FR2814009A1 - PROCESS AND DEVICE FOR CONVOLUTING DATA TRANSFORMATION AND VARIABLE OFFSETS, AND SYSTEMS IMPLEMENTING THEM - Google Patents

Abstract

The invention concerns a method for transforming a sequence of N original binary data (b>1<, , b>N<) representing a message, using at least a key, N being an integer greater than 1, which consists in producing a sequence (u>1<, , u>N<) of N algebraic offset values and in filling a table of N+1 lines where: the original sequence (b>1<, , b>N<) is written on the first line of the table; for each integer i included between 1 and N, on the (i +1)?th> line of the table is written an intermediate sequence of binary elements wholly or partly offset by ui columns relative to the sequence written on the first line, the intermediate sequence being, either a predetermined sequence contained in the key if the i<th> binary data (bi) of the original sequence is equal to 1, or a sequence of zeros otherwise; and in performing an addition modulo 2, column by column, of the binary elements contained in the table.

Description

<Desc / Clms Page number 1>
The present invention relates to a method and to a device for transforming data, which are convolutional in nature and preferably variable offsets, and to systems implementing them.

We consider the situation where a set of information to be transmitted is represented by a sequence of symbols belonging to the set {0,1}. This set is called the binary alphabet and its elements are called binary elements or bits.

To transmit these binary elements, they are converted into electrical quantities. For example, bit 0 is represented by a positive electrical signal and bit 1 by a negative electrical signal.

These signals can take any value deemed appropriate according to the envisaged application, such as, for example, an electric voltage of 5 volts.

It may be advantageous to encrypt a message formed from such binary elements, for example, for data protection or even error correction purposes.

The message sought to be encrypted may consist of signals representative of speech and / or images and / or data.

It is known, for example, to protect binary data frames by using a key.

In particular, a method is known for encrypting binary data frames which uses a key as well as regular and equal successive shifts.

FIG. 1 illustrates a known method of this type. This consists in transforming a sequence of N original binary data (b1, ..., bN) representative of a message. This method of the prior art uses a key K containing a determined sequence of M binary elements (ci, ..., cm), N and M

<Desc / Clms Page number 2>

being integers greater than 1. As shown in Figure 1, following this method, we fill a table with N + 1 lines as follows - we write the original sequence (bi, ..., bN) in clear on the first row of the table; - for each integer i between 1 and N, one writes on the (i + 1) lth row of the table an intermediate sequence of binary elements, shifted, with respect to the original sequence written on the first line, by as many bits as indicated by the row index i, that is to say that the intermediate sequence is shifted by one column with respect to the sequence written on the preceding row.

As shown in figure 1, the intermediate sequence corresponds, on each line i, to the start message multiplied bit by bit by the value of the ith bit of the key K (or added modulo 2, bit by bit, to the ith bit of the key K, which is obviously the same).

où O+ désigne l'addition modulo 2. The encrypted message S is the result of modulo 2 addition, column by column, of the various rows of the table, i.e.

where O + denotes the addition modulo 2.

Figure 2 illustrates this conventional encryption mode in more detail using an example where N = 6 and M = 4.

The object of the invention is to allow even more reliable coding, while retaining the advantages of known codings, and which can be faster to the point of being able to be carried out in real time.

With this aim, the present invention proposes a method for transforming a sequence of N original binary data representative of a message, using at least one key, N being an integer greater than 1, this method being characterized in that one constructs a sequence (ui, ..., UN) of N algebraic offset values and one carries out steps according to which (a) one fills a table with N + 1 rows as follows - one writes the sequence original on the first row of the table;

<Desc / Clms Page number 3>

- for each integer i between 1 and N, an intermediate sequence of binary elements shifted in whole or in parts of u is written on the (i + 1) i-th row of the table; columns with respect to the sequence written on the first line, said intermediate sequence being either a predetermined sequence contained in the key if the ith binary data item of the original sequence is equal to 1, or a sequence of zeros otherwise; and (b) adding modulo 2, column by column, the binary elements contained in the table, so as to obtain a transformed binary data sequence.

It is important to note that the notion of line used in the definition given above of the invention should not be considered as implying any direction in space: such a line can thus be horizontal as well (usual meaning of the term) that vertical; in any case, the concept of the invention is in no way modified if the notions of row and column are exchanged.

As will be shown in connection with FIG. 6, the present invention proposes an encoding which approaches the known encoding, but it allows better security than this encoding insofar as there is a shift between the intermediate lines which can be variable, that is to say not to be systematically greater by one unit than the offset of the preceding row. In addition, insofar as each of these intermediate lines depends only on a single term of the original signal, it is not necessary to wait for the complete signal to be available to develop these intermediate lines, allowing time coding. real. This results in greater speed, making this coding quite suitable for coding a large quantity of signals, for example for transferring images.

The invention can thus be applied to image processing, to the processing of digital signals of any significance, in a telecommunications network for example; it can also be used for error correction (calculation lag). It allows, by entering specific keys, to break codes, depending on whether or not the trail of messages is concealed.

<Desc / Clms Page number 4>

As in the known solutions, it suffices to know the key and the method of determining the offsets to ensure reliable decoding of the signal which has reached its destination.

According to a particular preferred characteristic, said entire intermediate sequence is shifted, but it is also possible, according to the invention, to shift only a part, for example by copying a first half of the key without shifting and by applying a shift. only to the second half of the key. In addition, the offset between two successive intermediate lines is preferably not identical for all the lines (or for all the parts of these lines which it is desired to offset).

The offset values can be chosen from any range: they are for example values chosen from the range from 1 to 256 (therefore within a byte); it is even possible to admit negative values if desired (it all depends on the complexity of the key that we are ready to accept).

According to another particular preferred characteristic, for each integer i between 1 and N, the offset value u is determined; associated with the (i + 1) 'th line from a certain part of the key. In what follows, the key is denoted K and the part of the key that can be used to determine the offset value u; is denoted v (i, K).

Advantageously, for each integer i between 1 and N, this part v (i, K) of the key K is obtained from the value of the row index i and possibly other binary elements contained in the key K. Thus, as an advantageous example, the key K contains a specific sequence of P binary elements (di, ..., dP), P being an integer greater than 1, and, for each integer i between 1 and N, said part v (i, K) of key K is determined from the value of row index i and said specific sequence (di, ..., dP). Various ways of doing this are possible, for example by multiplying i by the value of d ;.

For the same purpose as that indicated above, the present invention also proposes a device for transforming a sequence of N original binary data representative of a message, using at least

<Desc / Clms Page number 5>

a key, N being an integer greater than 1, this device being characterized in that it comprises means for developing a sequence (ui, ..., UN) of N algebraic offset values and (a) means for filling an array with N + 1 rows, comprising - means for writing the original sequence on the first row of the array; means for writing, for each integer i between 1 and N, on the (i + 1) 'th row of the table, an intermediate sequence of binary elements shifted in whole or in parts of u; columns with respect to the sequence written on the first line, u; being a selected offset value, said intermediate sequence being either a predetermined sequence contained in the key if the ith binary data item of the original sequence is equal to 1, or a sequence of zeros otherwise; and (b) means for adding modulo 2, column by column, the binary elements contained in the table, so as to obtain a transformed binary data sequence.

The aforementioned comments concerning the method apply to such a device.

The present invention also relates to an apparatus for processing digital signals, comprising means suitable for implementing a transformation method as above.

The present invention is also aimed at a digital signal processing apparatus, comprising a transformation device as above.

The present invention is also aimed at a telecommunications network, comprising means suitable for implementing a transformation method as above.

The present invention is also aimed at a telecommunications network, comprising a transformation device as above.

The present invention is also aimed at a mobile and / or base station in a telecommunications network, comprising means suitable for implementing a transformation method as above.

<Desc / Clms Page number 6>

The present invention is also aimed at a mobile and / or base station in a telecommunications network, comprising a transformation device as above.

The present invention is also aimed at a device for processing signals representative of speech, comprising means suitable for implementing a transformation method such as above.

The present invention is also aimed at a device for processing signals representative of speech, comprising a transformation device as above.

These digital signal processing devices, telecommunications networks, mobile and / or base stations and signal processing devices representative of speech having characteristics and particularities similar to those of the transformation method according to the invention, these are not not repeated here.

Other aspects and advantages of the invention emerge from the detailed description which follows of particular embodiments, given by way of non-limiting examples. The description refers to the accompanying drawings, in which - Figure 1, already described, schematically illustrates an encryption technique according to the prior art; - Figure 2, already described, schematically illustrates a digital example of application of the known encryption technique of Figure 1; FIG. 3 illustrates how to use the commutativity of addition in the present invention; FIG. 4 is a flowchart illustrating the steps of a transformation method in accordance with the present invention, in a particular embodiment; FIG. 5 schematically illustrates the transformation technique according to the present invention, in a particular embodiment; FIG. 6 schematically illustrates a digital example of application of the transformation technique of FIG. 5, in a particular embodiment;

<Desc / Clms Page number 7>

FIG. 7 schematically illustrates how to obtain offset values for transforming an original sequence in accordance with the present invention, in a particular embodiment; FIG. 8 is a block diagram illustrating a transformation device according to the present invention, in a particular embodiment; FIG. 9 diagrammatically represents an electronic device comprising a transformation device in accordance with the present invention, in another particular embodiment; and FIG. 10 is a simplified schematic view of a wireless telecommunications network capable of implementing the invention.

In what follows, we consider a sequence of N original binary data (bi, ..., b,), N being an integer greater than 1, these data being representative of a message, and a key also comprising binary elements.

In the following, the terms “row” and “column” used in connection with a table such as that of FIG. 2 or 6 denote the horizontal dimension or the vertical dimension of this table indifferently.

A relationship between the coding of the invention and the known one, described with reference to Figures 1 and 2, results from the observation that, in Figure 2, each diagonal (see the circled binary data sequences) consists of the encoding key when the corresponding term of the original sequence is 1, or zeros when the corresponding term of this sequence is zero. Now it is possible, in the intermediate lines which are added to give the encrypted signal, replace each diagonal sequence by a line, as is shown diagrammatically in FIG. 3 for the first diagonal; by iterating this replacement, the number of intermediate lines no longer being the number of bits in the key but the number of bits in the original signal, we obtain a set of lines formed either from the key or from a succession of zeros. The table of FIG. 6 is thus obtained, which will be commented on later in relation to the method of the invention. In any case, it can be seen that the transformation with respect to the table in FIG. 2 did not modify the encrypted signal.

<Desc / Clms Page number 8>

Very generally, the method of the invention, represented schematically in FIG. 4, consists in providing the following steps - from the original sequence, a table is initialized at 10 by copying this original sequence onto the first row (or column); - An intermediate sequence (see below) offset with respect to line 1 by an offset u is then produced at 14 on the next line; the value of which depends on i, the offset values being produced in a step 12; - the value of i is incremented at 16 by one unit; - if, in 18, it appears that i is equal to N + 1 (which means that we have developed as many intermediate lines as there are terms in the original sequence), we proceed in 20 to the summation , column by column, of the binary values of all the intermediate lines, which gives a transformed (encrypted) digital signal, otherwise operations 14 and 16 are carried out for this value of i.

Step 12 of developing the offset values (in practice between 1 and 256) can be carried out in parallel with the initialization step 10, or beforehand. The sequence of these values can simply be pre-established and contained as is in the key. It has been indicated that these offset values determine the offset between each intermediate line and line 1, but it should be understood that this amounts to the same thing to provide offset values for each intermediate line with respect to the preceding line (the new offset values are deduced therefrom by subtracting the offset associated with the value of i).

In a particular embodiment, the intermediate sequence is produced as being - either a sequence contained in the key K, such as the predetermined sequence cl, ..., cm of the key of the prior art, described above in connection with FIG. 1, if the ith binary data item b; of the original sequence is equal to 1, - or a sequence of zeros if b; = 0.

As a variant, it is of course possible to decide inversely that if b; = 1, the intermediate sequence is a sequence of zeros, and if b; = 0, the sequence

<Desc / Clms Page number 9>

intermediate is a sequence contained in the key K, such as the predetermined sequence ci, ..., cm.

FIG. 5 is a diagram showing the table completed in accordance with the flowchart of FIG. 4: in this particular embodiment, each intermediate line is defined as being the product of the key by the value of the term considered of the sequence of origin, which corresponds, in other words, to the construction method described above. This shows that the construction of these lines can be done by simple multiplication.

FIG. 6 represents a particular case, where the key is 1011 and is found on each intermediate line corresponding to a value of 1 in the original sequence, while the other lines are formed by zeros. The offset of each intermediate row is equal to the corresponding value of i. This amounts to a configuration where each intermediate row is shifted one column to the right from the previous intermediate row. This explains, as noted above, that the coded signal is identical to that of FIG. 2. However, the invention has the great advantage of being able to easily vary the offsets, which the known coding of the figures did not allow. 1 and 2.

FIG. 7 illustrates the general way of working out these shift values: in the key K are provided values (dl, ..., dP) for the number of P, P being an integer greater than 1, from which we deduce, for each value of i, according to a predetermined function, a part v (i, K) of the key K, from which the offset values (ui, ..., UN) are deduced. The values in memory are advantageously chosen with maximum entropy, that is to say they are chosen as being as different as possible. By way of example, the aforementioned P values are part of the M values ci, ..., cm (or contain these values, if M is less than P), and the values v (i, K) are deduced from these values by multiplication by i; as a variant, these shift values are formed jointly by P values counted in the M values of the key from the term of rank i (many functions are possible, depending on the

<Desc / Clms Page number 10>

needs, and the number of terms that we are willing to accept to define the key in its entirety, and it is not possible here to give an exhaustive list).

FIG. 8 is a block diagram corresponding to the flowchart of FIG. 4. It comprises - a module 80 for developing the offset values (it can be a simple memory, if these values have been completely predefined. ), a processing block 82 adapted to receive the original data and to process them as a function of the key K, the values v (i, K) and the offset values u; (by deducting them, if necessary, from the key K), - a write zone 84, for example formed of register memories, where the original and intermediate sequences can be written and temporarily stored and - a module d 'addition 86 adapted to add the content of the columns written in the zone 84.

This modulo 2 addition module 86 can include at least one exclusive-OR gate.

FIG. 9 schematically illustrates the constitution of a network station or computer coding station, in the form of a block diagram. This station comprises a keyboard 91, a screen 98, an external information source 90, a wireless transmitter 97, jointly connected to an input / output port 95 of a processing card 100.

The processing card 100 comprises, interconnected by an address and data bus 96 - a central processing unit 92; a random access memory RAM 94; a ROM 93 read only memory; and - the input / output port 95.

Each of the elements illustrated in FIG. 9 is well known to those skilled in the art of microcomputers and transmission systems and, more generally, information processing systems. These common elements are therefore not described here.

<Desc / Clms Page number 11>

The information source 90 is, for example, an interface peripheral, a sensor, a modulator, an external memory or other information processing system (not shown), and is preferably adapted to provide sequences of data. signals representative of speech, images, service messages or multimedia data, in the form of binary data sequences.

The term “register” used hereinafter designates, in each of the memories 93 and 94, both a low capacity memory area (some binary data) and a large capacity memory area (making it possible to store an entire program).

Random access memory 94 is suitable for keeping data, variables and intermediate processing results, in memory registers bearing, in the description, the same names as the data whose values they keep. The random access memory 94 comprises in particular - a "source data" register (not shown in the figure), in which are stored, in the order of their arrival on the bus 96, the binary data coming from the information source 90 , in the form of a sequence b1, ..., bN, - a register "P, which keeps an integer corresponding to the row index of the table described above, - a register" v (i, K) " , in which the values v (i, K) described above are stored, - a register "u; ', in which the shift values described above are stored, and - a" transformed data "register (not shown in the figure ), in which are stored the binary data transformed in accordance with the present invention.

The read only memory 93 is suitable for keeping in particular, in registers bearing, in the description, the same names as the data whose values they keep - the operating program of the central processing unit 92, in a "program" register. , and

<Desc / Clms Page number 12>

- a predetermined sequence contained in the key K, in a register "K".

The central processing unit 92 is suitable for implementing the present invention, and in particular the flowchart of FIG. 4.

As shown in FIG. 10, a network according to the invention consists of a so-called base station SB designated by the reference 180, and of several peripheral stations SPi, i = 1, ..., F, where F is an integer greater than or equal to 1, respectively designated by the references 2001, 2002, ..., 200F. The peripheral stations 2001, 2002, ..., 200F are remote from the base station SB, each connected by a radio link with the base station SB and capable of moving relative to the latter.

Each station (mobile or base) of the network is suitable for implementing the present invention, and in particular the flowchart of FIG. 4.

<Desc / Clms Page number 13>

Claims (22)

CLAIMS 1. Method for transforming a sequence of N original binary data (bi, ..., bN) representative of a message, using at least one key (K), N being an integer greater than 1, this method being characterized in that a sequence (ul, ..., UN) of N algebraic offset values is produced and steps are carried out according to which (a) a table with N + 1 rows is completed as follows - write the original sequence (bi, ..., bN) on the first row of the table; - for each integer i between 1 and N, an intermediate sequence of binary elements shifted in whole or in parts of u is written on the (i + 1) th row of the table; columns with respect to the sequence written on the first line, said intermediate sequence being either a predetermined sequence contained in the key (K) if the ith binary datum (b;) of the original sequence is equal to 1, or a sequence of zeros otherwise; and (b) adding modulo 2, column by column, the binary elements contained in the table, so as to obtain a transformed binary data sequence. 2. Method according to claim 1, characterized in that said entire intermediate sequence is shifted and an offset value u is chosen; not identical for all lines. 3. Method according to claim 1, characterized in that said intermediate sequence is shifted in parts and an offset value u is chosen; not identical for all parts. 4. Method according to claim 1, 2 or 3, characterized in that, for each integer i between 1 and N, the offset value u is determined; associated with the (i + 1) 'th line from a part (v (i, K)) of the key (K). 5. Method according to claim 4, characterized in that, for each integer i between 1 and N, said part (v (i, K)) of the key (K) is obtained from the value of the index line i and key (K). <Desc / Clms Page number 14> 6. Method according to claim 5, characterized in that the key (K) contains a specific sequence of P binary elements (di, ..., dP), P being an integer greater than 1, and in that, for each integer i between 1 and N, we obtain said part (v (i, K)) of key (K) from the value of row index i and said specific sequence (di, ..., dP). 7. Device for transforming a sequence of N original binary data (bi, ..., bN) representative of a message, using at least one key (K), N being a greater integer to 1, this device being characterized in that it comprises means for developing a sequence (u1, ..., UN) of N algebraic offset values and (a) means for filling a table with N + 1 lines, comprising - means for writing the original sequence (bi, ..., bN) on the first row of the table; means for writing, for each integer i between 1 and N, on the (i + 1) 'th row of the table, an intermediate sequence of binary elements shifted in whole or in parts of u; columns with respect to the sequence written on the first line, u; being a chosen offset value, said intermediate sequence being either a predetermined sequence contained in the key (K) if the th e binary datum (b;) of the original sequence is equal to 1, or a sequence of zeros otherwise; and (b) means for adding modulo 2, column by column, the binary elements contained in the table, so as to obtain a transformed binary data sequence. 8. Device according to claim 7, characterized in that it comprises means for shifting said entire intermediate sequence and in that the shift value u; is not the same for all lines. 9. Device according to claim 7, characterized in that it comprises means for shifting said intermediate sequence by parts and in that the shift value u; is not the same for all parts. 10. Device according to claim 7, 8 or 9, characterized in that it further comprises means for determining, for each integer i included <Desc / Clms Page number 15> between 1 and N, the offset value u; associated with the (i + 1) 'th line from a part (v (i, K)) of the key (K). 11. Device according to the preceding claim, characterized in that it further comprises means for obtaining, for each integer i between 1 and N, said part (v (i, K)) of the key (K) from the value of the row index i and the key (K). 12. Device according to the preceding claim, characterized in that the key (K) contains a specific sequence of P binary elements (di, ..., dP), P being an integer greater than 1, and in that said means d 'obtaining said part (v (i, K)) of the key (K) provide, for each integer i between 1 and N, said part (v (i, K)) from the value of the index of line i and of said specific sequence (d1, ..., dP). 13. Digital signal processing apparatus, characterized in that it comprises means adapted to implement a transformation method according to any one of claims 1 to 6. 14. An apparatus for processing digital signals, characterized in that it comprises a transformation device according to any one of claims 7 to 12. 15. Telecommunications network, characterized in that it comprises means suitable for implementing a transformation method according to any one of claims 1 to 6. 16. Telecommunications network, characterized in that it comprises a transformation device according to any one of claims 7 to 12. 17. Mobile station in a telecommunications network, characterized in that it comprises means adapted to implement a transformation method according to any one of claims 1 to 6. 18. Mobile station in a telecommunications network, characterized in that it comprises a transformation device according to any one of claims 7 to 12. <Desc / Clms Page number 16> 19. Base station in a telecommunications network, characterized in that it comprises means adapted to implement a transformation method according to any one of claims 1 to 6. 20. Base station in a telecommunications network, characterized in that it comprises a transformation device according to any one of claims 7 to 12. 21. A device for processing signals representative of speech, characterized in that it comprises means suitable for implementing a transformation method according to any one of claims 1 to 6. 22. A device for processing signals representative of speech, characterized in that it comprises a transformation device according to any one of claims 7 to 12.