METHOD FOR AUTHORIZED DISPLAYING INFORMATION DISTRIBUTED THROUGH PUBLIC COMMUNICATION MEDIA
Description FIELD OF INVENTION
The invention relates to the means for protection of information from unauthorized access and can be used in crypto systems for encrypting and decrypting information stored and distributed through communication media and the ether, in particular for digital TV, for receiving and displaying audio and video information.
BACKGROUND OF INVENTION
Systems for protection of information by using the method for encrypting, transmission the encrypted message and subsequent decrypting thereof at readout or displaying are known. In this case, different systems of encrypting are used.
Systems with secret or private keys such as DES have insufficient stability because encrypted information is semanticaily connected with the initial information. Moreover, such systems have a problem of keys distribution.
A crypto system with public RCA keys is known. This system is described in the U.S. Patent No. 4,405,829, entitled "Cryptographic Communications System and Method", issued on Sept. 20, 1983, in the names of Rivest, Shamir, and Adleman. This system uses a one-side function, i.e. a discrete involution.
The drawback of these systems is a short key length, which allows to perform decrypting in acceptable time limits. At the increase of the key length the speed of encrypting becomes unacceptable for real-time displaying.
A cryptographic algorithm MZ4 [wo 00/56004, Mischenko et al.] is the algorithm for functioning theoretically stable systems with a very large degree of randomization (109 per each symbol of the encrypted text), which allows to provide a code that is statistically independent from the initial text. This feature
allows to have stationary keys in symmetric systems. Nevertheless, this method is not quite applicable for the purposes of protection of recorded information, since the size of the encrypted text is essentially increased.
The closest in essence invention of the prior art is the system described in the US patent No. 6,252,964, Wasilewski A, et al. "Authorization of services in a conditional access system".
The cable television system provides conditional access to services. The cable television system includes a headend, from which service "instances", or programs are broadcasted, a radio transmitter and a plurality of set top units for receiving the instances and selectively dencrypting the instances for display to system subscribers. The service instances are encrypted using public and/or private keys provided by service providers or central authorization agents. Keys used by the set tops for selective dencryption can also be public or private in nature, and such keys may be reassigned at different times to provide a cable television system protected from piracy. However, the system has all the drawbacks of the encryption systems including such as transmission of keys to several users.
A method for encrypting [WO 00/65767, Mischenko et al.], is known, which allows to transform any machine text (any file) into two encrypted files (a core file and flags), each of said filed has no meaning unlike the existing encrypting algorithms. The characteristic feature of such representation is that one of the files (the core file) can have a small size (selected by the user). Unlike the hash-function operation, here the initial text (file) can be restored from a residual file (core) with the help of another file (flags). According to this method, transformation of a message in each cycle is performed in such a manner, as a result of which is formed a message ( ) transformed in the given cycle of transformation that is shorter in the length then the initial message or equal to it, and an accessory information for the given cycle (Fj). The number (n) of transformation cycles of the initial message is selected from a preset criterion (for example, the size of the finally transformed message).
The method further consists in forming an encrypted message consisting of two parts, one of which contains the finally transformed message
(Cn) that is shorter in the length than the initial message, and the second part contains a set of the accessory information (F = {F-i, F2, ..., Fπ} - flags).
This method of encrypting allows both parts of the encrypted message to be independent. In this case, the initial text cannot be restored by using any of these parts separately.
Nevertheless, this method is not quite applicable for public distribution of information, since it requires that the both encrypted parts should be transmitted through one communication channel. Besides, even in case the encrypted parts of information are transmitted through different communication channels, in order to displaye and distribute copies of the encrypted data, it is sufficient to dencrypt the main channel.
The aim of the invention consists in providing a safe method allowing to protect from unauthorized displaying information transmitted through public media, e.g. through the ether or a cable television network. The set aim is realized in the following manner.
The method for distributing and displaying the initial information with protection against unauthorized displaying comprises the following operations, their sequence and regimes:
- performing the main encrypting of information in such a manner, as a result of which two independent parts are formed: an informative part (core) and an accessory part (flags), each of the parts cannot apart displaye the initial information even in its separate parts;
• transmitting the accessory part of information and the keys for main encryption by any user; • cyclic changing the keys;
• additional encrypting of the informative part of information (core) by private keys of the user recorded on an additional carrier. The said carrier is a processor, in which is implemented the algorithm of encrypting with private keys of the user or the displaying device; • recording the additionally encrypted informative part of information on an additional carrier. Thereafter the said carrier interacts with the user's equipment for displaying the initial information. After encrypting the carrier has at its output the informative part of information encrypted by the private keys
of the user. Thus, one encrypted part of information is additionally encrypted by a private key recorded on a smart card by the encrypting algorithm and cannot be read by any other user.
• Thus, one encrypted part of information is additionally encrypted by the private key recorded on a smart card by the encryption algorithm and cannot be read by any other user.
The method is further characterized by that the main encrypting is performed in such a manner that the size of the accessory part substantially exceeds the size of the informative part. The method for restoration of the initial information for displaying comprises the following features:
- interaction of the additional data carrier in the displaying equipment is performed in such a manner that the informative part of information is additionally dencrypted by the private keys of the user's equipment and by the algorithm for additional dencryption;
- the accessory information is received as the main signal broadcasted through public media, e.g. through broadcasting station or cable television network;
- the initial information is restored in the displaying equipment by performing the operation of main dencrypting at the interaction of the accessory part of information received through the public channel and of the informative part restored in the displaying equipment. The system for distributing information comprises data encrypting unit and a unit for transmitting one part of the encrypted information through public communication channels to any user and a unit for additional transformation of the second part of information. The system further comprises an additional device for recording additionally encrypted information on a separate carrier with a processor.
The system for recording can additionally comprise a unit for individualization of a displaying device in the form of a device for additional encryption the second part of the encrypted information.
The system for displaying the encrypted information transmitted through communication media and recorded on an additional carrier
comprises a receiving unit, a decrypting unit and a unit for transformation of the encrypted information into a perceived form.
The system further comprises a unit for individualization of a dispalying device with the unit for readout of the additional carrier and a unit for dencrypting the accessory information.
A system for distributing information and a displaying system can use a smart card (simm card) or another rewritable carrier as an additional carrier for the accessory information. Preferably, such carrier should also have a built-in processor for additional encrypting as well as a recorded algorithm for encrypting and private keys. In this case, private keys are accessories of the displaying unit.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a schematic diagram of a system for transmitting, implementation and displaying information.
Fig. 2 shows a schematic diagram of a system for encrypting and distributing information with the use of a main encryption and an additional encryption.
Fig. 3 illustrates a schematic diagram of a device for displaying the received information with the use of the main encryption and an additional encryption.
Embodiments of invention
The claimed method is best illustrated by an example of broadcasting television programs, receiving thereof and subsequent dispalying on a specially equipped TV set.
Protection from unauthorized dispalying has always been a challenge for television that provides mass and cheap distribution of information and services. Generally, television broadcasting consists in transmitting information, movies, musical programs, etc. through the ether or cable channels. Nowadays, physically it is rather easy to receive the information and
to decrypt it, or to use one legal code for receiving and watching by many users.
According to the proposed method, the information subjected to transmission is most effectively encrypted by the method disclosed in WO 00/65767 (MV2). During the process of such encryption a preset number of encryption cycles is carried out, as a result of each cycle the encrypted information is shortened (compressed).
This process results in forming in every cycle an accessory information bearing data about transformation within the cycle, but as a matter of fact having no connections with the initial information.
The number of such cycles can be derived from the criterion of forming an encrypted text of a definite size, definite protection level, definite transformation time or other criterion. In this case, the accessory part of information is magnified with each cycle. In accordance with this method it is preferable, that the informative part were rather short, for example 1 Kilobyte. The accessory information can have the size comparable with the size of the initial file. Namely, the accessory information is transmitted through public media. In this case unauthorized receiving and displaying information becomes inept; decryption is impossible because the accessory part of information recorded on the carrier is not associated with the initial information. The short informative part can be additionally encrypted and dispatched to service centers or other agent points equipped with the devices for decryption and recording the codes for decryption, and for displaying on private receiving and displaying devices.
Thus, for displaying are required both parts of the encrypted information and the encryption algorithm. In this case, the encryption algorithm can be transmitted together with the accessory information, since it also has no connection with any information. On the other side, customers should have displaying devices (e.g. TV sets) equipped with special additional units with a possibility of recording on a rewritable carrier, e.g. a smart card. Preferably, such a carrier should have a built-in processor for encrypting by a private key.
If a customer is provided with a key for decryption, i.e. the informative part, which should be protected by encrypting thereof on a smart card, he can receive and encrypt programs and services encrypted in accordance with the described method. This method requires a private key for an additional encryption. The key should be stored in the displaying device, preferably on an additional carrier. A safe algorithm used for this encryption can be the MZ4 algorithm [WO 00/65767, Mischenko et al.].
For displaying a program on his special device, a user inserts into it a smart card and, in accordance with the conditions of the purchased right for watching or receiving information, he can receive and decrypt the respective information, obtain access to channels, databases, etc. In this case, at first the informative part of information is decrypted, thereafter the initial information is restored, the accessory part of which is transmitted through a communication channel. Thereby is provided full protection from unauthorized access and displaying information distributed through public media accessible to general public, because in this case simple displaying a signal that does not carry any initial information is useless. Additional encryption of the informative part of information by an private key makes the decryption thereof impossible, since this part itself has no meaning. Besides, the initial information can be displayed only on a special displaying device provided with a private key.
Fig 1 shows a general scheme for the system of transmitting, implementation and displaying information, comprising a unit for encryption information 1 , a unit for transmitting one part of the encrypted information (flags) 2 through public communication media, and the second part of information (core) 4. The system comprises an additional unit for recording additionally encrypted information 4 on a separate carrier with a processor, e.g. a smart card 5.
A system for displaying the encrypted information transmitted through communication media and recorded on an additional carrier comprises a receiving unit 6, a unit 7 for decrypting information recorded on the additional carrier 5 by means of the keys recorded in the individualization unit 8 and a unit for restoring of the initial information 9 for imaging it in a perceived form on a display 10.
The scheme of a system for encryption and distribution of information with the use of the main and additional encryption (Fig. 2) is preferable for distributing information through a broad distributor network.
In this case, beside encrypting in the encryption device 11 , transmitting the accessory information obtained as a result of encrypting under the claimed method via the transmitter 12 to any user through public transmission media, is performed the additional encryption of the remaining part (core) in a special device 4 for private encryption of the distributor network
Thus, each distributor decrypts the core by his private keys and thereafter sends the core to the device 16 for reading/recording user's smart cards for further encrypting by user's private keys in the processor of his smart card 17.
According to Fig. 3, the displaying device receives the accessory information through the communication media 21 by means of a common receiving device 22 and transmits the data to the decrypting device 23.
At the same time to ensure decrypting the user uses his smart card 24 with the core encrypted on it, which core provides purchasing the right for displaying the transmitted information. For this purpose the displaying device additionally comprises a device for reading/recording of smart cards, which is connected to the unit for additional decryption by individual keys 26 of the displaying device, which keys are recorded in the memory 27.
The core recovered in the additional decoder 26 arrives at the main decoder 23 and participates in the process of the main decryption of the transmitted information into the form useful for imaging on the display 28. The system allows to protect from unauthorized displaying information transmitted in accordance with the pre-announced program, e.g. movies, recorded programs, informational data, such as data bases, etc. The method and the system asumes that a user should purchase in advance the right to watch or to have an access to data. At the same time, the system and the method can be also used for transmitting the encrypting/decrypting information itself, e.g. dynamic keys of a large length disabling to select within the real time limits the keys or other means for breaking the encrypted information.