RU2103837C1 - Method for coding video signal to prevent unauthorized access - Google Patents

Abstract

FIELD: electronic engineering. SUBSTANCE: method involves transmission of composite video signals incorporating access pulses (ECM1 and ECM2); noise is eliminated by means of microprocessor card reader that has encoded numeric data; interactive method is used for identifying digital signature. Method is characterized in that batches of numeric data incorporating check word encoded according to coding algorithm are entered in lines not used by image. EFFECT: improved protection against unauthorized access. 3 cl, 5 dwg

Description

 The invention relates to a method for encoding video signals, as well as a device for its implementation.

 Currently used methods of interfering with video signals, in particular in the field of pay television, have the peculiarity of transmitting, on the one hand, access parcels that are equivalent for all televisions transmitted simultaneously with video signals, and, on the other hand, periodically transmitting specific parcels permissions for each receiver on a different path, for example, via mail or telephone. In connection with the type of transmission, the frequency of transmission of such permission packages may be relatively large, for example, once a month. Such a long period can easily be used by "pirates" who have enough time to find and use the noise coding key. On the other hand, the known method of noise can not partially pay for transmitted programs on one paid channel, if the subscriber is not interested in other programs.

 The aim of the invention is to increase the reliability of protection against unauthorized use when receiving composite video signals, the interference key of which cannot be found with fairly cheap means, for all types of subscription, including by the way (payment for "picture").

 A method of encoding video signals from unauthorized access consists in the fact that interference is generated by rearranging strings under control from a pseudo-random sequence, moreover, interference cancellation is performed by controlling from a pseudo-random sequence that is identical and synchronized with the sequence when creating interference, and the pseudo-random sequence when creating interference depends on control word (CW), the encoded value of which is embedded in the composite video signal, the method distinguishes I mean that they include at least portions of the transmitted images in the unused lines, a packet of digitally encoded data corresponding to different access packets, and that they combine confidentially when receiving these access packets data with the data received on the TV receiver from the video signals, and that is produced from this combination (combination) of the control word for a pseudo-random generator that controls the digital loop for cleaning the noise of the video signal.

 In accordance with the type of implementation of the invention, the data arriving at the receiver from the video signal should be those contained in the microprocessor card.

 In accordance with another type of method according to the invention, this combination is performed using such a combinatorics method, the security of which against unauthorized decryption increases as a function of the number of times it is used, in particular, an interactive method for identifying a digital signature is used, mainly a method using the Shamir algorithm.

 The device for interfering and purifying composite video signals from them in accordance with the invention is used in an image transmission system containing a transmitter and receivers, the interfering part of the system contains a digital interfering circuit in the transmitter connected to a pseudorandom sequence generator controlled from the control unit, and a part for cleaning from interference contains, in each receiver, a decoder with a digital interference cleaning circuitry connected to a pseudo-random sequence generator controlled from command unit, and in accordance with the image, the transmitter command unit contains means for creating access packets, and the command unit of each receiver (each decoder) is connected to a code verifier, which in turn is connected to a microprocessor card reader.

 According to an advantageous feature of the invention, the communication in each decoder between the command unit and the code verifier is a parallel communication.

 In FIG. 1 shows a simplified block diagram of a paid television program transmitter in which interference is generated in accordance with the method of the invention, and one of the receivers for receiving these programs, comprising a device for correspondingly removing (cleaning) interference; in FIG. 2 is a timing diagram of signals showing the location of various data necessary for noise removal relative to the first lines of images emitted by the transmitter of FIG. 1. in FIG. 3 is a timing chart showing the structure of data packets emitted by the transmitter of FIG. 1, for a period of 10, 24 sec. in FIG. 4 and 5 are timing diagrams of signals after exchange in a decoder according to the invention.

 The system for transmitting paid television programs described above has the European standard of 25 full images per second, but it goes without saying that it can be applied to any other standard if changes are made to it that are obvious to a specialist. For example, it goes without saying that interference can only occur in certain programs, while other programs can be transmitted clean (without interference).

 The transmitter and receiver 1 are described below briefly, since most of their circuits are well known. Only parts related to the invention are described; in the receiver, these are chains for creating packets, access packets and chains for introducing these packets into the data of some lines of the image to be jammed, and in the receiver, these are chains for clearing interference.

 The transmitter 1 contains an image source that creates composite video signals. Its output is connected using an analog-to-digital converter 3 with an intermediate circuit for creating video interference 4 of a known type. This circuit 4 is controlled from the control unit 5 by means of a pseudo-random sequence generator 6, and it sends synchronization signals corresponding to the video signals to this central unit. Circuit 4 is connected through an analog-to-digital converter 7 with a power transmitter 8, the antenna of which has position 9.

 In FIG. 1 is a block diagram of one of television receivers having the ability to receive transmissions from a transmitter 1 equipped with an interference cleaning circuit according to the invention. This receiver 10 comprises a receiving antenna 11 connected to a tuner (“tuner”) 12, followed by an analog-to-digital converter 13, a digital video noise filter 14 and a digital-to-analog converter 15, at the output of which 16 noise-free video signals are received.

 The output of block 12 is also connected through an amplifier 17 to a filter 18 and a peak detector 19 connected in series at the output of the shift register 20. The parallel outputs of the register 20 are connected through a buffer register to the data inputs of microprocessor computing unit 22, for example, microprocessor type EF 6805.

 The computing unit 22 is connected in two directions with the security code verifier 23. This verifier (code verification device) 23 is connected to a microprocessor credit card reader.

 Computing unit 22 is also connected to a pseudo-random sequence generator 25, which in turn is connected to circuit 14.

 In the transmitter 1, the video signals emitted by the source 2 are converted into a digital code using the converter 3 and then noisy in the circuit 4 by the command of the pseudo-random sequence produced by the generator 6. Each of the binary characters of the sequence appears synchronously with the successive lines of the video signal and determines the break point in the corresponding line, and this break point can be located anywhere on the line. Interference is the rearrangement of parts of the line located on one or the other side of this break point. This method of creating interference, referred to as “line swapping”, known per se, is not described in detail hereinafter.

 The periods of the pseudo-random generator 6 are relatively short: 2.65, 5.12, or 10.24 s. The 2.56 s cycle is especially interesting for decreasing the access time to the decoder after applying the supply voltage. The various period values indicated above are dynamically selected at the transmitter. The control of these sequences using the control unit 5 in the function of sending access to the program referred to here as the ECM ("Entitlement Checking Message"), common to all receivers. In the well-known pay-TV system, parcels of permission are notified to the subscriber by mail, using a modem, or in another possible way. Thus, access parcels cannot be changed as soon as at significant intervals (usually several weeks), which allows the pirates to find (detect) them (suggest that these parcels can be detected within one to two days) much before their next modification.

 In accordance with the invention, the control unit 5 of the transmitter includes access messages in the composite video signal (at the input of the converter 7). This central unit 5 provides, among others, an image counter function (FCNT). This counter is started from this block once every two rasters (half-frames), that is, with each full image (every 40 ms for the 50 Hz standard for interlaced scanning), due to the vertices of the video signal transmitted by block 4. In this case, it has a maximum state equal to 255 (8-bit counter). After reaching its maximum state, the counter is reset to zero and allows you to synchronize control words (CW, from "Control Word"), the value of which is encrypted in the specified access message. This control word may, for example, have a length of 60 bits and is randomly selected. This control word defines a new generator 6 cycle.

 The command unit 5 sends to the circuit 7 the following information: counter status (FCNT), signals of the beginning of access packets H1 and H2, data regarding the state of the transmission system (with or without interference, free or paid access, consumption of data of the packages). The central unit sends this information during transmission of lines not used in the image. According to the CCTT standard for 625 lines, there are visible lines that are not used in the image, before the 23rd line and after the 310th line. In the present example, four of these lines not used in the image are used for coding, for example, lines 12-15, for half frame E1, and lines 325-328 for second half frame E2, as shown in FIG. 2. In each of these lines, during the useful line length, the central unit sends five bytes for each field (half frame), that is, 40 bits per line and 20 bytes for each field (half frame) with four lines. Binary zeros correspond to black level, and “1” to white level. Thus, at the beginning of each full image (every 40 ms for the indicated example), a data packet (40 octets) is introduced into the composite video signal.

 Two types of data packets are emitted: ECM1 and ECM2. An example of the structure of each of these types of packets is shown in FIG. 2. Advantageously, these data packets are encoded, for example, with a Hamming code of 8-4, so as to have better protection against spurious signals during transmission. According to an embodiment of the invention, various bytes may be bound (intertwined) in this packet to improve resistance to spurious effects. Needless to say, this interweaving is immediately eliminated in each decoder.

In the FIG. In the time diagram, the various ECM1 and ECM2 packets contain at the beginning the corresponding markers H1 and H2. These markers allow discrimination of the ECM1 and ECM2 packages in accordance with the following ratio:
(О _H + О _L ) _ECM1 = (О _H + О _L ) _ECM2 = F _hexa
in which O _H and O _L are quartets of markers.

For example, if H1 = A5 _hexa for ECM1, then you must have H2 = 5A _hexa for ECM2, and the check should give A + 5 = F _hexa .

 The data packets ECM1 and ECM2 then contain for the E1 field 16 octets D AND payload for the verifier, two bytes "checr sum; then, for the half-frame E2: two bytes for FCNT, sixteen bytes D and payload for the verifier and two bytes" checr sum ". For ECM2, FCNT data is replaced by ES system state data.

 In FIG. 3, the second line shows the counting cycle of the FCNT image counter from 0 to 255, that is, for a time period of 10.24 s. During this time, the central unit 5 continuously produces values ECM1 and ECM2, alternating and repeating shown in line 1 of FIG. 3 way. For the FCNT cycle, the central unit can produce eight packets, each of which contains ECM1 four times and ECM2 also four times. Referring to FIG. The 3 abbreviations CNCW and TMTV mean respectively “load new control word CW” and “maximum verifier processing time”.

 During this ECNT period, the codeword CW can be changed four times, two or one time, that is, with a period of 2.56 s or 10.24 s, respectively, as shown in the third, fourth and fifth lines of FIG. 3.

 In the first case (period 2.56 s), the central unit 5 sends at least one decoding packet on each period 2.56 s, which allows the verifier 23 to have a maximum time of 2.2 s to process it before loading the next codeword. In the second case, the central unit 5 sends at least four decoding packets for each period of 5.12 s, which leaves the verifier with a maximum processing time of 3.8 s. In the third case, the central unit sends a minimum of 8 decoding packets for each period of 10.24 s, which leaves the verifier with a maximum processing time of 7.84 s. These different period values are supplied with byte data E.

 In each receiver, such as that shown in FIG. 1 receiver 10, the composite signal received at the output of circuit 12 is amplified, filtered and detected (in blocks 17, 18, 19, respectively) and thus the detected serial data octets are transmitted to the central block through buffer 21. The shift register 20 is filled in the rhythm of clock signals (SK) produced by the processor 22.

 It goes without saying that the data arriving at the processor 22 from the register 21 is ECM1 and ECM2. After recognition in the processor 22 of the ECM1 and ECM2 packets (by their markers H1 and H2), the FCNT value is extracted from ECM1, which serves, if necessary, to adjust the state of its image counter (subroutine of this processor). The processor 22 produces the FCNT value and enters it in bytes 21 and 22 of line 325, creating the true current value of the FCNT value, which is predominantly encoded in the Hamming code.

 The zero state of the image counter, which is repeated every 40 ms, determines the phases of processing the packets by the central unit and loading the pseudo-random generator. Active windows of a pseudo-random generator occur during useful image lines, that is, for the CCTT standard of 625 lines on lines from 23 to 310 and from 336 to 623 (respectively for the first and second half-frames of the image). The processor 22 produces a delay of approximately 20 lines at the moment of crossing FCNT zero to be able to receive data packets that arrive from line 12. Data acquisition windows extend from line 12 to line 25 and from line 325 to line 328 Outside of these windows and almost to the nearest zero, the FCNT processor processes the data packets.

 The dialogue between the processor 22 and the verifier 23 is made by sending in parallel (on one octet) to minimize data processing time and the possibility of its implementation in real time.

 In addition to the useful data ("DATE") of the ECM1 and ECM2 (32 octets in total in this example), the processor 22 sends the following data to the verifier (Fig. 4): RWN (write) read (and SENON) data download, and receives ACKN ( command acknowledgment signal).

 The verifier 23 sends to the processor 22 (Fig. 5), in addition to the control word CW for 8 bytes, the following data: RWN (record / play) and SENON (data download) and receives ACKN (command acknowledgment signal).

 The verifier 23 combines the data of the ECM1 and ECM2 with the data contained in the microprocessor card C, entered for use by the reader 24. The role of the verifier is to verify the correctness of the processing performed inside the microprocessor card, while maintaining the confidential aspect of data exchange between the verifier and processor 22, on the one hand, and between the verifier and the reader, on the other.

, то это может быть выражено серией факторов продуктов с определенными коэффициентами, поэтому найти это число х. Для осуществления очистки от помех декодер должен доказать свое знание секретной величины

без ее реального открытия. Таким образом, считывающее устройство выбирает случайное число R, затем вычисляет T = R₂[mod(n)] и посылает Т в верификатор, который случайным образом выбирает между:
1. Запросом в считывающем устройстве величины R, такой, что

и проверяет, что R₂ = T(mod(n))
2. Запросом в считывающем устройстве VTX=RY[mod(n)]

Таким образом, можно видеть, что диалог между верификатором и считывающим устройством заканчивается передачей чисел и вычисление квадратных корней производится в данное время и с определенными коэффициентами. Таким образом, данные, доступные пирату между микропроцессорной картой и декодером, не позволяют ему произвести декодирование послания в течение времени, совместимого с временем функционирования системы, так как для этого требуется чрезвычайная мощность вычислений, требующая для осуществления значительных средств, что делает бесполезным, как дорогостоящее, пиратство.The combination may be based on the interactive principle of digital signature identification. The dialogue between the microprocessor card and the verifier 23 should allow to verify the presence of the secret desired value in the decoder, but without a serial explanation. The basic principle is the answer that the result is known at the level of each decoder, but while maintaining an unknown value of this result. Therefore, if transmitted

, then this can be expressed by a series of product factors with certain coefficients, so find this number x. To perform interference cleaning, the decoder must prove its knowledge of the secret value

without her real discovery. Thus, the reader selects a random number R, then calculates T = R ₂ [mod (n)] and sends T to the verifier, which randomly selects between:
1. By request in a reader, an R value such that

and checks that R ₂ = T (mod (n))
2. By request in the reader VTX = RY [mod (n)]

Thus, it can be seen that the dialogue between the verifier and the reader ends with the transmission of numbers and the calculation of square roots is performed at a given time and with certain coefficients. Thus, the data available to the pirate between the microprocessor card and the decoder does not allow him to decode the message for a time compatible with the operating time of the system, since this requires extraordinary computational power, which requires significant funds, which makes it useless as expensive piracy.

Claims (3)

 1. A method of encoding video signals from unauthorized access, which consists in the fact that on the transmitting side, some of the lines of the transmitted image are rearranged under the control of a pseudo-random sequence, while the pseudo-random sequence depends on the control coded word, the control coded word is input into the video signal and transmitted, and on the receiving side, the received signal is restored in accordance with a pseudo-random sequence identical and synchronous with a pseudo-random sequence in transmission, characterized in that digital data packets containing a control word encoded according to the encoding algorithm are inserted into strings not used by the image, while at least some packets contain data enabling a control word to be loaded in a pseudo-random sequence generator .  2. The method according to claim 1, characterized in that the data packets are processed by means of a verifier and a microprocessor card, while the decoded control word is fed to the microprocessor.  3. The method according to claim 2, characterized in that the verifier and the microprocessor card use an algorithm for identifying a numerical value, such as the Shamir algorithm.

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