JPH0574275B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a pay television device in a CATV system or the like that prevents subscriber terminals that do not pay fees from receiving regular video and audio. Conventional configuration and its problems In the conventional CATV system, encryption was performed using a key code K _C as an encryption key _to prevent eavesdropping.
Although it changed every month, it was common to all terminals. Therefore, it was relatively easy to operate a paid terminal, read K _C from it, and use it to spy on other terminals. First, the configuration of such a conventional example is shown in FIG. In the figure, 1 is the center computer of the CATV station, which manages the subscriber's viewing fee payment status, the specification of broadcast programs according to the subscriber's wishes, and the creation of control codes.
The control code is added to a video signal from a studio or the like and sent out. 3A is the head end,
For example, multiple video signals from CATV center 2
Transmit in line with VHF mid-band. 3B is a buffer circuit that receives upstream signals from each terminal, and the head end 3A, the tuner/converter 4 on the terminal side of CATV, and the buffer circuit 3B are connected by the same cable or another cable. Also, from the tuner/converter 4 to the buffer circuit 3
A telephone line may be used instead of a cable to B. This tuner/converter 4 is a tuner or converter on the terminal side that converts a mid-band signal to one channel (or two channels) of VHF, and according to a command from the keypad 5, one channel of the mid-band CATV signal is converted to VHF. Convert to 1 channel. In addition,
If the CATV signal is scrambled,
In some cases, the signal is first converted to a baseband signal, descrambled, and then converted back to an RF signal and output as a single VHF channel signal. 6 is a television receiver that receives normal VHF band reception. The viewer operates the keypad 5 or uses the telephone 7.
Apply for the program you want to watch (charged) to the center computer 1 via . In the center computer 1, the charge is set for each terminal, and if it is scrambled, the decoding key code is sent in the order of the center computer 1 → CATV center 2 → head end 3 → tuner/converter 4. Inside, this key code is used to declassify the normal image of the NTSC video signal, convert it to one channel of VHF,
It is supplied to the television receiver 6. There are a large number of tuners/converters 4 to telephones 7, and a telephone office is interposed between the telephones 7 and the telephone interface 8. The telephone interface 8 is generally operated by a human who listens to requests from each terminal and sends them to the center computer 1.
is converted to the input form. This is an example. OBJECTS OF THE INVENTION It is an object of the present invention to provide a pay television device which eliminates the above-mentioned conventional disadvantages and whose key code is difficult to read, thereby effectively preventing unauthorized viewing. Structure of the Invention In the pay television device of the present invention, billing information corresponding to the content of the program watched is received at regular intervals in the form of a digital signal, and the terminal receives billing information in the form of a digital signal at regular intervals. In a device that determines and stores the charge amount in a charging amount determination circuit in the receiving device, and reads out and displays charge data proportional to the amount as necessary, a unique address code ID _i that is different for each terminal is assigned. key code K ₁
The first signal is stored in the form of a signal EK ₁ (ID _i ) encrypted with
a second memory that stores a key code K _n that is different for each terminal in the form of a signal EK ₁ (K _n ) encrypted with K ₁ , and a second memory that changes every month and is used for decryption.
a third memory for storing a signal EK _n (K _T ) sent as part of the television signal in a form in which a key code K _T indicating a coefficient of a generating polynomial for generating a PN sequence is encrypted with the K _n ; , said EK ₁ (ID _i ) and EK ₁
A fourth memory stores a decoding program for decoding (K _n ) and obtaining ID _i and K _n , and EK ₁ in the first memory stores the address code sent to the terminal.
Compare (ID _i ) with the decoded ID _i , and if they match,
Let EK _n (K _T ) in the third memory be
It is equipped with arithmetic processing means for decoding EK ₁ (K _n ) with K _n to obtain K _T , and decoding the video signal and audio signal using the deciphering PN sequence determined by this K _T. be. This makes it possible to send a key code in a different encryption format to each terminal, effectively preventing unauthorized viewing of the key code. DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment in which the present invention is applied to a satellite broadcasting system will be described with reference to the drawings. First, FIG. 2 shows an example of a satellite broadcasting system.
In the figure, 11 is a satellite broadcasting transmission center called the DBS center. 12 is a large parabolic antenna that sends signals to a geostationary satellite 13. 13 is a geostationary satellite, which is a broadcasting satellite that relays signals sent from the ground and retransmits them to the ground. 14 is a receiving antenna installed on the ground. A low-noise converter 15 converts, for example, a received 12 GHz band signal into a 1 GHz band signal and transmits it to the receiver 16. Reference numeral 19 in the receiver 16 is an intermediate frequency demodulation unit (IDU), which converts, for example, a 1 GHz input into a 400 MHz second IF signal, amplifies it, detects it, and outputs a baseband signal. 20 is a data processing circuit that extracts the output digital signal, processes it, and supplies it to the descrambler 21. Assume now that the video signal is scrambled using a method of synchronous shifting and randomly inverting the video components, and the audio is scrambled using a method of randomly changing the bit arrangement using digital audio. If the output of the IDU 19 is directly displayed on the CRT of the color television receiver 17, the brightness of the screen will be reversed and horizontal and vertical synchronization cannot be achieved, so the content will be blurred and the content will not be clear. Also, if you listen to the voice as it is from the speaker, it becomes noise. Therefore, the descrambler 21 switches between inverting and non-inverting the video according to the output of the data processing circuit 20, and rearranges each bit of the audio digital signal to restore (descramble) normal video and audio. . A/V
The reproduction circuit 22 changes the DC level only during the horizontal retrace period during the output of the IDU ₁₉ , that is, from t ₁ to _{t 2} in FIG. ~ _t11 to reproduce the original video signal (FIG. 3A), and convert the digital audio signal output from the descrambler 21 into an analog audio signal. The output of this A/V regeneration circuit 22 is transmitted to the RF modulator 2.
3 to convert it to an appropriate channel signal in the VHF band,
If the output is supplied to the antenna input of an ordinary color television receiver 17, the scrambled video and audio can be viewed in their normal, descrambled state. If you want to watch such scrambled video and audio back to normal images and sounds, you often have to pay a fee. If there is a charge, the charge is indicated by a control digital signal that is folded over the vertical blanking period (VBL) of the video signal of the program, and the charge is recorded in the memory within the receiver. Generally, if you receive a certain program for more than 2 to 10 minutes, you are often required to pay for the entire program. To pay the fee, for example, add a card reader to the data processing circuit 20 in Figure 2, insert the purchased card (such as a coupon ticket), and check the amount paid. There is a method of sending a descrambling control signal from the data processing circuit 20 to the descrambler 21 only for a time corresponding to the amount of time. Alternatively, you can pay the fee in advance to the bank 18 and use the prepaid fee as data for DBS.
A code representing the paid fee is sent from the center 11 via the geostationary satellite 13 to each terminal (individually assigned an address), and the fee code is written in the memory of the terminal. Change (decrease) the rate code of "0"
There is also a method in which the user pays the money to the bank 18 again and repeats the above procedure. Now, here, data processing circuit 2 in FIG.
The contents of 0 are configured as 31 to 50 in Figure 4, and when a pay program is received, the charge corresponding to the viewing time is non-volatile according to the charge data superimposed on the VBL period of the video signal. Write the viewing fee to the digital memory, pay the viewing fee to the bank every month, and send the payment fee to the DBS Center 1 for each terminal (each address).
The system polls and transmits data from 1 to reduce the contents of the memory 47, and makes it impossible to watch pay programs from the next month unless the contents of the memory 47 become ``0''. In Figure 4, 31 is the VBL output from IDU19.
This is a 2-digit circuit for shaping the waveform of a binary data signal superimposed on a period to form a pulse waveform as shown in the left end portion of FIG. 5B. 32 is a clock detection circuit which uses the clock run signal CR (Clock Run), which is a repetition of the 2-byte "1" and "0" signals at the beginning of FIG. A framing code is detected at the 8th bit of the framing code signal FC in B, establishing frame synchronization, and the sampling clock generated by the sampling clock generation circuit 33 is synchronized with the received signal B. 33 is a circuit that forms a sampling clock with an appropriate phase controlled in this way, and the output thereof is divided by a main clock generation circuit 34 to be outputted to the work RAM.
37, it forms a main clock that drives the work ROM 38, center processing unit (CPU) 39, etc. A clock synchronized with each bit of the received signal shown in FIG. 5B is supplied from the output of the sampling clock generation circuit 33 to the sampling circuit 35, and each bit of the received signal B is sampled. If the pulse width of each bit of the received signal B is 5/8 sc, it will be approximately 175 ns, and at this period, the work RAM 37 in Fig. 4
~CPU 39 is difficult to operate. Furthermore, when an 8-bit microprocessor is used as the CPU 39, it is more convenient to handle the received data as 8-bit parallel signals. Therefore, a serial input/parallel output type shift register such as SN74LS164 is suitable as the sampling circuit 35. When the output is memorized in the latch circuit 36 every 8 bits with the 8th bit of the framing code as a reference, the output is 8 x 8 bits in parallel.
It changes with a period of 5/8sc=1.4μs. This cycle is suitable for the operation of each circuit. Its output is connected to bus line 40. 37 is the work RAM of CPU39, 38 is CPU3
The CPU 39 is an 8-bit microprocessor (for example, MB6809E). Now, the control code C _O in the received signal B in Fig. 5,
To explain C ₁ to _{C 7} , C _O and C ₁ are "1",
It is a clock run signal CR that repeats “0”,
_C2 is a framing code signal of "11100101". _C3 consists of 4 bits of information, 3 bits of humming check code, and 1 bit of parity. _C4
The data after this also has the same structure for each byte. The contents of the information section of C ₃ and C ₄ are summarized in Table 1. Here, only three types necessary for explanation are described. In reality, several types or more are possible. Similarly, Table 2 shows the contents of the 4-bit information section of _C5 .

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【table】

Claims (1)

[Scope of Claims] 1. A circuit that receives and temporarily stores billing information in the form of a digital signal at regular intervals in the form of a digital signal, which corresponds to the content of the program viewed, and a circuit that combines the information and the time the television program was viewed. a charging amount determination circuit in a receiving device of a terminal that determines a charging amount by a circuit, a circuit that stores the charging amount, and a circuit that reads and displays charging data proportional to the charging amount stored in this circuit as necessary. It receives billing information that changes depending on the content of the program watched, determines the billing amount based on this and the viewing time, stores it, and reads out the stored billing data as necessary. In pay television equipment _configured to _display
A first memory that stores it in the form of EK ₁ (ID _i ), and a second memory that stores a key code K _n that is different for each terminal in the form of a signal EK ₁ (K _n ) that is encrypted with K ₁ . Then, the key code K _T that changes every month and indicates the coefficient of the generating polynomial for generating the PN sequence for decoding is expressed as K _n
a third memory for storing the signal EK _n (K _T ) sent as part of the television signal in encrypted form; and a third memory for decoding the EK ₁ (ID _i ) and EK ₁ (K _n ID _i
and a fourth memory that stores a decoding program to obtain K _n , and an ID _i obtained by decoding the address code sent to the terminal from EK ₁ (ID _i ) in the first memory.
and if they match, the data in the third memory is
EK _n (K _T ) is decoded using K _n , which is obtained by decoding EK ₁ (K _n ) in the second memory, to obtain K _T , and the video signal and audio are determined by the PN sequence for decoding determined by K _T. A pay television device equipped with arithmetic processing means for decoding signals. 2. A pay television set as claimed in claim 1, characterized in that EK ₁ (K _n ) and EK ₁ (ID _i ) are stored in the same memory, and the memory is configured to be freely attachable and detachable using a socket. Device.