the spirit of the invention.

As described above, the present invention has the effect of providing a lightweight key management protocol compatible with OAM DRM.

In addition, the present invention transmits the session key transmitted under the device public key in the symmetric key certificate format by using the master key shared by the authority issuer device and the consumer terminal device in the registration process to calculate the amount of computation related to key management of the frequently used protocol. The effect is to reduce a lot.

Claims (5)

In the key distribution method for digital content distribution, Transmitting, by the consumer terminal device, a hello message including the identifier of the terminal device to the authority issuer device (S100); Transmitting, by the authority issuer device, a hello message of the authority issuer device including the authority issuer identifier, a random number of the authority issuer device, and a session identifier in response to the hello message from the consumer terminal device (S200). ); Wherein the consumer terminal device transmits a message and a signature relating to a registration request to the authority issuer device, wherein the registration request of the consumer terminal device includes a registration including a session identifier, a random number of the consumer terminal device, request time information, and a signature; Transmitting a request message (S300); And When the authority issuer device is found to be valid in the registration process of the public terminal certificate of the consumer terminal device, the master key (MK) encrypted with the public key of the consumer terminal device, a session identifier, a web address (URL) of the authority issuer device, and the And transmitting a registration response message including a signature of the registration request message (S400). The method of claim 1, wherein the signature of the step (S300), A session identifier, a random number of the consumer terminal device, and request time information; An effective key distribution method for digital content distribution, comprising: a Hello message of a consumer terminal device and a Hello message of an authority issuer device. The method of claim 1, And in response to the license request of the consumer terminal device, the authority issuer device encrypting and transmitting the authorization key (REK) and the message confirmation key (MAK) with the master key (MK) (S500). An Effective Key Distribution Method for Digital Content Distribution. The method of claim 1, And in response to the request for joining the domain of the consumer terminal device, the authority issuer device encrypting the domain key (DK) and the message confirmation key (MAK) with the master key (MK) and transmitting the data (S600). Effective key distribution method for digital content distribution. In the key distribution method for digital content distribution, Transmitting, by the consumer terminal device, a hello message including the identifier of the terminal device to the authority issuer device (S100); Transmitting, by the authority issuer device, a hello message of the authority issuer device including the authority issuer identifier, a random number of the authority issuer device, and a session identifier in response to the hello message from the consumer terminal device (S200). ); Wherein the consumer terminal device transmits a message and a signature relating to a registration request to the authority issuer device, wherein the registration request of the consumer terminal device includes a registration including a session identifier, a random number of the consumer terminal device, request time information, and a signature; Transmitting a request message (S300); And When the authority issuer device is found to be valid in the registration process of the public terminal certificate of the consumer terminal device, the master key (MK) encrypted with the public key of the consumer terminal device, a session identifier, a web address (URL) of the authority issuer device, and the Transmitting a registration response message including a signature regarding the registration request message (S400); In step S500, in response to the license request of the consumer terminal device, the authority issuer device encrypting the authorization key REK and the message confirmation key MAK with the master key MK; And And encrypting, by the authority issuer device, a domain key (DK) and a message confirmation key (MAK) with a master key (MK) in response to the domain join request of the consumer terminal device (S600). An Effective Key Distribution Method for Digital Content Distribution.

Images