Copy method avoiding bit-to-bit duplication of digital data and reading device for implementing same

p0001The present invention relates to a method of avoiding the copy bit by bit duplication of digital data from a first source on a support. It also relates to a device for implementing this method.

p0002Digital data has the property of being copied without significant loss of quality. Indeed, the copy is to be transmitted from the source to the recording device a series of binary information, namely "1" and "0". Errors usually occur when copying are easily corrected using correction methods well-known errors. Thus, when a data carrier or data source contains numeric data, it is relatively simple to record the same on a recordable medium.

p0003For protecting digital data against unauthorized copying, different methods are used.

p0004Most often, the supplier endow the digital data medium such as the disk in the case of software, mark prohibit any copying.

p0005In documents <patcit id="pcit0001" dnum="EP0773490A"><text>EP-A-0773490</text></patcit> and <patcit id="pcit0002" dnum="EP0802527A"><text>EP 0802527</text></patcit>There is provided a system for protecting information stored in recording media in which each carrier has an identifier.

p0006Another way to protect digital data against copying is to provide them with a tattoo or "watermark" that is to say, auxiliary data attached to digital data. The tattoo must be non-changeable and non-erasable. In this case, reading of data is done using a private key that identifies the tattoo. During any copy digital data tattooed, a private key is required to replace the tattoo on the copy, otherwise the copy becomes illegal as devoid of tattoo. The digital data copied without tattoos are not read by the reader because it does not identify a tattoo where it should find one. Thus, the tattoo does not make a copy without the private key.

p0007These known methods of copy protection are generally effective when the support is treated with compliant playback devices or recording. However, these methods do not avoid duplication by a hacker who creates a duplicate or clone the most similar possible to the original by performing what is called a bit-by-bit copy.

p0008The present invention aims to propose a method for copying preventing the unauthorized duplication of digital data from a first source on a support, this method does not allow bit-by-bit copy of digital information.

p0009The present invention also aims to provide a playback device including circuitry for the implementation of said method.

p0010Accordingly, the present invention relates to a method of avoiding the copy bit by bit duplication of digital data from a digital data source on a carrier.

p0011Characteristics of the present invention are defined in the appended claims.

p0012Other characteristics and advantages of the present invention appear on reading the description of a preferred embodiment made with reference to the accompanying drawing wherein:<ul><li>The <figref idrefs="f0001">figure 1</figref> is a schematic view in block form of a read device and a recorder device capable of making copies of a first support on a second support.</li></ul>

p0013The present invention will be described with reference to reading digital data recorded on a digital medium such as a DVD for Digital Versatile Disc and copied to a second blank media also made a DVD which in this case must be recordable in Read DVD-R. However, it is obvious to those skilled in the art that other sources of digital information may be used, including digital information from a decoder and sent to a "broadcaster" or digital information stored on media such as magnetic tape, optical disk recordable or not, namely a CD, CD-R, CD-RW, DVD, DVD-R, a magneto-optical disk or the like. The recording medium comprises a magnetic tape recordable, CD-R, CD-RW, a DVD-R or a magneto-optical disk for storing audio information and / or video in digital form.

p0014As shown in <figref idrefs="f0001">figure 1</figref>The copy method according to the present invention allows copying of digital information recorded on a DVD D 1 using a reading device 2 with a formatting circuit 3 and the FD data that can be duplicated, are recorded on an DVD-R 4 inserted in a recording device 5.

p0015According to the present invention, the DVD-R 4 consisting of a DVD-R disc has a serial number which is stored so unforgeable during the manufacture of the DVD-R. This serial number is chosen to be single or have a very low probability of being present on two different media is stored in a hidden area of ​​the disk such that the box labeled "lead-in area" in English , namely the beginning of the track. As explained in more detail below, this serial number is used to format digital data read from the DVD 1 original.

p0016According to the method claimed in the present invention, the data read from the DVD 1 by the reading device 2 are sent to a formatting circuit 3 which performs formatting of the data using the serial number read from the DVD-R disc . Is thus obtained at the output of the reading device, FD data formatted in a specific manner, which are sent to the recording device 5 where it is recorded on the DVD-R 4.

p0017To make a formatting data as the data recorded on the DVD-R can not be copied bit-by-bit, but can however be played back later by the reading device, namely to achieve a so-called lawful copying, different methods of formatting may be used. A conventional formatting process is an encryption algorithm with a secret key as the DES for "Data Encryption Standard" in the English language well known to specialists. To avoid a pirate copy, the key used in this case will be a key built using a secret key and serial number read from the DVD-R disc. To carry out the formatting using this algorithm, the data recorded on the original DVD are cut into blocks of 64 bits then formatted by the DES using a 56-bit key derived from the serial numbers. At the output of the formatted data packets or encrypted 64 bits that are recorded through the camera-recorder 5 of the DVD-R 4. If the key is constituted by the serial number itself, the serial number will include 56 bits. However, the number of bits of the serial number is given by way of example. Indeed, it is possible to apply the invention to carriers whose serial numbers have higher or lower length of 56 bits. In this case, we can apply a truncation or channel coding to bring these serial numbers to the right length. If the key is, for safety reasons, a function of the serial number, it may be obtained as follows:<ul><li>Knowing that NS is the serial number of the recording medium, and PS is the parameter stored in the playback devices in accordance securely:<ul><li>one carries out the concatenation of NS and PS for a word (NS / PS)</li><li>applying a hash function such as SHA-1 function (standard from the National Institute of Standards and Technology) and the result will be the word SHA (NS / PS) having a length of 64 bits, and</li><li>truncation is made of this word for a 56-bit word that will serve as key for the DES.</li></ul></li></ul>

p0018The length of binary words and NS PS is not fixed because SHA-1 does not require precise length for the input word. The function f adapts to any serial number length.

p0019The DVD-R 4 and lawfully copied can be read by the reading device 2 and original digital data is recovered using the corresponding decryption algorithm.

p0020It is also possible to perform the formatting of digital data to be duplicated using a public key algorithm such as the RSA algorithm. This public key algorithm is an asymmetric algorithm which does not allow, when one knows the public key, to easily copy the formatted data when they are read by the reading device 2.

p0021The data on the DVD-R copy does not have the same structure as the original DVD data, so it is not possible to recover with a reading device other than a device of reading . On the other hand, if a bit-by-bit copy of the original DVD has been performed, the reading device of the present invention does not find the original digital information and will not read.

p0022According to a further feature of the present invention, the copying method may be preceded by a copy permission verification step such as that described in French patent application No. <patcit id="pcit0003" dnum="FR9811860"><text>98 11860 filed September 23, 1998</text></patcit> in the name of THOMSON multimedia and entitled "Protection against copying of digital data stored on an information carrier." This copy authorization check applies to an information carrier comprising a first identification of an encryption of digital data, a dry wave identification of a digital data tattoo, a first determining a first mark if the encryption and watermarking have been identified, a third identification of a type of information carrier, a second determining a second brand if the first mark could be determined and if a particular type of information carrier could be identified, a fourth identification of cryptographic signature data accompanying the digital data, a third determination of a third brand if the second brand could be determined and if a cryptographic signature data has been identified, the first issue of a permission for digital copying of digital data if the third mark could be determined.

p0023All the features described in this French patent application is incorporated in this application to produce the copy enable verification.

p0024According to the present invention, the reading device 2 of the digital data which may be a DVD player, a decoder, a CD or the like, comprises a formatting circuit 3 consists essentially of an integrated circuit including all the means necessary for the realization of the chosen algorithm for formatting and can store so falsified certain data such as a secret key or copy authorization means.

p0025The embodiment described above is given by way of example and can be modified within the scope of the appended claims.