Patent Publication Number: US-2012042379-A1

Title: System and method for detecting genuine copies of pre-recorded digital media

Description:
TECHNICAL FIELD 
     The present invention relates generally to pre-recorded digital media, and more particularly to a system for offering services to users that possess a genuine pre-recorded medium. 
     BACKGROUND 
     This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Given the wide-spread copying of digital content—for example films, music and computer programs—there is an interest for the provider of the digital content to detect whether or not a user possesses a genuine copy of a digital medium storing such digital content. Such a digital medium may for instance be a DVD, a CD-ROM or a Blu-ray™ disc. 
     The content provider may then deliver further services and content than those originally provided with the digital medium. Examples of these comprise providing bonus tracks and providing enhanced versions that were not ready when the digital medium was manufactured. This may be done for free, but it may also be at a cost that is lower than it would be for customers who do not possess such a medium. 
     A typical test that is sometimes implemented verifies whether or not the digital medium is recordable or not. If it is recordable, then it cannot be a pre-recorded medium. Nevertheless, this is insufficient to prove the ownership of a given title. 
     The game industry uses systems, for instance SecuROM provided by Sony, that measure “physical” characteristics of a disc. Unfortunately, such systems are often defeated by emulation software such as Alcohool120% and Daemon Tools. 
     WO 01/90860 proposes another method for authenticating that a user possesses a specified pre-recorded digital medium. Such ownership allows the user to download further content or information. The user places the medium in a driver, downloads an application from the Internet, and executes that application. The application then accesses the medium via its driver and generates an identifier for the medium. The identifier is then sent to a script on the Internet that confirms or not that the medium is the selected medium. In this case, further download is allowed. 
     The application generates a unique identifier for the medium by combining at least two attributes in an algorithm. Such attributes may be “the number of tracks, the length of each track, and the total track length”. The unique identifier should provide a reasonable indication that the medium is the correct medium. 
     The unique identified is then passed over the Internet to a verification script that compares the unique identifier thus received with a stored identifier. In case of a match, the script instructs the application to start the download of the additional features. 
     This solution is unfortunately not very secure and it is believed that hackers may easily overcome any security provided by it. 
     It can therefore be appreciated that there is a need for a solution that overcomes these problems and increases the security. The present invention provides such a solution. 
     SUMMARY OF INVENTION 
     In a first aspect, the invention is directed to a system for authentication of a pre-recorded digital medium. The system comprises an authentication server adapted to authenticate the pre-recorded digital medium, a media reader comprising a media driver adapted to interact with the pre-recorded digital medium, and an authentication application adapted to be executed on the media reader and to interact with the media driver to obtain information about the pre-recorded digital medium. The authentication server is adapted to store, for the pre-recorded digital medium, a set of challenges and corresponding expected responses; send a plurality of challenges, selected from the set of challenges, to the authentication application, each challenge requesting information about a characteristic of the pre-recorded digital medium, wherein correct responses to at least a subset of the plurality of challenges allow authentication of the pre-recorded digital medium; receive responses corresponding to the plurality of challenges from the authentication application; authenticate the pre-recorded digital medium if the responses to at least the subset of the plurality of challenges are correct; and update a set of challenges and corresponding responses for a pre-recorded digital medium. 
     In a first preferred embodiment, the authentication server is adapted to accept a number of false responses. It is advantageous that there are challenges to which a correct answer is mandatory. 
     In a second preferred embodiment, the authentication server is adapted to allow the media reader to download content upon successful authentication of the pre-recorded digital medium. 
     In a third preferred embodiment, the authentication server is further adapted to receive, from the authentication application, a request to authenticate the pre-recorded digital medium. 
     In a fourth preferred embodiment, the authentication server is further adapted to send the plurality of challenges in a determined order. It is advantageous that the determined order of the plurality of challenges is random. 
     In a fifth preferred embodiment, the plurality of challenges is a subset of the stored set of challenges. 
     In a second aspect, the invention is directed to a method of authenticating a pre-recorded digital medium in a media reader. An authentication server selects a plurality of challenges from a stored set of challenges, wherein the plurality of challenges is a subset of the stored set of challenges; sends the plurality of challenges to the authentication application, each challenge requesting information about a characteristic of the pre-recorded digital medium, wherein correct responses to at least a subset of the plurality of challenges allow authentication of the pre-recorded digital medium; receives responses corresponding to the plurality of challenges from the authentication application; and authenticates the pre-recorded digital medium if the responses to at least the subset of the plurality of challenges are correct. 
     In a first preferred embodiment, the answer to a first challenge is received before the next challenge is sent. 
     In a second preferred embodiment, each received answer is verified, and it is verified if an incorrect answer corresponded to a challenge to which a correct answer is mandatory and, if so, the pre-recorded digital medium is not authenticated. It is advantageous that an error counter is incremented for each incorrect answer and that the pre-recorded digital medium is authenticated if the error counter has not attained a threshold value. 
     In a third preferred embodiment, an authenticated pre-recorded digital medium is deemed to be a genuine pre-recorded digital medium. 
     In a third aspect, the invention is directed to a method of authenticating a pre-recorded digital medium in a media reader. An authentication application executed on the media reader obtains a plurality of challenges, each challenge requesting information about a characteristic of the pre-recorded digital medium, wherein correct responses to at least a subset of the plurality of challenges allow authentication of the pre-recorded digital medium; obtains an expected answer to each obtained challenge; requests information regarding the characteristic of the pre-recorded digital medium from a media driver of the media reader; receives an answer to each challenge from the media driver; and authenticates the pre-recorded digital medium if the responses to at least the subset of the plurality of challenges are correct. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Preferred features of the present invention will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which 
         FIG. 1  illustrates schematically the system according to a preferred embodiment of the present invention; 
         FIG. 2  illustrates a flowchart for an authentication method according to a preferred embodiment of the present invention; and 
         FIG. 3  illustrates a title record according to a preferred embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  illustrates schematically the system according to a preferred embodiment of the present invention. 
     The system  100  comprises a media reader  110  adapted to read a digital medium  140 . The media reader  110  comprises a media driver  114  adapted to read the digital medium  140  and an authentication application  112  adapted to communicate, preferably over the Internet, with an authentication server  120  and to give instructions to the media driver  114 . The system  100  also comprises the authentication server  120 , which is adapted to interact with an authentication database  130 , which advantageously is a SQL database such as mySQL. 
     When a user wants to have the medium  140  authenticated, it instructs the media reader  110  to initiate the authentication. The media reader  110  then uses the media driver  114  to read the title or other preferably unique identifier of the digital medium  140 . It is advantageous that the media driver  114  also reads an identity of the authentication server  120  to use for authentication of the digital medium  140 . The authentication application  112  then informs the authentication server  120  that it wants digital medium “Title” authenticated. 
     The skilled person will appreciate that other ways to initiate authentication are possible, such as having the user connect to a download site provided by the content provider and then having this site contact the authentication server  120  when the user desires to download specific content. In this case, the authentication server  120  may send instructions to the media reader  110  in order to ensure that the digital medium  140  is inserted therein. Such instructions may comprise a message to the user. 
     The authentication server  120  retrieves, preferably at random, from the authentication database  130  a number of challenges that it sends, either singly or grouped, to the authentication application  112 , possibly encrypted. Using random challenges can overcome the use by hackers of response databases to find the correct response. The authentication database  130  stores, for each digital medium, a title record  132  comprising a plurality of challenges and the corresponding responses. 
     Each challenge preferably has two characteristics:
         Whether the challenge is unique or multiple. A unique challenge has a unique value to be checked, whereas a multiple challenge can check multiple values and, possibly, return multiple values.   Whether or not the challenge is absolute. An absolute challenge requires an exact answer, while a non-absolute challenge may tolerate errors.       

     For each challenge, the title record  132  preferably comprises:
         A challenge identifier that is unique for this type of challenge; the same type of challenge uses the same challenge identifier throughout the authentication database  130 . It will however be appreciated that, the answers to the challenges may be different for different titles.   A challenge record that contains all possible responses. In the case of a unique challenge, there is only one value. In the case of a multiple challenge there are ordered values.       

     Upon reception of a challenge, the authentication application  112  sends a set of corresponding commands to the media driver  114 . The set of commands is advantageously given by the challenge identifier. The authentication application  112  then receives the response (or responses) from the media driver  114  and sends this to the authentication application  120  that verifies whether or not the response matches the expected answer. 
       FIG. 2  illustrates a flowchart for an authentication method according to a preferred embodiment of the present invention. 
     The authentication server  120  selects  202  in the authentication database  130  the title record  132  corresponding to the title to verify. The authentication server  120  then selects  204  a set of challenges for the title and resets  206  an error counter. The first selected challenge is then sent  208  to the authentication application  112 . 
     If the challenge is unique, then the authentication application  112  sends the corresponding commands to the media driver  114  and receives a unique response that it returns to the authentication server  120 . 
     However, if the challenge is multiple, then the authentication server  120  selects randomly among the authentication values before sending  208  the challenge to the authentication application  112 . The authentication application  112  sends the corresponding commands to the media driver  114  and receives a set of responses that it returns to the authentication server  120 . 
     Upon reception  210  of the response, the authentication server  120  checks  212  if the response is correct. If this is the case, then it is checked  214  if there are more challenges to send; if so, a new challenge is sent  208  as described hereinbefore. 
     However, if the answer is not correct, then it is verified  218  if the challenge is absolute, i.e. if errors are tolerated or not. If the challenge is not absolute, then the error counter is incremented  220  and the method then continues with step  214 , where it is checked if there are remaining challenges to be sent. On the other hand, if the challenge is absolute (and the answer was incorrect) then it is deduced  224  that the medium is not genuine, which means that any download or other services are not provided. 
     When it is determined in step  214  that there are no more challenges to be sent, then the error counter is compared  216  to a limit value. If the comparison shows that there are not too many errors, then it is deemed  222  that the medium is genuine and that the further content and/or services may be obtained. However, in the opposite case, the method goes to step  224  described hereinbefore. 
     In a variant embodiment, it is the authorisation application  112  that authenticates the digital medium  140 . In this case, the challenges may be provided in the authorisation application  112  itself, but it is also possible for it to request challenges from the authentication server  120  and receive the necessary challenges and responses afterwards, not necessarily at the same time. When the authentication application  112  has authenticated the digital medium  140 , it allows download of further content. 
     An advantage of the variant embodiment is that the load on the application server  120  can be lessened. 
       FIG. 3  illustrates a title record according to a preferred embodiment of the present invention. The title record  132  comprises:
         A challenge identifier  310 .   A challenge record  320  that depends on the challenge. It may contain information necessary to find the proper response, such as for example a physical address on the digital medium to read from.   An absolute challenge flag  330 . This flag is ‘true’ if the challenge is absolute and ‘false’ otherwise.   A challenge tests number  340 , whose value is the number of potential values that can be tested. For a unique challenge, the value is one; for a multiple challenge, it corresponds to the number of possible tests.   One or more expected answers  350 .       

     A number of examples of challenges that will be further described hereinafter are:
         Disc Type,   Disc recorded length, and   Track length.       

     The Disc Type challenge verifies information in the so-called lead-in area of a digital medium, such as a DVD that will be used hereinafter as a non-limitative example. The lead-in area comprises physical information, such as the disc type, the start and end positions of tracks, and so on. 
     A first challenge using this information is to check the disc type to see if the DVD is a recordable DVD or a DVD-ROM. Parameters are:
         Challenge identifier  310 =TEST_DISC_TYPE   Challenge record  320 =void   Absolute challenge flag  330 =TRUE   Challenge tests number  340 =1   Answer  350 =DVD_ROM       

     It will be appreciated that this challenge is absolute and that a single answer is expected: if the answer is ‘DVD_ROM’, then the medium passed this test, but the medium will be deemed not to be genuine in any other case. 
     A second challenge checks the DVD track length. Parameters are:
         Challenge identifier  310 =TEST_TOTAL_TRACK_LENGTH   Challenge record  320 =void   Absolute challenge flag  330 =FALSE   Challenge tests number  340 =1   Answer  350 =‘first possible length’, ‘second possible length’       

     As can be seen, this challenge is not absolute, which means that no immediate decision will be taken in case the answer is incorrect. Only one answer is expected, but it may take any one of two different values. 
     A third challenge checks the track length of a set of randomly chosen tracks of the disc. Parameters are:
         Challenge identifier  310 =TEST_TRACK_LENGTH   Challenge record  320 =a set of ordered Boolean flags; each true represents a track to check.   Absolute challenge flag  330 =FALSE   Challenge tests number  340 =The maximum number of tracks.   Answer  350 =the expected track lengths       

     The authentication server  120  advantageously selects a plurality of tracks to check. It sends a challenge with the list to the authentication application  112 , which commands the media driver  114  (in this case a DVD driver) to return, for each indicated track, the length of the track. The authentication application  112  then returns these lengths (or a sum thereof). 
     The challenge may be considered successful if there is at most one wrong answer, but it is naturally also possible to require a different number of correct answers, in particular to require all of them to be correct. 
     An exemplary authentication process for a given digital medium  140 —in this case a DVD—comprises the three challenges described hereinbefore, sent sequentially by the authentication server  120  to the authentication application  112 . The limit for the error counter may be set to 2, i.e. if the error counter is greater than 1, then the DVD is considered as non-genuine. Examples of possible results of the authentication process include:
         If the authentication server  120  receives correct responses for the ‘disc type’ challenge and the ‘total length’ challenge, and an incorrect response for the ‘track length’ challenge, then the DVD is considered genuine. There is only one error and that for a challenge that is not absolute.   If authentication server  120  receives good responses for the ‘total length’ challenge, the ‘track length’ challenge and an incorrect response for the ‘disc type’ challenge, then the DVD is considered not genuine. While there is a single error—i.e. the error limit is not attained—the error occurred for an absolute challenge.   If authentication server  120  receives a good response for the ‘disc type’ challenge, and incorrect responses for the ‘total length’ challenge and the ‘track length’ challenge, then the DVD is considered not genuine. While no absolute channel failed, the error counter attained the limit value.       

     It should be noted that it is possible for discs of the same title to have different instances, for instance if they are manufactured from different masters. In this case, the title may have a plurality of title records. The authentication server then preferably sequentially uses the title records until it receives a satisfactory answer or until there are no more title records. 
     It is preferred to protect the communication between the authentication server  120  and the authentication application  112 . Examples of protections that may be applied comprise:
         Mutual authentication between the authentication application  112  and the authentication server  120 . Each of these advantageously has a certificate with a unique 1024-bit RSA key pair that may be used for prior art RSA authentication. The authentication server  120  checks that the certificate of the authentication application  112  is valid and that it is not entered in a revocation list.   Use of a common session key to protect the communication. For instance, AES with a 128-bit session key may be used.   The use of nonces to mask challenges and/or to ensure that an answer may not be reused. Nonces can be for example used by the authentication application  112  to send dummy commands to the media driver  114  or by the authentication server  120  to set the order of the different challenges.       

     The present authentication system can allow verification that a user possesses a legitimate instance of a given title. The use of a remote database of challenges and the fact that the verification occurs in the authentication server  120  and not on media reader can offer a greater resistance to attacks, as anti-copy solutions operating on the user&#39;s media reader are prone to reverse engineering attacks. 
     The storage of Challenge records  320  in an authentication database  130  allows updating of these challenges if they are defeated for one title. Existing challenges in the database may then be replaced or extended with new ones. 
     It will be appreciated that the present invention can allow a more flexible way of authenticating a digital support than the ones found in the prior art. In particular, as the challenges can be changed easily and their order modified, it can be possible to overcome replay attacks that some prior art methods may have been subject to. 
     Each feature disclosed in the description and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.