DE3513860A1 - Method of coding and decoding for a coin-operated television system - Google Patents

Abstract

The coding method according to the invention allows an access unit to be formed which authorises or bars access to a coin-operated television network. …<??>According to the invention, the access unit comprises at least two words: a selection word which represents the authorised transmission, and an access word which is formed from a coded combination of the first word and a further word which represents the authorisation period. …<IMAGE>…

Description

PRINZ, LEISER, BUNKE & PARTNER>

Patent Attorneys · European Patent Attorneys O C 1 O Q C Π

Munich . Stuttgart

Cc -

April 17, 1985

SOCIETE D'ELECTRONIQUE DE LA
PAYS DE LOIRE SEREL REGION
74, rue du Surmelin
75080 PARIS, France

Our reference: S 3258

Method of encoding and decoding for a coin operated television system

The invention relates to a method of coding and decoding for a pay television system. A coin-operated television system is to be understood here as a system in which the broadcasts are disrupted. Proper reception of these broadcasts is only possible with the help of a decoding or interference suppression device, the is only handed over to an authorized person, for example after paying a fee.

There are various methods of disrupting broadcasts. Mention should be made, for example, of a ^{method described in I 1} R-PS 2 330, in which, for each image line, the time interval between the line synchronization pulse and the

Image signal is changed. The shift between the synchronizing pulse and the image signal changes according to a law determined by coding. Without decoding, the received image will be distorted and can only be viewed with difficulty. The decoding device of the receiver sets the correct phase of the picture signal with respect to the line sync pulse. The decoding apparatus includes, for example, one variable delay line according to a generator, which has the reverse code of when the transmission is disrupted codes used.

Whatever method may be used to interfere: the user of a receiver must constantly have a Decoding device can have. According to the invention, however, there is a desire that the effectiveness of the decoding device will only be released if your user is a subscriber. Therefore it is envisaged that the effectiveness of the decoding device is dependent on a release according to a device for release access to the programs or a key. Of course, the data of the device must be used for Access authorization must be coded so that they cannot be easily forged. This type of coding and the corresponding decoding - to which the invention relates - must not be confused with the above mentioned type of coding, which causes a disruption of the broadcasts.

The coding of the device for the release of access - which enable the operation of the decoder for the interference suppression should - should meet the following conditions:

1. The coding must be able to relate to a person. This means that access to the reception of broadcasts, which is granted via a key, for example in the form of a card containing coded data, for only one person only recipient may be valid.

2. The release is only for a certain subscription period valid.

3. Each subscriber must be able to purchase different types of subscriptions. The programs are, for example, in divided into two categories, the first is offered to all subscribers and the reception of programs of the second category is only released for those subscribers who have paid an additional fee.

In addition, the coding of the device for enabling access to the pay television must be well protected against fraud.

The coding of the device for enabling access is referred to here as an access record. It contains at least two words. The first, C, represents the selection of the type of broadcasts or programs to be granted access. The second Word, M, is formed from a coded combination of the first word G and another word, B, and represents the The time period of the release, i.e. the subscription time. The different words are represented by binary numbers, for example.

The selection word C may contain a reduced number of bits and therefore look so that it is relatively easy to read by the subscriber. This increases readability not the opportunity to forge the access record. If

namely the place G is changed on its own, without the word M is also changed, the access record cannot clear the interference suppression. The reading device for the access record the recipient then recognizes a contradiction between the words C and M.

In the preferred embodiment, the access record contains a third word T, which identifies the access record as person-related or not. In this case the access word M is formed from the coded combination of the words G and B as well as an additional word N. The additional word N represents the personal code or the standard code N index O and is identical for all subscribers. The words N and N ₀ do not appear as such in the access record; these words are - inaccessible to the user - in the memory of the access authorization device. Like the word C, the word T only needs to contain a reduced number of bits, for example one bit or two bits, which can only assume two values. The easy legibility of the word T is not a disadvantage, since this word, like the selection word G, results in the effectiveness of the interference suppression decoding device being blocked if it is changed without the word M being changed at the same time.

In one embodiment, the access record is in the form of a card with encoded data. The data will be represented by an authority, and the card is produced with the aid of a coding device, in particular a computer. The computer contains a random generator for generating this coded combination.

In order to make fraud as difficult as possible, the program selection word C, possibly with the word N, is accordingly the subscriber's code or the word Nq des

Standard codes, for example also coded with the aid of a random generator, before it is combined with the word B. For decoding, the same coding must be applied to the word C and, if necessary, to the word N or the word N _0. The combination of the word B with the word that results from the coding of C corresponds to an inverse transformation of this combination, which is formed for the coding.

The device for controlling access or blocking the reception of broadcasts preferably includes one a chip integrated circuit, which is a one-piece semiconductor substrate in such a form that access to the internal connections of this integrated circuit is not possible.

To make decoding particularly difficult, a pseudo-random generator is used for coding and uses it in a special way. It is recalled that a pseudo-random generator contains a shift register with N ₁ digits and an exclusive-or gate for periodically changing the content of each digit in accordance with a timer signal. The final number is reached after X pulses from the timer. It is formed either by the content of all positions or a part of them or by a sequence of N2 bits of the output of the last position, provided that the timer remains in operation.

According to the invention, the number X is not a fixed number, but a function of the initial word, i.e. the initial number.

In the same way one can create such a pseudo-random number generator by programming a microprocessor or build through an analog program.

Further features and advantages of the invention are referenced in the description of some exemplary embodiments described on the accompanying drawing. Show it:

- Figure 1 shows the structure of an access record,

FIG. 2 shows a diagram of an encoder and a coding method ,

- Figure 3 shows a scheme of a decoder and a decoder

procedure,

- Figure 4- a scheme to explain a Godier method

with a pseudo-random generator,

- Figure 5 shows the structure of a word at the exit of a pseudo

Random generator,

- Figure 6 is a scheme of a pseudo-random generator,

- Figure 7 a code card,

- Figure 8 is a diagram of a decoder and

FIG. 9 shows an implementation example for the coding method according to FIG. 2.

In the exemplary embodiment, the access set is composed of four words T, C, M and V (FIG. 1). Each of these four Words is formed by a number of encoded binary numbers that are shown on a card by a bar code in two Strips are applied (Figure 7)

The first V / ort T indicates whether the access record is personal or is of the standard type. The personal access record can of course only from a special one Decoders are read; a standard access satζ

can be read by all decoders. In the simplest case, the word T comprises one bit or two bits.

The second word C corresponds to the selection of television programs, to which access is granted. One of the choices is that there are several types of television broadcasts there are, for example, three types, and that the subscription has a right of access to the first or second or third type or to a combination of two or three types. The first type of shipment includes, for example Broadcasts with general information, the second type of cultural broadcasts and the third type of sports reports. It is also possible to provide that the various types of broadcast differ according to the time blocks, during which these programs are broadcast.

However, one type of selection is firmly planned: a basic or minimum program, to which the subscription is the lowest Tariff access granted, and sub-programs with a special access right. The word C indicates whether a subroutine is released or which subroutines are released. In the exemplary embodiment, the word C - like that Word T - be printed on the access card in a practically clearly legible form. The basic program and the Sub-programs are generally only valid for a certain subscription period. This validity period goes into the third word M a.

The third word M is a fixed access word that forms the actual access phrase; it grants the right for approval. Mind you, great care must be taken when coding this access word.

The fourth word V is a simple test key, the it allows to check whether the access record was read correctly.

A computer 10 is used to generate the access word M, into which the following input variables are entered become: the word T indicating the personal identifier or the absence of such an identifier forms for the release, the selection word C, and a word B, which specifies the basic program or minimum program. This word B must be protected as well as possible. It is changed periodically, for example monthly, if the subscription period is one month; it then indicates the subscription time.

The subroutines are indicated by words S ^, to S, however, these words are not used to process the word M.

The basic program B is always available in the exemplary embodiment; the number of subroutines is equal to the number 2 ⁿ of options. In this way the word C can comprise η bits. It has already been pointed out that it is not necessary to encrypt the word G in a complicated form.

In addition, the coding computer 10, the encoder _{} contains} in its memory the word N corresponding to the code of the subscriber and the word N ₀ corresponding to the data of the standard program type.

If the access record is personal, the word N is brought into a memory A of the encoder 10.

Otherwise the word Nq is stored in this memory A. entered.

The words C and N (or Nq) are according to a certain Law combined. An example of this law is given below in connection with FIG.

This combination forms a word G, which is encrypted according to a pseudo-random law FK. This law will be discussed further below in connection with Figures 4 ·, 5 and. 6 explained. The pseudo-random law must be used Transformation must be such that it yields a word K (or Kq) with a sufficient number of bits because the number of possible values is extremely important in making fraud more difficult.

The word K or Kq is combined with the word B according to another law FM, which can be of a simpler form than the law FK and which gives the accession word M or M _Q. For example, this law reads FM (B, K) = B + K.

The simplicity of this law makes it easier, as will be seen, to implement decoding without endanger the confidentiality of the access word.

So that the operation of the interference suppression device is released for the user, the card with the access record is read by a reading device (FIG. 8) in order to decode the access word. The reading device 20 transmits the read data to a microprocessor chip 21 (Figures and 8). The following words are entered into the microprocessor 21 for this purpose: T, C and M (or M _Q ) and also the word V for the validity or authenticity check. In addition,

the words N and Nq are found in the memory of the microprocessor 21.

For decoding (FIG. 3), the word K or K ₀ is generated from the words T and C in exactly the same way as in the encoder. A combination of the words C and N (or N _Q ) is thus formed to generate the word G, which is transformed by a pseudo-random generator according to the law FK.

The word M or M _Q is combined with the word K or K _Q according to a law PB which is the reverse of the coding law PM, * in this way the word B, which corresponds to the basic program, is formed again. In the exemplary embodiment, M = B + K and thus PB (M, K) = B = M - K.

If the disturbance consists in the distance between the line synchronization pulse and the To change the image signal pseudo-randomly, then forms the word B is the start word for a video pseudo-random generator applied to the basic program. It creates a variable line delay to get the correct one for each line Restore the phase of the image signal with respect to the line sync pulse.

The pseudo-random sequence is different because of the subroutines, it is also different from a subroutine to another. One therefore sees the words S ^ to S for provide access to these subroutines.

When the word C enables access to the first subroutine, the word C is combined with the word B according to a law F i to produce the word F-. The word N _x . is also a start word for a pseudo-random generator,

which, as with word B, acts on a variable line delay. To combine the word B with the word C to generate the words Sp through S, laws Fo ^ is ^{F are} provided.

The access set is particularly well protected against fraud. In particular, the word M (or M _Q ) is a function of the words B, C, and N (or N _Q ). It follows that any change in the word T or the word C changes the word K (or K _Q ). The word B, which is a combination with the word K, cannot therefore be recovered due to this change. In addition, the word N and the law FK are in the memory of the microprocessor chip 21 ^ and the user is denied access to this memory.

Knowledge of the word B, accidentally or as a result of fraud, is also sufficient for gaining an Zu-r does not exit because this knowledge does not enable the access record to be processed.

The access record also includes a word V, which is intended to check whether the sequence coming from the reading device 20 is obtained, perfectly corresponds to a complete access record. One such test word is, for example a sum test, this then gives the number of ones and zeros that make up the words T, C and M. contain. The word V can also be obtained by an equality check method.

In the following, reference is made to Figures 4-, 5 and 6, which present an example of a pseudo-random coding FK that is particularly well protected against fraud.

The generator in Figure 6 comprises a number N ,. of bistable multivibrators 22 ^ ... 22 _m ... 22 ^. Each flip-flop 22 comprises a set input 23 _{5 to} which a set word G is fed. Each flip-flop is controlled simultaneously by a signal from a timer, not shown. The group of these flip-flops 22 forms a shift register. The output of the trigger circuits 22 is - like the other trigger circuits in each case - connected to the input of the following trigger circuit. The output of the flip-flop 22 is also connected to the first input 24 of an exclusive-OR gate 25. The second input 26 of the gate 25 is connected to the output of the last flip-flop 22, -. The output of the gate 25 is connected to the input of the first flip-flop 22-. The set word G is fed to the inputs 23 of the flip-flops 22; the position of the flip-flops changes in time with the pulse of the timer. After a certain number X of timer pulses, this number X is recorded by a mentioned pseudo-random generator, the output signal is then the position of the flip-flops 22 or the position of some of these flip-flops. It can also be formed by a sequence of encrypted numbers through the output of the last flip-flop if the timer continues to operate.

In a preferred variant, the number X is not a fixed one Number, but a function of the input word.

The pseudo-random coding can also be done by a Programming can be realized (Figures 4 and 5)

Figure 4- represents an essential part of the present

a
Invention, namely flow chart showing how that

γ-

Word K is derived from the word G. The function of the flowchart corresponds to a pseudo-random generator of the type shown in FIG.

With each clock signal of the timer, the output signal H of the exclusive-or gate is in the first digit of the Entered shift register. The content of this point is consequently - if the entrance is on the left and the exit right is - pushed to the right. The content of the place η is therefore equal to the content of the place (n - 1) at the time of the previous clock signal of the timer.

The sequence of bits at the output of the shift register is called sequence S. It is periodic. The length of a period is L = 2 - 1, i.e. P = in seconds (2 - 1) T seconds, where T is the period of the timer signals is. Because of the periodic property of the sequence S, it is shown in FIG. 5 in the form of a circle.

The output word is either determined by the content of all positions in the shift register at the end of a certain number by timer pulses or by the content of some of these positions or by a sequence of bits at the output of the shift register, ie at the point N ,,, formed. The beginning of this sequence appears at time t ^ = X. "C, where X is constant in one embodiment. The duration of the episode is also determined by a particular one Pseudo-random generator.

To increase the number of possible output words, that is to considerably increase the period L or P, and also to make fraud more difficult, is included in the

play the beginning 60 or the output window 61 of the sequence a function of the beginning word G, which is in the shift register was pushed in. Instead or in addition, the duration of the window 61 is a function of the mentioned V / place G.

In the flow chart of FIG. 4, the output word K (or G ^f ) runs parallel to it: it is the content of the digits after a certain time, which is a function of the input word. The number A determines the time according to a complicated law, as you will see below.

T is the content of a buffer at the beginning

same.

of the sequence / t_, and which is reduced by one unit or by one period for each pulse of the timer. For reasons of protection against fraud, tn preferably has a value that is not too small, rather it should have a minimum value. Therefore, the value of the bit is set from the JT position. the binary number T fixed to the value 1, so that T _min = 2τ.

The rhombus in which m. = N. ^ Stands corresponds in their Function of an exclusive or, A is the number of work cycles. A cycle is defined as follows: when the time

ΐ _{Ώ is} reached, puts the content G ^{1 of} the shift register κ

set a new value of ΐ _π . By then, a

ix

first cycle carried out. The new value of t _R defines the instant at which the second cycle is held and at which the third cycle starts, and so on.

At the end of the cycle of rank A, the output word K is equal to the word G ¹ , the content of the shift register.

It can be seen from this that the output word K appears after a variable time after the input word has been entered. The law that connects the input word with time between the input word and the output word, is relatively complicated. It is therefore particularly difficult, if not impossible, to use the input word to find out if you know the starting word.

In the embodiment shown in FIG is, the access record is housed on an optically readable card 30. The card has a hole 31 in the Near one end of the card 32 is provided. The access rate is inscribed between the hole 31 and the other end of the card 33. The set itself is shown in the form of lines in two stripes 34 and 35 · A black line 36 on strip 34- represents a one, a black one Line 37 on strip 35 is a zero. Two black lines can therefore not appear on both stripes at the same time 34 and 35 appear. Except for the spaces in between between the lines there is a black line either on stripe 34 or on stripe 35 Such a barcode on two strips is particularly easy to write and read.

To read the card, a reading device 38 (Figure 8) provided, which contains two pairs of light emitters and light receivers, one pair for each strip. The absence of light that would have reflected off the surface of the card indicates the presence of a black one Dash 36 or 37.

In front of the reading device 38, the decoder contains a Photoelectric switch passing through one on one side of the card

arranged light source and arranged on the other side of the card 30 detector 4-1. Introducing the Card 30 in slot 4-3 of the detector causes one Interruption of the light beam 4-2, which is emitted by the light source 40, and thus the determination the introduction of this card. The end of the insertion process is determined when the hole 31 the light beam 4-2 can pass again to detector 4-1.

Between the reading device 38 and the detector 4-1 on the one hand and the microprocessor 21 on the other hand, the decoder contains a processing circuit 4-5 and an electrical power supply source 4-6 for supplying the reading device 38 »of the light source 40, des Processing circuit 4-5 and the microprocessor

Finally, the cover plate 50 of the reading device and the decoder has two light sources 51 and 52 different colors. The light source 51 is, for example an electroluminescent diode of red color, it is turned on when / is read incorrectly or is not granted access to decode a current program. The light source 52 is one in this example Electroluminescent diode of green color, it confirms the possibility of access to receive a current broadcast.

In the following, exemplary embodiments of the coding and decoding methods according to the invention are given.

The word T comprises two bits.

The word N is 24 bits.
/ the access rate

The word N ₀ is also represented by 24 bits.

A basic program and three sub-programs are provided, Among these you can choose between programs O, 1, 2 or 3. This way there are eight possible Combinations. The word C comprises 3 bits for this purpose.

The word B representing the basic program is in FIG. 24 Bits coded.

The combination of the words N (or N _Q ) and C to generate the word G is effected in the following way (Figure 9): The V / ort N is converted into three eight-digit numbers (in 3 binary numbers with 8 bits each) N ,,, N ₂ and N ^ decomposed; the combination of N and C is then the number D = D _x , Dp D ,. The following applies here: D ^ = N ^, D ₂ = N ₂ + C, D ^ = N * + Ö.

C means the complement of C and is the number that goes through the transformation of the zeros to ones and the ones to zeros is obtained.

In the event that this combination gives a value of zero for D, then a slightly different combination is used, namely D ₂ = N ₂ + U. The result is then D ^, D ₂ D ^ = G _Q.

For the function FK, a pseudo-random coding is used to break off the sequence of the type described in connection with FIG. In this case, the cycle A = N ₂ + N, + C applies.

However, if the third bit of this number is zero, the zero is transformed into a one, making it the smallest Cycle number is 2 ^ = 8.

Otherwise, the puncture FK corresponds exactly to that which is described in FIG.

The word K obtained according to the pseudo-random sequence comprises 24 bits.

The word M = »B + K contains 25 bits, each of the numbers B and K contains 24 bits.

The laws F ₁ , F ₂ , F ₂ . for the decoding (FIG. 3) restore the words S ₁ , S ₂ and S _{in the following way: F 1} (S ₁ ) ο B? F ₂ (S ₂ ) = B ₂ B ^ B ₁ (B ₁ B ₂ and B ₅ are the eight-digit numbers that make up the word B = B ₁ B ₂ B ^)

Finally, the word V contains 5 bits.

The access record TCMV thus comprises a total of 35 bits, namely 2 bits for T, 3 bits for O, 25 bits for M and 5 bits for V.

Claims (1)

PRINZ, LEISER, BUNKE & PABTITSlER: -: ⁷ -. Patent Attorneys · European Patent "Attorneys * O r Ϊ Ö Q C Π Munich Stuttgart 00 IO ÖD U April 17, 1985 SOCIETE D'ELECTRONIQUE DE LA PAYS DE LOIRE SEREL REGION
74-, rue du Surmelin
73020 PARIS, France Our reference: S 3258 Claims A method for coding and forming an access record for checking a possibly existing release of interference suppression of the reception of broadcasts in a coin-operated television system, characterized in that several types of broadcasts are offered and the release only for a single broadcast or a combination of broadcasts and for a predetermined period of time is granted and that an access set is formed which comprises at least two words C and M , of which the first, called the layout word C, represents the approved programs or the combination of the approved programs and the second, called access word M, consists of one coded combination of the first word C and a V / ort B is formed and represents the release period. 2. The method according to claim 1, characterized in that that each read-decoder of access records a certain word N is assigned, which differs from reading device to reading device, so that the Access set grants the release only to a predetermined reading device, and that the access word M from a Combination of the words N, C and B is formed. 3. The method according to claim 2, characterized in that that each access record includes an additional word T, which is a personal identifier or a standard release represents, and that if there is a standard release, the access word M from a combination formed from a V / ort Nq and the words C and B which are common to all read-decoder devices will. 4. The method according to any one of claims 1 to 3 _T, characterized in that the access word M is formed from a combination of the word B and a word K (or K ₀ ) that the word K (or Kq) from the word C by a Combination G is formed from the word C and the word N (or Nq) and that the coding law FK of C (or G) with K is a pseudo-random law. 5. The method according to claim 4, characterized in that that the pseudo-random coding works according to the impulses of a timer and that the end word of the law FK after a certain constant number X of pulses from the timer after the start of the Coding method appears. 6. The method according to claim 4, characterized in that the pseudo-random coding in accordance with pulses of the timer is working and the end word K after a number X of timer pulses after that of one The beginning of the coding process depends on the beginning of the word. 7. The method according to claim 4 or 6, characterized in that that the pseudo-random coding works in accordance with clock pulses of a timer and the number of digits in the end word K depends on the value of the beginning word G. 8. The method according to claim 6, characterized in that the beginning word and the end word by the content is formed by places of a shift register and that the coding FK is carried out according to the following scheme will: - a first number A is formed, which is a function of the initial word, - a time value t _{n is formed} between the supply of the start word and the beginning of the appearance of the end word, the time value t ^ being a function of the start word, a pseudo-random sequence is formed during the time t "and at the end of this sequence the end word is used to form the input word of a new time value t _D , the end word appearing after A interruptions in the pseudo-random sequence. 9. The method according to claim 2, characterized in that the word N contains three eight-digit numbers N ^ N ₂ N * and that the word G of the combination of N and C has the form G = D ₁ D ₂ D ^ has with D ^ »^ ₁ D ₂ « N ₂ + O and D, = N * + C *, where however D ₂ = N ₂ + ö, if that results from the combination Word G is zero. 10. The method according to any one of claims 8 and 9 »thereby characterized in that A = N ^ + N ^ + C. 11. The method according to claim 4, characterized in that that M «is B + K. 12. The method according to any one of the preceding claims, characterized in that among the various Released types of programs a minimal program or basic program is provided, where the word B denotes Represents the basic program and is periodically changed. 13- method for decoding an access set obtained from a coding method according to claim 4, characterized in that the word K (or K ₀ ) is derived from the word C or from a combination of G and G or from the word N (or N _Q ) is obtained according to the same law (FK) that is used for coding. 14. A method of decoding according to claim 13 for a reading device of coded according to the method of claim 12 access records, characterized in that the words (S ^ ... S) for the release of sub-programs from the word C, the released type of broadcast or the Released types of broadcast represents, and the word B is formed in accordance with the coding laws (F ,, ... F _1n ). ι η 15. A decoder for practicing a method according to claim 13. characterized in that it comprises a microprocessor chip (21) whose inaccessible memory contains the law FK for coding the word C or a combination of the words C and N (or N _Q ). 16. Decoder according to claim 15, characterized in that the inaccessible memory of the microprocessor also contains the words R and N _Q. 17. Apparatus for enabling access to broadcasts in a coin operated television system for initiating the method according to one of claims 1 to 14, characterized in that the coding is in the manner of a bar code is. 18. The device according to claim 17, characterized in that the coding comprises two strips of bars and one for the zeros and one for the ones, and that the ones by a line on the first strip and the zeros are represented by a dash on the second stripe.