JPH08288939A - Broadcast system - Google Patents

Abstract

PURPOSE: To provide the broadcast service to only plural contract terminal equipments connected to each subscriber line without the use of a timewise broadcast switch. CONSTITUTION: A broadcast cell ciphering section 823, a cryptographic key generating section 824, and a clock section 824 or the like of a line terminator 80 have a function of using a cryptographic key K2 updated by a prescribed period to cipher a broadcast cell. A cell processing section 829, a file storage section 830 and a usual cell ciphering section 721 or the like process the cryptographic key K2 into a cell every time the cryptographic key K2 is updated to cipher the cell by a cryptographic key K1 provided in advance to each contractor. A usual cell decoding section 101 of a subscriber terminal equipment 100 has a function of using the cryptographic key K1 provided in advance to its own terminal equipment to decode a received cell. A cryptographic key extract section 105 has a function of extracting the cryptographic key K2 from the decoded output. A broadcast cell decoding section 102 has a function of using the extracted output to decode the received cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a broadband service integrated digital network (hereinafter referred to as "B-IS") as a transmission line.
It is called "DN". ) Related to a broadcasting system for broadcasting.

[0002]

2. Description of the Related Art In recent years, in the field of telecommunications, introduction of B-ISDN has been promoted as a subscriber network such as a telephone network. In this B-ISDN, it is expected that broadcast-type services such as cable television (hereinafter referred to as "CATV") will be provided as communication services. Therefore, for example, as described in the following documents and the like, research and development relating to the provision of broadcast-type services in B-ISDN are being actively conducted.

[0003] Reference: "A Study on Broadband Access Systems for Providing Multimedia Services" TECHNICAL REPORT OF IEICE.CS94-18.OSC94-
8 (1994-05) FIG. 2 is a block diagram showing an example of the configuration of a CATV system using B-ISDN.

In the illustrated CATV system, CA
A broadcast cell of a CATV signal output from the TV supply device 10 is supplied to a subscriber line terminating device (SLT) 30 via a long distance network 20 which is the core of B-ISDN.

Broadcast cells supplied to the subscriber line terminating device 30 are distributed to a plurality of subscriber lines 40. The broadcast cell distributed to each subscriber line 40 is
Are distributed to a plurality of subscriber terminals (ONUs) 50 connected to.

Each subscriber line 40 is composed of, for example, a passive double star transmission line. That is, each subscriber line 40 has one optical fiber 41 connected to the subscriber line terminating device 30 and a star coupler (SC) 4.
2 and a plurality of optical fibers 43 connected to each subscriber terminal 50.

However, in the structure in which the subscriber line 40 is formed by a passive double star transmission line, there arises a problem that the broadcast service is provided to a person other than the subscriber of the broadcast service.

That is, a broadcast service contract is usually
It is performed for each broadcast channel. Further, in the case of a broadcasting service using B-ISDN, it is possible to further consider an hourly contract. In other words, a program-based contract can be considered.

Under such a contract environment, not all of the subscriber terminals 50 connected to each subscriber line 40 are subscriber terminals of the subscriber (hereinafter referred to as "contract terminals"). Therefore, in a configuration in which the subscriber line 40 is formed by a passive double star type transmission line, there arises a problem that the broadcast service is provided to a person other than the subscriber of the broadcast service.

In order to deal with this problem, conventionally, in the subscriber line terminating device 30, an encryption key provided in advance to each subscriber terminal 50 is used to encrypt a broadcast cell for each subscriber and then transmit it. It was supposed to do.

According to such a configuration, each contract terminal 50
Since only the receiving cell can be decoded, the broadcast service can be provided only to the contractor.

[0012]

However, in such a configuration, there is a problem in that a broadcast switch for a broadcast cell requires a temporal broadcast switch in addition to a spatial broadcast switch.

Here, the spatial broadcast switch 31 is
As shown in FIG. 3, this is a switch for allocating broadcast cells supplied from the CATV supply device 10 to a plurality of outgoing lines 32.

Further, as shown in FIG. 4, the temporal broadcast switch 33 is used to copy broadcast cells by the number of contract terminals,
It is a switch that distributes broadcast cells to a plurality of contract terminals 50 connected to one subscriber line 40 by outputting each copy cell to each output line 32 in a time-division manner.

The need for such a temporal broadcast switch causes a problem that the usable bandwidth of each subscriber is narrowed.

Also, as shown in FIG. 5, the broadcast switch 3
In the configuration in which the broadcasting cell copying unit 34 is provided inside the broadcasting cell 3, the broadcasting cells must be copied for a maximum of [the number of outgoing lines] * [the number of subscriber terminals connected to the outgoing line]. Becomes a problem.

Further, as shown in FIG. 6, in the structure in which the broadcasting cell copying unit 34 is provided on the outgoing line 32 of the broadcast switch 33, there is a problem that a buffer memory must be provided for each outgoing line 32. Occurs.

Therefore, in the broadcasting system using the passive double star system transmission line as the subscriber line 40, without using the temporal broadcasting switch 33,
A technology capable of broadcasting is desired.

[0019]

In order to solve the above problems, the present invention encrypts and transmits a transmission signal of broadcast information using a first encryption key updated at a predetermined cycle, and Every time the first encryption key is updated, the transmission signal of the first encryption key is assigned to the second subscriber, which is previously assigned to each contractor.
The encryption key is used for encryption and transmission.

[0020]

In the above structure, on the transmission side of the broadcast information,
A process of encrypting the transmission signal of the broadcast information with the first encryption key and transmitting the encrypted signal is executed. Also, every time the first encryption key is updated, a process of encrypting the transmission signal of this encryption key with the second encryption key previously given to each contractor and transmitting it is executed.

On the other hand, on the receiving side of the broadcast information, a process of decrypting the received signal by using the second encryption key given to itself is executed. Further, the process of extracting the first encryption key from the decrypted output is executed. Further, a process of decoding the received signal is executed using this extracted output.

According to such a configuration, the first received
If the transmission signal of the encryption key is encrypted with the second encryption key given to itself, the first encryption key can be accurately extracted from this reception signal. This allows
The transmission signal of the received broadcast information can be accurately decoded without using a temporal broadcast switch.

[0023]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

Incidentally, FIG. 1 shows the invention according to the B-ISDN.
A case where the present invention is applied to a CATV system using is shown as a representative. Further, FIG. 1 shows a typical case where the present invention is applied to a system having a transmission function of a normal cell in addition to a broadcast cell. Here, the normal cell is an ATM (asynchronous transfer mode) that is supplied to only one subscriber terminal 100.
It is a cell.

The illustrated broadcasting system has a CATV supplying device 60, a long distance network 70, a subscriber line terminating device 80, a plurality of subscriber lines 90, and a plurality of subscriber terminals 100. In the figure, one subscriber line 90 and one subscriber terminal 100 are shown.

Here, the CATV supply device 60 is a CAT.
It has a function of outputting a V signal broadcast cell. Long distance network 7
0 has a function of transmitting an ATM cell (broadcast cell or normal cell) to the subscriber line terminating device 80. The subscriber line terminating device 80 has a function of terminating the subscriber line 90. The subscriber line 90 includes a subscriber terminal 100 and a subscriber line terminating device 80.
It has the function of connecting with. The subscriber terminal 100 is a CA
It has a function of receiving ATM cells of TV signals.

The subscriber line terminating device 80 is the broadcast switch 8
1 and a plurality of subscriber line interfaces 82.

Here, the broadcast switch 81 is used for the long distance network 7.
It has a function of distributing ATM cells sent via 0 to a plurality of subscriber line interfaces 82. In the figure, 1
One subscriber line interface 82 is shown. Each subscriber line interface 82 includes a broadcast switch 81 and a subscriber line 90.
It has the function of connecting with.

Each subscriber line 90 has one optical fiber 91.
, One star coupler 92, and a plurality of optical fibers 93
It is configured as a passive double star transmission line.

Here, the optical fiber 91 has a function of connecting the corresponding subscriber line interface 80 and the star coupler 92. The optical coupler 92 has a function of branching the ATM cell supplied from the optical fiber 91. The optical fiber 93 has a function of connecting the star coupler 92 and each subscriber terminal 100.

The subscriber line interface 82 includes a normal cell encryption unit 821, an encryption key storage memory 822, a broadcast cell encryption unit 823, an encryption key generation unit 824, and a clock unit 8.
25, a cell determination unit 826, and selectors 827 and 828.
And a cell conversion unit 829 and a file storage unit 830.

Here, the normal cell encryption unit 821 has a function of encrypting the normal cell by using the encryption key K1 given in advance to the destination subscriber terminal 100 of the normal cell. The encryption key storage memory 822 stores the corresponding subscriber line 90.
It has a function of holding an encryption key K1 previously given to each of the plurality of subscriber terminals 100 connected to each subscriber line 100.

The broadcast cell encryption unit 823 has a function of encrypting a broadcast cell using the encryption key K2. The encryption key generator 824 has a function of outputting the encryption key K2. The encryption key generation unit 824 has a function of updating the encryption key K2 at a predetermined cycle based on the control signal supplied from the clock unit 825. The clock unit 825 has a function of outputting a control signal indicating the update timing of the encryption key K2.

The cell determination unit 826 has a function of determining whether the ATM cell output from the broadcast switch 81 is a normal cell or a broadcast cell.

When the cell determination unit 826 determines that the ATM cell is a normal cell, the selector 827 selects the output of the normal cell encryption unit 821, and when it is determined that it is a broadcast cell,
It has a function of selecting the output of the broadcast cell encryption unit 823. The selector 827 has a function of temporarily selecting the output of the normal cell encryption unit 821 regardless of the determination result of the cell determination unit 826 when the encryption key K2 is changed.

The selector 828 is usually an ATM cell (broadcast cell or normal cell) output from the broadcast switch 81.
And the encryption key K2 is updated, it has a function of temporarily selecting the cell of the encryption key output from the cell assembling unit 830. This selected output is supplied to the normal cell encryption unit 821.

The cell conversion unit 829 has a function of converting the encryption key K2 into cells when the encryption key K2 is updated. This cell is formed as a normal cell. This normal cell is hereinafter referred to as an encryption key cell. The file storage unit 830 has a function of storing a subscriber information file (hereinafter referred to as “subscriber file”). Various information regarding the subscriber is registered in the subscriber file.

The encryption key generator 824 generates an encryption key K2 for each broadcast channel. Further, the broadcast cell encryption unit 823 determines the broadcast channel of the received broadcast cell, and encrypts the broadcast cell with the encryption key K2 corresponding to the determined broadcast channel.

The subscriber terminal 100 has a normal cell decoding unit 10
1, a broadcast cell decoding unit 102, a cell determination unit 103,
It has a selector 104, an encryption key extraction unit 105, a data extraction unit 106, and a data decryption unit 107.

Here, the normal cell decryption unit 101 has a function of decrypting the reception cell sent through the corresponding optical fiber 93 by using the encryption key K1 assigned to the own device in advance. Similarly, the broadcast cell decryption unit 102 has a function of decrypting the received cell using the extraction output of the encryption key extraction unit 105.

The cell determination unit 103 has a function of determining whether the reception cell is a normal cell or a broadcast cell. Selector 104
Has a function of selecting the output of the normal cell decoding unit 101 when the cell determination unit 103 determines that the cell is a normal cell, and selecting the output of the broadcast cell decoding unit 102 when it is determined to be a broadcast cell. The encryption key extraction unit 105 uses the selector 10
4 has the function of extracting the encryption key K2 from the selected output.

The data extraction unit 106 has a function of extracting the data inserted in the payload portion of the ATM cell from the selection output of the selector 104. Data decoding unit 10
Reference numeral 7 has a function of decoding the data extracted by the data extraction unit 106.

The operation of the above configuration will be described.

First, the operation of the entire broadcasting system will be described.

The broadcast cell output from the CATV supply device 60 is supplied to the subscriber line termination device 80 via the long distance network 70. The subscriber line terminating device 80 is also supplied with normal cells other than broadcast cells.

If the input cell is a normal cell, the subscriber line terminal device 80 sends it to any one of the plurality of subscriber lines 90 based on its destination. The normal cell sent to the subscriber line 90 is supplied to the plurality of subscriber terminals 100 connected to the subscriber line 90. The normal cells supplied to the plurality of subscriber terminals 100 are normally decoded only by the subscriber terminals 100 corresponding to their destinations.

On the other hand, if the input cell is a broadcast cell, it is distributed to a plurality of subscriber lines 90. The broadcast cell assigned to each subscriber line 90 is
Is supplied to a plurality of subscriber terminals 100 connected to. The broadcast cell supplied to the plurality of subscriber terminals 100 is normally decoded only by the contract terminal 100 of the broadcast channel. The above is the overall operation of the broadcasting system in FIG.

Next, the operation of the subscriber line terminating device 80 will be described.

The broadcast cell sent from the CATV supply device 60 to the subscriber line termination device 80 is first supplied to the broadcast switch 81. If the input cell is a normal cell, the broadcast switch 81 supplies this to the subscriber line interface 82 corresponding to the destination among the plurality of subscriber line interfaces 82. On the other hand, if it is a broadcast cell, it is supplied to a plurality of subscriber line interfaces 82.

The operation of the subscriber line interface 82 is the operation during the period other than when the encryption key K2 is updated and the encryption key K2.
It is roughly divided into the operations when updating. Therefore, in the following description, the operation of the subscriber line interface 82 will be described separately for these two cases.

First, the operation during a period other than when the encryption key K2 is updated will be described.

The ATM cell (normal cell or broadcast cell) output from the broadcast switch 81 is supplied to the selector 828, the broadcast cell encryption section 823, and the cell determination section 826. The encryption key cell output from the cell conversion unit 829 is supplied to the selector 828.

The selector 828 selects the ATM cell output from the broadcast switch 81, except when the encryption key K2 is updated. As a result, in this case, the AT output from the broadcast switch 81 is sent to the normal cell encryption unit 821.
M cells are provided.

The cell determination unit 826 determines whether the input cell is a normal cell or a broadcast cell. The determination result is supplied to the normal cell encryption unit 821, the broadcast cell encryption unit 823, and the selector 827.

When the input cell is a normal cell, the normal cell encryption section 821 determines the destination subscriber terminal 10 of the input cell.
This input cell is encrypted using the encryption key K1 which is predetermined to 0. This encryption key K1 is stored in the encryption key storage memory 8
It is read from 22. On the other hand, in the case of a broadcast cell, this encryption process is stopped. The output of the normal cell encryption unit 821 is supplied to the selector 827.

When the input cell is a broadcast cell, the broadcast cell encryption section 823 encrypts this input cell using the encryption key K2 output from the encryption key generation section 824. On the other hand, in the case of a normal cell, this encryption process is stopped.
The output of the broadcast cell encryption unit 823 is the selector 827.
Is supplied to.

The selector 827 selects the output of the normal cell encryption unit 821 when the cell is a normal cell, and selects the output of the broadcast cell encryption 823 when the cell is a broadcast cell. As a result, when the cell is a normal cell, the encrypted output of the normal cell is output from the selector 827, and when the cell is a broadcast cell, the encrypted output of the broadcast cell is output.

This encrypted output is sent via the subscriber line 90 to all subscriber terminals 10 connected to this subscriber line 90.
0 is supplied. The above is the operation during the period other than when the encryption key K2 is updated.

Next, the operation when updating the encryption key K2 will be described.

Also in this case, the ATM cells output from the broadcast switch 81 are the selector 828 and the cell determination unit 82.
6 and the broadcast cell encryption unit 823. The encryption key cell output from the cell conversion unit 829 is the selector 8
28. Furthermore, the determination result of the cell determination unit 826 is the normal cell encryption unit 821 and the broadcast cell encryption unit 8
23 and the selector 827.

However, in this case, in the selector 828,
The output of the cell assembling unit 829 is selected according to the control signal output from the clock unit 825. Further, in the normal cell encryption unit 821, regardless of the determination result of the cell determination unit 826,
The normal cell input operation is performed. Furthermore, selector 8
In 27, the output of the normal cell encryption unit 821 is selected regardless of the determination result of the cell determination unit 826.

As a result, in this case, the cell assembling unit 828.
The encryption key cell output from is supplied to the normal cell encryption unit 821 via the selector 828 and encrypted. This encrypted output is output to the subscriber line 90 via the selector 827 and supplied to the plurality of subscriber terminals 100 connected to this subscriber line 90. The above is the operation when updating the encryption key K2.

Here, the operation of the cell conversion section 829 will be described in detail.

At the time of updating the encryption key K2, the cell conversion unit 829 first executes a process of converting the encryption key K2 of a certain broadcast channel output from the encryption key generation unit 824 into cells. Thereby, the encryption key cell is obtained. This encryption key cell is formed as a normal cell. However, at this stage, the destination information (virtual path identifier, virtual channel identifier, etc.) is not inserted.

Next, the process of copying this encryption key cell is executed. This copying is repeated for the number of subscribers of the broadcasting channel. However, the number of contractors in this case is the number of contractors connected to the corresponding subscriber line 90.

At this time, at the same time, a process of inserting the destination information of each contractor is also executed. This destination information is read from the subscriber file stored in the file storage unit 830.

The encryption key cells for the number of contractors thus generated are sequentially supplied to the normal cell encryption unit 821 via the selector 828. After that, the above-described processing is executed for the encryption key K2 of the next broadcast channel. Hereinafter, similarly, the encryption keys K2 of all broadcast channels
The process described above is repeated.

The encryption key cell supplied to the normal cell encryption unit 821 is encrypted by using the encryption key K1 corresponding to its destination, like the normal cell supplied from the broadcast switch 81. The above is the operation of the cell assembling unit 829.

Next, the operation of the subscriber terminal 100 will be described.

The reception cells (normal cells (including encryption key cells) and broadcast cells) sent via the optical fiber 93 are
It is supplied to the normal cell decoding unit 101, the broadcast cell decoding unit 102, and the cell determination unit 103.

The reception cell supplied to the normal cell decryption unit 101 is decrypted using the encryption key K1 assigned to the terminal. This decoded output is supplied to the selector 104. Further, the reception cell supplied to the broadcast cell decoding unit 102 is decoded using the extraction output of the encryption key extraction unit 105. This decoded output is supplied to the selector 104.

The reception cell supplied to the cell determination unit 103 is determined to be a normal cell (including an encryption key cell) or a broadcast cell. This determination result is supplied to the selector 104. If the received cell is a normal cell, the selector 104
The decoding output of the normal cell decoding unit 101 is selected, and in the case of a broadcast cell, the output of the broadcasting cell decoding unit 102 is selected.

As a result, when the received cell is a normal cell, the decryption output of the normal cell decryption unit 101 is the encryption key extraction unit 1
05 is supplied to the data extraction unit 106. On the other hand, in the case of broadcast cells, the decoded output of the broadcast cell decoding unit 102 is supplied to them.

The encryption key extracting section 105 extracts the encryption key K2 from the selection output of the selector 104. This extracted output is
It is supplied to the broadcast cell decryption unit 102 as an encryption key for decryption. The data extraction unit 106 extracts the data inserted in the payload from the selection output of the selector 104. However, if the input cell is an encryption key cell, this extraction
It will be canceled. The extracted data is stored in the data decoding unit 107.
By this, the digital signal is returned to the analog signal.

Cryptographic key K1 used for normal cell encryption
Is the same as the encryption key K1 assigned to the terminal, this normal cell is correctly decrypted. As a result, in this case, the data inserted in the payload of this normal cell is accurately extracted. As a result, in this case, the information sent using this normal cell will be reproduced correctly.

Further, in this case, if this normal cell is an encryption key cell, the encryption K2 is accurately extracted from this encryption key cell. As a result, in this case, the broadcast cell is correctly decoded. As a result, in this case, the data inserted in the payload of this broadcast cell is accurately extracted. As a result, in this case, the information sent using this broadcast cell can be accurately reproduced.

On the other hand, if the encryption key K1 used for encrypting the normal cell does not match the encryption key K1 given to the terminal itself, the normal cell cannot be decrypted correctly. As a result, in this case, the information sent using this normal cell cannot be reproduced correctly.

Further, in this case, the encryption key K2 is not accurately extracted, so that the broadcast cell is not accurately decrypted. As a result, in this case, the information sent using this broadcast cell will not be reproduced correctly.

According to this embodiment described in detail above, the following effects can be obtained.

(1) First, according to this embodiment, the broadcast cell is encrypted by using the encryption key K2 that is updated at a predetermined cycle and transmitted, and each time the encryption key K2 is updated, Since this encryption key K2 is made into a cell, and this encryption key cell is encrypted by using the encryption key K1 given in advance for each contractor, the plurality of contract terminals are connected to each subscriber line 90. Even if 100 is connected,
It is possible to broadcast the broadcast cell at once to these.

As a result, broadcast cells can be supplied to a plurality of contract terminals 100 connected to each subscriber line 90 without using a time-dependent broadcast switch, so that the bandwidth used by each subscriber can be narrowed. It is possible to avoid the problem that the load and the amount of the buffer memory become large.

(2) Further, according to this embodiment, since the encryption key K2 is updated at a predetermined cycle, in the contract in which the contract is updated in program units, the encryption key K2 is updated.
By setting the update cycle of 2 to be, for example, a unit of 5 minutes, there is an advantage that the contract can be substantially canceled by updating the encryption key K2. On the other hand, in a contract in which the contract is renewed every year, there is an advantage that the secret name of the encryption key K2 can be increased by updating the encryption key K2.

(3) Further, according to this embodiment, when the encryption key K2 is transmitted to the contractor, all the encryption keys K are previously set.
Random numbers can be used as the encryption key K2 because the encryption key K2 is sent one by one each time the encryption key K2 is updated instead of sending 2. As a result, the encryption key K
The secrecy of 2 can be improved.

(4) Further, according to this embodiment, when the encryption key K2 is transmitted to the contractor, the encryption key K2 is made into cells and then encrypted with the encryption key K1 given to each contractor. Since the encryption key K2 is transmitted, the encryption key K2 can be transmitted using the transmission system of the normal cell. As a result, the amount of hardware to be added for transmitting the encryption key K2 can be minimized.

The embodiment of the present invention has been described above.
The present invention is not limited to the embodiments described above.

(1) For example, in the above embodiment, the case where the present invention is applied to the broadcasting system using the subscriber line 90 of the passive double star system has been described. However, the present invention may be applied to a broadcasting system using an active double star subscriber line. That is, it may be applied not only to a system that broadcasts to a plurality of subscribers including a contractor, but also to a system that broadcasts only to a contractor.

(2) Further, in the above embodiment, the case where the present invention is applied to a broadcasting system for broadcasting using a storage exchange type communication network such as a cell exchange type has been described. However, the present invention can also be applied to a broadcasting system that performs broadcasting using a circuit switched communication network.

(3) Further, in the above embodiment, the case where the present invention is applied to a broadcasting system for broadcasting using an exchange type communication network has been described. However, the present invention can also be applied to a broadcasting system using a communication network in which a plurality of nodes are connected in a mesh shape, instead of the exchange type communication network.

(4) In addition to this, it is needless to say that the present invention can be modified in various ways without departing from the scope of the invention.

[0091]

As described above in detail, according to the present invention,
The transmission signal of the broadcast information is encrypted by using the first encryption key that is updated at a predetermined cycle and transmitted, and each time the encryption key is updated, the transmission signal of this encryption key is sent to each contractor. Since the encrypted data is transmitted using the second encryption key given in advance, even if a plurality of contract terminals are connected to one subscriber line, the broadcast information can be sent to them at once. Can be broadcast.

As a result, the broadcast information can be supplied to a plurality of contract terminals connected to each subscriber line without using a temporal broadcast switch, so that the bandwidth used by each subscriber can be narrowed. Then, it is possible to avoid the problem that the load and the amount of the buffer memory become large.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an example of a CATV system.

FIG. 3 is a block diagram illustrating a function of a spatial broadcast switch.

FIG. 4 is a block diagram illustrating a function of a temporal broadcast switch.

FIG. 5 is a block diagram showing an example of a configuration of a temporal broadcast switch.

FIG. 6 is a block diagram showing another example of the configuration of the temporal broadcasting switch.

[Description of Reference Signs] 60 ... CATV supply device 70 ... Long distance network 80 ... Subscriber line termination device 90 ... Subscriber line 100 ... Subscriber terminal 81 ... Broadcast switch 82 ... Subscriber line interface 91, 93 ... Optical fiber 92 ... Star coupler 821 ... Ordinary cell encryption unit 822 ... Encryption key storage memory 823 ... Broadcast cell encryption unit 824 ... Encryption key generation unit 825 ... Clock unit 826, 103 ... Cell determination unit 827, 828, 104 ... Selector 829 ... Cellification Part 830 ... File storage part 101 ... Normal cell decryption part 102 ... Broadcast cell decryption part 105 ... Encryption key extraction part 106 ... Data extraction part 107 ... Data decryption part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 7/167

Claims (2)

[Claims] 1. A first device which is provided on a broadcast information transmitting side and which encrypts a broadcast information transmission signal using a first encryption key.
Encryption means for updating the first encryption key, which is provided on the transmitting side of the broadcast information, for updating the first encryption key at a predetermined cycle, and the encryption key updating means for updating the first encryption key each time the first encryption key is updated. Second encryption means for encrypting the transmission signal of the first encryption key by using the second encryption key given in advance for each contractor; and the reception signal provided in advance on the receiving side of the broadcast information. A first decryption means for decrypting using the second encryption key assigned to the user; and a decryption output of the first decryption means, which is provided on the receiving side of the broadcast information, for decrypting the first encryption key. A broadcast characterized by comprising encryption key extracting means for extracting, and second decrypting means provided on the receiving side of the broadcast information and decrypting the received signal by using the extraction output of the encryption key extracting means. system. 2. The first encryption means, the encryption key update means, and the second encryption means are provided in a subscriber line terminal device of a subscriber network, and the first decryption means is provided. 2. The encryption key extracting means and the second decryption means are provided in a subscriber terminal connected to the subscriber line terminating device via a subscriber line. Broadcast system.