United States Patent
`Guillou
`‘
`
`[19]
`
`[54] TEXT VIDEO-TRANSMISSION SYSTEM
`PROVIDED WITH MEANS FOR
`CONTROLLING ACCESS TO THE 5
`INFORMATION
`
`[75]
`
`Inventor:
`
`Louis C. Guillou, Bourgbarre-Saint
`Erblon, France
`
`[73] Assignees: Etablissement Public de Diffusion dit
`“Telediffusion de France”,
`Montrouge; L’Etat Francais,
`represente par le Secretaire d’Etat
`aux Poste et Telecommunications
`(Centre National d’Etudes des
`Telecommunications), Issy les
`Moulineaux, both of France
`
`[21] Appl. No.: 117,234
`
`[22] Filed:
`
`Jan. 31, 1980
`
`Foreign Application Priority Data-
`[30]
`Feb. 6, 1979 [FR]
`France .............................. .. 79 02994
`
`H04N 7/15; HO4K 1/00
`Int. ‘CL3
`[51]
`[52] U.S. c1. .................................. .. 358/114; 340/706;
`_
`358/147; 340/825.54; 340/325.5
`[58] Field of Search ........ .; .......... .. 455/2; 358/86, 114;
`340/147 LP, 149 A, 149 R, 152 R, 152 T, 706;
`178/22.08
`
`[5 6]
`
`References Cited
`8
`U.S. PATENT DOCUMENTS
`
`1/1976 Barnhart ..............
`3,934,079
`5/1976 Anderson et al.
`3,956,615
`3,997,718 12/1976 Ricketts .........
`
`358/86
`340/152 R
`..................... .. 455/2
`
`[11]
`
`[45]
`
`4,337,483
`
`Jun. 29, 1982
`
`................ 358/122
`3/1978 Sherman ...........
`4,081,132
`4,214,230 7/1980 Fak et al.
`...................... .. 340/149 A
`
`Primary Examiner—Howard A. Birmiel
`
`[57]
`
`ABSTRACT
`
`A text video-transmission system comprising an infor-
`mation emitting center and receiving stations, the emit-
`ting center comprising encryption means using an oper-
`ating key, each receiving station comprising decryption
`means using the operating key, wherein in this system,
`the encryption means of the emitting center comprise: a
`generator delivering a numerical signal representing an
`operating key K, this key changing randomly at prede-
`termined intervals; an automatic encryption means
`comprising: a discriminator with an input connected to
`a magazine memorizing circuit from which it receives
`clear octets, this discriminator being capable of distin-
`guishing, among these clear octets, those wherein the
`7th and 6th binary elements are zero, an OR-exclusive
`logic circuit connected to the discriminator from which
`it receives octets wherein the 6th and/or 7th binary
`elements are not zero, this logic circuit having an output
`which carries encrypted octets; a generator of encoding
`octets, the decoding means of each receiving station
`comprising: a generator of a numerical signal represent-
`ing the operating key K in use in the emitting center,
`automatic decryption means comprising: a discrimina-
`tor adapted to distinguish, among the encrypted octets,
`those wherein the 7th and 6th binary elements are zero,
`an OR-exclusive logic circuit connected to the discrimi-
`nator; and a generator for decoding octets.
`
`11 Claims, 10 Drawing Figures
`
`GENERATOR
`2
`EMITTWG
`CENTER
`
`
`
`RECEIVING
`
`I
`
`l
`RECENING
`CCT
`' -35 orsmrmc
`KEY
`
`
`
`
`Apple Exhibit 1011
`
`Page 00001
`
`Apple Exhibit 1011
`Page 00001
`
`

`
`U.S. Patent
`
`Jun. 29, 1982
`
`INFORMATION
`SOURCE.
`I
`
`RECEIVING
`STATIONS
`
`RECEIVING
`CCT
`
`Page 00002
`
`

`
`US. Patent
`
`Jun. 29, 1982
`
`4,337,483
`
`INFORMATION
`SOURCE
`
`GENERATOR
`
`EMITTING
`
`2
`
`CENTERJ Ml
`
`DISCRIMINATOR
`
`24
`ENCRYPTlON/
`
`RECEIVING
`STATION
`
`DISCRIMINATOR
`
`DISPLAY
`MEANS
`
`j
`j
`
`Page 00003
`
`

`
`US. Patent
`
`200919,2m
`
`1.
`
`Sheet 3 of 9
`
`4,337,483
`
`Page 00004
`
`

`
`US. Patent
`
`Jun. 29, 1982
`
`Sheet 4 of9
`
`4,337,483
`
`; E
`
`RATOR
`
`V GENERATOR
`61/
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`
`Page 00005
`
`

`
`U.S. Patent;
`
`Jun. 29, 1982
`
`4,337,483
`
`Page 00006
`
`

`
`US. Patent
`
`Jun. 29, 1982
`
`Sheet 6 of9
`
`4,337,483
`
`I I I I
`
`I I
`
`INFORMATION
`SOURCE
`
`I
`
`EMITTING
`I
`'
`CENTER
`21/1 K
`ENCRYPTION
`MEANS
`SUBSCRIPTION
`CENTER
`
`24
`
`'
`
`-
`
`GENERATOR
`MEMORY
`22
`V
`DISCRIMINATOR
`JUNCTION
`3 K 2 11
`25
`GENERATOR 4’
`31 Q
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`UNCTION
`MULTIPLEXER
`
`MESS_A?5E
`FORMING
`CIRCUIT
`
`I
`
`SUBSCRIPTION
`HOLDER
`I105/
`
`103
`—
`
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`L
`
`I
`
`RECEIVING
`
`L____________I
`
`CHARG ING/
`STATION
`
`Page 00007
`
`

`
`U.S. Patent
`
`Jun. 29, 1982
`
`Sheet7 of9
`
`4,337,483
`
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`

`
`U.S. Patent
`
`Jun. 29, 1982
`
`Sheet 8 of 9
`
`4,337,483
`
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`Page 00009
`
`

`
`U.S. Patent
`
`Jun. 29, 1982
`
`.
`
`Sheet9of9
`
`4,337,483
`
`DECODING
`CIRCUIT
`
`3
`
`DISCRIMINATOR
`
`JLXQQTION
`
`_
`
`‘
`
`MEMORY
`
`SUBSCRIPTION
`
`OPERATING
`K SUPPLY
`
`FIG. 10
`
`Page 00010
`
`

`
`1
`
`4,337,483
`
`TEXT VIDEO-TRANSMISSION SYSTEM
`PROVIDED WITH MEANS FOR CONTROLLING
`ACCESS TO THE INFORMATION
`
`BACKGROUND OF THE INVENTION
`
`.
`
`The present invention relates to a text video-transmis-
`sion system provided with means for controlling access
`to the information.
`It can be used in the transmission and display of infor-
`mation on television receivers for purposes of entertain-
`ment, information or education. The invention applies
`essentially to a broadcase system (i.e. unidirectional) by
`means of which alphanumerical information organised
`_into pages and magazines can be put into television lines
`and to interactive system (i.e. two-directional) affording
`access to data bases (general information, directories,
`etc.) and to interactive services (transactions, messages,
`education) through the telephone system.
`In the first system, the distribution of information is ,
`effected by a method of distribution in bundles, compat-
`ible with the distribution of the television signal.
`These systems have already been described in numer-
`ous articles or patent applications. Reference is made
`hereinafter essentially to the so-called ANTIOPE sys-
`tem, a detailed description of which can be found par-
`ticularly in the following documents:
`.
`the article by Y. GUINET entitled: “Etude compara-
`tive des
`systémes de télétexte en radiodiffusion.
`Quelques avantages de la diffusion des donnees par
`. paquets appliquee au teletexte” which appeared in the
`U.E.R. Cahier Technique, no. 165,—October 1977, pages
`242 to 253;
`the article by B. MARTI and M. MAUDUIT entitled
`“ANTIOPE, service de télétexte”, which appeared in
`the journal “Radiodiffusion Télévision”, 9th year, no.
`40. November-December 1975, 5/5, pages 18 to 23;
`the “Sp’écif1cation du Systeme de télétexte ANTI-
`OPE”, edited by the Centre Commun d’Etudes de Té1é-
`vision et Telecommunications (CCETT);
`French patent application no. 75 18319, filed on June
`6th 1975 and entitled “Data distribution system”;
`French patent application Peg. no. 76 27212, filed on
`Sept. 6th 1976 and entitled “System for the numerical
`transmission and displaying of text on a television
`screen”;
`French patent application no. 76 29034, filed on Sept.
`22nd 1976 and entitled “Improvements to systems for
`the numerical transmission and displaying of texts on a
`television screen”;
`the French application for a certificate of addition no.
`77 17625, filed on June 3rd 1977 and entitled “Data.
`distribution system”.
`As this video-transmission system is thus widely
`known, it will not be described in detail here. Only the
`essential principles will be mentioned, to make the in-
`vention easier to understand. For any details of design
`or construction, reference can be made to the docu-
`ments cited above which in turn refer to others, and all
`these documents should be regarded as incorporated in
`this description.
`FIG. 1 shows, in highly diagrammatic form, the es-
`sential elements of such a system. Such a system com-
`prises a.n emitting centre 2 and receiving stations 4, 4’,
`etc.
`The emitting centre receives information from one or
`more sources 5 and comprises:
`
`2
`means 6 for composing a ‘magazine consisting of
`pages organised into lines of characters, if the supplier
`of the information has not already composed it in this
`way;
`a magazine memorising circuit 10 ‘in the form of ‘nu-
`merical signals grouped into octets (8 binary elements);
`a junction 11 connected to the circuit 10,
`a distribution multiplexer 12 serving to form bundles
`of octets and insert information in the lines of a televi-
`sion signal, this device using the procedure mentioned
`above.
`,
`‘
`Each receiving station comprises:
`a circuit 14 for receiving and demodulating said tele-
`vision signal;
`a line 16 for processing the video picture signals;
`a line 18 for processing numerical signals,
`this line
`comprising notably a numerical data decoder, and fi-
`nally
`p
`,
`._
`..
`‘
`.
`display means 20._
`In a system of this kind, the flux of information from
`the suppliers of information to the distributionvcentres
`has the following general characteristics.
`The source 5, which is an information-supplying data
`bank,
`is, for example, a meteorological service,_ the
`Stock Exchange, an information agency, etc. This bank
`supplies the composing means 6 which puts the infor-
`mation into pages of the suitable format.
`_
`‘
`To indicate the size scales involved, it can be stated
`that, in the ‘case of an experimental magazine produced
`for share values, there may be about 80 pages containing
`on average 800 octets, i.e. a total of 64000 octets. A
`shares magazine of this kind uses a resource of 10 lines
`per frame. A television line lasts 64 its and can carry 32
`useful octets, and there are 50 frames per second.«Thus,
`the resource of a line/frame makes it possible to trans-
`mit 50X32X 8= 12800 b/s (binary elements per sec-
`~ ond). The entire magazine is thus transmitted in
`
`30
`
`81
`
`12.8
`
`0 = 41 seconds,
`
`which means that the magazine is transmitted cyclically
`with a periodicity of 4 seconds.
`g
`It will be noted that an interactive line connecting the
`distribution centre to the information supplier typically
`operates at 4800 b/s and this difference in speed relative
`to the speed of broadcasting at 12800 b/s explains the
`need to memorise the information at the distribution
`source.
`,
`
`In such system, the octets carrying the information
`are traditionally marked as follows:
`
`bs
`Odd-numbered
`
`j
`,.‘_a_\
`b7 be b5
`High weight
`
`k
`{thug
`b4 b3 b2 b1
`Low weight
`
`wherein the binary element bg is an odd-numbered ele-
`ment, in other words an element wherein -the total num-
`ber of “1” appearing in the octet is odd.
`.the
`Thus,
`according
`to
`this
`notation,
`(j/k)=(4/7) corresponds to the octet 11000111.
`The octets are divided into control octets and data
`octets. The control octets indicate,
`in particular, the
`beginnings and ends of pages and the beginnings and
`ends of lines. The data octets, inserted between the
`control octets, correspond to the characters contained
`
`octet
`
`40
`
`Page 00011
`
`

`
`4,337,483
`
`3
`in the lines. All these octets, both control and data oc-
`tets, comprise a heavy weight binary element which is
`an odd-numbered element.
`All the codes, identified by such octets, are organised
`into a table as follows:
`
`In this table,
`the columns 0 and 1 which correspond to the octets
`wherein the 6th and 7th binary elements are zero
`(b5=b7 = 0), contain control octets;
`columns 2 and 3 contain essentially numbers and
`punctuation marks;
`columns 4 and 5 contain essentially capital letters,
`columns 6 and 7 chiefly contain lower case letters.
`As an example, a current page of information accessi-
`ble to the user is in the following form:
`(1) First, it contains a page heading, which is made up
`of the control codes (ETX) FF RS NP1 NP; NP3:
`wherein:
`ETX is a code which terminates the preceding page,
`FF is a code indicating a new page,
`RS is a page flag,
`NP], NP2, NP; are codes indicating a page number
`‘from 001 to 999.
`(2) After the page heading there is a "zero” line: US
`00C1C2C3.
`.
`.
`.
`.
`. ..RC LF,
`wherein:
`'
`.
`US is a line flag,
`00_indicates the zero line,
`C1, C2, C3 are supplementary codes,
`RC LF terminate the line.
`The zero line may also contain an operating name, a
`date, a time and optionally information on charges. This
`zero line does not carry any information which consti-
`tutes the service. It is part of the procedure.
`(3) After the zero line come the information lines
`comprising first of all a line heading which is made up of
`the codes (RC LF) US NR1 NR2, wherein:
`RC LF ‘terminate the previous line,
`US is a line flag,
`NR1 NR2 constitute the line number, which goes
`from 01 to 24.
`. d,,. These octets are
`Then come the data octets d1, d2. .
`inserted between the start of the current line and either
`a line end——start of new line - or the end of a page.
`These octets d1, d2,
`.
`.
`.
`(1,, represent the information
`constituting the service being broadcast. Thus the infor-
`mation element in a system of this kind is the displayable
`line.
`There are also other pages in addition to these current
`pages of information. They are functionally accessible
`by means of the supplementary codes C1, C2, C3 con-
`tained in the zero line. These are, for example, cover
`sheets and warning pages. All these pages are part of the
`procedure. Finally, there is a page of summary which
`can be regarded as part of the data.
`
`’
`
`4
`Now that these points regarding the general system
`have been mentioned, we can deal with the problem
`which the invention sets out to solve.
`The advent of the new services above mentioned
`raises the question of how to charge for them, i.e. how
`to implement a system for identifying and controlling
`the audiences. This question arises more generally for
`any broadcast service which tends to make the broad-
`casting networks more profitable by making better use
`of the resources.
`Taxation of the subscription type constitutes a both
`flexible and durable relationship between a service and
`its users. Such a method of taxation is particularly justi-
`fied in broadcasting.
`Taxation of the type based on consumption may also
`be used; this method of taxation is fundamental for “in-
`teractive” systems (where there is a dialogue between
`the subscriber and the information source; however, it is
`of secondary value in broadcasting systems (in which
`information is transmitted in one direction to the sub-
`scribers).
`There may be intermediate systems known as “quasi-
`interactive” systems wherein the content of the distribu-
`tion source is continuously modified to meet the re-
`quirements of the users, which are transmitted via a
`public data network. The advent of new distribution
`means with a very large capacity, such as satellites, will
`develop this quasi-interactive mode considerably, thus
`. making it necessary to implement a system for control-
`ling access to the information provided.
`This problem of access control raises above all the
`problems of encrypting the information when it
`is
`broadcast and decrypting when it
`is received. Natu-
`rally, these problems must be resolved in accordance
`with the specificity of the teletext system which is to be
`controlled. In particular, the method of scrambling the
`information and restoring the intelligibility of the infor-
`mation should not harm the performance of the system.
`Now,
`it is known that messages translated into the
`suitable language are characterised by a substantial
`redundancy so that the incidence of transmission errors
`on the intelligibility of the information broadcast
`is
`minimised. Thus, alphabetic texts are intrinsically very
`redundant, as are the majority of semi-graphic draw-
`ings;
`the character display controls use escapement
`characters; the page and line numbering uses Hamming
`codes; all the octets constituting a magazine are trans-
`mitted with imparity, etc. .
`.
`. Thus, there is no attempt
`to compress the information and the method of recover-
`ing the intelligibility of the information must therefore
`respect this redundancy and not propagate the deleteri-
`ous Consequences of transmission errors, which are
`difficult to monitor in broadcasting.
`The means for recovering the intelligibility of infor-
`mation which has been locked up beforehand consti-
`tute, to some extent, an “electronic lock”, and the intel-
`ligibility of the locked up information can only be re-
`covered by the use of a suitable key.
`The first question which arises is therefore the room
`to be allotted to this electronic lock in the system to be
`monitored. In fact, in the case of the teletext system,
`two procedures are used: the transporting procedure
`and the operating procedure. At what level of the pro-
`cedure should this lock be placed?
`BRIEF SUMMARY OF THE INVENTION
`
`The invention answers this question by proposing a
`lock which is attached to the operating level. This
`
`Page 00012
`
`

`
`4,337,483
`
`5
`method has a number of advantages. First, it respects all
`the constraints of synchronisation and non-propagation
`of the transmission errors. Furthermore, it is indepen-
`dent of the transporting network used by the system.
`Finally, it does not require any adjustment of the exist-
`ing standards and will accommodate any future devel-
`opment of these standards.
`In other words, and according to a first feature of the
`invention, the encryption of the information constitut-
`ing a magazine is carried out at the distribution source.
`More precisely, the encryption means are located up-
`stream of the multiplexer, which has reference numeral
`12 in the plan in FIG. 1.
`»
`Now that room has been found for the encryption
`means, there is still the question of the object to which
`these means are applied.
`The invention answers this second question by pro-
`posing means whose function is to encrypt up only the
`information carried in the displayable lines of the ordi-
`nary pages of the magazine. In other words, the encryp-
`tion does not affect the control codes appearing in col-
`umns 0 and 1 of the table of codes given hereinbefore
`and, in particular, the codes ETX, FF, RS, RC, LF and
`US. It affects only the data codes d1, d2, etc. This is the
`second feature of the invention.
`Finally, the invention sets out to solve a third prob-
`lem, that of respecting the imparity of the octets broad-
`cast.
`'
`All these aims are achieved by the use, according to
`the invention, of automatic encryption means which
`comprise means for forming a succession of encoding
`octets wherein the binary elements marked c1 to C3 are
`generated as follows:
`c1, c2, c3, c4 and c5 are taken at the output of a pseudo-
`‘ random series generator which is reset at the start of 35
`each displayable line by an operating key K and by the
`page and line numbers in question;
`c5 and c7 are at zero, and
`cg is an even-numbered element.
`Thus, the coding series obtained is made up of even
`octets. These octets are marked C1, C2. .
`. C,, or, generi-
`cally, CI‘. The clear octets constituting a line of informa-
`tion form a series marked d1, d2 .
`.
`. d,, or, generi-
`cally, dj. These octets are odd-numbered and are
`locked up by the encoding octets in accordance with
`the following rules:
`At each new clear octet of the displayable line, an
`octet is taken from the encoding series. There are two
`possibilities:
`If the clear octet belongs to columns 0 and 1 of the
`table of codes (b6=b7=0) the clear octet is transmitted
`as it stands, and the encoding octet is not used;
`If the clear octet does not belong to column 0 or 1,
`then the clear octet and the encoding octet are com-
`bined by an “OR-exclusive” logic circuit to form a
`broadcast octet: D].:dJ.$Cj, where the symbol 6B repre-
`sents the “OR-exclusive” logic operation.
`Because of the parity of the encoding octets, the
`broadcast octets are odd,
`like the clear octets,
`thus
`satisfying the requirement mentioned above.
`Moreover,
`the “OR-exclusive” operation is mani-
`fested by the substitution of the clear octet by a broad-
`cast octet belonging to the same group of columns as
`the clear octet, namely:
`the group of columns 2 and 2 which contains essen-
`tially the numbers and punctuation -marks,
`the group of columns 4 and 5 which contains mainly
`capital letters,
`
`6
`and the group of columns 6 and 7 which contains
`mainly lower case letters.
`Finally, the octets belonging to columns 0 and l are
`not modified, particularly the octets corresponding to
`the codes ETX, FF, RS, RC, LF and US, which are
`transmitted as they stand. Moreover, owing to the fact
`that the 6th and 7th binary elements of the encoding
`octets are zero, no new octets belonging to these col-
`umns are introduced. Thus the desired transparency is
`ensured.
`-
`In this way, all the aims listed above are attained with
`the locking means used according to the invention.
`To reinforce the inviolability of the lock thus formed,
`the operating key K is advantageously modified at ran-
`dom at predetermined, relatively short intervals (of the
`order of a few minutes, for exam.ple).
`It then remains to decrypt the information when it is
`received. To do this, the receiver should comprise a
`generator of decoding octets which delivers octets
`formed as follows:
`the low weight 5th binary elements are taken from a
`quasi-random series obtained from a generator reset at
`each start of a line by the operating key K, by the page '
`and line numbers in question;_
`the 6th and 7th binary elements are zero, and
`the 8th binary element is forced to zero.
`The rules for decryption are analogous to the rules
`for encryption; at each new octet received, belonging to
`an encrypted line, a new decoding octet is generated.
`There are two possibilities:
`If the octet received belongs to columns 0 and 1, it is
`transmitted as it stands to the interpreting circuits;
`If the octet received does not belong to columns 0
`and 1 (because its 6th and/or 7th binary elements are
`not zero) it is combined by an OR-exclusive circuit with
`the decoding octet before interpretation is carried out.
`Interpretation of the language is thus closely inter-
`connected to the encryption of the lines of information,
`and the robustness of the structure of the language
`broadcast is not affected by the encryption operations.
`Now that these general comments have been made
`regarding the invention, the precise definition of the
`object of the invention can then be worded as follows:
`Transmission system comprising an information emit-
`ting centre and receiving stations, the emission centre
`comprising:
`means 6 for composing a magazine consisting of
`pages organised into lines of characters, if such means
`are not already contained in the information source,
`a circuit 10 for memorising the magazine in the form
`of numerical signals grouped in octets (8 binary ele-
`ments), these octets comprising control octets and data
`octets, the control octets indicating in particular the
`beginnings and ends of pages and the beginnings and
`ends of lines, the data octets corresponding to the char-
`acters contained in each line, all these control and data
`octets comprising a binary element of high weight
`which is an odd-numbered element, the octets wherein
`the 6th and 7th binary elements are zero being control
`octets,
`a junction 11 connected to the circuit 10, and
`a distribution multiplexer 12 serving to insert infor-
`mation in the lines of a television signal, this emitting
`centre also comprising means for encoding the informa-
`tion using an operating key, each receiving station com-
`prising:
`a circuit 14 for receiving and demodulating said tele-
`vision signal,
`
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`4,337,483
`
`7
`a line 16 for processing the video picture signals,
`a line 18 for processing numerical signals, containing
`in particular a numerical signal decoder, and
`display means 20, each receiving station further com-
`prising means for decoding the coded information using
`said operating key, the system being characterised in
`that:
`(A) the encoding means of the emission centre com-
`prise:
`(a) a generator 22 delivering a numerical signal repre-
`senting an operating key K, this key changing randomly
`at predetermined intervals,
`(b) automatic encryption means 24 comprising:
`(i) a discriminator with an input connected to the
`magazine memorising .circuit from which it receives
`clear octets, this discriminator being adapted to distin-
`guish, among these clear octets, those wherein the 7th '
`and 6th binary elements are zero,
`this discriminator
`having two outputs,
`the first carrying these octets
`wherein the 7th and 6th binary elements are zero, and
`connected to the distribution multiplexer through the
`junction, and the second carrying the clear octets dj
`wherein the 7th and/or 6th binary elements are not
`zero,
`’
`(ii) an OR-exclusive logic circuit with two inputs, one
`of which is connected to the second output of the dis-
`criminator from which it receives the clear octets d_,-
`wherein the 6th and/or 7th binary elements are not
`zero, this logic circuit having an output which carries
`odd—numbered coded octets DJ-, the coded octets then
`_being directed towards the distribution multiplexer
`through the junction;
`(c) a generator of encoding octets controlled by the
`automatic encryption means from which it receives
`octets indicating the page and line numbers of the data
`to be transmitted and the signal corresponding to the
`7 operating key, this generator of octets delivering, for
`each data octet dj of a displayable line, an encrypted
`octet C,-, this octet having an even-numbered 8th binary
`element and 7th and 6th binary elements of zero, this
`octet being applied to the other input of the logic cir-
`cuit,
`(B) the decoding means of each receiving station
`comprise:
`(d) a generator of a numerical signal representing the
`current operating key K in the emitting centre,
`(e) automatic decryption means comprising:
`(i) a discriminator with an input connected to the
`numerical signal decoder of the receiving station, from
`which it receives the coded octets, this discriminator
`being adapted to distinguish, among these coded octets,
`those wherein the 7th and 6th binary elements are zero,
`this discriminator having two outputs, the first carrying
`these octets wherein the 7th and 6th binary elements are
`zero, this first output being directly connected to the
`display means, the second carrying the coded octets D,-
`wherein the 7th and/or 6th binary elements are not
`zero,
`(ii) an OR—exclusive logic circuit with two inputs, one
`connected to the second output of the discriminator
`from which it receives the coded octets Dj, this logic
`circuit having an output which carries decoded octets
`dj which are then directed towards the display means;
`(i) a generator of decoding octets controlled by the
`automatic decryption means which transmits to it the
`octets indicating the page and line numbers of the data
`transmitted and the signal corresponding to the current
`operating key K,
`this generator of decoding octets
`
`8
`having an output which delivers, for each encrypted
`octet received, a decoding octet Cj having a high
`weight binary element which is forced to zero and 7th
`and 6th binary elements of zero.
`Encryption and decryption means of this kind pro-
`vide an advantageous solution to the problem of charg-
`ing mentioned hereinbefore. For this purpose, the in-
`vention proposes that in addition to the operating key
`whose function has been defined above, subscribers’
`keys should be used, which are generated randomly by
`a charge administration centre. These keys have a rela-
`tively long service life (from 1 to 12 months), compared
`with the operating key (which is of the order of a few
`minutes).
`To illustrate the functioning of this double key sys-
`tem, one could take the example of a subscription plan
`using four types of subscriptioml month, 3 months, 6
`months and one year. In addition to its duration, 21 sub-
`scription is characterised by the month in which it be-
`gins. With a plan of this kind, in a given month and for
`a given service, there are thus 22 subscribers’ keys liable
`to be used by the users: a monthly key, three three-
`monthly keys, six six-monthly keys and ‘twelve yearly
`keys.
`.
`Each month, the charge administration centre pro-
`vides each distribution centre with a list of 22 subscrib-
`ers’ keys in use for each service distributed by this cen-
`tre. It also provides the subscription sales points with
`another list of 4 keys which are to start in the following
`month (one month, three months, six months and a
`year), for each service, with the prices of the subscrip-
`tions.
`A suitable machine installed in each sales point re-
`cords some of these keys, in the form of subscription
`blocks, on holders provided for this purpose (for exam-
`ple, information-bearingcards of the credit card type).
`These cards are then inserted by the users of the service
`in the receiver.
`,
`p
`.
`-
`For each chargeable service, approximately every
`five minutes, a new operating key K is generatedat
`random, by each distribution centre concerned. Thus, in
`the course of a session of a service (one ormore hours),
`several dozen operating keys may succeed one another.
`As soon as a distribution centre generates a new oper-
`ating key K, it calculates, for each current subscribers’
`key in use C; for this service, a message M,- by means of
`an algorithm M,-=Fc,- (K), with the keys C; acting as
`parameters.
`Thus, for a service using the subscription plan de-
`scribed above, there are 22 different messages in force at
`any one time. The duration of a message is equal to that
`of the operating key K, and for a given service, at any
`one time, there are as many messages as there are sub-
`scribers’ keys in use.
`All the messages M1 in force together constitute the
`information for access control associated with the ser-
`vice being broadcast. This access control information is
`obviously not locked up by the electronic lock.
`A particular application of this system is envisaged
`within the scope of the present invention. In this in-
`stance, the messages M,- are grouped in a special page,
`known as the access control page, which is updated
`each time the operating key is changed. The access
`control page is distributed cyclically, like the ordinary
`pages of information constituting the service. However,
`it is not locked up by the electronic lock. The access
`control page is read systematically by the receiver
`when it is put into contact with the service, then each
`
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`4,337,483
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`9
`time this page is updated, during the period of consulta-
`tion of the service, but it is not displayable.
`The messages are therefore, in fact, motifs of primary
`synchronisation of the lock and these motifs can be
`interpreted by an algorithm supplying the operating
`key. This algorithm is in the form: K=Gc,~(M,-), and is
`developed by a restoring circuit (which may also be
`part of the subscription holder which already contains
`the subscribers’ key C,-) to which the messages M; are
`supplied. This circuit therefore provides the automatic
`unlocking means with the operating key K which ena-
`bles it to unlock the information received.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In any case, the features and advantages of this inven-
`tion will become more apparent from the following
`description of some, exemplary embodiments given by
`way of explanation and not in a restrictive capacity.
`This description refers to the accompanying drawings,
`wherein:
`FIG. 1, already described, shows a synoptic plan of
`transmission system according to the prior art;
`FIG. 2 shows a synoptic plan of a system according
`to theinvention;
`FIG. 3 shows a plan of acircuit for obtaining a partic-
`ular primitive generating polynomial;
`FIG. 4 shows a pseudo-random series generator con-
`sisting of a combination of three circuits of the type
`shown in the previous figure;
`FIG. 5 shows a synoptic plan of a generator of encod-
`ing octets or decoding octets;
`FIG. 6 shows a diagram illustrating the different
`states which an automatic encrypting means can as-
`sume;
`'
`FIG. 7 shows a synoptic plan of a system provided
`I with access control means operating by means of sub- ’
`scribers’ keys;
`FIG. 8 shows the means used in the distribution cen-
`tre for encryption the information,
`.
`FIG. 9 shows a synoptic plan of a receiver according
`to the prior art,
`FIG. 10 shows a synoptic plan of the means to be
`‘inserted in the receiver of the type shown in the previ-
`ous figure, in order to decrypt the information.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The system of the invention, in the form which it
`takes in the case of pages broadcasting system, is shown
`in the plan in FIG. 2. This system comprises known
`elements already shown in FIG. 1, namely:
`in the emitting centre 2:
`means 6 for setting up a magazine consisting of pages
`organised into lines of characters, unless such means are
`already provided in the information source,
`a circuit 10 for memorising the magazine in the form
`of numerical signals,
`a plurality ofjunctions 11 connected to the circuit 10,
`and
`
`a distribution multiplexer 12 serving to insert the
`information in the lines of a television signal,
`in each receiving station 4:
`a circuit 14 for receiving and demodulating said tele-
`vision signal,
`a line 16 for processing the videopicture signals, a line
`18 for processing numerical signals containing, in par-
`ticular, a numerical signal deco