Abstract:
To protect device keys, an optical media recording device capable of performing AACS encryption on data does not have any device keys, and the optical media recording device performs AACS encryption by activating recording software stored in a memory the optical media recording device, and utilizing a pre-calculated media key stored in the memory of the optical media recording device to perform AACS encryption on the data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to optical media recording devices, and more particularly, to an optical media recording device capable of performing AACS encryption and related method for protecting device keys of the optical media recording device. 
     2. Description of the Prior Art 
     In the past, a variety of recordable media have been developed for use in recording and distributing commercial films, as well as home videos. Examples of such include video CDs (VCDs), VHS tapes, LaserDiscs, DVDs, and Blu-ray Discs (BDs). With the exception of VHS tapes and LaserDiscs, which may be considered analog media, modern media, such as DVDs and BDs, may be considered digital media. In other words, digitally encoded video data may be recorded to DVDs and BDs using an optical media recording device, and then read out, decoded, and played back using an optical media playback device. 
     One advantage of digital encoding over analog encoding is ability to encrypt the digitally encoded video data, which may prevent unauthorized copying and distribution of copyrighted media. A Content Scramble System (CSS) is employed as a Digital Rights Management (DRM) scheme for protecting commercially produced DVDs. CSS key sets are licensed for use in DVD burners and DVD players, and manufacturers desiring to make compliant devices are expected to follow all requirements of the CSS system. For example, all compliant disks incorporate keys written into a lead-in portion of the DVD, so a compliant DVD player must be able to read the keys in the lead-in portion to be able to play the rest of the DVD properly. However, as CSS employed a relatively weak encryption algorithm, with key lengths of around 25 bits, a brute-force algorithm was later developed which could crack the keys in the lead-in portion in under a minute. Thus, the CSS encryption system is easily compromised. 
     As new high-definition (HD) media types, such as the BD mentioned above, are developed, new encryption schemes are also employed. Blu-ray discs utilize an Advanced Access Content System (AACS) licensed by an AACS Licensing Administrator (AACS LA), a consortium including Disney, Microsoft, Matsushita, Sony, and others. The AACS encryption scheme uses Advanced Encryption Standard (AES) encryption and decryption. In AACS title keys utilized for encrypting and decrypting content on the BD are derived from a media key and a random number written on the BD. More particularly, the random number and the media key are used to encrypt/decrypt the title key for authority management. Device keys, assigned to each individual device compliant with the AACS encryption scheme, is utilized for determining the media key from a media key block (MKB) based on a subset difference tree scheme. As the device keys may be unique to each player or recorder, if the device keys are compromised, the AACS LA may update the MKB to revoke the player or recorder. Thus, all releases made after revocation of the player or recorder will become unusable by the player or recorder. 
     The AACS encryption scheme first appeared in Blu-ray devices in 2006, and since then, some decryption keys have already been determined from software BD players with weak protection and released on the Internet. Typically, a hacker will attempt to gain access to the device keys mentioned above by analyzing memory for presence of the device keys. If the device keys are obtained, and the player, whether software or hardware, is revoked, this may cause inconvenience to the software vendor or hardware manufacturer as they must update the device keys issued with their product each time the device keys are compromised. Likewise, if the player software uses the same device keys for each install, all users of the software must update their software version to be able to play the latest releases. Further, for the player software and recorder software, they would be installed in the same device as the player and a recorder. This further increases the risk of the device keys being exposed. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a method of performing AACS encryption in an optical media recording device comprises activating recording software having no device keys stored in the optical media recording device, and the recording software utilizing a pre-calculated media key stored in a memory of the optical media recording device to perform AACS encryption of data. 
     According to the present invention, a method for recording encrypted content in an optical storage medium comprises receiving content, receiving a pre-calculated media key, encrypting the content using a title key, encrypting the title key using the pre-calculated media key, and recording the encrypted content and the encrypted title key into the optical storage medium. 
     According to the present invention, an optical media recording device having no device keys for performing AACS encryption of data comprises a memory including a media key storage region storing a pre-calculated media key, and an AACS encryption program code region storing program code for performing AACS encryption based on the pre-calculated media key. The optical media recording device further comprises a processor for executing the program code to generate AACS-encrypted data. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an optical media recording system according to the present invention. 
         FIG. 2  is a flowchart of a process for performing AACS encryption according to the present invention. 
         FIG. 3  is a flowchart of a process of use of recording software according to the present invention. 
         FIG. 4  is a flowchart of a process for encrypting and recording content according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which is a diagram of an optical media recording system including an optical media recording device  10  and a server  12  according to the present invention. The optical media recording device  10  may be a standalone recorder or a computing device, such as a personal computer. The optical media recording device  10  comprises a non-volatile memory  100 , a processor  102  coupled to the memory  100 , an optical drive  104  coupled to the processor  102 , and a network interface  106  coupled to the processor  102 . The non-volatile memory  100  includes a media key storage region  110  storing a pre-calculated media key, and an AACS encryption program code region  112  storing program code for performing AACS encryption based on the pre-calculated media key. The processor  102  may be utilized for executing the program code stored in the AACS encryption program code region  112  to generate AACS-encrypted data. The optical drive  104  may be a Blu-ray Disc (BD) drive, an HD-DVD drive, or another drive compliant with the AACS licensing agreement. The network interface  106  may be a wired interface or a wireless interface, and may be utilized for establishing a data connection with the server  12 . The server  12  may comprise a media key processing module  120  for generating the pre-calculated media key, and a transceiver  122  coupled to the media key processing module  120  for establishing the data connection with the optical media recording device  10  and sending the pre-calculated media key to the optical media recording device  10 . In the present invention, the optical media recording device  10  may not comprise any device keys related to, or used in, performing AACS encryption. In other words, the optical media recording device  10  may comprise the pre-calculated media key, or pre-calculated media keys, without need for calculation of any media keys on the fly based on the device keys. 
     If the optical media recording device  10  is a personal computer, a burning software, or recording software, may be installed in the non-volatile memory  100  of the optical media recording device  10 . The burning software may provide a graphical user interface (GUI) that may be displayed in an operating system (OS) GUI of an OS stored in the non-volatile memory  100  of the optical media recording device  10 . The OS may comprise drivers stored in the non-volatile memory  100  for controlling the optical drive  104  to record data to an optical disc, which may be a blank optical disc or a pre-formatted optical disc. The burning software may access the drivers to control the optical drive  104 . Before recording the data to the optical disc, the burning software may encrypt the data using an AACS encryption method, such as an AES encryption scheme. 
     Please refer to  FIG. 2 , which is a flowchart of a process  20  for performing AACS encryption on the data according to the present invention. The process  20  may be compiled into the burning software, or may be compiled into an executable accessible by the burning software. The process  20  begins with activating the recording software having no device keys stored in the optical media recording device  10  (Step  200 ). The recording software may be activated through input from an input device, e.g. a mouse click or a key strike, directing the processor  102  to execute an executable of the recording software. Then, the recording software may utilize the pre-calculated media key stored in the non-volatile memory  100  of the optical media recording device  10  to perform AACS encryption of the data (Step  202 ). The pre-calculated media key stored in the non-volatile memory  100  of the optical media recording device  10  may be stored as a registry entry of a registry of the OS. In other words, the media key storage region of the non-volatile memory may be located in a registry storage region of the non-volatile memory, in which the registry of the OS is stored. The data that may be encrypted and recorded to the optical disc, such as the BD mentioned above, may be audiovisual data, such as a commercial film production. The data may optionally be encrypted and recorded to an ISO file and stored in the non-volatile memory  100 . 
     Please refer to  FIG. 3 , which is a flowchart of a process  30  for use of the recording software according to the present invention. The process  30  starts with a computing device calculating the pre-calculated media key based on the device keys not existing in the optical media recording device  10  and a media key block (Step  300 ). The pre-calculated media key may then be packaged with an installation file of the recording software (Step  302 ). The installation file may then be utilized to install the recording software on the optical media recording device  10  (Step  304 ). As mentioned above, at this point, the pre-calculated media key may be stored in the non-volatile memory, either in a file, or as a registry entry. If, at some point, an update is needed for the pre-calculated media key, e.g. if the pre-calculated media key is revoked or becomes obsolete, the pre-calculated media key may be updated, or replaced, with an updated pre-calculated media key from the server (Step  306 ). The server may calculate the updated pre-calculated media key, and send the updated pre-calculated media key to the optical media recording device through the data connection. The optical media recording device stores the updated pre-calculated media key in a corresponding memory space of the recording software. More particularly, the updated pre-calculated media key may be stored in a storage device, such as a hard disk drive, or a non-volatile memory, for example. Then, the recording software may utilize the pre-calculated media key, or the updated pre-calculated media key, to perform AACS encryption of the data (Step  308 ), and the data may be recorded to the BD (Step  310 ). 
     Please refer to  FIG. 4 , which is a flowchart of a process  40  for encrypting and recording content according to the present invention. The process  40  starts with receiving the content to be recorded (Step  400 ), e.g. audio, video, or audiovisual content. Then, a pre-calculated media key is received (Step  402 ). A title key is utilized for encrypting the content (Step  404 ). The title key is then encrypted using the pre-calculated media key (Step  406 ), and the encrypted content and the encrypted title key are recorded into the optical storage media (Step  406 ). The pre-calculated media key may be received from a storage device, such as a non-volatile memory, where the pre-calculated media key has been stored, or from a server via networking. The server may calculate the pre-calculated media key based on a device key of the server and a media key block. And, the pre-calculated media key may be packaged with an installation file of a recording software. 
     By only storing the pre-calculated media key in the optical media recording device  10 , the present invention prevents discovery and distribution of the device keys licensed to the software company responsible for developing the recording software. Thus, revocation of the device keys licensed to the software company and end users of the recording software may also be prevented. New media keys may be obtained from the server run by the software company, such that the device keys may be omitted from the recording software without hindering usage of the recording software by the end user. The present invention thus increases security by reducing the risk of exposure of the device keys in the player/recorder, while maintaining high quality of service to the end user. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.