JPS62193384A - Scramble system - Google Patents

Abstract

PURPOSE:To perform surely scramble operation even when a scramble signal is distorted due to distortion, etc. of a transmission system by digital converting original video signals, and after scramble processing, converting original video signals, and after scramble processing, converting to analog quantity and transmitting scramble signals. CONSTITUTION:Scrambled video signals are applied to an input terminal IN, and unnecessary high band component is removed by a filter 10. Then, analog signals scrambled by an A/D converter 30 are converted to digital data by a clock obtained in a clock oscillator, and the scramble signals converted to digital data are applied to an ROM 40. Digital data made by digitalizing original signals are obtained as output of the ROM 40 by referring to a data table that returns amplitude value to original value basing on scramble signals inputted as address data. Then, the data are converted to analog signals by a D/A converter 50 and original video signals are obtained through a filter 60.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a video signal scrambling system, and in particular to a video signal scrambling system that increases security against eavesdropping and simplifies system circuitry.
[Technical background of the invention and its problems] In paid broadcasting such as paid CATV that generally requires charging, the transmitted video is scrambled and the descrambling process is only applied to the bill payer. This will make it possible to view Ryotsu.

Conventionally, video scrambling systems have used digital scrambling, which involves converting the transmitted image from analog to digital and transposing horizontal lines; line permutations, which subdivide pixels for lines, and then randomly transposing the order of the pixels; There is analog scrambling, which inverts the polarity of a video signal at a predetermined level.

In both digital scrambling and analog scrambling, it is necessary to consider the influence of transmission distortion in order to increase security against eavesdropping. For example, in the case of digital scrambling, a key for descrambling is distributed to perform descrambling, but if the key data is not received correctly at the subscriber side due to transmission distortion or the like, the descrambling operation cannot be performed normally.

Furthermore, in analog scrambling, when the DC level changes due to transmission distortion, for example, when a signal scrambled by video inversion is descrambled, the video inversion level changes and flicker becomes noticeable in the descrambled image.

In the conventional video signal scrambling system described above, a correction means for correcting transmission distortion is required during the descrambling operation.

[Summary of the Invention] In the scrambling system according to the present invention, a video signal is scrambled in the form of a digital quantity on the encoder side, and then subjected to analog iK conversion and transmitted to the decoder side. On the decoder side, the scrambled analog video signal is once converted into a digital signal and descrambled.

This reduces the influence on descrambling even if there is distortion in the transmission system. [Objective of the Invention] The present invention has been made in view of the above points. This data is temporally replaced and then converted to analog values again to obtain a scrambled image.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an encoder section of a scrambling system according to the present invention, and an analog video signal to be scrambled is manually inputted to an input terminal IN. The video signal applied to this input terminal IN is inputted to the A/D converter after removing unnecessary high-frequency 8 wave number components through a filter. The /D converted signals are output to output terminals D1 to D7 of the A/D converter 3. The video signal converted into a digital quantity is added to the ROM 4, where a scrambling operation is performed on the digitized video IK.

This video scrambling operation is performed in the ROM 4 by exchanging data from the A/D converter t3 using a conversion table.

That is, the data from the A/D converter 3 is used, for example, as address data for the ROM 4, and is written into the R, OM 4, and digital data corresponding to the amplitude of the video signal is converted and scrambled using the nine conversion table. The ROM 4 stores amplitude data (Do~) from the A/D converter.
D7) as an address, it is converted to a random value using its own conversion table.

In other words, the data appearing at the output of the A/D converter 3 and digitizing the amplitude of the nine video signals functions as address data for the ROM 4. The ROM 4 is provided with a table in which numbers are assigned randomly corresponding to each address value, and amplitude data of the video signal is generated in the A/D converter 3 in accordance with the output of the clock generator 2. Each time, the ROM refers to a table in which random values are written. Then, the above ROM with scrambled amplitude data
The digital output of 4 is applied to a D/A converter 5 where it is converted into an analog value.

In this way, the amplitude is replaced with a random value, derived from the output terminal OUT, and sent to the transmission system.

In addition, in the above-mentioned OM4, the operation of randomly referring to the table and recommending the control of the address data obtained manually is as follows.
It depends on the random numbers generated by the random number generator 7. As this random number generator, an M-sequence code generator formed of a cyclic shift register is used.

The random number generated by the random number generator 7 is used to randomize the correspondence between the address of the ROM 4 and the data table written to the address. Control at this time is performed under the control of the CPU 8. Furthermore, by randomizing the correspondence between the data table and the address, the amplitude information of the optical video signal is kept secret, but the decoder that performs the descrambling operation can check the relationship between the randomized address and the data table. I need information to undo it. An example of key information for this purpose is the initial value for the random number generator 7 described above. The initial value that functions as this key data is generated by the data generation circuit 9, added to the above R and OM4 at a timing corresponding to the vertical blanking period of the older image canceling signal, and further encrypted by the ROM table and then output terminal OUT).

Note that the vertical blanking period is detected by performing vertical synchronization separation using the timing oscillator 10. At this timing, initial value data is sent to the random number generator 7 in the data generation circuit 9 and is also supplied to R, 0M4. Furthermore, the initial value data that functions as key data is R,
It is encrypted with 0M4 and sent to a transmission system such as a cable.

FIG. 2 is a waveform diagram showing the waveforms of each part of FIG. 1, and the scrambling operation will be explained using this waveform.

In the figure, (A) shows a scrambled single-source video signal. This optical video signal is sampled by the A/D converter 3 at the clock frequency shown in B. The sampling frequency at this time is preferably sampling at the Nyquist interval, but sampling at the sub-Nyquist interval is also possible. Sampling using the sub-Nyquist interval refers to sampling at a frequency of 2fS, which is lower than the Nyquist interval zfo, and is suitable for encoding signals.In sampling using the sub-Nyquist interval, the frequency components between fS- and fo are It is folded back within the Q-fs frequency band and included in the signal bandwidth. This means that there will be noise within the signal band, but there is no problem as long as this noise level is below a permissible level. Since a video signal has a wide frequency bandwidth and an extremely small high-frequency component, it is possible to reduce the bit rate and lower the sampling frequency by performing sub-Nyquist sampling when digitizing the signal. Based on this, the sampling frequency shall be determined appropriately, and the sampling pulse shown in Fig. 2 (CB) is an enlarged time axis for the optical video signal, and the optical image corresponding to the expanded time axis. The enlarged portion of the signal is shown in FIG. 2(C), and the scrambling operation will be described next.

The optical video signal (FIG. 2(C)) is transmitted to the A/D in accordance with the clock (◎ in FIG. 2) generated by the clock oscillator 2.
It is converted into a digital value by the converter 3 (Fig. 2 (
D)). The output data of the A/D converter 3 (FIG. 2(D)) obtained at this time is used as address data for the ROM 4.

In this ROM4, as mentioned above, it corresponds to the address. There is a translation table for the address.

The corresponding relationship between and the conversion table is randomized by the output data of the random number generator 7. Therefore, the above R
At the output of the OM4, data (FIG. 2)) obtained by scrambling the amplitude information of the optical video signal is obtained. After this, the above R
The output data of OM4 (Fig. 2 (E)) is sent to D/A converter 5.
Then, it is converted into the digital quantity shown in FIG. 2(F).

That is, the optical video signal shown in FIG. 2(C) is as shown in FIG. 2(F)K.
Note that the synchronization signal of the optical video signal is not scrambled, but the timing generator 10 separates the synchronization signal from the optical video signal, and during this time, the scrambling by the OM4 is performed under the control of the CPU 8. Stop at. Then, the synchronization signal is scrambled.

In the figure, a scrambled video signal is applied to an input terminal IN, and a filter 10 removes unnecessary high-frequency components. Then, the scrambled analog signal is converted into digital data by applying the clock signal obtained by the clock oscillator to the A/D converter. This digitized scramble signal is applied to the ROM 4. Here, a data table is referred to which restores the amplitude value based on the scramble signal input as address data. As a result, digital data obtained by digitizing the original signal is obtained at the output of the 9ROM 40.

Thereafter, it is converted into a child analog signal by a D/A converter and passed through a filter 60 to obtain a 9-element video signal.

In order to obtain an optical video signal, it is necessary to refer to the table in the ROM 40 in correspondence with the encoding side.

Reference to the data table in R,0M40 depends on the output data of the random number generator 707. However, the scrambled initial value data superimposed on the vertical blanking period on the encoder side is separated by the synchronization separation circuit 71, and the CPU 80 determines whether or not the subscriber is a subscriber, after which it is confirmed that the subscriber is a subscriber. Then, initial value data is obtained by referring to a table in the ROM 40. This initial value data is
is added to the random number generator 70 under the control of the encoder, and the random number generator 70 obtains a random number corresponding to each encoder. In this manner, the random number generator 70 generates random numbers corresponding to the encoder side, thereby making reference to the data table necessary for descrambling.

Note that synchronization is ensured by using the synchronization signal separated by the synchronization separation circuit 71.

〔Effect of the invention〕

As explained above, according to the present invention, an optical video signal is first converted into a digital signal and then scrambled, and then converted into an analog signal and transmitted as a scrambled signal. Even though
Descramble operation can be performed reliably. In other words, it is possible to alleviate both the limitations caused by eye pattern deterioration caused by digital transmission and the limitations caused by noise in analog transmission.

Further, in the above embodiment, the width information is scrambled, but it is also possible to scramble the phase, frequency information, etc. according to the modulation method of the optical video signal using a conversion table.

Furthermore, if necessary, key data may not be set, and ROMs having the same data table on both the encoder and decoder sides may be used to simplify the process.

[Brief explanation of drawings]

1 and 3 are circuit diagrams showing an embodiment of the scrambling system according to the present invention, and FIG. 2 is a time chart for explaining the circuit operation of FIG. 1.03.30...A/D Converter, 4.40...ROM. 5.50...D/A converter, 7,70...Random number generator, 71...Synchronization separation circuit, 9...Data generation circuit.

Claims (1)

[Claims] In the encoder section, the input analog video signal is converted into a digital quantity, the digital quantity is digitally scrambled, and then converted back into an analog quantity and the scrambled analog video signal is sent to the transmission system. . A scrambling system, characterized in that the decoder converts the scrambled analog video signal into a digital amount, and then performs descrambling on the digital amount to restore the video signal.