KR0160456B1 - Method and apparatus of scrambling and unscrambling a composite video signal - Google Patents

Abstract

In order to scramble the pay-TV transmission as effectively as possible, the transmitter 1 will send an access message and an entitlement message at the same time, both of which are encrypted and periodically into the pseudo-random sequence generator 6. Corresponds to the control word loaded into. At each receiver, the decoder has a computer 22 which processes various messages and sends them to the secure processor 23, which is arranged on the pseudo-random sequence generator 24 which controls unscrambled. Supply awards.

Description

Method and apparatus for scrambling and unscrambling composite video signal

The present invention relates to a method and apparatus for scrambling and unscrambling a composite video signal.

In particular, in the field of pay-television, currently implemented methods for scrambling video signals transmit on the one hand a valid access message to all receivers simultaneously with the video signal, and on the other hand for example a set or telephone channel. Periodically transmits a specific entitlement message (entitlement message) to each receiver through the same other channel. Due to such a transmission mode, the periodicity of transmission of these messages can only be as long as 1 month. This long period is enough time for the eavesdroppers to find the scrambling key and take some benefit from it.

The present invention relates to a method of scrambling and unscrambling a composite video signal, which makes it possible to modify the scrambling key at sufficiently short periods, eliminating any possibility of finding a scrambling key between two consecutive changes. do.

The invention also relates to an apparatus for carrying out this method.

The method according to the invention comprises the step of including a data packet corresponding to an entitlement message and an access message in at least some unused lines of the transmission picture.

According to the present invention, the data packet also includes an access message immediately following the message used when the unscrambler proceeds.

Preferably, one data packet is included at the time of each complete picture.

According to one embodiment of the present invention, at least one access message during the progression period at the start of each picture during each period of at least ten consecutive pictures, at least one access message for the subsequent consecutive periods, and An entitlement message for each of the other pictures is included.

The present invention will now be better understood from the detailed description of the embodiments with reference to the accompanying drawings.

1 is a schematic diagram of one of a transmitter of a pay-TV program scrambled according to the method of the present invention and one of the receivers having the corresponding programs and an unscrambled device corresponding thereto;

2 is a signal time line showing the arrangement of the various data required for unscrambled in relation to the first few lines of the picture transmitted by the transmitter of FIG.

3 is a timeline diagram showing the structure of a data packet transmitted by the transmitter of FIG. 1 over a period of 20 seconds;

4 is a timeline diagram of a signal generated while one complete picture is being transmitted by the transmitter of FIG.

The Pay-TV program broadcast system described below refers to a European shipping standard with 25 full pictures per second, but as some experts in the art will appreciate, some modifications can be made to other broadcast standards. Can be. Moreover, transmissions are only scrambled for some programs and broadcast in plain text, not ciphers, for other programs.

The transmitter and television receiver 1 are well known in the majority of these circuits, and will be described briefly below. On the transmitter side, circuits for generating entitlement and access message packets, circuits for inserting these data packets into arbitrary lines of the picture to be scrambled, and unscrambled circuits on the receiver side form part of the present invention.

The transmitter 1 has an image source for supplying a composite video signal. The output of the transmitter 1 is connected via an A / D converter 3 to an intermediate video scrambling circuit 4 of known type. The circuit 4 is controlled by the control unit 5 via the pseudo-random sequence generator 6 and transmits a synchronization signal corresponding to the video signal to the control unit. The circuit 4 is connected to the power transmitter 8 via a D / A converter 7, the transmission antenna of which is indicated by reference numeral 9.

1 shows a block diagram of a television receiver capable of receiving transmissions from the transmitter 1 and provided with an unscrambled circuit according to the invention. This receiver is indicated by reference numeral 10. The receiver 10 includes a receiving antenna 11, a tuner, an A / D converter, a digital video unscrambled circuit, and a D / A converter 15 which are sequentially connected to each other, so that the output of the D / A converter 15 ( An unscrambled video signal is collected at 16).

The output of the circuit 12 is also connected to the series input of the shift register 20 via an amplifier 17, a filter 18 and a peak value detector 19. The parallel output of the shift register 20 is connected via a buffer register 21 to the data input of a computer having, for example, an EF6805 type microprocessor.

The computer 22 is bidirectionally connected to an 1821 type security processor such as used for chip cards (also microprocessor cards known as smart carts) and bank credit cards.

In the transmitter 1, the video signal coming from the source 2 and digitized by the converter 3 is scrambled in the circuit 4 under the control of a pseudo-random signal sequence generated by the generator 6. Each of a series of binary numbers in a sequence appearing synchronously with a series of lines of the video signal determines a break point at that line, which break point can be placed anywhere in the line. Such a so-called line interchange scrambling method is well known, and thus a detailed description thereof will be omitted.

The sequence of pseudo-random sequence generator 6 has a relatively long period (e.g. 20 seconds) and is a function of a program access message (here, an Entitlement Checking Message (ECM)) common to all receivers by the control unit 5 And as a function of an entitlement message specific to each receiver (here, an Entitlement Management Message (EMM)). In known pay-TV systems, entitlement messages are communicated to the subscriber via a receiver, modem or other telecommunications channel.

Therefore, an access message can be modified in a relatively long period of time (typically several weeks), which allows eavesdroppers to discover these messages much earlier than when they require subsequent modification of the messages (one day or Estimated to be found in two days).

According to the invention, the transmitter 1 comprises an access message and an entitlement message in the composite video (from the input of the converter 7). This also has the advantage of including the current access message (ECMn) and the next access message (ECM _{n + 1} ) in the composite video at the same time. The current access message serves to decode the video signal through the switching on of the decoder, and the next access message is pseudo-when the frame counter value is increased from its maximum value (255 in this case) to zero by one unit. It serves to synchronize the decoder as a result of the value of the frame counter which controls the loading of the control word CW into the random sequence generator.

Because access and entitlement messages are sent in composite video and access messages can be modified in a short period of time (eg, 20 seconds), it is impossible to decrypt the decoder and eavesdrop.

The control unit 5 at the transmitter 1 provides a frame counting function FCNT. This counter is incremented by one unit every two frames, i.e. for each complete picture (every 80 ms by the interlaced frame 50 Hz standard), taking into account the harmonic pulses of the video signal transmitted by the circuit 4. In this case, this counter has a maximum counting state equivalent to 255 (8 bit counter). The counter returns to zero after reaching this maximum state. This transition to zero controls the transmission of the control word CW to the pseudo-random sequence generator 6, which is the access message. This control word may have a length of 60 bits, for example, and is randomly selected. This control word determines the new period of generator 6.

Furthermore, the control unit 5 transmits to the circuit 7 information indicating the status of the counter FCNT, the entitlement message, the current access message, the next access message and the current date at a specific instant.

The control unit 5 transmits this information during the transmission of the line not used by the image. According to the CCETT 625 line standard, there is a line that is not used by the visible image prior to line 23. In this example, four of these lines, such as lines 17 to 20, which are not taken by an image, are used for coding purposes as shown in FIG. During the line duration, the control unit sends seven coded data bytes, 56 bits per line and 28 bytes corresponding to these four lines, to each of the lines. Binary 0 corresponds to the black level, and 1 corresponds to the white level. Thus, at the beginning of each complete picture (every 80 ms in the above example) a data packet (28 bytes) is combined with the composite video signal transmitted by the transmitter 1.

Three different kinds of data packets EMM, ECMn and ECM _{n + 1} are transmitted. It is shown in Figure 2 for the structure of each of these three different data packets. These data packets are, for example, coded with Hamming codes to have the best immunity to transmission interference. According to a variant of the invention, the bytes of each packet can be interlaced into these packets to improve immunity to transmission interference. They are first deinterlaced at each decoder.

In the timing diagram of FIG. 2, each packet includes an identification header. This header, having a length of 2 bytes, has the values (in hexadecimal) of A5, E7 and 99, respectively, for example for packets EMM, ECMn and ECM _{n + 1} .

The EMM data packet then contains 6 bytes UA for address coding of a specific decoder that enables coding of 2 ²⁴ different decoders and 4 bytes for coding the current date, with the remaining 16 bytes qualifying. It is used to code the (encoding) value of the message.

The coding of the ECMn packet is the same as the coding of the packet of ECM _{n + 1} . After two header bytes, it has two bytes giving the FCNT value.

In this case, the last three bytes of the first line and the first byte of the next line are not used. Next, four bytes are designated for the current date, and the last 16 bytes are used to code the value of the current or next access message (encoding).

In FIG. 3, a frame counter FCNT is shown that counts periods ranging from 0 to 255 for a period of 20 seconds. During this time period, the control unit 5 continuously generates the values of ECMn and ECMn + 1 at the ratio of 16 values for each during the 20 second period. Therefore, during this 20 second period, 480 values are generated.

In an embodiment, the control unit transmits the sequence 1.ECMn, 15.EMM, 1.ECM _{n + 1} , 15.EMM, 1 ECMn ... etc. To the input of the circuit 7. Thus, in each period of 20 seconds during the 0-255 state of the FCNT, the control unit includes 16.ECMn, 16ECM _{n + 1,} and 480 EMM in the composite video signal. One million different EMMs are sent by the transmitter 1.

In each receiver, such as receiver 10 shown in FIG. 1, the synthesized signals gathered at the output of circuit 12 (at 17, 18 and 19, respectively) are amplified, filtered and demodulated and thus a series of data bytes demodulated. The buffer 21 is transferred to the computer. Charging of the shift register 20 occurs at the rate of the clock signal CK generated by the computer 22.

The data arriving at the computer 22 from the shift register 21 are EMM, ECMn and ECM _{n + 1} . The computer 22 recognizes the ECMn or ECM _{n + 1} packets (from header E7 or 99) and extracts the FCNT value from it, which is the counter state of the frame counter (subroutine of this computer if necessary). ) Can be corrected. The computer 22 uses the free wheel to generate (or synchronize) the FCNT with bytes 3 and 4 of the line 17, which advantageously provides the current value of the FCNT, which is coded with a Hamming code. ).

As shown in Figure 4, the zero state of the frame counter (returned every 40 ms) determines the processing phase of the packet by the computer and the loading phase of the pseudo-random sequence generator. The active window of the pseudo-random sequence generator occurs in the 625 line CCETT standard, on the valid lines of the picture, i.e. lines 23 to 310 and lines 336 to 623 (corresponding to each of the first and second frames of each picture). The computer 22 generates a standby loop with a duration of about 20 lines at each instant of transition of the FCNT to zero and places it in a position for receiving data packets from the line 17. The data reception window extends from line 17 to 21. The computer processes the data packet until it reaches the next zero of this window and FCNT. After recognizing the data packet, the computer sends the encoding values of EMM, ECMn and ECMn _H to the processor 23, which processes the encoding values in a known manner. Based on these encoding values, the processor 23 formulates a control word (unencoded) that it sends to the computer 22, which is the pseudo-random sequence when the computer 22 transitions to zero of the FCNT. To the generator 24. Thus, this generator 24 is synchronized with the generator 6 of the transmitter. The pseudo-random sequence for each line of the image provided by generator 24 provides the corresponding value of the break point of the line as determined by generator 6 for that line.

Since the transmitter sends a large number of ECMn and ECM _{n + 1} values (16 each in this example) frequently (every 20 seconds), the decoder can decode the received signal very quickly (in about 3 seconds or less). have.

Since the processing for decoding the video occupies the duration of the scan line, the present invention shifts the chromaticity burst associated with the line to the next line in transmission, so that at each decoder (e.g. in the form of a FIFO) Memory can be saved.

At the time of reception, because video processing is done on the current line, it transmits sync signals and chromatic bursts transparently without affecting the buffer register (its price is lower than FIFO type memory for example). It is also possible to recover the unscrambled signal corresponding to the burst.

In contrast, if the chroma burst is not transmitted with a delay of one line relative to its corresponding video signal, the memory is read and written simultaneously to shift the sync signal and chroma burst for as long as video unscrambled continues. Depending on whether it is desired to do so, it is necessary to use one or two additional memories, which increases the cost of the decoder (in mass production).

Claims (8)

12. A composite video signal scrambling method comprising scrambling a video signal using a line-cut-and-rotate method, wherein the blocking point for the line blocking and rotation method is assigned to a control word (CW). And wherein said method comprises: shifting a chromaticity burst of a predetermined line of said composite video signal to a next line. 2. The method of claim 1, comprising the step of including a data packet corresponding to an entitlement management message (EMM) specific to each user and an entitlement check message (ECM) common to all users in at least a portion of the unused lines of the transmitted image. And wherein the entitlement check message comprises an encrypted control word (CW). 3. The composite video signal scrambling of claim 2, wherein the grant check message comprises an entitlement check message (CEMn) for a current cycle and an entitlement check message (ECM _{n + 1} ) for the immediately following cycle. Way. 4. A method as claimed in claim 2 or 3, comprising counting the number of radiated fields (FCNT) and loading a new control word (CW) into the pseudo-random generator each time the number of radiated fields reaches a predetermined value. And further comprising said pseudo-random generator generating a pseudo-random sequence that defines said interception point. 4. The method of claim 2 or 3, wherein each entitlement management message comprises at least one specific address (UA) of a decoder. In the method of unscrambled scrambled video signal according to the line blocking and rotation method, the chroma burst of a predetermined line of the video signal is shifted to the next line during scrambling, and the time delay for unscrambled one line is Transmitting the chroma burst through a buffer, the same as the sustain period, and continuously repositioning the unscrambled video line corresponding to the chroma burst. An apparatus for scrambling a composite video signal according to a line blocking and rotation method, the apparatus comprising: a video signal source (2) and means for shifting a chromaticity burst corresponding to a predetermined video line to a next video line, the video signal being a line And a scrambling circuit (4) according to the blocking and rotation method. In an apparatus for unscrambled scrambled composite video signal according to the line-blocking and rotation method, the chroma burst of a predetermined line of the video signal is shifted to the next line during scrambling, and immediately without remembering the sync signal and chroma burst. And a buffer for transmitting the composite video signal.