CA1167562A - Television system with access control - Google Patents

Television system with access control

Info

Publication number
CA1167562A
CA1167562A CA 353905 CA353905A CA1167562A CA 1167562 A CA1167562 A CA 1167562A CA 353905 CA353905 CA 353905 CA 353905 A CA353905 A CA 353905A CA 1167562 A CA1167562 A CA 1167562A
Authority
CA
Grant status
Grant
Patent type
Prior art keywords
circuit
key
signal
subscription
service
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA 353905
Other languages
French (fr)
Inventor
Gerard Babonneau
Claude Sechet
Louis C. Guillou
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telediffusion de France ets Public de Diffusion
Original Assignee
Telediffusion de France ets Public de Diffusion
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Grant date

Links

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04KSECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00Secret communication
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00Television systems
    • H04N7/16Analogue secrecy systems; Analogue subscription systems
    • H04N7/166Passage/non-passage of the television signal, e.g. jamming, band suppression

Abstract

ABSTRACT OF THE DISCLOSURE

A television system with access control comprises a transmitter and receivers. The transmitter comprises a video signal and sound signal formation circuit, means for transmitting these signals and a jamming circuit using a service key. Each receiver comprises means for receiving the transmitted signals, means for the display of the picture and for restoring the sound and an un-jamming circuit connected to the reception means and working with the service key. It also comprises a sub-scription management centre and in the transmitter a digital signal generator, a circuit for the formation of digital messages and a data broadcasting system of the type known under the trademark DIDON and in the receiver a subscription card, an extraction circuit for the DIDON
data, and a circuit for restoring the service key.
There is also at least one subscription support loading station connected to the subscription management centre.

Description

TELEVIS ION SYSTEM
BACKGROUND OF THE INVENTION
The present invention relates to a television system with access control using a variable electronic key.
The problem of access control of broadcast infor-mation mainly consists of the jamming of information on transmission by means of an appropriate key, as well as unjamming or deciphering on reception by means of an identical key, which is only in possession of users who have regularly paid a subscription fee.
Numerous television systems ~re already known which are equipped with jamming means on transmission and un-jamming means on reception. Such systems are more par-15 ticularly described in French Patent 106 670, German Patent 1 907 580, French Patent 2,330,236 dated May 27, 1977 in the joint name of the French State and Tele-diffusion de France, French Patent 1 034 776, German Patent 1 254 676 and U.S. Patents 2 510 046, 2 619 530, 20 2 892 882 and 2 972 009.
The jamming processes used in these systems are based on the introduction of a displacement of the position of the line synchronization pulse on a periodic reversal of the complete signal and on the polarity change of the video signal or on a combination of these operations. In all these processes it is necessary for the receivers to receive in some way or the other signals making it possible to restore the key necessary for covering the clear information.
The present invention relates to a television system of this type, but in which the key which permits unjamming is transmitted to the receivers in an original and advantageous manner.
In the prior art systems the transmission oE this key does not give entire satisfaction because it is not , ..~ .

` :', ~ .tj~7~2 generally compatible wlth the recently developed digital services and which are being or will be offered to viewers. They consist more particularly of the "ANTIOPE" system (digital acquisition and television display of pictures organized in writing pages), the "TITAN " system (interactive terminal for teletext with call-in by numbering), the "EPEOS" system (programmed recording of transmissions on command from the sources), etc.
The first system consists of a broadcast videotex system making it possible to insert alphanumeric infor-mation organized in pages and in magazines on television channels. The second comprises an interactive videotex system compatible with the ANTIOPE system and giving access to data bases (general informatlon, lists, etc.) and to interactive services (transactions, messages, instruction) by the telephone system. The third system is a programme message system consisting of offering by means of a data broadcasting channel the remote control from a transmission source of the recording action by a receiver (e.g. a magnetoscope) of a preselected tele-vision programme.
For broadcasting information these three systems use means and a process called "DIDON " (broadcasting of digital data), which~is compatible with the broadcasting of the television signal.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to an access control means having a complete compatibility with these differ-ent systems.
To this end the system according to the inventionhas two essential features:

1) In the first place it uses a double key system, namely with a service key K
making it possible to jam information and which changes in a random manner at relatively short intervals of approxi-mately a few minutes, and a subscrlption key which can assume several values C
depending on the type of subscription, said key also changes in a random manner but at longer intervals of approximately one month. This subscription key appears on a subscription card introduced into each receiver. The two keys R and Ci are combined on transmission for forming messages Mi.

2) Secondly the messages Mi and not the actual service key K are transmitted from the transmitter to the receivers. This transmission takes place in accordance with the aforementioned DIDON process, which gives the system compatibility with all digital services based on this pro-cedure. On reception the messages Mi received are combined by the subscription key Ci supplied by a subscription card, making it possible to restore the key K
necessary for unjamming the signal re-ceived.
More specifically the present invention relates to a television system provided with access control means and which comprises a transmitter and receivers, trans-mitter comprising a formation circuit for a videosignal organized in lines and in fields and a sound circuit, as well as a transmission means for said signals, each receiver comprising a reception means for the trans-mitted signals and means for the visual display of the picture and the restoration of the sound, wherei~ it also comprises:
A) a subscriptlon management centre comprising the means for generating a plurality of digital signals constituting subscription keys Ci changing in random manner at rela-tively long intervals of approximately one month;
B) a transmitter comprising:
a) a digital signal generator constituting a service key K, said key changing in random manner at relatively short inter-vals of approximately a few minutes, b) a circuit for the formation of digital messages Mi obtained from the sub-scription keys Ci and the service key K
by an algorithm parametered by the sub-scription key, i.e. Mi = FC (K), said circuit supplying the same number of messages as there are subscription keys, said messages changing with the service key, c) a system for broadcasting data of the DIDON type able to insert messages Mi in the field blanking intervals of the video signal, '1 j,s 7~6;~

d) a jamrning circuit using the service key K, said jamming circuit receiving the video and/or sound signal and supplying jammed video and/or sound signals which are then transmitted to the transmission means, said jamming not affecting the messages contained in the field blanking intervals:;
C) in each receiver are provided:
a) a subscriptlon card on which is entered a signal corresponding to at least one of the subscription keys Ci, b) a circuit for the extraction of the DIDON
data contained in the signal received, said circuit restoring the messages Mi, c) a circuit for restoring the service key receiving on the one hand messages sup--plied by the preceding circuit and on the other the subscription key Ci supplied by the subscription card, said circuit per-forming an algorithm K = GCi (Mi) g it possible to restore the signal corre-sponding to the service key K used in the transmitter, d) an unjamming circu.it connected on the one hand to the reception means from where it receives the jammed video and optionally sound signals and on the other hand to the restoration circuit from where it receives the service key K, said un-jamming circuit supplying unjammed video and optionally sound signals which are then transmitted to the means for the display of the picture and the resto-ration of sound;

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D) at least one subscription card loading station, which is connected to the sub-seription management centre from which it receives signals corresponding to the different subscription keys Ci generated by the said centre, each station being able to temporarily receive subscription cards and write therein one of the sub-scription keys Ci.
Preferably the jamming circuit comprises a pseudo-random sequence generator re-initialized at the start of eaeh field by the service key K and supplying a digital jamming signal at the start of each line, and a video and optionally sound signal conversion circuit~ the eonversion being carried out by this cireuit being defined by the digital signal supplied by the pseudo-random sequence generator.
In this case the unjamming circuit comprises a pseudo-random sequence generator identical to that of the jamming circuit and in the same way re-lnitialized at the start of each field by the service key K and supplying an unjamming digital signal at the start of each line and a circuit able to carry out the reverse conversion to that of the jamming circuit on the video and optionally sound signal, said eonversion being determined by the digital unjamming signal supplied by the pseudo-random sequenee generator.
The jamming operation on transmission can be of any known type and particularly in aceordance with the pro-eesses deseribed in the doeuments referred to herein-before. However, according to an advantageous variant a means based on a cireular permutation of the samples to be jammed is used. Such a means is more particularly described in Freneh Patent Application 76/24304 publish-35 ed on 4.3.1977 under No. 2 320 676 and in Freneh Patent ~ ~ ~t75,~

2,431,802 of February 15, 1980 in the joint names of the Rublic Broadcasting Establishment called Telédiffusion de France, André LOUI~EAU and Gerard BABONNEAU and entitled "Jamming and Unjamming Processes and Devices for Television Plctures".
Naturally the jamming operation can affect both the picture and the sound. With regard to the transmission of sound it can be carried Ollt either by an ordinary sound channel, or a digital channel using the fi.eld blanking intervals and operating in accordance with the DIDON procedure, or a digital channel using the line blanking intervals, or a digital channel using supple~
mentary signals inserted in the chrominance colour bursts.
The means used for the transmission of sound can be marked by means of bits forming part of the service key K.
The insertion of sound in a digital channel located in the line blanking interval forms the object of French 20 Patent 2,459,594 dated January 9, 1981 in the names of the Public Broadcasting Establishment called Télédiffu-sion de France and Gerard BABONNE~U and entitled "Television System with Multiplexing of Videosignals and/or Data and Digital Sound Signals".
2~ BP~IEF DESCRIPTION OF THE DR~WINGS
The invention is described in greater detail herein-after relative to non-limitative embodiments and the attached drawings, wherein show:

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Fig. 1 - a block diagram of a television system with access control according to the invention.
Fig. 2 - diagrammatically jamming means using a circular permutation of samples.
Fig. 3 - the standard pre~erably adopted for the videosignal.
Fig. 4 - diagrammatically the locations in the field synchronization signal of the signals indicating a change of key.

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Fig. 5 - the organization of the key change detection means.
DETAILED DESCRIPTION OF ~HE PREFERRED EMBODIMENTS
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The system shown in Fig. 1 firstly comprises a sub-scription management centre 10 which generates a plu-rality of signals constituting subscription keys Ci, which change in a random manner at relatively long intervals of approximately one month.
The actual television system is organized around the transmitter 12 and has a plurality of receivers 14.
Transmitter 12 comprises:
a) a circuit 16 for the formation of television signals incorporating a part relative to a video-signal carried by a connection 17 and a part rela-tive to the sound carried by a connection 19;
b) a generator 1~ of a signal consti-tuting a service key K, said key changing in a random manner at relatively short intervals o~ approximately a few minutes;
c) a circuit 20 for the formation of digital messages Mi from subscription key Ci generated by centre 10 and the service key K generated by gener-ator 1~, for which purpose the circuit 20 performs an algorithm parametered by the subscription keys, i.e. Mi = FC (K), and suppl:ies the same number of messages Mi as there are subscription keys, said messages changing with the service key Ki d) a DIDON-type data broadcasting system 22 ';' .. ~.~; .

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able to insert messages Mi into the field blanking intervals of the videosignal coming from circuit 16 by means of connection 17, e) a jamming circuit 20 using the service key K for jamming the video and/or sound signal, said jamming not affecting the messages Mi contained in the field blanking intervals, the ja~med signal supplied by this circuit are -then transmitted to the transmission means 26.
Each receiver 14 of the present system contains:
a) a broadcast signal reception means 30;
b) an unjamming circuit 32 connected to the reception means 30 from which it receives the jammed video and optionally sound signals and which operates: by means of the service key K, supplying the unjammed video and sound signals respectively carried by connections 31 and 33;
c) a circuit 34 for the extraction of DIDON-data contained in the video signal received, said circuit restoring messages Mi by a connection 35;
d) a subscription card 36 on which is entered a signal corresponding to at least one of the subscription keys Ci;
e) a circuit 38 for restoring the service key K from messages Mi supplied by the circuit 34 and the subscription key Ci supplied by the subscription card 36, said circuit 38 per-forming an algorithm K = GC (Mi) making it ~t~

possible to restore the signal correspondiny to the service key K used in the trans~
mitter, said key then being addressed to the unjamming circuit 32;
f) means ~0 Eor the display of the pictures and the restoration of sound.
The system shown also has at least one loading station 42 suitable for the subscription card 36, This station is connected to the subscription management centre lO from which it receives signals corresponding to the different subscription keys Cl generated by the centre. Each station 42 is temporarily able to receive the subscription cards and to write therein in a lasting manner (e.g. in a memory) one of the subscription keys Ci.
For the purpose of illustrating the operation of this double key s~ystem it is possible to take the example of a subscription scheme using four types of subscriptions, i.e. one month, three months, six months and one year. In addition to its duration a sub-scription is characterized by the starting month. In the case of such a scheme for a given month and for a given service there are consequently 22 subscription keys which are likely to be used by users, namely one monthly key, three quater-yearly keys, six half-yearly keys and twelve yearly keys.
Every month the subscription management centre lO
supplies transmitter 12 with a list of 22 subscription keys Ci for each service broadcast by this transmitter.
In addition, it supplies loading stations 42 with another list of four keys for starting the following month (one month, three months, six months and one year), for each service with the subscription rates.

, , 7~2 A suitable machine installed at each point oE sale enters certain of these keys in the form of subscription blocks on the cards 36. A subscription block can for example consist of four fields:
1) a service code having 16 bits designating the service in question:
2) a subscription symbol of 8 bits which charac-terizes the subscription for a service in question, whereby 2 of said bits indicate the subscription type (1, 3, 6 or 12 months) and the 6 others indicate the subscription starting month (1 to 60 modulo 5 years);

3) a subscription key of 128 bits which is the fundamental information of the block; 5 4) a cyclic redundancy code of 16 bits and relates to the preceding 152 bits and makes it possible to check the subscription block before using the same.
Thus, a subscription block is formed by 168 bits, i.e. 21 octets. Such a block can easily be entered in a credit card-type support provided with a PROM memory (Programmable Read-Only Memory) with a capacity of 4096 bits usable for this purpose. Such a card can receive up to 24 subscription blocks having the indicated 5 characteristics.
For each paying service, approximately every five minutes, a new service key K is generated in a random manner in the transmitter. Thus, during a session of a service (one or several hours) a few dozen service keys can follow one another. As soon as a transmitter gener-ates a new service key K it calculates for each sub-scription key Ci in operation for said service a message Mi by an algorithm in which the keys Ci act as para-meters.

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Thus, for a service with the subscription scheme referred to hereinbefore 22 different messages are in force at all times. The life of a message is equal to that of the service key K and for a given service there is the same number of messages as there are subscription keys being used at all times.
The calculation of the messages Mi from the sub-scription keys Ci and key K takes place in the trans-mission centre by means of circuit 20, organized around a micro-processor. This circuit can be in accordance with that described in European Patent publication 0,014,652 dated August 20, 1980 and entitled "Videotex system provided with Data Access Control Meansi and European Patent publication 0,014,653 dated August 20, 1980 and entitled "System or Transmitting :tnformation between a Transmission Centre and Receivers, said System being provided with an Access Control Means to the Transmitted Information".

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Such a circuit is programmed so as to realize an algorithm using the subscription keys Ci (127 bits) and the service key K (56 bits) in the following way:
1) a confusion redundancy word ~ is formed which consists of 61 bits generated at random on each performance of the algorithm;
2) ~ 1 i5 calculated being the opposite to the modulo 261 - 1 by an arithmetic programme using a variant of the Euclidian algorithms; 0 3) a first multiplication is performed by another arithmetic proyramme v = K ~ l modulo (251 - 1);

4) ~ is calculated, being the opposite of C modulo 2l27 - 1, by a programme similar to that of 2);

5) finally the message is calculated by a programme similar to 3)o M = ~.(v + 264.~) modulo (2127 - l).
The programmes necessary for these calculations can be developed by a type 8080 microprocessor of the INTEL
Company.
All the messages Mi in force constitute the access 0 control information associated with the broadcast service. According to the essenti.al feature of the invention this information is broadcast by the DIDON
process at circuit 22 and is restored on reception at circuit 34.
This DIDON process is known per se and is described more particularly in:

French Patent 2,313,825 dated December 31, 1976 in the joint name of the Public Broadcastiny Establishment called Tëlédiffusion de France and the French State represented by the Secretary of State for Posts and Telecommunications (Centre National d'Etudes des Telécommunications) and entitled "Data sroadcasting System";
the first certificate of addition to the above Patent 2,393,480 dated December 29, 1978;
French Patent 2,404,350 dated April 20, 1979 and which is a divisional of the first Application;
the article by Y. GUINET published in the "Revue de l'U.E.R. Cahier Technique", No. 165, October 1977, p. 242 and entitled "Comparative Study of Radio-teletext Systems - Certain Advantages of the Broadcasting of Data in Packets applied to the Teletext".
It is briefly pointed out that the DIDON system is a radio system for broadcasting data using the tele-vision channel. Broadcasting is performed by bringing the data into packets. Each packet occupies the active part of the television line making it possible to ensure a good compatibility with the conventional modes of use of the channel.
As in the present invention the radio channel is allocated to a television programme, only the marginal resource constituted by the field blanking interval can be used for the transmission of messages Mi.
In the DIDO~ process each packet has two parts, one called the prefix and the other called the data block.
The prefix is used for the management of the packet and has eight octets, two for the synchronization of the bits, one for the octet synchronization, three carry the channel code, including its protection, one carries the continuity symbol and the final octet describes the ~,~tjt7~6~

format (or length) of the data block.
The data block follows the prefix. Its maximum length is dependent upon the timing-pulse rate and the active duration of the line. The timing-pulse rate is adapted to the channel band width. The modulation used is the "non-return to zero" (NRZ) brought into a form for adapting the spectral energy distribution to the transmission channel.
When the messages Mi have been transmitted and received by the DIDON process it is necessary to re-constitute the service key K. This is the function of circuit 38 which can be formed in the manner described in the two European Patent publications 0 014 652 and 0 014 653 referred to hereinbefore. This circuit is programmed to develop an algorithm K = GC (Mi) which is, like on transmission, a double field algorithm. The operations are as follows:
1. The message Mi (127 useful bits) is acquired octet by octet and a multiplication by Ci is carried out on the first field CG (2127 -1).
Thus a word ~ is formedO
~ = M.C modulo (2127 -1) On the basis of the construction of M on transmission bits 1 to 61 of ~ represent the word v, while bits 65 to 125 represent the word ~. Obviously bits 62, 63, 64, 126 and 127 must be zero. If they are not zero the word v is brought to zero before continuing the calculation.

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2. ~ and v are multiplied on the second field CG ~261 ~1), which brings about the disap-pearance of the con~usion redundancy and one obtains K = v.~ modulo (261 -1).
A -Eurther probability test now takes place, because as K has 56 useful bits, bits 57, 58, 59, 60 and 61 must be zero. If this is not the case K is brought to zero before continuing the operation. 0 3. The 56 useful bits of K are then available inthe form o~ 8 uneven octets.
The means making it possible to have a subscription support 36 and a loading station 42 can be in accordance with those described in European Patent publication 0 014 654 and entitled "Subscription Card for Videotex Receiver and Loading Station for the said Card".
The jamming and unjamming of the video signal 2Q taking place respectively in circuits 22 and 32 can advantageously be obtai;ned by the method described in the aforementioned French Patent 2 431 802 dated February 15, 1980. In this process the following operations are performed. The signal to be jammed is firstly sampled and then the samples are inserted in a video signal line. The n samples VO to Vn constituting are permutated in circular manner by (p+l) positions, so that the samples V(p+l) to Vn are placed before samples VO to Vp, the samples are then transmitted in this per-mutated order. On reception the samples of the jammedsignal are again circularly permutated by (n-p) po-sitions to restore the initial sequence, The number n is determined line by line, according to a law which is fixed by the transmitter and is transmitted to the receivers.

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Fig. 2 shows the block diagram of a jamming cireuit which can be used in the invention. The video signal to be jammed is introduced by connection 50 into a separating circuit 51 which supplies a line synchroni-zation pulse to a time base cireuit 52 and the luminaneeand chrominanee signals to a sampling eireuit 53. In the time base eireuit 52 the line synehronization pulses are used in conventional manner for generating timing signals H at the sampling frequeney and line parity and imparity signals 2p and 2p respeetively. The output of the sampling eireuit 53 is connected in parallel to the signal inputs of two AND gates 54 and 55, whose-outputs are respectively eonneeted to two input eireuits 56 and 57. The outputs of these cireuits are respeetively eonneeted to the inputs of two delay eireuits 58 and 59, respeetively eonnected to the output cireuits 60 and 61.
The outputs of eireuits 60 and 61 are eonneeted to the inputs of an OR gate 62, whose output is eonneeted to the input of a smoothing eircuit 63 joined to a cireuit 64 in whieh a line synchronization pulse is inserted into the signal leaving 63.
The coder of Fig. 2 also comprises a pseudo-random digital sequence generator 65 whieh, like that deseribed in Freneh Patent 2,330,236 dated May 27, 1977, ean be a ten-stage shift register provided with nine re-looping points, whereby there is direct re-looping between last and first stage. The eight intermediate loops are put into effeetive operation when a level 1 is applied to the eontrol input of the corresponding stage. These re-looping control levels are applied from a loading ., ,~

register 66, which permanently contains an eight bit word. This word defines the configuration of the generator. For each field synchronization signal trans-mitted by the separating circuit 51 and carried by a connection 67 to a register 68 which carries a ten bit word generator 65 is initialized in accordance with this word, each stage assuming the state defined by the corresponding bit. For each field the same digital sequence of ten bits is generated with the timing of the line synchronization pulses supplied by circuit 51 to generator 65. The eight bit word contained in register 66 and the ten bit word con-tained in register 68 together form the axis key to the jammed trans-mlsslon .
The output of generator 65 supplies a ten bit word to the initialization input of a counter 69, whose counting input receives the timing pulses H from the tirne base circuit 52. Counter 69 counts bac~wards on transmission. When counter 69 is not at zero its signal output is at level 1, but as soon as it is at zero thisoutput passes to 0.
The second input of gate 54 i5 connected to an output 2p of 52 in such a way that the uneven line signals transmitted by circuit 53 are transmitted to circuit 54. The second input of gate 55 is connected to the output 2p in such a way that the even line signals are transmitted to circuit 57.

One control input of circuit 56 is connec-ted to the output of an AND gate 70r whose first input is connected to the output 2p of 53 and whose second input is connected to the output of counter 69. The control input of circuit 57 is connected to -the output of an AND gate 61, whose first input is connected to ou-tput 2p of 52 and whose input is connected to the output of counter 69.
The control input of circuit 60 is connected to the output 2p of 52, whilst the control input of circuit 61 is connected to output 2p of 52.
Finally an input of circuit 64 is connected to an output of circuit 52 which supplies a synchronization signal S', deduced from the incoming synchronization signal.
The circuit of Fiy. 2 functions as follows. During an uneven line signal 2p is at the high level, gate 54 is open, circuit 60 is open towards gate 62, circuit 61 is closed and gate 55 is closed. In addition, gate 70 is closed, whilst gate 71 is open and the output of counter 69 is at high level. Thus, samples from an uneven line enter circuit 58 and jammed samples from the uneven line leave it.
During the following even line signal 2p is at high level, gate 54 is closed, circuit 60 is closed, circuit 61 is open and gate 55 is open. Moreover, gate 71 is closed whilst gate 70 is open and output of 69 is at high level. The first samples are transmitted to the input of 58, whilst the last are moved towards the output of 58, the content of 58 remaining unchanged until the end of the even line. Finally there is an uneven line and the operation described h~reinbefore is repeated. Jamming oE the even lines takes place in the same way with respect to circuit 59.
It is clear that the circuit of Fig. 2 can be used on reception for restoring the initial forms of lines by using the same circuits 66 and 68, by connecting counter 60 in such a way that after its , .,, ~

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initialization at each line by 60 it counts towards itsmaximum content instead of counting towards zero as was the case for the coder on transmission.
When the treated samples are in analog form, the delay circuits 58 and 59 are advantageously load transfer circwits. When the processed samples are in the coded digital form these delay circuits are shift registers.
In the described embodiment the digital signal used by the pseudo-random sequence generator contains 10 +
8 = 18 bits, but the key can be constituted by a word having more than 18 bits, e.g. 32 bits. The 1~ other bits of the key make it possible to determine which con-version functions are active and which are not (2 bits), what divisio~ of the resource is chosen, what relation-ship exists between the 10 bits of the shift register and certain parameters of the conversions of pure delays or circular displacement. In general terms the key can carry complementary information relating to the possible configurations of the signal. This is utilized for pro-viding the possibility of replacing a single full defi-nition sound and video programme hy four independent low definition progra~mes, this result being obtained by dividing up the screen space into four quadrants re-ceiving four independent pictures ob-tained by reduction by digital means in the case of the video and the sound channel into four narrow band sound channels. This possibility can be provided in the definition of the ~'7~
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jamming system. The general public recelvers are not necessarily provided with these rneans which can be re-served for special users.
The jamming of the picture sensitizes the latter to transmission faults and makes it necessary to provide redundancies. In the video standard adopted a time interval of 2.6 ~s is provided for this purpose. This interval remains free of any signal before jamming.
This standard is shown in Fig. 3O Each video signal line has:
a blanking interval Is which is not affected by the pseudo-random transformations or conversions, except with regard to the content of any digital signal which may be present, said interval containing the line synchronization and optionally a digital channel N for carrying sound.
An interval IT containing the picture which is affected by the pseudo-random transformations or con-versions and necessarily containing 7.5 ~s reserved for the chrominance colour burst C (4.9 ~s) and to the jamming operations (interval B of 92.6 ~s), the latter margin may ox may not be continuous and may be at the start or finish oE lines, depending on the particular circumstances.
During the blanking of the field or DIDON window there is no transfor~ation of picture space in order to retain the possibility of broadcasting data in clear in a signal whose picture and sound are jammed.

When the sound is carried by a digital channel using intervals IS or by a digital channel using the insertion of supplementary signals into the chrominance colour bursts it is sampled at one of the following frequencies which are compatible with the synchroni-zation:
fO = 7812~5 Hz fl = 15625 Hz f2 = 31259 Hz However, as stated hereinbefore the jammed image can be accompanied by a good quality sound. In the same way it is possible to adopt a division of the capacity of the channel between at least four sounds of at least telephone quality (300-3400 Hz, signal to noise ratio 40 dB). As stated hereinbefore the choice of the mode used can be indicated in the key word.
With regard to the change of key it is pointed out that a co-ordination system i5 necessary on the one hand for indicating authorized receivers which key is in service and on the other to fix the exact time, to within one field, at which one passes from one key to the next. This can be obtained by the use of:
1. messages indicative of the future key broadcast by the DIDON system, but only interpretable by th~ key calculation means provided with the appropriate subscription support;

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2. time marking signals inserted in a field before the chanye of key and as illustrated in Fig. 4.
In Fig. 4, which shows the field signal, the spaces S marked S correspond to the synchronization lntervals of the standard of Fig. 3 and the spaces marked R designate the intervals containing a marking indicating a change of key and which can be constituted by the bit at 1.
The key restoration circuit 38, as shown in Fig. 1, then has in accordance with Fig. 5 a control circuit 39 connected to the key calculation system 41. This control circuit receives messages from the DIDON data extraction circuit 34, and supplies them to the key calculation circuit 41 after carrying out a possible shaping (e.g. parallel-series conversion).
Two cases must be considered for the control circult:
on energizing the receiver it extracts a message, requests its translation from the key calculation system 41 and immediately validates this key towards the picture and/or sound unjamming means 32;
during operation the circuit listens to messages reaching it, ~hilst maintaining the previously calculated key in force and when the messages have a bit indicating a change of key the automaton again requests the translation thereof which restores the future ~ey K' and as from this time the circuit awaits a key change pulse to replace the old key K by the new key K'.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A television system with access control constituted by a transmitter and receivers, the trans-mitter comprising a circuit for the formation of a video signal organized in lines and fields and a sound signal, the transmission means for said signals and a jamming circuit using a service key K, said jamming circuit receiving the video and/sound signal and supplying jammed video and/sound signals which are then trans-mitted to the transmission means, each receiver com-prising a reception means for the transmitted signals, means for the display of a picture and for the resto-ration of the sound and an unjamming circuit connected to the reception means and working with the said service key K, said unjamming circuit supplying unjammed video and optionally sound signals which are then transmitted to the means for the display of the picture and the restoration of the sound, wherein it also comprises:
A) a subscription management centre com-prising means for generating a plurality of digital signals constituting sub-scription keys Ci changing in random manner at relatively long intervals of approximately one month;
B) in the transmitter:
a) a generator of a digital signal constituting the service key K whic changes in random manner at rela-tively short intervals of approxi-mately a few minutes, b) a circuit for the formation of digital messages Mi obtained from the sub-scription keys Ci and the service key K by an algorithm parametered by the subscription keys, i.e. Mi = FCi(K), said circuit supplying the same number of messages as there are subscription keys and these messages change with the service key, c) a DIDON data broadcasting system able to insert messages Mi in the field blanking intervals of the video signal, jamming not affecting the messages contained in the field blanking interval;
C) in each receiver:
a) a subscription card on which is entered a signal corresponding to at least one of the subscription keys Ci, b) a circuit for the extraction of the DIDON data contained in the signal received and which restores the messages Mi, c) a circuit for the restoration of the service key receiving on the one hand messages Mi supplied by the preceding circuit and on the other the sub-scription key Ci supplied by the sub-scription card, said circuit per-forming an algorithm K = GCi(M) which makes it possible to restore the signal corresponding to the service key K used in the transmitter;

d) at least one subscription card loading station which is connected to the sub-scription management centre from which it receives the signals corresponding to the different subscription keys Ci generated by the centre, each station being able to temporarily receive the subscription cards and enter in them in a lasting manner one of the sub-scription keys Ci.
2. A television system according to Claim 1, wherein:
A) the jamming circuit comprises:
a) a pseudo-random sequence generator re-initialized at each start of the field by the service key K and which sup-plies at the start of each line a digital jamming signal, b) a circuit for the transformation or conversion of the video and optionally sound signal, the transformation carried out by this circuit being defined by the digital signal supplied by the pseudo-random sequence gener-ator;
B) the unjamming circuit comprises:
a) a pseudo-random sequence generator identical to that of the jamming circuit and which, like it, is re-initialized at each start of the field by the service key K and which sup-plies at the start of each line a digital unjamming signal, b) a circuit which is able to carry out on the video and optionally sound signals the opposite transformation or conversion to that of the jamming circuit, said transformation being determined by the digital unjamming signal supplied by the pseudo-random sequence generator.
3. A television system according to Claim 1, wherein the service key contains bits indicating the means used for transmitting sound and which can be:
an ordinary sound channel, a digital channel using the field blanking intervals and operating in accordance with the DIDON process, a digital channel using the line blanking intervals, a digital channel using supplementary signals inserted into the chrominance colour bursts.
4. A television system according to Claim 1, wherein the transmitter comprises a means for generating time marking signals inserted in a field and which indicate a change of service key and wherein the re-ceiver comprises means for detecting said marking signals, starting the investigation of a future service key K', and maintaining said future key on hold.
5. A television system according to Claim 4, wherein each message comprises a bit indicating the change of key in the transmitter, the corresponding key change taking place in the receivers as soon as the bit is detected.
CA 353905 1979-06-15 1980-06-12 Television system with access control Expired CA1167562A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
FR7915400A FR2459595B1 (en) 1979-06-15 1979-06-15
FR7915400 1979-06-15

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CA1167562A true CA1167562A (en) 1984-05-15

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CA 353905 Expired CA1167562A (en) 1979-06-15 1980-06-12 Television system with access control

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US (1) US4354201A (en)
EP (1) EP0021938B1 (en)
JP (1) JPH027235B2 (en)
CA (1) CA1167562A (en)
DE (1) DE3066372D1 (en)
ES (1) ES492393A0 (en)
FR (1) FR2459595B1 (en)
WO (1) WO1980002901A1 (en)

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Also Published As

Publication number Publication date Type
EP0021938A1 (en) 1981-01-07 application
CA1167562A1 (en) grant
ES492393D0 (en) grant
EP0021938B1 (en) 1984-02-01 grant
ES492393A0 (en) 1980-12-16 application
WO1980002901A1 (en) 1980-12-24 application
JPS56500714A (en) 1981-05-21 application
DE3066372D1 (en) 1984-03-08 grant
FR2459595B1 (en) 1984-03-16 grant
ES8102445A1 (en) 1980-12-16 application
FR2459595A1 (en) 1981-01-09 application
US4354201A (en) 1982-10-12 grant
JPH027235B2 (en) 1990-02-16 grant

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