JPH0218783B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a method for transmitting control information that controls the scrambling of broadcast program signals in scramble broadcasting that conceals broadcast program contents from non-subscribing receivers, and in particular, relates to a method for transmitting control information that controls the scrambling of broadcast program signals. This allows the contents of the program to be kept secret.

BACKGROUND OF THE INVENTION In general, in scrambled broadcasting, a broadcast signal is scrambled in advance and broadcast so that only the receiver used by a specific subscriber can receive the broadcast program. This is a broadcast format in which the scrambled broadcast signal is descrambled and restored using a specific receiver or decoder so that normal broadcast programs can be viewed. In such scrambled broadcasting, subscribers are given some control information, ie, key information, for normally restoring the scrambled broadcast signal. On the other hand, some receivers of non-subscribers may not be able to properly restore the scrambled broadcast signal, making it impossible to view the broadcast program.

However, if the scrambling mode is simple, it may be possible to illegally view a broadcast program even in a receiver that does not perform proper descrambling by making slight modifications or adding circuits. Therefore, in order to realize completely scrambled broadcasting that completely eliminates such unauthorized viewing, it is essential to develop a system in which unauthorized viewing is extremely difficult.

There are two ways to strengthen scrambled broadcasting against unauthorized viewing.

(1) Making the scramble and descramble aspects of broadcast signals complicated to make exploratory unauthorized viewing extremely difficult.

(2) Although the configuration of the descrambling circuit itself is not complicated, it is extremely difficult to decipher the key information for descrambling.

The former method of complicating the descrambling aspect has the difficulty of developing a scrambling method that is cheap for official receivers and expensive for eavesdropping receivers, as it is necessary to avoid increasing the price of official receivers. There is a problem.

Summary of the Invention An object of the present invention is to solve the above-mentioned conventional problems, and in particular, to improve the degree of completeness by complicating only the configuration of the descrambling key information without complicating the configuration of the latter descrambling circuit itself. An object of the present invention is to provide a control information transmission system for scrambled broadcasting that can realize high quality scrambled broadcasting.

That is, in the control information transmission system of the present invention, the second key signal, which controls the change of the code sequence in the first key signal that is composed of a predetermined pseudo-random code sequence and scrambles the broadcast program signal, is replaced by the third key signal. The third key signal is encrypted and transmitted together with the scrambled broadcast program signal through a broadcast transmission path, and the third key signal is transmitted by a fourth key signal that is individually set and stored in each subscriber receiver in advance. Encrypted and transmitted via separate transmission path,
Each participating receiver decodes the third key signal using the fourth key signal stored in advance, decrypts the second key signal using the decrypted third key signal, and regenerating the first key signal by controlling a change in the code sequence generated in the joining receiver using the decoded second key signal;
The scrambled broadcast program signal is descrambled using the reproduced first key signal, and the broadcast program signal is reproduced.

EXAMPLES The present invention will be explained in detail below using examples with reference to the drawings.

Generally, in broadcasting by radio waves, the broadcast program signals themselves such as video signals, audio signals, data, etc.
Of course, it is transmitted by broadcast radio waves, but the following transmission methods are conceivable for transmitting the descrambling usage information, that is, the key information, each having its own characteristics.

(1) A method in which key information is also transmitted via broadcast radio waves.

When transmitting key information by multiplexing it onto a portion of broadcast waves, the key information can be transmitted at a high speed, for example, at a speed of several tens to hundreds of kilobits per second. Easiest to update. However, if all the key information is transmitted via broadcast radio waves, if an unauthorized recipient can manufacture a special receiver and decode the key information, he or she will be able to view the entire broadcast program. Therefore, it becomes necessary to encrypt key information to be transmitted via broadcast radio waves, and to transmit key information for decoding the encrypted key information via a transmission path other than broadcast radio waves.

(2) A method of transmitting key information using a wired communication system such as a telephone line.

Since the key information is transmitted through a transmission path separate from the broadcast radio waves, security in preventing eavesdropping is increased. In addition, the information transmission speed after connecting the communication line is
For example, it is quite high, on the order of several kilobits per second. However, when using a telephone line, it is impossible to transmit key information to all subscribers at the same time, and it is necessary to connect the lines one after another and transmit the key information sequentially. It is difficult to update, and providing a dedicated transmission line for key information is economically disadvantageous.

(3) A method of transmitting key information using distribution media such as cards.

Distribution media include magnetic cards and semiconductor ROMs.
(read-on memory), IC cards, etc.
The amount of information per sheet varies depending on the medium, but is on the order of several hundred bits to several hundred kilobits. Since key information transmission via distribution media is completely asynchronous with broadcast radio waves, the update speed of key information is quite slow. Further, the content of the information transmitted by the distribution medium can be distributed centrally to all subscribers, or it is possible to individually distribute information with different content to each subscriber. Note that distribution media can often be copied, so it is necessary to take measures to prevent copying.

(4) A method in which encryption key information and decryption key information are fixedly built into the descrambling decoder itself.

Key information is built into the decoder in the receiver during system configuration, and the decoder itself is replaced to update the key information. Note that the built-in key information needs to be in the form of a semiconductor memory or the like, and must be made difficult to read from the outside.

On the other hand, the functions that scramble control information, that is, key information in scramble broadcasting should have are as follows.

(1) Cannot be directly detected by anyone other than the subscriber.

(2) Since it would take a long time to indirectly detect key information from a scrambled broadcast signal, even if it were possible, it is not possible to provide an opportunity to use the key information obtained through such indirect detection. Therefore, the key information is updated frequently, and the key information can be used immediately after the update in the authorized receiver.

(3) The key information given to each subscriber shall be kept private so that it cannot be used by others.

As mentioned above, there are various types of control information transmission systems for scrambled broadcasting, but in the past, there was no system that had all the functions required for scrambled broadcasting, but in the present invention, By integrating the above-mentioned features of the various embodiments, control information can be transmitted in a manner optimal for scrambled broadcasting as described in detail below.

First, FIG. 1 shows an example of the configuration of a control information transmission system for scrambled broadcasting according to the present invention. In the illustrated configuration, an original signal, that is, a broadcast program signal 1, is converted into a scrambled broadcast signal 3 by changing the signal form by a scrambler 2, and then sent to a broadcast transmission path 3.
Transmit via. Although radio waves are primarily considered as the broadcasting transmission line 4, the same applies when broadcasting to an unspecified number of subscribers via a wired transmission line. On the other hand, on the receiving side,
A descrambler 5 performs the reverse conversion to that on the transmitting side and converts it into a restored broadcast program signal 6. Note that the broadcast program signal may be in any form such as a video signal, audio signal, or data signal.

The signal format conversion in the scrambler 2 or descrambler 5 described above is performed based on the respective circuit configurations and algorithms and the scramble control signal 7 or descramble control signal 8 supplied from the outside.
The content of the signal processing is determined by the In other words, the scramble control signal 7 and the descramble control signal 8 are the keys when descrambling the broadcast program signal after scrambling it, and the control signal when directly processing the broadcast program signal is used as the first signal. This will be referred to as a key signal. This first key signal may be the same or different on the transmitting side and the receiving side depending on the form of signal processing within the scrambler 2 and descrambler 5, but this will not be specified in the following explanation. As far as possible, they will be collectively referred to as the first key signal without distinguishing from any of them.

Although this first key signal differs depending on the scrambling method, it is generally set so that the form of the signal changes pseudo-randomly according to a certain rule. For example, for a digitized audio signal, as shown in FIG. A typical form of signal processing is to perform scrambling by adding modulo 2 for each signal. The pseudorandom code string in this signal processing form is the above-mentioned first key signal, and on the receiving side, the pseudorandom signal generator 36 generates a pseudorandom code string that is the same as that at the transmission speed, and is scrambled. The original signal can be restored by adding it to the received signal in the exclusive OR circuit 37. Note that when scrambling analog video signals, scrambling is also performed in which the positional relationship of pixel signals and synchronization signals, or the amplitude, polarity, etc. of the signals are changed based on pseudo-random values.

The above-mentioned pseudo-random code strings and pseudo-random numerical values are generated by pseudo-random signal generators 9 and 10, and their generation speed is set to the speed necessary for processing. As such a pseudo-random signal generation circuit, a pseudo-random (PN) signal generator using a feedback shift register or the like is generally used.

The above-described pseudo-random signal generator using a feedback shift register is configured, for example, as shown in ^FIG . A pseudo-random code string with a period of is obtained. This period increases exponentially as the number of stages n of the shift register increases. For example, when the clock frequency is 1 MHz, if n = 8, the period length becomes 255 μs, but if n = 32, the period length increases. The length will be 1.2 hours, and if n = 64, it will be 5.8 x 10 ⁵ years. Now, if the period of the pseudorandom code string is short and the probability of occurrence of 0 and 1 in the digitized code string of the original signal is biased, for example, the exclusive OR circuit 33 in the configuration shown in FIG. By observing the bits of the output code string that are separated by the number of bits of one period of the pseudo-random code string, it is possible to estimate the structure of the pseudo-random code string being added. Therefore,
In order to prevent the first key information from being decrypted in this way, it is necessary to increase the number of stages of the shift register to several tens or more and to make the cycle length of the code string sufficiently long.

Furthermore, in a pseudo-random signal generator using a feedback shift register, if the feedback connection logic is set, then if the same initial value is given to the shift register, a code string of the same form will be repeatedly generated. Although this property is extremely important in ensuring that the same code string is generated on the transmitting side and the receiving side, it also has the following problems. Now, from the nature of the broadcast program signal, if it is possible to correctly estimate the part of the code string of the digitized original signal that is longer than the number of stages of the shift register, then the code string of the output transmission signal of the exclusive OR circuit can be estimated from the code string of the output transmission signal of the exclusive OR circuit. By subtracting the code string of the original signal, we get
It is possible to correctly estimate the pseudorandom code string being added. Therefore, if the estimation results are sequentially set in each stage of the shift register, the code string generated from the feedback shift register will completely match the code string on the transmitting side, and the first key information will be It will be deciphered.

Generally, the redundancy of the signal waveform of a broadcast program signal is quite large, so if the key information is estimated or decoded in the manner described above, it becomes difficult to completely prevent eavesdropping. As a measure to prevent such key information decoding, even if such key information decoding is successful, the manner in which pseudo-random code strings are generated is changed over time so that continuous eavesdropping for a long period of time becomes impossible. do. Furthermore, if the time interval between such changes in the generation pattern is made shorter than the cycle length of the code string, the above-mentioned decoding using periodicity itself becomes impossible, so the number of stages of the shift register can be reduced.

On the other hand, the manner in which the pseudorandom code string is generated is changed, for example, as follows.

(1) Change the initial value of the shift register.

For example, if the initial value in the four-stage feedback shift register shown in FIG. 3 is 1111, a code sequence as shown in FIG. 4a is obtained,
The period is 15 bits. However, if the initial value is reset during the shift, a code string without periodicity is obtained, as shown in FIG. 4b. Note that the underlined portions in the illustrated code string are the portions where the initial values have been changed.

(2) Change the wiring logic of the feedback shift register.

For example, as shown in FIG. 5, if the connection logic in a five-stage feedback shift register is changed, completely different code strings can be obtained even if the same initial value is set. Obtaining different code strings by changing the wiring logic is possible if the feedback shift register has five or more stages.

All of the above can be controlled by using an n-stage shift register and supplying digital information of at most n bits to the shift register circuits on the transmitting side and the receiving side, respectively. That is, the pseudo-random (PN) signal generator control information signals 11 and 12, which are composed of initial value data given to each stage of an n-stage shift register or data indicating the presence or absence of a feedback connection in each stage, are used as second key information. I will call it .

As a transmission path for the second key information 11, it is necessary to transmit it to the receiving side each time the state of the pseudo-random signal generator is updated, so from the viewpoint of transmission speed, it is transmitted on a part of the broadcast radio waves. is optimal. However, since the second key information is also transmitted to the unauthorized recipient at the same time each time it is updated, it is difficult to further encrypt the second key information itself, transmit it, and decrypt it using the decryption circuit 14 on the receiving side. , so that additional key information is required.
Key information 15 for encryption and decryption of the key information itself
and 16 will be referred to as third key information.

As the transmission path for the third key information 15 on the transmitting side, it is appropriate to use a separate transmission path different from the broadcast radio waves in order to prevent this third key information from leaking to anyone other than the subscriber. . Moreover, this third
Since the key information does not need to be updated as frequently as the second key information, it can be transmitted using a wired communication system such as a telephone line or a distribution medium such as a card. It is possible to store the third key information in the decoder itself, but if the third key information becomes known to someone other than the subscriber by some means and it becomes necessary to change it, The problem is that the decoder itself needs to be modified or replaced.

In addition, when transmitting the third key information using a distribution medium such as a card, if the same card etc. can be used in other receivers, for example, if the card is duplicated, charges can be collected, etc. A big problem arises in terms of An appropriate way to avoid this problem is to make the key information for receiving scrambled broadcasting different for each subscriber. However, the first
The key information needs to be common to all subscriber receivers due to restrictions on radio broadcasting, such as frequency allocation constraints, and the second key information that controls this first key information is also unique to each subscriber. It is necessary to make it common to all people. Regarding the second key information,
If there is sufficient data capacity on the key information transmission path, multiple types of change methods can be set to obtain the same first key information, and multiple pieces of second key information can be created with each change made. On the other hand, it is conceivable to divide each subscriber into a plurality of groups and set an inverse conversion method for each group. A possible method is to add different code strings. However, the method of transmitting a plurality of pieces of second key information is not a very desirable method because setting different key information for each subscriber requires increasing the control information transmission capacity by radio waves. . That is, when recording the third key information for encrypting the second key information on the distribution medium, the third key information itself is further encrypted, and the key information used for the encryption is added. It is possible to make it different for each case.

The third key information described above is encrypted by the encryption circuit 17 in the configuration shown in the first diagram, and is recorded by the writing device 22 on a distribution medium 23 such as a magnetic card or ROM. On the receiving side,
The distribution medium 23 is attached to the reading device 24, and the read output signal is decrypted by the decryption circuit 18 to extract the third key information 16. This third key information 16
The key information for encrypting is referred to as fourth key information, and is unique key information that differs for each subscriber. This fourth key information is set and stored in advance inside the decoder of each subscriber receiver, and when issuing and distributing distribution media, all the fourth key information built into the decoder is added. The third key information is recorded and managed in the user's individual key information file 21 or the like, and the third key information encrypted based on the recorded fourth key information is distributed on a distribution medium.

As detailed above, at least four types of key information are required for complete control of broadcast program signal concealment in scrambled broadcasting.
The relationship between the update periods for each of the key information is summarized as follows.

The first key information continues to work during broadcasting.

The second key information needs to be updated while the first key information is not decoded from the scrambled and broadcast broadcast program signal. The appropriate length of time for the update period depends on the deciphering skills of the fraudulent recipient, but it is considered appropriate to set it within a few seconds. In other words, even if the first key information can be decrypted by chance, if the first key information is updated within a few seconds, the decryption must be continued without any time for eavesdropping. Eavesdropping on broadcast program signals becomes virtually impossible. Furthermore, if digital information of several tens of bits is to be transmitted with a period of several seconds or less, the transmission of control information will not place a large burden on the broadcast wave transmission path.

Since the third key information is transmitted to each subscriber via telephone line, distribution medium, etc., the update period is considered to be longer than about once a month. Since this third key information appears in the signal form as it is only inside the receiving decoder, the integrated circuit is designed so that the third key information appearing inside the receiving decoder cannot be read out. It is necessary to keep it. Note that there is no need to update the third key information unless it is known to a non-subscriber, so it is sufficient to use a transmission form that can be updated if it becomes known by chance and needs to be updated. become.

The fourth key information is fixedly stored inside the decoder when it is manufactured, and is not updated except when the decoder is repaired or replaced. Note that this fourth key information also needs to be prevented from being read out from the decoder.

Next, the amount of information required for each of the above-mentioned key information will be explained.

The first key information is continuously used to scramble the broadcast program signal during the broadcast period, but it is generated separately on the receiving side using the second key information, so there is no need to transmit it.

The second key information has an amount of information corresponding to the number of stages of the shift register to be controlled. In addition, in order for the unauthorized recipient to know this second key information, it is necessary to repeat trial and error decryption using all similar key information that may be used.
It is necessary to make the update period longer than the update period of the key information. For example, if trial and error for 1-bit key information takes 0.1 seconds, trial-and-error for 4-bit key information requires 0.1 x 2 ⁴ = 1.6 seconds, and trial-and-error for 8-bit key information requires 0.1 x 2 4 = 1.6 seconds. 25.6 seconds for 16-bit key information, 1.8 seconds for 16-bit key information
It will take time. Therefore, if the amount of second key information is set to be larger than about 16 bits, such trial-and-error decryption will actually become impossible within the update period.

Regarding the third and fourth key information, even if it takes a long time to decrypt it through repeated trial and error as described above, the update period of the key information is long, so the result of the decryption can be used to prevent eavesdropping. There is a risk of For example, the DES standard (Data Encryption) is an encryption standard standardized for information processing in the United States.
Standard) sets the amount of key information to 64 bits,
Since the actual amount excluding bits for error checking is specified as 56 bits, it is safe to keep this amount of information. Note that the number of subscribers to whom these key information should be transmitted needs to be individually assigned to tens of millions of subscribers, so from this point of view,
An amount of information in the order of 26 bits (corresponding to 2 ²⁶ = 6.7×10 ⁷ subscribers) is sufficient.

As described above, according to the present invention, the mode of transmitting the control information, that is, the key information necessary for restoring the scrambled broadcast program signal, to the receiving side safely, that is, so as not to be decoded by non-subscribers, has been described in detail. In scrambled broadcasting, it is also necessary to have a function to control the operation of the receiver according to the contents of the subscriber's contract due to the connection with the charge collection system for paid broadcasting. For example, it is necessary to have a function that stops the descrambling function of the receiver if the contracted broadcasting station, contract period, type of viewing group such as special program with special charge, etc. do not match the broadcast signal content. be. To provide this kind of functionality, control information related to the contract content is included in the distribution data of the distribution medium used to transmit the third key information, and on the other hand, the control information related to the contract contents is included in the distribution data of the distribution medium used to transmit the second key information. It is also conceivable that information regarding the program, a broadcasting station code, a date code of year, month, day, etc. are transmitted therein, and the descrambling is controlled after checking the control information on the receiving side. An example of the structure of transmission data in such a case is shown in FIG. 6, and an example of the structure of distribution data is shown in FIG. Note that when the capacity of information transmission by broadcast radio waves is large, it is also possible to carry out radio addressing, in which information such as a number indicating the identity of each subscriber is carried on the radio waves and transmitted, thereby individually controlling the reception decoder. An example of the structure of transmission data in such a case is also shown in FIG. On the receiving side, it is possible to control the descrambling operation according to the result of checking the above-mentioned subscriber information and the subscriber-specific information in the distributed data such as the decoder number. The contents of such control include operating the decoder of a receiver with a contract, and stopping the operation of the decoder of a receiver whose contract has expired or has been stolen. In the former case, the amount of data to be transmitted is large, the transmission takes time, and the receiver must always be in a receiving state. On the other hand, in the latter case, the amount of data to be transmitted is small, and even if the information is not transmitted to a receiver that is not in a receiving state, there is no problem compared to the former case, and it is considered easier to implement than the former case.

FIG. 8 shows a configuration example of a reception decoder that adds the above-mentioned fee collection-related information processing function to the scrambled broadcast control information transmission system having the basic configuration shown in FIG.

As the encryption method for realizing the control transmission function according to the present invention, any encryption method can be used as long as it is possible to encrypt and decrypt all information of the transmission data within the transmission interval of the transmission data. Also, the second
Since it is not necessary to encrypt and decrypt the key information and the third key information at the same time, the same circuit can be used alternately in a time-sharing manner as the same encryption method. Note that a specific example of the encryption method is the aforementioned DES method.

Further, as a circuit for generating a pseudo-random code string constituting the first key information, an example using a feedback shift register was mainly explained, but the circuit is not limited to this example, and for example, as shown in FIG. A circuit or the like that generates a block encryption circuit as shown can be similarly used. However, the key 63 in FIG. 9 is different from the first to fourth keys described above, and is set in advance.
It is also possible to share the key with Note that the above-mentioned DES method or the like can be used as this encryption method.

Effects As is clear from the above explanation, the following points can be cited as advantages and effects of the method for transmitting control information for scrambled broadcasting, that is, key information, according to the present invention.

(1) Regardless of whether the broadcast program signal to be scrambled is a video signal, audio signal, data signal, etc., the control information transmission system can be realized with a similar configuration regardless of the signal format. .

(2) To prevent unauthorized recipients from decoding key information by taking advantage of the redundancy and other properties of transmitted signals,
Since the contents of the key information can be updated over time and the control information for updating can be transmitted to the receiving side at high speed, the key information can be updated frequently to improve security.

(3) Encrypting the control information for updating the key information mentioned above and transmitting the control information for decoding the encrypted control information to non-subscribers using a transmission path different from broadcast radio waves. The chances of leakage can be greatly reduced.

(4) The first key information, which directly controls the scrambling of broadcast program signals, is not directly encrypted and transmitted, but is generated using the second key information, so the amount of information is extremely small. can be transmitted.

(5) Key information for encrypting control information transmitted via broadcast radio waves can also be updated as needed.

(6) According to the configuration of the control information transmission system according to the present invention, key information for encrypting distributed data can be individually set for each receiver, and distributed transmission media such as cards can be reproduced. Even in such a case, it is possible to prevent other receiving decoders from operating depending on the duplicated card or the like.

(7) Not only the control of broadcast program signal scrambling, but also the control information related to fee collection in paid broadcasting can be transmitted in an integrated manner, making it possible to realize a scrambled broadcasting system that is highly flexible in terms of operation. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of a control information transmission system for scrambled broadcasting according to the present invention, and FIG.
The figure is a block diagram showing an example of the configuration of a scrambling circuit based on the addition of pseudo-random code strings.
FIG. 3 is a block diagram showing a configuration example of a pseudo-random signal generator using the same feedback shift register, and FIGS. 4 a and 4 b show examples of output code strings of the pseudo-random signal generator. Figures 5a and 5b are block diagrams respectively showing other configuration examples of a pseudorandom signal generator using the same feedback shift register.
6a and 6b are diagrams showing an example of the structure of the transmitted data, FIG. 7 is a diagram showing an example of the structure of the distributed data, and FIG. 8 is a block diagram showing an example of the structure of the receiving decoder. FIG. 9 is a block diagram showing an example of the configuration of a pseudorandom signal generator using the same block encryption circuit. 1...Broadcast program signal, 2...Scrambler, 3
...Scrambled broadcast signal, 4...Broadcast transmission line,
5, 61... Descrambler, 6... Restored broadcast program signal, 7... Scramble control signal (part of first key information), 8... Descramble control signal (part of first key information) ,9,10,32,36,
60-2...pseudo random signal generator, 11,1
2... Second key information, 13, 17... Encryption circuit, 14, 18, 52, 53... Decryption circuit, 1
5, 16...Third key information, 19,20...Fourth
key information, 21...Subscriber individual key file, 22
...Writing device, 23...Distribution medium, 24...Reading device, 25, 26...Control information, 27, 30
...Digital code string, 31, 35... Pseudo-random code string, 33, 37, 44, 45, 46...
Exclusive OR circuit, 40, 60-1, 62...Initial value setting circuit, 41-1 to 41-4, 51...Switch, 42...Shift register, 43...PN
Signal output, 47... Broadcast reception signal, 48... Distribution data, 49... Operation data, 50... Equipment number, 54, 55-1, 58, 63... Key signal memory circuit, 55-2... Contract content data extraction circuit,
56...Subscriber number information extraction circuit, 57...Transmission data extraction circuit, 59...Decoder control circuit, 6
4...Input buffer circuit, 65...Block encryption circuit, 66...Pseudo random signal output.

Claims (1)

[Scope of Claims] 1. A second key signal that controls the change of a code sequence in a first key signal that is composed of a predetermined pseudo-random code sequence and scrambles a broadcast program signal.
The third key signal is encrypted using a fourth key signal and transmitted along with the scrambled broadcast program signal through a broadcast transmission path, and the fourth key signal is individually set and stored in each subscriber receiver in advance. The key signal is encrypted and transmitted through a separate transmission path, and each participating receiver decodes the third key signal using the fourth key signal stored in advance, and the decrypted third key decoding the second key signal by a signal, controlling the change of the code sequence generated in the participating receiver by the decoded second key signal, and reproducing the first key signal; A control information transmission system for scrambled broadcasting, characterized in that the scrambled broadcast program signal is descrambled by a first key signal and the broadcast program signal is reproduced. 2. In the transmission method according to claim 1, the first and second key signals are changed in short cycles, and the third key signal is changed in long cycles. A control information transmission method for scrambled broadcasting characterized by: 3. In the transmission system according to claim 1 or 2, by updating the initial value of the generator of the pseudorandom code string with the second key signal, A control information transmission system for scrambled broadcasting, characterized in that code sequence changes are controlled. 4. In the transmission system according to claim 1 or 2, the second key signal is used to change the connection logic of a pseudo-random code string generator consisting of a feedback shift register. 1. A control information transmission system for scrambled broadcasting, characterized in that changing of a code sequence in a key signal of No. 1 is controlled.