DE3513860C2 - Coding and decoding method for a coin television system - Google Patents

Description

The invention relates to a method to create an access code for a subscription Television system according to the preamble of claim 1. This generic method is from the US-A 4,354,201 is known.

Furthermore, the invention relates to a corresponding decoder and a corresponding one Device for enabling access to shipments a subscription television system.

Under a subscription television system, a system is here to ver stand in which the programs are disrupted. The proper receipt of these programs is only with Possible with the aid of a decoding or interference suppression device only to an authorized person, e.g. after paying a fee.

There are various methods of disrupting shipments. An example would be mentioned in FR-PS 2 330 236 described method, in which for each image line Time interval between the cell synchronization pulse and the  Image signal is changed. The shift between that Synchronizing pulse and the image signal changes after a law that is determined by the coding. Without decoding is distorted and the received image can only be viewed with difficulty. The decoding device the receiver sets the correct phase of the image signals related to the line sync pulse forth. The decoding device includes, for example variable delay line according to a generator, which is the reverse code of when the shipment is disrupted generated codes generated.

Whatever method is used to disrupt likes: the user of a recipient must constantly have a Decoder device can have. It exists the desire that the effectiveness of the decoding Device is only released if its user Is a subscription holder. It should therefore be provided that the effectiveness of the decoding device from a free The delivery is dependent on a device for free giving access to the programs or a key. Of course, the data of the device for Access clearance must be coded so that it is not easily ge can be faked. This type of coding and appropriate decoding - to which the invention relates relates - must not be confused with the above mentioned coding type, which is a disruption of the broadcasts causes.

The coding of the device for access authorization - the operating the decoder for interference suppression should - should meet the following conditions:

• 1. The coding must be related to a person. That means that access to receive programs, who has a key, for example in the form of a co dated data-containing card is granted only for one only one recipient may be valid.
• 2. The release is only for a certain subscription tent valid.
• 3. Each subscriber must have different types of subscriptions can acquire. The shipments are, for example, in divided into two categories, the first being all subscribers offered and the reception of programs of the second Kate gorie is only released for those subscribers who have a Have paid an additional fee.

In addition, the coding of the device for releasing the Access to coin television is well protected against fraud.

The object of the present invention is that genus educational procedures regarding controlled release to simplify certain programs and at the same time the To minimize the risk of manipulation to a minimum Zen.

This object is achieved in that the generic method the characteristic features of the Claim 1 has.

Furthermore, the invention provides a corresponding one Decoder according to claim 16 and a corresponding pre Direction to release access to a subscription nement television system according to claim 18.

Preferred further developments are the respective subordinate to take sayings.

The coding of the device for access approval is here as Entry record called. It contains at least two words. The first, C, represents the selection of the type of broadcast or Programs to which access is granted. The second Word, M, is made from a coded combination of the first Word C and another word, B, formed and represents the Time period of release, i.e. the subscription time. The different words are shown, for example by binary numbers.

The selection code word C can ent a reduced number of bits hold and therefore look so that it ver is relatively easy to read. This readability increases not the ability to forge the entry rate. If  namely the word C is changed on its own without even the word N is changed, the entry sentence can Do not release interference suppression. The reader for the Zu then set in the receiver then recognizes a contradiction saying between the words C and N.

In the preferred embodiment, the entry set contains a third word T, which defines the access phrase as personal identifies or not. In this case, the To transition word N from the coded combination of the words C and B as well as an additional word N. That too Additional word N represents the personal code or is the replacement word N₀, the latter for all subscribers ten is identical. The words N and N₀ do not appear as such in the Access rate; these words are - inaccessible to the user - in the memory of the access authorization device. Like the word C, the word T only needs a diminished one Number of bits included, for example one bit or two Bits that can only take two values. The easy Les The availability of the word T is not a disadvantage, since this word is like the selection code word C blocks the effectiveness of the Ent interference decoding device entails if it is without a simultaneous change in the word M is changed.

In one embodiment, the access set is Ge creates a card with encoded data. The data will represented by an authority, and the map is made using a coding device, in particular a computer poses. The calculator contains a random number generator testify to this coded combination.

To make fraud as difficult as possible, it will Selection code word C, optionally with the word N ent speaking the subscriber's code or the replacement word N₀,  for example also with the help of a Random generator coded before it with the word B combi is renated. For decoding you have to use the word C and, if necessary, the word N or the word N₀ apply the same coding. The combination of the word B with the word resulting from the coding of C ent speaks of an inverse transformation of this combination, which is formed for coding.

The device for controlling access or blocking the reception of programs preferably contains one a chip integrated circuit, that's one piece ges semiconductor substrate in such a form that the Zu go to the internal connections of this integrated circuit circle is not possible.

So that decoding is particularly difficult, you grab it when coding back to a pseudo-random generator and use it in a special way. It will be he inside that a pseudo-random generator is a shift register with N₁ digits and an exclusive OR gate to the perio changing the content of each position as required of a timer signal. The final number is after X Pulse of the timer reached. It is either through the content of all or part of them or but by a sequence of N₂ bits of the output of last digit provided that the timer remains in operation.

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

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

Further details of the invention are in the Description of some embodiments under Be train described on the accompanying drawing. Show it:

Fig. 1 shows the structure of an access rate,

Fig. 2 is a diagram of an encoder and an encoding method,

Fig. 3 is a diagram of a decoder and a decoding method,

Fig. 4 is a diagram for explaining an encoding method with a pseudo-random generator,

Fig. 5 shows the structure of a word at the output of a pseudo-random generator,

Fig. 6 is a schematic of a pseudo-random generator,

Fig. 7 is a code card,

Fig. 8 is a diagram of a decoder and

Fig. 9 shows a realization example of the Codierver drive of FIG. 2.

In the exemplary embodiment, the access sentence 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 applied to a card by a bar code in two stripes ( Fig. 7).

The first word T (replacement word) indicates whether the access phrase is personal pulled or is of the standard type. The personal Zu course set can of course only from a special Decoders are read; a standard entry set  can be read by all decoders. The word T comprises one bit or two bits in the simplest case.

The second word C (selection code word) corresponds to the selection of the television programs to which access is granted. To a Selection includes that there are several types of television programs there, for example three types, and that the subscription a right of access to the first or second or third type or a combination of two or three types can last. The first shipment type includes, for example wise programs with general information, for two th kind of cultural programs and the third kind of sport reports. One can also provide that the different Consignment types differ according to the time blocks, during which these programs are broadcast.

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

The third word M is a fixed access code word that forms the actual entry rate; it grants the right for approval. Mind you, for coding this Zu Gangcode words must be exercised with the greatest caution.  

The fourth word V is a simple verification key that it allows to check whether the entry rate is correct was.

A computer 10 is used to generate the access code word M, into which the following input variables are input: the word T, which constitutes the personal identifier or the absence of such an identifier for the release, the selection code word C, and a word B (base code word), the indicates the basic program or minimum program. This word B must be protected in the best possible way. It is changed periodically, for example monthly, if the subscription time is one month; then it gives the subscription time.

The subroutines are indicated by words S 1 to S _n (operating key), but these words are not used to process the word M.

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

In addition, the coding computer 10 , the encoder, contains in its memory the word N corresponding to the subscriber's code and the word N₀ corresponding to the data of the standard program type.

If the access set is personal, the word N is placed in a memory A of the encoder 10 .

Otherwise, the word N₀ in this memory A entered.

The words C and N (or N₀) are combined according to a specific law. An example of this law is given below in connection with FIG. 9.

This combination forms a word G, which is encrypted according to a pseudo-random law FK. This Ge law is explained below in connection with FIGS. 4, 5 and 6. The pseudo-random law for transformation must be such that it provides a word K (or K₀) with a sufficient number of bits, because the number of possible values is extremely important to make fraud difficult.

The word K or K₀ is replaced by the word B after another combined law FM, which is of simpler form than the law can be FK and the access word M or M₀ delivers. This law is, for example, FM (B, K) = B + K.

The simplicity of this law makes it easier how to do it will still see to realize the decoding without endanger the confidentiality of the access word.

In order that the operation of the interference suppression device is released for the user, the card with the access set is read by a reading device 20 ( FIG. 8) in order to decode the access word. The reading device 20 transmits the read data to a microprocessor chip 21 ( FIGS. 3 and 8). The following words are entered into the microprocessor 21 : T, C and M (or M₀) and also the word V for the validity or authenticity check. In addition, the words N and N₀ are found in the memory of the microprocessor 21 .

For decoding ( Fig. 3) from the words T and C, the word K or K₀ is generated in exactly the same way as in the encoder. A combination of the words C and N (or N₀) is thus generated for generating the word G, which is transformed by a pseudo-random generator in accordance with the law FK.

The word M or N₀ is replaced by the word K or K₀ Law FB combined, the reverse of the coding law FM runs; in this way the word B, which corresponds to the Ba sis program corresponds, formed again. In execution example is M = B + K and thus FB (M, K) = B = - K.

If the problem is, for each image line Distance between the line synchronization pulse and the Change pseudo-random image signal, then forms the word B the starting word for one on the basic program applied video pseudo-random generator. It creates one variable line delay to get the correct one for each line Phase of the image signal with respect to the line synchronizer to restore impulse.

The pseudo-random sequence is different because of the subroutines; it is also different from one subroutine to another. One therefore sees the words S₁ to S _n for access to these subroutines.

If the word C gives access to the first subroutine, the word C is combined with the word B in accordance with a law F 1 to produce the word F 1. The word N 1 is also a starting word for a pseudo-random generator which, like word B, acts on a variable line delay. To combine the word B with the word G to generate the words S₂ to S _n laws F₂ to F _n are seen before.

The access rate is particularly well protected against fraud. In particular, the word M (or M₀) is a function of the words B, C and N (or N₀). It follows that any change in word T or word C changes the word K (or K₀). The word B, which is a combination with the word K, can therefore not 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.

The accidental or fraudulent knowledge For this reason, word B is enough to win a Zu did not go out because this knowledge processing the Access rate not allowed.

The entry set also includes a word V, which is intended to check whether the sequence obtained from the reading device 20 corresponds correctly to a complete entry set. Such a test word is, for example, a sum test, which then specifies the number of ones and zeros that contain the words T, C and M. The word V can also be obtained by an equality test.

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

The generator in Fig. 6 comprises a number N₁ of bi stable flip-flops 22 ₁. . . 22 _m . . . 22 _N1 . Each flip-flop 22 includes a set input 23 to which a set word G is supplied. 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 toggle switches 22 _m is - like the other toggle switches - connected to the input of the following toggle switch. The output of the flip-flop 22 _m 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 _N1 . From the output of the gate 25 is connected to the input of the first flip-flop 22 ₁. The set word G is fed to the inputs 23 of the flip-flops 22 ; it changes the position of the flip-flops in time with the pulses of the timer. After a certain number X of pulse pulses, this number X is recorded by a pseudo-random generator, the output signal is then the position of the flip-flops 22 or the position of a part 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 number Number, but a function of the input word.

The pseudo-random coding can also be implemented by programming ( FIGS. 4 and 5).

Fig. 4 represents an essential part of the present invention, namely a flow chart showing how the word K is extracted from the word G. The flowchart corresponds in its function to a pseudo-random generator of the type described in FIG. 6.

With each clock signal of the timer, the output signal H of the exclusive OR gate in the first position of the Shift registers entered. The content of this point consequently - if the entrance is left and the exit right is - pushed to the right. The content of the Digit n is therefore equal to the content of digit (n-1) at the time of the previous clock signal of time donor.

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 ^N1 -1, so in seconds P = (2 ^N1 -1) τ seconds, where τ is the period of the time signal. Because of the periodic nature of the sequence S, it is shown in FIG. 5 in the form of a circle.

The output word is formed either by the content of all positions of the shift register at the end of a certain number of 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 1. The beginning of this sequence appears at time t _R = X · τ, with X being constant in one exemplary embodiment. The duration of the sequence is also determined by a specific 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, in the exemplary embodiment, the beginning 60 or the output window 61 of the sequence is a function of the starting word G, which is pushed into the slide gate has been. Instead or in addition, the duration of the window 61 is a function of the word G mentioned.

In the flowchart of Fig. 4, the output word K (or G ') 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 will be seen below.

T is the content of a buffer which is equal to t _R at the beginning of the sequence and which is reduced by one unit or by one period for each pulse of the timer. For reasons of protection against fraud, t _R preferably has a value that is not too small; it should rather have a minimum value. Therefore, the value of the bit is set from the position Ω of the binary number T to the value 1, so that T _min = 2τ.

The diamond, in which m _j = n _i stands, corresponds in its function to an exclusive or. A is the number of work cycles. A cycle is defined as follows: when the time t _{R is} reached, the content G 'of the shift register defines a new value of t _R. Until then, a first cycle had been carried out. The new value of t _R defines the moment when the second cycle is held and when the third cycle starts, and so on.

Output word K is rank A at the end of the cycle equal to the word G ', the content of the shift register.  

It can be seen that the starting word K after a va time after entering the input word seems. The law that the input word with time between the input word and the output word verbin det is relatively complicated. It is therefore be particularly difficult, if not impossible, the one find out the starting word when looking at the starting word knows.

In the exemplary embodiment which is illustrated in FIG. 7, the access set is accommodated on an optically readable card 30 . The card is provided with a hole 31 near a card end 32 . The access set is written between the hole 31 and the other end of the card 33 . The sentence itself is shown in the form of lines in two strips 34 and 35 . A black line 36 on strip 34 represents a one, a black line 37 on strip 35 represents a zero. Two black lines can therefore not appear on both strips 34 and 35 at the same time. Apart from the spaces between the lines, there is a black line on either strip 34 or strip 35 . Such a bar code on two strips is particularly easy to write and read.

To read the card, a reading device 38 ( FIG. 8) is provided which contains two pairs of light transmitters and light receivers, one pair for each strip. The absence of light that would have been reflected from the surface of the card 30 indicates the presence of a black line 36 or 37 .

In front of the reading device 38 , the decoder contains a light barrier, which is arranged by a light source arranged on one side of the card 30 and a detector 41 arranged on the other side of the card 30 . The insertion of the card 30 into the slot 43 of the detector causes an interruption of the light beam 42 , which is emitted by the light source 40 , and thus the determination of the introduction of this card. The end of the insertion is then determined when the hole 31 allows the light bundle 42 to pass through again to the detector 41 .

Between the reading device 38 and the detector 41, on the one hand, and the microprocessor 21, on the other hand, the decoder contains a processing circuit 45 and an electrical power source 46 for providing the reading device 38 , the light source 40 , the processing circuit 45 and the microprocessor 21 .

Finally, the cover plate 50 of the reading device and the decoder have two light sources 51 and 52 with different colors. The light source 51 is, for example, an electroluminescent diode of red color, it is switched on if the access set is read incorrectly or does not provide access for decoding a current program. In this example, the light source 52 is an electroluminescent diode of green color, it confirms the possibility of access for receiving a current broadcast.

In the following, embodiments of the coding and Given decoding method according to the invention.

The word T comprises two bits.

The word N is 24 bits.  

The word N₀ is also represented by 24 bits.

There are a basic program and three sub-programs seen, among these you can switch between programs Select 0, 1, 2 or 3. This way there are eight possible combinations. The word C comprises 3 bits.

The word B, which represents the basic program, is in 24 Bits coded.

The combination of the words N (or N₀) and C for generating the word G is effected in the following way ( Fig. 9): the word N is in three eight-digit numbers (in 3 binary numbers with 8 bits each) N₁, N₂ and N₃ disassembled; The combination nation of N and C is then the number D = D₁ D₂ D₃. D₁ = N₁, D₂ = N₂ + C, D₃ = N₃ + C.

C means the complement of C and is the number by the transformation of zeros into ones and ones into Zeros is obtained.

In the event that this combination has a zero value for D results in a combination that is somewhat different nation used, namely D₂ = N₂ + C. The result is then D₁ D₂ D₃ = G₀.

For the function FK, a pseudo-random coding is used to cancel the sequence of the type described in connection with FIG. 4. In this case, the cycle A = N₂ + N₃ + C.

However, if the third bit of this number is zero, trans you form the zero into a one, so that the smallest Cycle number 2³ = 8.  

Otherwise, the function FK corresponds exactly to that which is described in FIG. 4.

The word K um obtained after the pseudo-random sequence holds 24 bits.

The word M = 3 + K contains 25 bits, each of the numbers 3 and K containing 24 bits.

The laws F₁, F₂, F₃ for decoding ( Fig. 3) restore the words S₁, S₂ and S₃ in the following manner: F₁ (S₁) = B; F₂ (S₂) = B₂ B₃ B₁ (B₁, B₂ and B₃ are the eight-digit numbers that form the word B = B₁ B₂ B₃); F₃ (S₃) = B₃ B₂ B₁.

Finally, the word V contains 5 bits.

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

Claims (19)

1. A method of forming an access code for a subscription television system in which the programs delivered by a transmitter are disrupted by means of at least one operating key and in an interference suppression device of a recipient by means of the relevant operating key (s), provided that the user the recipient is entitled to receive, this authorization being given for one or more programs or several types of programs and being issued in the form of the access code contained on a data carrier, which is read and decoded by a reader-side reading and decoding device, to possibly provide at least one operating key and thus release the interference suppression device for the corresponding program or combination of programs, characterized in that the access code given to the data carrier at least from a representative code for the released programs word C and an access code word M is put together, the access code word M being formed by a coded combination of the selection code word c and a base code word B for calculating at least one operating key. 2. The method according to claim 1, characterized in that the access code word M by a combination of the off  choice code word C, the base word B and one for each Receiver representative identification word N formed becomes. 3. The method according to claim 1 or 2, characterized in that the access code receives an additional code word T that indicates whether the access code is assigned to a specific recipient is ordered or not, and that for a given assignment the access code word M to a specific recipient a combination of the representative for the respective recipient sentative identification word N, the selection code word C and the base word B is formed, while a missing one Assignment to a specific recipient instead of for representative identification of each recipient words N a common replacement word N₀ ver for all recipients is applied. 4. The method according to any one of the preceding claims characterized in that the access code word M by a Combination of the base word B and a word K or K₀ is formed, wherein the word K from a combination G. the selection code word C and that for a respective recipient representative identification word N is formed while the word K₀ by a combination G₀ from the selection code word C and the replacement word N₀ common to all recipients or the selection code word C is formed, and that the combination nation G from the selection code word C and the identification word N or the combination G₀ from the selection code word C and the replacement word N₀ or the selection code word C by a pseudo Random coding law FK in the word K or K₀ transfor is lubricated. 5. The method according to claim 4, characterized in that the one determined by the pseudo-random coding law FK Coding according to the impulses of a timer follows, whereby the pseudo-random coding law FK follows a certain constant number X of pulses after the The beginning of the coding provides the word K or K₀ as the end word.   6. The method according to claim 4, characterized in that the one determined by the pseudo-random coding law FK Coding according to the impulses of a timer, the pseudo-random coding law FK after an An number X of pulses after the start of coding the word K or K₀ as the end word, and that the beginning of the Codie defined by the starting word to be transformed which is the result of the combination G from the selection code word C and the identification word N or the combination G₀ the selection code word C and the replacement word N₀ or the off election code word C is formed. 7. The method according to claim 4 or 6, characterized in that that determine by the pseudo-random coding law FK te coding according to the impulses of a timer follows, with the pseudo-random coding law FK the word K or K₀ as the end word, and that the number of digits this end word of the value of the beginning to be transformed word depends on the combination G from the selection code word C and the identification word N or the Kombina tion G₀ from the selection code word C and the replacement word N₀ or the selection code word C is formed. 8. The method according to claim 6 or 7, characterized in that the start word and the end word are formed by the content of digits of a shift register and that the coding determined by the pseudo-random coding law FK is carried out as follows:

• a) a first number A is formed, which is a function of the starting word,
• b) a period of time t _{R is} formed, which is a function of the starting word and determines the time period between the feeding of the starting word and the beginning of the occurrence of the ending word,
• c) a pseudo-random sequence is formed during the time period t _R ,
• d) at the end of the time t _R , a new time value t _{R is} formed, which is a function of the word occurring in the shift register,
• e) steps c) and d) are repeated (A-1) times,
• f) the end word is formed by predefinable digits of the word that is present in the shift register at the end of this coding.

9. The method according to any one of claims 4 to 8, characterized characterized in that the identification word N three eight digit binary numbers N₁, N₂, N₃ contains that the selection codeword C is a binary number through which all combinations NEN of programs can be represented, and that the word of the Combination G from the selection code word C and the identifi cation word N has the form G = D₁ D₂ D₃, with D₁ = N₁, D₂ = N₂ + C and D₃ = N₃ + C, but where D₂ = N₂ + C, if the word G resulting from the combination G is zero is. 10. The method according to claims 8 and 9, characterized records that A = N₂ + N₃ + C. 11. The method according to claim 4, characterized in that M = B + K. 12. The method according to any one of the preceding claims, since characterized in that the base word B changes periodically and a basic program among the various represents the approved types of programs, the corresponds to a minimum subscription. 13. Method for decoding one according to the method one of the preceding claims formed access codes,  characterized in that the word K or K₀ by dassel be pseudo-random coding law FK, which also for education of the access code was used from the combination G. the selection code word C and that for a respective recipient representative identification word N or from the Kombina tion G₀ from the selection code word C and all recipients common replacement word N₀ or from the selection code word C to is recovered. 14. The method according to claim 13, characterized in that the base word B from the access code word M and the word K or K₀ is recovered by applying a law that is inverse to that which is in the formation of the Zu gang code word M from the base word B and the word K or K₀ was applied. 15. The method according to claim 13 or 14, characterized in that the operating key (S₁,... S _n ) for releasing the interference suppression device for programs provided in addition to the basic program or types of programs from the selection code word C and the base word B according to the respective broadcasts associated laws (F₁,... F _n ) are determined, while the operating key for releasing the interference suppression device for the basic program is determined directly from the basic word B. 16. Decoder for executing the decoding method according to one of claims 13 to 15, characterized in that it comprises a microprocessor chip ( 21 ), the memory of which is not accessible from outside the chip contains the pseudo-to-case coding law FK. 17. Decoder according to claim 16, characterized in that the memory of the microprocessor chip ( 21 ) which is not accessible from outside the chip also contains the identification word N and the replacement word N₀. 18. Device for releasing access to programs of a subscription television system by means of an access code which is formed and decoded according to the method according to one of claims 1 to 15, characterized in that the access code by means of a bar code on a data carrier ( 30 ) is printed. 19. The apparatus according to claim 18, characterized in that the barcode is in two parallel barcode strips is divided, one of these strips for the zeros and the other is intended for the ones of the access code, and that the ones on one stripe and the zeros on the other strip represented by a dash are.