WO1988002899A1

WO1988002899A1 - Monitoring card for generating very long secret codes

Info

Publication number: WO1988002899A1
Application number: PCT/FR1987/000382
Authority: WO
Inventors: Yvon Fouche
Original assignee: Thomson-Csf
Priority date: 1986-10-07
Filing date: 1987-10-06
Publication date: 1988-04-21
Also published as: FR2604809A1; FR2604809B1; AU8035887A

Abstract

Monitoring card for generating very long secret codes, consisting of a memory card having in association with its reader (6) a shift register (1) having n cells (11 to 1n) and a logic exclusive-OR gate (2). The invention applies particularly to the generation of long pseudo-random secret codes. The invention applies essentially to the reception of prepayment television programs. The decoding of scrambled emissions is obtained by correlation with a pseudo-random code generated by the card reader (6) associated with the monitoring card (4).

Description

CONTROL CARD FOR GENERATING SECRET CODES OF LONG LENGTH

The present invention mainly relates to control charts for generating secret codes great ₅ length.

On the one hand, it is known to produce control cards, commonly called memory cards, making it possible to generate or control a secret code. The exchange rate between the known type of control cards and their reader is very low. Thus, the J Q control cards of known type are mainly used to verify that a secret code supplied to them is correct. In this case the codes are used to validate the desired operations.

On the other hand, it is known to generate pseudo-random codes by looping back certain cells of a shift register at _5 through an OR-exclusive gate. It is thus possible to generate very long pseudo-random codes. The rapid generation of a very long pseudo-random code makes it possible to use this code for treatments such as for example for testing electrical circuits.

Similarly, it is known from French patent n ° 8406220 the use of a shift register of which only two cells are connected to the input of an OR-exclusive logic gate to modify in a predetermined manner a binary word. In said device, the fact of using only two cells connected to the exclusive OR- logic gate considerably reduces the possible combinations. In fact, it is very difficult to predict the transformation of a binary word after a predetermined number of clock cycles. Thus, said device does not make it possible to generate long codes but allows transcoding to be carried out.

The present invention relates to a control card capable, associated with a card reader, of generating very long pseudo-random codes in real time. For this purpose, the control card-control card reader assembly includes a register with offset, some cells of which are looped back onto a logic circuit such as for example an OR-exclusive logic gate. Depending on the degree of protection desired, the control card will include more or less of the electronics necessary for the generation of the pseudo-random code.

In a variant embodiment, the control card according to the invention only delivers the very long pseudo-random code after having received a secret code. Thus, not only is it not possible to copy such a card, but even the real card can only be used by authorized personnel. Such a card comprises, in combination with the means for generating the pseudo-random code, for example a microprocessor and memories.

Advantageously, the electronic control cards are produced in credit card format. The main object of the invention is a control card, characterized in that, associated with a card reader, it is capable of generating a pseudo-random code from a shift register including a plurality of cells. is connected to the inputs of a logic circuit, for example, of an OR-exclusive logic gate, the output of said OR-exclusive logic gate being connected to the input of said shift register.

The invention will be better understood by means of the description below and of the figures given as nonlimiting examples among which: FIG. 1 is a diagram illustrating the known principle of a pseudo-random code generator using a register shift looped back through an OR logic gate;

- Figure 2 is a diagram illustrating a first embodiment of the device according to the invention; - Figure 3 is a diagram illustrating a second embodiment of the device according to the invention;

- Figure 4 is a diagram illustrating a third embodiment of the device according to the invention;

- Figure 5 is a diagram illustrating a fourth example of realization of the device according to the invention;

- Figure 6 is a diagram illustrating a fifth embodiment of the device according to the invention;

- Figure 7 is a diagram illustrating a sixth embodiment of the device according to the invention.

In Figures 1 to 7 the same references have been used to designate the same elements.

In Figures 1 to 7 the arrows designate the direction of propagation of the signals.

10 In FIG. 1, we can see the principle of a pseudo-random code generator. Said generator comprises a shift register 1 comprising n cells referenced l i a In, and a logic circuit 2. Circuit 2 is, for example, an OR-exclusive logic gate. Shift register 1 shifts with each pulse

• ₅ clock (not shown) the information present in a cell in the direction of decreasing references. So after. n clock cycles information presented at the input of cell In is present at the output of cell 11. Cell 11 is connected to one of the inputs of the OR-exclusive logic gate 2 by a line 31. The output of the

2 _Q OR-exclusive logic gate 2 is connected by a line 3 to cell In.

Certain cells of shift register 1 are connected to inputs of the OR-exclusive logic gate 2. In the example, not optimized, of the register illustrated in the figure cell 12 is connected by line 32 to an input of gate OU-exclusive logic 2, cell 15 is connected

25 by line 35 to an input of the OR-exclusive logic gate 2 as well as the cell In which is connected by line 3n to an input of the OR-exclusive logic gate 2. Table I gives the non-trivial powers of polynomials generators allowing for a shift register 1 comprising n cells to obtain 2n words of n bits

-3 different _Q. TABLE I

Generating volumes

Degree Non-trivial powers

16 9, 7, 4

20 3

21 2

22 1

23 5

24 24, 7 2 1

25 3

26 6 2 1

27 5 2 1

28 3

29 2

30 23 2 1

31 3

32 • 22 2 1

^'33 13

So if for example we want to use the generator polynomial of degree 27:

P ₂₇ (X) = X ²⁷ + X ⁵ + X ² + X + 1 we will use a shift register 1 comprising 27 cells.

In this case, in addition to the first cell 11 always looped over to an input of the OR-exclusive logic gate 2, we will loop the second, third and sixth cells referenced respectively 12, 13 and 16 in FIG. 1.

For applications that do not require very long codes it

It is possible to use shift registers with trivial loopbacks. Indeed, the number of different codes, for a maximum length n of the shift register 1 risks being too limited if the trivial solutions are eliminated.

The words of the pseudo-random code are retrieved from the shift register 1 on the lines referenced 5.

The generated code is called pseudo-random because at each initialization of the system for a given wiring the system will deliver exactly the same code.

In FIG. 2, one can see an embodiment of the control cards according to the invention comprising only electrical connections making it possible to generate a pseudo-random code at a shift register 1 looped back by a logic gate OR- exclusive 2 contained in the control card reader. The card reader comprises a shift register 1 of n cells connected to an OR-exclusive logic gate 2. Cell 11 of the shift register 1 being always connected to one of the inputs of the OR-exclusive logic gate 2 this connection can be performed inside the control card reader. Similarly, the connection of the output of the OR-exclusive logic gate 2 via line 3 to the last cell In of the shift register 1 can also be internal to the control card readers according to the invention. Cells 12 to In du _; shift register 1 are connected by lines respectively 312 to 3 In to the contacts referenced respectively 322 to 32n. Similarly, the inputs of the OU-exclusive logic gate 2 are connected to a set of contacts referenced 350. The control card 4 includes electrical contacts making it possible to connect some of the cells of the shift register 1 to inputs of the logic gate 2 In the examples illustrated in FIGS. 1h 7 all of the devices generate the same pseudo-random codes. Thus in FIG. 2 are connected, via the control card 4 to an input of the OR-exclusive logic gate 2, the cells 12, 15 and In of the shift register 1. The cell 4 therefore comprises at least contacts 332, 335 and 33n electrically connected to contacts 342, 345 and 34n. The contacts 332, 335, 33n, 342, 345 and 34n are arranged in such a way that once the control card 4 is inserted in the card reader, said contacts allow the electrical connection with the contacts 322, 325, 32n as well as the contacts 350. _.

Advantageously, the control card 4 includes other electrical contacts, in particular 333, 334, 33 (nl) which are not connected to any of the contacts capable of being connected to the contact 350 connected to the inputs of the OR-exclusive logic gate. 2. These

I contacts are intended to make it more difficult to manufacture a false control card from a real control card 4. These points are for example in open circuit or interconnected.

The control card illustrated in FIG. 2 has the advantage of being of low cost price. It is intended in particular to allow the distribution to a large number of people of the same code for a predetermined period of time.

For example, such a card would make it possible to decode emissions, for example from television, radios or information transmission by electromagnetic means.

For example, the transmissions are carried out in phase modulation, the decryption being carried out on reception by correlation of the data received by a pseudo-random code. Advantageously, the coded information makes it possible to obtain a correlation peak capable of ^• synchronizing the transmission and the reception. The low cost of making the cards, control 4 according to the invention allows for example the frequent change of code, it is for example possible to change the pseudo-random code every day or once a week. The cards will be sold, for example, in tobacconists or newspaper kiosks shortly before the change in remission coding, leaving little time for people wishing to defraud to make copies of the control cards 4.

In an alternative embodiment not illustrated, line 3 makes it possible to connect the output of logic gate 2 to the last cell of the shift register 1 included in the control card 4. Thus, it is possible to change the number p of the cells actually used p being less than or equal to n. The device according to the invention has the advantage of requiring to operate that the connections between the cells of shift register 1 and the inputs of logic gate 2 are all correct. Indeed the slightest difference in the connection will cause the generation of a completely different pseudo-random code. Thus, it is possible to generate a very large number of codes. j; To change codes simply change one or more connections.

! xions. The code words are read in parallel on lines 5 connected to cells l i to In (or 11 to lp) of shift register 1.

In FIG. 3, a control card 4 can be seen comprising 0 at least part of the shift register 1. For example illustrated in FIG. 3, the card 4 comprises the last three cells l (n-2) at In shift register 1. Such a card has a higher cost price. However, it is also much more difficult to falsify. Card reader 6 has an OR-exclusive logic gate

2 and a part of the shift register 1. In the illustrated embodiment, the connections of the part of the shift register 1 included in the card reader 6 are made inside said card reader, for example by lines 31, 32 and 0 35. In this alternative embodiment, the various possible pseudo-random codes are obtained by choosing the number of cells contained in the control card 4 as well as by the choice of cells connected to one of the inputs of the logic gate. OU- exclusive 2. In the example illustrated, only the cell In belonging to 5 the control card 4 is connected to one of the inputs of the OR-exclusive logic gate 2 via the contacts 33n and 32n.

In an alternative embodiment, not illustrated, it is the control card 4 which interconnects the cells of the shift register 1 belonging to the card reader 6 to the inputs of the 0 OR-exclusive logic gate 2.

In all cases, the control card 4 includes contacts 36 (n-2), 36 (nl) and 36n and the card readers 6 include the contacts 37 (n-2), 37 (nl) and 37n allowing to recover pseudo-random code bits generated by the cells included in the control card 4.

A reset 7 command enables the pseudo-random code generator to be reset. For example, a periodic reset allows the length of the generated code to be limited.

In addition, the card reader 6 supplies the control card 4 with all the signals which are necessary for its operation, such as, for example, the power supply, the clock pulses and the reset commands.

In FIG. 4, an exemplary embodiment of the device according to the invention can be seen in which the control card 4 comprises part of the shift register 1 as well as the OR-exclusive logic gate 2.

In FIG. 5, an exemplary embodiment of the device according to the invention can be seen in which the control card 4 comprises only the OR-exclusive logic gate 2 as well as the connections necessary for its proper functioning. i Advantageously, the control card 4 includes contacts for example 33 (n-3), 33 (n-2) and 33 (n-1) intended to make it more difficult to falsify the control card.

In FIG. 6, one can see an exemplary embodiment of the control card 4 comprising a shift register 1, an OR-exclusive gate 2 as well as the connections for example 31, 32, 35, 3n and 3 making it possible to generate the pseudo-random codes. In this exemplary embodiment of the card 4 according to the invention, the card reader 6 not shown will directly recover the pseudo-random codes generated on the lines 5 via the contacts not shown. In such a case, the reset command 7 enabling the generator to be reset is applied directly to the control card 4. The card 4 is capable of receiving the electrical power supplies, the synchronization clock signals required. to ensure its proper functioning.

In an alternative embodiment, the control card 4 according to the invention comprises a counter 60 placed for example at the output of the OR-exclusive logic gate 2. This counter allows the card to be inhibited and / or destroyed after d 'a predetermined period of operation. For example, when the counter 60 arrives at the maximum value for which it was designed, line 3 connecting the output of logic gate 2 to the input of cell In of the shift register I is cut.

10

In Figure 7 we can see a control card 4, according to the invention whose copying and fraudulent use are particularly difficult. The control card of FIG. 7 only delivers the true pseudo-random code if it has previously been supplied with a secret code.

, 5 The control card 4 also includes the shift register

* 1 of the OR-exclusive logic gate 2 and connections of a microprocessor 93 connected to a permanent memory 94 comprising the operating programs of the microprocessor 93. The memory 94 is for example a read only memory (ROM in English terminology

20 Saxon). In the case where the secret code has not been supplied to the microprocessor 93, this prevents the provision of the pseudo-random code provided. The secret code is a short code comprising for example between 4 and 10 digits.

In a first embodiment of the device according to

2 the invention the microprocessor 93 causes the generation of a false pseudo-random code not allowing the correct operation for example of the decoding by correlation. For example, the control card 4 comprises a multiplexer 91 controlled by the microprocessor 93 making it possible to modify the connections of the cells of the 0 shift register 1 to the inputs of the OR-exclusive logic gate 2. For example, on command of the microprocessor 93 the multiplexer 91 connects lines 31, 32 and 33 to a single input of the OR-exclusive logic gate 2. This modification of data paths 10

modifies the pseudo-random code generated by the control card 4.

Generating a pseudo-random code, different from the desired pseudo-random code, makes it more difficult to fraudulently use the control card 4. In fact, the fraudster cannot check in advance the feasibility of the fraud . It is only during an attempted fraud that the fraudster will realize the non-functioning of a device whose control is ensured by the control card 4. Advantageously, the control card 4 generates codes i pseudo- different random codes for various secret codes presented to the microprocessor 93. Thus it is possible to use the same card 0 to generate pseudo-random codes allowing various execution functions and / or makes fraud more difficult. For example, the same control card 4 allows, on presentation of a first secret code, access to premises comprising a transmitting and / or receiving apparatus; and on presentation of a second code

15 secret the proper functioning of the transmitting and / or receiving apparatus.

In a second embodiment in the absence of a valid secret code, the control card according to the invention does not generate the random code. For example, a device 92 inserted between the

20 output lines 5 and cells 11 to In of shift register 1 prevent the transmission of the desired random code. For example, on command from the microprocessor 93, the device 92 performs a bonding at "0", a bonding at "1" or the isolation by an impedance of _ _ almost infinite output of the lines 5. The bonding at "0" corresponds to the presence, permanently, of an electrical level corresponding to a "0". Bonding at "1" corresponds to the presence, permanently, of an electrical level corresponding to a "1". The electrical insulation is obtained by using a 92 "three device

30 states ".

Advantageously, the control card comprises a permanent programmable memory 95, for example of the EPROM type. The permanent programmable memory 95 stores either a record of all the uses of the card, or a record of all attempts to fraudulently use the card.

Advantageously, the control card 4 is locked, and no longer provides a pseudo-random code after the presentation, for example, of four false secret codes.

Advantageously, the electronics of the control card 4 is produced in the form of a single integrated circuit. Thus, it is not possible to individually test the electrical and logical behavior of the various components like. for example the multiplexer 91.

The control cards 4 illustrated in FIGS. 3 to 7 being much more difficult to falsify than for example the card 4 illustrated in FIG. 2, are likely to be used for access control, the generation of a pseudo code - random validation, the recognition of people or the generation of pseudo-random code making it possible to operate devices such as, for example, transmitters and / or receivers for television, radio or digital transmissions.

The invention mainly applies to the generation of secret pseudo-random code for the processing of information by correlation. The invention applies mainly to television transmitted in phase modulation, the decoding and / or synchronization of which are obtained by correlation with a pseudo-random code.

Claims

1. Control card (4), characterized in that, associated with a card reader (6), it is capable of generating a pseudo-random code from a shift register (1) including a plurality of cells is connected to the inputs of a logic circuit (2), the output of said logic circuit being connected to the input of said shift register (1).

2. Control card (4) according to claim 1, characterized in that the logic circuit (2) is an OR-exclusive logic gate. •,

3. Card according to claim 1 or 2, characterized in that it contains the connections making it possible to connect certain cells of the shift register (1) to the inputs of the logic circuit (2) making it possible to determine the pseudo-random code likely to be generated.

4. Card according to claim 1, 2 or 3, characterized in that it comprises at least certain cells of the shift register (1).

5. Card according to claim 1 or 2, characterized in that it comprises the logic circuit (2).

6. Card according to claim 4, characterized in that it comprises at least certain cells of the shift register (1).

7. Card according to claim 1, 2, 3, 4 or 5, characterized in that it comprises the shift register (1), the logic circuit (2) and the connections between certain cells of the shift register and said logic circuit (2), necessary for the generation of a pseudo-random code.

8. 'Control card (4) according to claim 1, 2, 3, 4, 5, 6 or 7, characterized in that it comprises a microprocessor (93) associated with a program memory (94 or 95) .

9. Control card (4) according to claim 8, characterized in that it comprises a permanent programmable memory (95) capable of storing the partial or complete history of the control card (4).

10. Control card (4) according to claim 8 or 9, characterized in that it comprises at least one multiplexer (91) capable of modifying the internal connections of said card on command from the microprocessor (93).

11. Control card according to claim 8, 9 or 10, characterized in that it comprises means (92) making it possible to generate, permanently, on command of the microprocessor (93), "0" s on at least some of the output connections (5) of said card.

12. Control card according to claim 8, 9, 10 or 11, characterized in that it comprises means (92) making it possible to generate, permanently, on command of the microprocessor (93) "1" on at minus some of the output connections (5) of said card.

13. Control card (4) according to claim 8, 9 or 10, characterized in that it comprises means (92) making it possible to isolate, on command from the microprocessor (93) at least some of the output connections ( 5) of said control card.

14. Method for decrypting information transmitted by modulated electromagnetic waves, characterized in that the correlation of said waves is carried out with a pseudo-random code generated by a control card (4) according to any one of claims previous associated with a card reader (6).

15. The method of claim 14, characterized in that said waves are phase modulated.

16. A decryption method according to claim 14 or 15, characterized in that the information transmitted is television programs.

17. A decryption method according to claim 14, caracté¬ ized by the fact that the information transmitted are radio programs.

18. A decryption method according to claim 14 or 15, characterized in that the information transmitted is digital data.