FIELD OF THE INVENTION

The invention relates to a device for decrypting an encrypted content received through a network. The invention further relates to a system for providing an encrypted content through a network and decrypting the encrypted content, which system includes a server for providing the encrypted content, said device for decrypting the encrypted content and a storage medium (e.g., a record carrier, or a recording medium) for providing a decryption key, and its corresponding method and software program.

BACKGROUND OF THE INVENTION

Nowadays content protection becomes one of the major concerns of the content providers when publishing content through e.g. an optical disc or the internet. The Sapphire system provides fine-grained protection mechanism and is incorporated by CD2 standard. In Sapphire system, contents (i.e. A/V streams, files, etc.) on disc are encrypted and the corresponding decryption key is stored as Asset Key (or Asset ID) in Sapphire Key Locker.

An European Patent Application 03102257. 7 describes a disc player, a record carrier and method for reading and protecting network data, which is related to data stored in the record carrier, by using the above-mentioned Sapphire system protection mechanism.

Figure 1 is a schematic block diagram illustrating a system including a disc player, disc and server of the patent application 03102257. 7. The system of figure 1 comprises a disc player 11, a disc 12 and a network unit 13 (e.g., a server) for supplying network data related to carrier data 122 stored on the disc 12. The network unit 13 is connected with the disc player 11 through the Internet. Besides the disc data 122, a key locker 121 is stored on the disc 12, as shown in Figure 2 in details. Figure 2 shows a table illustrating the contents of the key locker. In the Sapphire system, the key locker 121 is usually a table containing four column: an application ID used as an identification for an application run by the disc player and to restrict the access of a subset of the key locker; an asset ID used as an identification of (a group of) files that are encrypted in the same key and have the same usage rights; an asset key used as a key for decryption which is required to be kept secret from the public; and a rightstring, which has an undefined format and a variable length. In the system shown in Figure 1, the rightstring includes a network identifier, like URL of the network unit 13, and the asset key used as a decryption key for decrypting the network data.

The disc player 11 includes two parts: a drive 111 for reading data from the record carrier 12, and an application unit 112. The application unit 112 is comprised of a check element, an access element and a decrypt element. During this European Patent application, the access element of the application unit 112 first send a request for a specific network data from the network unit 13. Then, the drive 111 retrieves a rightstring from the record carrier according to its application ID and sends the retrieved rightstrings to the application unit 112. The check element of the application unit 112 checks whether the URL stored in the rightstring matches with that of the specific network unit 13 providing the network data. If so, the decrypt element of the application 112 decrypts the encrypted network data provided by the network unit 13 with the decryption key stored in the rightstring. If not, the drive 111 will retrieve a rightstring again and the whole process as described above will be performed once again.

It can be seen from the prior art that the application unit uses the decryption key, which is identical with the asset key, to decrypt the network content. Usually, the application unit is a piece of hardware for executing a (software) application, which is similar with the case of an operating system (OS) or software running on a computer. In this case, the application running in the application unit can be easily attacked/hacked, just as what hackers do to software running on a computer. Therefore, it is relatively easy to access the decryption key, which is used by the application unit to decrypt the network content and should be kept secret from the public and protected against key publishing.

SUMMERY OF THE INVENTION It is therefore an object of the invention to provide a new system, device and method for providing and decrypting an encrypted network content, which is effective for reducing the possibility of secret keys being attacked.

In accordance with a first aspect of the present invention, this object is achieved by providing a device for decrypting an encrypted content received through a network, comprising: an application unit for receiving the encrypted content and an encrypted first key through the network, in which the first key is associated with encryption of the content, and a dedicated second key is associated with encryption of the first key; and a key management unit for acquiring the dedicated second key from a storage medium, and decrypting the encrypted first key by using the dedicated second key to provide the first key for the application unit to decrypt the encrypted content.

In accordance with a second aspect of the present invention, there is provided a system for providing and decrypting an encrypted content, the system comprising a server for providing the encrypted content, a device for decrypting the encrypted content and a storage medium, wherein, the server is further arranged to comprise: a receiver for • receiving a request for a content download from the device for decrypting; a generator for generating a first key in response to the request; an encryptor for encrypting the content by using the first key to provide the encrypted content and encrypting the first key by using a dedicated second key to provide an encrypted first key; and a transmitter for transmitting the encrypted content and the encrypted first key; and the device for decrypting the encrypted content is further arranged to comprise: an application unit for receiving the encrypted content and an encrypted first key through the network, in which the first key is associated with encryption of the content, and a dedicated second key is associated with encryption of the first key; and a key management unit for acquiring the dedicated second key from the storage medium, and decrypting the encrypted first key by using the dedicated second key to provide the first key for the application unit to decrypt the encrypted content.

In accordance with a third aspect of the present invention, there is provided a method of decrypting an encrypted content received through a network, comprising steps of: receiving the encrypted content and an encrypted first key through the network, in which the first key is associated with encryption of the content, and a dedicated second key is associated with encryption of the first key; acquiring the dedicated second key from a storage medium; and decrypting the encrypted first key by using the dedicated second key to provide the first key for the application unit to decrypt the encrypted content.

In accordance with a fourth aspect of the present invention, there is provided a computer program for decrypting an encrypted content received through a network, comprising: a first software means for receiving the encrypted content and an encrypted first key through the network, in which the first key is associated with encryption of the content, and a dedicated second key is associated with encryption of the first key; a second software means for acquiring the dedicated second key from a storage medium, and decrypting the encrypted first key by using the dedicated second key to provide the first key for the application unit to decrypt the encrypted content.

The applicant notices that the key management unit (e.g., a drive) is basically a piece of component used by the device, which has its own conformance rules (e.g., rules complying with the Sapphire system) and has an interface between itself the and the application unit via a secure authentication channel (SAC) pre-defined by the Sapphire system. Therefore, the key management unit as a single component is very hard to be attacked, like what happens to the application unit.

According to the system, device and method for decryption of the present invention, the second keys (i.e., the asset keys) are kept secret from the application unit, the application unit uses the first key which is randomly generated in response to the request for content download, and the key management unit, which is relatively safer and more stable than the application unit, is the only unit in the device which knows the asset keys. In view of this, the device and method of the present invention is more effective for preventing the content protection keys (e.g., asset keys) from being attacked.

BRIEF DESCRYPTION OF DRAWINGS Embodiments of the invention will now be discussed, by way of example, with reference to the accompanying drawings, in which like reference numbers refer to like parts, and in which:

Fig. 1 is a schematic block diagram illustrating the structure of a system of providing and decrypting network data according to prior art, which system includes a disc player, a server and a record carrier;

Fig. 2 shows a table of a key locker stored on the record carrier of Fig. 1;

Fig. 3 is a schematic block diagram illustrating the structure of a system of providing and decrypting network data according to a first embodiment of the present invention, which system includes a disc player, a server and a record carrier; and

Fig. 4 is a schematic block diagram illustrating the structure of a system of providing and decrypting network data according to a second embodiment of the present invention, which system includes a disc player, a server and a record carrier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In Figure 3 the structure of a system for providing and decrypting network data according to the first embodiment of the present invention is shown. The system includes a server 31 for providing an encrypted content, a disc player 32 for decrypting the encrypted content and a disc 33 for storing a key locker 121 as shown in Fig. 2 as well as disc data 122, in which the disc player 32 connects with the server 31 through a network, and the server shares the information about the key locker stored on the disc. The server further comprises a receiver (not shown in the figure) for receiving a request for downloading network content related to the disc data from the disc player, in which the request is preferably includes an application ID (e.g., application ID 2 in the key locker of Fig. 2) in the case that there are a variety of disc applications stored on the disc (e.g. multiple Java applications packages); a generator 311 for randomly generating a pass phase in response to the request; an encryptor 312 for encrypting a network content as requested, which is stored in a content pool 313, by use of the pass phase, and then encrypting the pass phase by use of an asset key selected from the key locker shared with the disc, for instance, the asset key ASDF 1234 in the key locker as shown in Fig. 2 (hereinafter, the asset key is called dedicated asset key, in order to distinguish it from other asset keys stored in the 5 key locker. The dedicated asset key can also be selected to encrypt other randomly generated pass phases); and a transmitter for sending the encrypted content, encrypted pass phase and the asset ID associated with the dedicated asset key, for example, the asset ID 80 in Figure 2.

.0 The disc player 32 comprises an application unit 321 for receiving the encrypted content, encrypted pass phase, and the associated asset ID from the server 31 and decrypting the encrypted content with the pass phase; a drive 322 for retrieving the dedicated asset key from the key locker 121 stored in the disc 33 according to the associated asset ID and decrypting the encrypted pass phase with the dedicated asset key to provide the pass phase [ 5 for the application unit.

The application unit 322 further includes an access element for receiving the encrypted content, encrypted pass phase and the asset ID from the server, sending the encrypted pass phase to the drive and receiving the decrypted pass phase from the drive; and an decrypt 20 element for decrypting the encrypted content by use of the decrypted pass phase. The drive 322 further includes an access element for retrieving the dedicated asset key from the key locker stored on the disc according to the asset ID and passing the decrypted pass phase to the application unit via Secure Authentication Channel (SAC), and a decrypted element for decrypting the encrypted pass phase received from the application unit with the retrieved 5 dedicated asset key.

The process of providing and decrypting network data by the system of the first embodiment of the present invention is described below:

0 First, the access element of the application unit sends a request for content download to the server. Then, the server randomly generates a pass phase in response to the request. Here, the request for content download is optional for the generation procedure of the random pass phase, and the server can generate the pass phase on the time basis. Then, the server encrypts the network content as required with the pass phase, and encrypts the pass phase with the dedicated asset key.

The data, including the asset ID, the encrypted pass phase and encrypted content, is sent to 5 the application unit, in which the asset ID and the encrypted pass phase are sent to the drive. The drive receives the encrypted pass phase and asset ID from the application unit and then retrieves the asset key according to the asset ID from the key locker on the disc. Then, the drive decrypts the pass phase with the retrieved asset key and send the decrypted pass phase to the application unit via SAC. Finally, the application unit decrypts the 0 encrypted content by use of the decrypted pass phase sent by the drive.

It can be seen from the above description that in the whole process of decrypting the content received through a network, the application unit does not exactly directly hold and handle the asset key. Instead, the application unit uses the randomly generated pass phase 5 to decrypt the network content. Therefore, the possibility for the asset keys to be retrieved from the application unit is substantially zero. Moreover, since the described embodiment of the present invention does not use the rightstring field in the key locker stored on the disc, the column of righstring is left blank. Whether to use the rightstring field depends on applications. >0 The structure of a system for providing and decrypting network data according to the second embodiments of the present invention is shown in figure 4. The differences between the systems of figures 3 and 4 are that the generator 311 of the application unit 421 of figure 4 further generates a test sequence (i.e., a bit sequence) complying with a .5 pre-defined data structure, such as length of sequence, definitions of certain bits, and the application unit 421 further comprises a retrieve element for retrieving the pass phase for the decrypt element to decrypt the network content.

The process of providing and decrypting network date by the system of Figure 4 according 0 to the second embodiment of the present invention is described below.

In Figure 4, the access element of the application unit 421 sends a request for content download to the server 31. Then, the generator 311 of the server randomly generator a pass phase and the test sequence in response to the request. As mentioned above, the request is optional for generation of the pass phase, and the generator can generator the data on time basis. The encrypt element 312 of the server encrypts the content stored in the content pool 313 with the generated pass phase and then encrypts the pass phase and the test sequence with a dedicated asset key, which is selected from the key locker information shared with the disc 33. The transmitter of the server (not shown in Figure 4) sends the encrypted content, encrypted pass phase and test sequence to the disc player 32.

The access element of the application unit 421 of the disc player transfers the encrypted pass phase and test sequence to the drive 322. The access element of the drive 322 reads all of the asset keys in entries associated with its application ID from the key locker 121 stored on the disc 33, and the read asset keys include the dedicated asset key which is selected by the server to encrypt the pass phase and test sequence. Then, the decrypt element of the drive decrypts the pass phase and the test sequence with each of the read asset keys to provide to the application unit 421 pairs of decrypted pass phase and test sequence with respect to each asset key. After the access element of the application unit 421 receives the pairs from the drive, the retrieve element of the application unit 421 retrieves a pair of decrypted pass phase and test sequence, in which the decrypted test sequence complies with the pre-defined data structure. Then, the decrypt element of the application unit decrypts the encrypted content received from the server by use of the retrieved pass phase.

To summarize, the system, device and method for providing and decrypting network data has been disclosed. It can be understood that a skilled person may make any modifications, additions and insertions to the present invention which fall into the protective scope as claimed in the appended claims.

For instance, in accordance with the second embodiment, the encrypt element of the server 31 encrypts the test sequence with the dedicated asset key. However, the skilled person can reckon that the encrypt element can also encrypt the test sequence with the pass phase. In this case, the decrypt element of the drive 322 only decrypts the encrypted pass phase with each of the read asset keys and provides pluralities of decrypted pass phases to the access element of the application unit 421. Then the decrypt element of the application unit decrypts the encrypted test sequence with each of the decrypted pass phases and provides pairs of decrypted test sequence and pass phase to the retrieve element to retrieve a pair of decrypted test sequence and pass phase, which test sequence complies with the pre-defined data structure. Then, the decrypt element of the application unit decrypts the encrypted content downloaded from the server with the retrieved pass phase.

Moreover, in all the embodiments of the present invention, the network content is encrypted by the pass phase, and the pass phase is encrypted by the dedicated asset key. It can be understood by the skilled person that any alternatives could be made concerning the encryption of the network content and pass phase. For example, the network content is not totally encrypted by the content protection key (e.g., the dedicated asset key), just partially encrypted, e.g. only file headers/important parameters/or a specific portion are encrypted, while the pass phase consists of not only the encrypted content protection key, but also some data that indicates which portion of the content are encrypted.

Further, in the embodiments, the device for decrypting the network data is a disc player. However, any skilled persons can expected that other devices, like a computer with a drive for reading data stored on a storage medium. The function of the drive of the disc player can also be fulfilled with a key management unit in a compact flash card (e.g. smartcard or a USB memory stick), or with a chip affixed to a record carrier (the so-called Chip-in-Disc technology).