Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/06—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols the encryption apparatus using shift registers or memories for block-wise or stream coding, e.g. DES systems or RC4; Hash functions; Pseudorandom sequence generators
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/002—Countermeasures against attacks on cryptographic mechanisms
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/06—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols the encryption apparatus using shift registers or memories for block-wise or stream coding, e.g. DES systems or RC4; Hash functions; Pseudorandom sequence generators
  • H04L9/0618—Block ciphers, i.e. encrypting groups of characters of a plain text message using fixed encryption transformation
  • H04L9/0625—Block ciphers, i.e. encrypting groups of characters of a plain text message using fixed encryption transformation with splitting of the data block into left and right halves, e.g. Feistel based algorithms, DES, FEAL, IDEA or KASUMI
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L2209/00—Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
  • H04L2209/16—Obfuscation or hiding, e.g. involving white box

Definitions

• the invention relates to a method of providing a cascaded signal processing function to an execution device in a secure and/or personalized way.
• the invention also relates to a system for providing a cascaded signal processing function to an execution device in a secure and/or personalized way.
• the invention further relates to an execution device for executing a cascaded signal processing function provided in a secure and/or personalized way.
• the Internet provides users with convenient and ubiquitous access to digital content. Because of the potential of the Internet as a powerful distribution channel, many CE products strive to interoperate with the PC platform — the predominant portal to the Internet.
• the use of the Internet as a distribution medium for copyrighted content creates the compelling challenge to secure the interests of the content provider. In particular it is required to warrant the copyrights and business models of the content providers.
• Control of the playback software is one way to enforce the interests of the content owner including the terms and conditions under which the content may be used.
• the user In particular for the PC platform, the user must be assumed to have complete control to the hardware and software that provides access to the content and unlimited amount of time and resources to attack and bypass any content protection mechanisms.
• Those content formats may include AVI, DV, Motion JPEG, MPEG-1, MPEG-2, MPEG-4, WMV, Audio CD, MP3, WMA, WAV, AIFF/AIFC, AU, etc.
• the player and plug-in structure is illustrated in Fig. 1, where a media player 100 includes a core player 100 and several format- specific plug-ins (shown are plug-ins 120, 122 and 124).
• the core player 100 may, for example, provide the user interface for controlling the player.
• Each plug-in includes a respective decoder. It may send the decoded content directly to rendering HW/SW, such as a sound-card, or pass it on to the core player 100 for further processing.
• a secure plug-in is used that not only decodes the content in the specific format but also decrypts the content. This is illustrated in Fig.2, where the encrypted content is first fed through a decryptor 230 and next the decrypted content is fed through the format-specific decoder 220.
• the decryptor 230 may receive a decryption key/license from a license database 210.
• the largest vulnerability of digital rights management relying on encryption is the key distribution and handling. For playback, a software player has to retrieve a decryption key from the license database, it then has to store this decryption key somewhere in memory for the decryption of the encrypted content.
• the algorithm can be described as a function cascade f N °---°f x (x) , where function /, represents the functionality of round i .
• Most block algorithms are Feistel networks. In such networks, the input data block JC of even length n is n divided in two halves of length — , usually referred to as L and R. So, the input x fed to the
• a method of providing a digital signal processing function / to an executing device in an obfuscated form includes: selecting a set of 2N invertible permutations p, , l ⁇ i ⁇ 2N ; calculating a set of N functions g , where g, is functionally equivalent to calculating a set of N - 1 functions h t , where h, is functionally equivalent to
• P2ll °P2,-2 > f ⁇ 2 ⁇ i ⁇ N ' > equipping the executing device with an execution device function cascade that includes y N °h N ° y N _ x ° h N _ x °...°y , where y , ... , N are function parameters (for example, ED X ( > intersect..., y N ) ⁇ y N ° h N o y N _ ⁇ h N _ ⁇ ... y ⁇ ), providing the functions g x , ...
• the constituent functions f are provided in an encapsulated form as g, , where g, is functionally equivalent to ⁇ °f, ° p 2l - ⁇ , for 1 ⁇ ? ⁇ N .
• the functions p, used for the encapsulation are also hidden by being supplied in the form of h, which is a multiplied version of ⁇ )_ x ° p 2l _ 2 , for 2 ⁇ i ⁇ N .
• the execution function device cascade may form the core functionality of a media player, where the set g x , ... , g N enables the player to execute a function cascade containing /j up to and including f N .
• the dependent claims 2 and 3 show two respective alternative embodiments for protecting the (functional) beginning of the function cascade.
• the execution device function cascade starts with p x l , for example
• security is increased by extending the function cascade with a starting function / 0 that aids in hiding p x ⁇ x .
• f 0 is a global secret.
• the dependent claims 4 and 5 show two respective alternative embodiments for protecting the (functionally) ending of the function cascade in a manner analogous to claims 2 and 3
• the chosen sequence of permutations p is unique for the device.
• the function cascade is supplied to the execution device not only in an obfuscated form but also in a personalized form.
• the function cascade represents a Feistel cipher with embedded decryption key, cryptanalytic or brute force attacks may result in obtaining the black box functionality of g x , ... , g N .
• the execution device function cascade is embedded in a program, for example in the form of a media player or a plug-in for a media player.
• the execution device is thus provided with secure, personalized software.
• the functions g x ,...,g N form a plug-in for the program. If the program itself is a plug-in, then the functions g x , ... , g N are in effect a plug-in for the plug-in.
• g N may be embedded in the same program as the execution device function cascade.
• a computer program product operative to cause a processor in an execution device to execute a digital signal processing function / including a function cascade including a plurality of signal processing functions f, , where
• g is functionally equivalent to p 2 ⁇ ) ° f ° p 2i _ x , for 1 ⁇ i ⁇ N ; h j is functionally equivalent to p 2 _ x °p 2lêt 2 for l ⁇ i ⁇ N; and p, is an invertible permutation, for l ⁇ i ⁇ 2N .
• P I °P 2I and r ⁇ is functionally equivalent to p 2 ,- ⁇ l °P ,2,- ⁇ > providing to the executing device the functions g x , ... , g N ; and in the executing device, executing ED j (loader ⁇ (g x ,...,g N )) -
• the functions f are obfuscated in the form of the functions g x ,...,g N in the same way as described for claim 1.
• the functions g i ⁇ ...,g N are the same for each device and can be seen as corresponding to one default/anonymous device.
• the execution devices are equipped with a device specific ("personalized") execution device cascade.
• a device specific loader function is used to convert the respective anonymous functions g, to corresponding device specific functions that can be fed to the execution device cascade.
• the loader function uses conversion functions l J t and r that are based on a set sequence of permutations that are not revealed.
• the functions g can be supplied to all devices in a same way, for example, using broadcasting or on a storage medium, such as a CD-ROM or DND.
• Fig.1 shows a block diagram of a prior art plug-in based decoding
• Fig.2 shows a block diagram of a prior art based decryption
• Fig.3 shows a block diagram of a prior art integrated decryption/decoding system
• Fig.4 shows the obfuscating according to the invention
• Fig.5 shows a simple example of obfuscation
• Fig.6 shows a block diagram of a system according to the invention
• Fig.7 shows a further embodiment of a system according to the invention
• Fig.8 illustrates anonymous obfuscation according to the invention
• Fig.9 illustrates an alternative embodiment for anonymous obfuscation.
• Fig.3 shows a block diagram of prior art system in which the invention may be employed.
• content typically Audio andor video content
• the medium may be the same for each player.
• the medium may be of any suitable type, e.g. audio CD, DVD, solid state, etc.
• the content on the medium is copy protected, preferably by being encrypted under using an encryption algorithm, such as a Feistel cipher.
• the storage medium may include information relating the decryption key.
• the storage medium may include information 312 (such as an identifier) that enables the player to retrieve the information, for example by downloading it from a server in the Internet.
• the decryption key is created in a secure module 320 by using a key-specific key 322 and the information 312 to calculate 324 the decryption key 326.
• the decryption key is the received 332 in a second module 330.
• the second module 330 decrypts 334, decodes 336 and renders 338 the content 314 of the medium 310.
• Fig.4 illustrates the method according to the invention.
• a digital signal processing function/ is provided to an executing device in an obfuscated form.
• the function/ includes a function cascade including a plurality of signal processing functions , l ⁇ i ⁇ N .
• the core of the function cascade may be formed by EC, (x) ⁇ f N ° • • • • o f ⁇ (x) .
• the function cascade may be any digital signal processing function.
• the function cascade includes a cipher.
• the function/ may represent the i round (i>0) of a Feistel cipher.
• the digital signal input x is a multi-dimensional parameter, for example of 64 or 128 bit block/vector, to be able to perform a useful permutation.
• a set of N-l functions is calculated, where h x is functionally equivalent to ° P 21 - 2 » f° r 2 ⁇ ⁇ N .
• / is an invertible function that converts a number between 0 and 8 to a number between 0 and 8, e.g. value 0 is converted to value 3, value 1 to 1, value 2 to 6, etc.
• the executing device is equipped with the execution device function cascade that includes y N °h N ° y N _ x h N _ ° ...
• y x , ... , y N are function parameters. This is shown in Fig.4 as a sequence of functions h H , h N _ x , ... , ⁇ 410.
• An exemplary execution device function cascade is ED (y ...,y N ) ⁇ y M ° N ° y N _ x ° h N _ x °...°y x .
• the functions g x ,-.-,g N are provided to the executing device. This is shown in Fig.4 as a sequence of functions g N ,g N ⁇ ,...,g x 420.
• the execution device function cascade is applied to the functions g, , ... , g N .
• This function can then be applied to the digital signal input x. Taking a look at a middle part of the chain like h l+x °g, °h t > this gives:
• K °g l 0 P2I1 ° ⁇ i ° P ° f, ° A ° P2I1 ° P 2 ,-2 ⁇ P2 1 ° f, ° P2-2 ⁇
• the firat d Ieast term of this expression will be eliminated by the respective g terms.
• the total outcome is that the executing device executes a function that includes the function cascade f N ° ⁇ • - o / (x) without having access to any of the functions/. These functions are thus obfuscated. In preferred embodiments, options are given for dealing with the beginning and ending of the chain.
• the resulting total signal processing function in the executing device may be ED X (g, g N ) ⁇ p 2N x _ x °f N °--'°f i (x)°p i .
• the tetmpi can be eliminated by using an execution device function cascade that includes y N ° N y N _ x o h N _ ⁇ o ... o y ⁇ o p ⁇ ⁇ .
• p x is kept secure in the executing device.
• a preferred way of doing this is to extend the function cascade with a further signal processing function ), (for example, FC 2 (x) ⁇ f N °---°f ⁇ a f 0 (x))-
• the execution device function cascade then includes y N °h N ⁇ > y N _ x h N _ x o,..oy l oS x , ⁇ ox example (ED 3 0>, y N ) ⁇ y N h N y N i oh N _ x 0...0 y oS, ) , where S, is functionally equivalent to A -1 ° /o • hi ⁇ s a m e individual terms p x ⁇ ⁇ and fo need not be revealed, but only the multiplicated form ?, -1 °f Q exists.
• the execution device function cascade may include P 2N °y N ° h N °y N - ⁇ ° t 0 ---° y ⁇ ( ⁇ S,ED 4 (y x ,...,y N ) ⁇ p 2N °y N °h N °y N _ h N _ x °...°y x ).
• the function cascade may end with a further signal processing function fif+ ⁇ , (for example, EC 3 (JC) ⁇ f N+x 0 f N 0 ---°f l (x))-
• the execution device function cascade then includes S 2 y N oh N ⁇ > y N _ o h N _ x °...°y x (e.g., ED 5 (y x ,...,y N ) ⁇ S 2 y N oh N °y N _ x °h N _ °...°y x ) , where S 2 is functionally equivalent Fig.6 illustrates a system in which the invention may be employed.
• the system 600 includes a server 610 and at least one executing device 620.
• the server may be implemented on a conventional computer platform, for example on a platform used as a server, such as a web server, or file server.
• the server includes a processor 612.
• the processor 612 is operated under control of a program.
• the program may be permanently embedded in the processor in an embedded storage, like embedded ROM, but may also be loaded from a background storage, such as a hard disk (not shown).
• the processor 612 Under control of the program, the processor 612: • selects the set of 2N invertible permutations p, , l ⁇ i ⁇ lN ; • calculates the set of N functions g, , where g, is functionally equivalent to , l o - r °A,- ⁇ > for ! ⁇ *' ⁇ ; and • calculates the set of N-l functions h, , where h, is functionally equivalent to A ⁇ ,-. °A,- 2 > for 2 ⁇ t ⁇ ; N.
• the permutations may be selected (e.g. randomly or pseudo-randomly) chosen from a very large set of permutations that may be stored in a (preferably secure) storage (not shown).
• the server may also use a suitable program to generate the permutations. It is well-known how to create invertible permutations and this will not be described here any further. Additionally, the server includes means 614 for equipping the executing device with an execution device function cascade that includes y N ° N ⁇ > y N _ ⁇ o h N _ x °...°y x , where y utilizat ... , y N are the function parameters. The server may do this in any suitable form. For example, in a factory the terms h, may be stored in a storage module of the executing device during the manufacturing of the executing device 620. Fig.6 shows that the terms are downloaded through the Internet 630 directly to the executing device 620. The server 610 also includes means 616 for providing the functions g x ,...,g N to the executing device 620.
• the functions g incorporate the respective functions / .
• the functions / may be chosen specifically for the digital signal input x .
• each video title may be encrypted with a corresponding encryption function (e.g. using a same cipher but with a content specific key).
• the server 610 may also include the software for controlling the processor 612 to encrypt the content 640 and supply the encrypted content 642 to a distribution medium, e.g. for distribution on a storage medium or through a communication medium like the Internet.
• the executing device 620 includes means 626 for obtaining the functions g, , ... , g N from the server 610. These means cooperate with the means 616 of the server and will not be described further.
• the executing device 620 further includes a processor 622.
• the processor may be of any suitable type, such as a processor known from personal computers or an embedded microcontroller.
• the processor 622 is operated under control of a program.
• the program may be permanently embedded in the processor 622 using an embedded storage, like embedded ROM, but may also be loaded from a background storage, such as a hard disk (not shown).
• the processor 622 loads the execution device function cascade and applies the loaded execution device function cascade to the functions g, , ... , g N , for example by executing ED (g, , ... , g M ) .
• the resulting signal processing function may then be applied to the signal input x (e.g. content received from a medium).
• the processor 622 may load the execution device function cascade in any suitable form.
• the cascade may have been pre-stored during manufacturing in a storage, reducing the loading to a straightforward memory read access.
• the executing device 620 includes means 624 for retrieving the cascade (or the terms of the cascade), for example, through the Internet 630 or from the medium 650.
• the executing device 620 may retrieve encrypted content 652 from the medium 650, and decrypt this using the processor 622.
• the processor may also decode the decrypted content.
• Fig.7 shows a preferred embodiment wherein the execution device function cascade is provided to the executing device 620 embedded in a software program 710 for execution by the processor 622.
• the software program 710 may be a plug-in for a program like a media player.
• the means 614 of Fig.7 may supply this plug-in 710 via the Internet (e.g. item 630 of Fig.7) or embed it directly into the executing device 620 during manufacturing.
• the functions g x ,...,g N are supplied to the executing device 620 in the form of a plug-in for the program 710.
• the functions g , ... , g N are effectively a plug-in for a plug-in.
• the functions g, ,... , g N are provided to the executing device 620 by embedding the functions g ,...,g N in the software program 710 by applying the execution device function cascade to the function parameters g, , ... , g N .
• the program 710 embeds both the functions h, and g, .
• each executing device and/or user of the executing device is unique and identified by a unique identity (e.g., a unique number ). In the system and method according to the invention, it is ensured that the sequences g, and h, are unique for the involved party.
• the server stores (in a secure way) the unique set/sequence for each unique identity.
• each software media player in a personal computer can be supplied with a unique plug- in for decrypting and/or decoding a media title. The medium it self need not be unique.
• the encrypted content only depends on the encryption functions, not on the unique set/sequence of permutations.
• a signal processing function cascade is supplied to executing devices in an obfuscated way.
• the same set/sequence of permutations may be used or a device-specific set/sequence may be used.
• an preferred approach is described for achieving a device-specific set sequence by distributing the signal function cascade ('key') in an obfuscated way that is the same for each device and using a conversion routine ('loader') that converts the common key to a device-specific key.
• the 'common key' is created in much the same way as described before.
• the common key can in principle 'unlock' a reference player or anonymous player that, however, in this embodiment is not executed by any actual executing device.
• the method includes selecting a set of 2N invertible permutations ?,, where 1 ⁇ / ⁇ 2N and calculating a set of N functions g, , where g, is functionally equivalent to
• the method includes selecting for each executing device, each identified by a unique index/, a corresponding set and/or sequence of 2N invertible permutations p , that is unique for the device and/or a user of the device. This set is used to provide each device a unique 'player'.
• This unique player is formed by calculating for each executing device/ a corresponding set of N-l functions h , where h ⁇ _, is functionally equivalent to A ,2 ⁇ - ⁇ ° h ⁇ - ⁇ f° r 2 ⁇ / ⁇ N and equipping each executing device/ with a respective execution device function cascade ED ⁇ (y x ,...,y N ) that includes y N o h J>N ° y N _ ° h N _ °...°y x .
• This device-specific set h )Jt does not match the obfuscated function cascade, that can 'unlock' a reference player that uses set h, .
• each executing device is provided with the same functions g, , ... , g N .
• the executing device then executes ED J (loader J (g x ,...,g N )) .
• loade ⁇ ,...,g N effectively converts the anonymous key g ⁇ ,...,g N into a device-specific key that optimally matches the execution device function cascade ED ) (y ,...,y N ) .
• loader J (g x ,...,g N ) (g JiX ,g j 2 ,--- > g JtN )
• the concept of using an anonymous obfuscated key and a device-specific loader is also illustrated in Fig.8.
• the anonymous player Pl-R 810 incorporates the functions h,.
• the anonymous player Pl-R can be unlocked by the corresponding key K-R 812 that includes the obfuscated signal processing functions / in the form of the set g, .
• the anonymous player Pl-R is not disclosed to any party.
• Each party is instead provided with a unique, device-specific player, shown are players Pl-1 830 and Pl-2 840.
• the common key K-R is provided to all parties. However, this common key does not match the specific players.
• each party is also provided with a device-specific key loader K-L, shown are 820 and 825.
• the loader 820, 825 is used to convert the anonymous key K-R 812 into a device-specific key K-j..
• loader K-L includes the functions l M , and r J>t .
• a device-specific loader is used.
• the loader may be the same, but fed with the device-specific functions / and r .
• Fig.9 being fed with/, , and ⁇ , converts the anonymous key K-R 812 into the device-specific key 832 for device 1; being fed with 2 , and r 2 , converts the anonymous key
• the device-specific players 830, 840 are then unlocked using the device-specific key sets h ⁇ , 832 and 842, respectively.
• the phrase 'key' and 'player' is interchangeable since two chains of functions intre-lock.
• the example of Fig.4 illustrates both chains as keys. In an analogous way, it could also be illustrated as two interlocking players.
• the anonymous player 810 (incorporating gN,.- » gi) may advantageously be provided to each executing device through broadcasting andor distribution on a storage medium with a same content for each executing device, simply because this player is the same for each device.
• the digital signal input x to be processed by each executing device can be distributed through broadcasting and/or distribution on a storage medium with a same content for each executing device.
• the loader- specific aspects are preferably provided to executing device/ through a 'one-to-one communication channel' and/or a storage medium with a device-specific content with at least one the following sets of corresponding functions: h j , l j , ⁇ ,o ⁇ r .
• the 'one-to-one communication channel' may be achieved in any suitable way.
• the server downloads the device-specific information via a secure link (e.g. SSL) using Internet.
• SSL secure link
• the function/ may be a decryption function based on a Feistel cipher network and each of the signal processing functions/ is a respective Feistel decryption round function.
• the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice.
• the program may be in the form of source code, object code, a code intermediate source and object code such as partially compiled form, or in any other form suitable for use in the implementation of the method according to the invention.
• the carrier be any entity or device capable of carrying the program.
• the carrier may include a storage medium, such as a ROM, for example a CD ROM or a semiconductor ROM, or a magnetic recording medium, for example a floppy disc or hard disk.
• the carrier may be a transmissible carrier such as an electrical or optical signal that may be conveyed via electrical or optical cable or by radio or other means.
• the carrier may be constituted by such cable or other device or means.
• the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant method.

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