WO2002023799A1

WO2002023799A1 - Method and device for transforming data with convolutional character and variable offsets, and systems using same

Info

Publication number: WO2002023799A1
Application number: PCT/FR2001/002868
Authority: WO
Inventors: Jean-Roland Riviere; Cyril Fay; Frédéric LEPRIEUR; Jean-Pierre Barbot
Original assignee: Riviere Jean Roland; Cyril Fay; Leprieur Frederic; Barbot Jean Pierre
Priority date: 2000-09-14
Filing date: 2001-09-14
Publication date: 2002-03-21
Also published as: FR2814009B1; FR2814009A1; AU2001290029A1

Abstract

The invention concerns a method for transforming a sequence of N original binary data (b1, , bN) representing a message, using at least a key, N being an integer greater than 1, which consists in producing a sequence (u1, , uN) of N algebraic offset values and in filling a table of N+1 lines where: the original sequence (b1, , bN) 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 u¿i? 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 (b¿i?) 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

DATA TRANSFORMATION METHOD AND DEVICE

CONVOLUTIVE AND VARIABLE OFFSETS,

AND SYSTEMS IMPLEMENTING THEM

The present invention relates to a method and a device for transforming data, which are of convolutional 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 electrical voltage of + 5 volts.

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

The message that one seeks to encrypt can consist of signals representative of speech and / or images and / or data.

We know for example how to protect binary data frames by using a key. A method is known in particular for encrypting binary data frames which uses a key as well as successive regular and equal offsets.

Figure 1 illustrates a known method of this type. This consists in transforming a sequence of N original binary data (bι, ..., b) representative of a message. This prior art method uses a key K containing a determined sequence of M binary elements (ci, ..., CM), N and M being integers greater than 1. As shown in Figure 1, using this method, we fill an array with N + 1 lines as follows:

- the original sequence (bi, ..., b _N ) is written in clear on the first line of the table; - for each integer i between 1 and N, we write on the (i + 1) ' ^th line of the table an intermediate sequence of binary elements, offset, compared to the original sequence written on the first line, d 'as many bits as indicated by the line index i, that is to say that the intermediate sequence of a column is shifted with respect to the sequence written on the previous line.

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 i ^th bit of the key K (or added modulo 2, bit by bit, to the i ^th bit of the key K, which obviously amounts to the same). The encrypted message S is the result of the modulo 2 addition, column by column, of the different rows of the table, namely:

M

S ≈ θ ^ _j XC _j i = 1 where θ denotes the addition modulo 2.

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

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

To this end, the present invention provides a method for transforming a sequence of N binary data of origin representative of a message, using at least one key, N being an integer greater than 1, this method being characterized in that a sequence (ui, ..., UN) of N algebraic offset values is worked out and steps are carried out according to which:

(a) we fill an array with N + 1 lines as follows: - we write the original sequence on the first line of the array; - for each integer i between 1 and N, we write on the (i + 1) ^th row of the table an intermediate sequence of binary elements shifted in whole or in parts of Uj columns compared to the sequence written on the first line , said intermediate sequence being either a predetermined sequence contained in the key if the i ^th binary datum of the original sequence is worth

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 concept 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 sense of term) than vertical; in any case, the concept of the invention is in no way modified if the concepts of row and column are exchanged.

As will be shown with reference to FIG. 6, the present invention proposes a coding which is close to the known coding, but it allows better security than this coding 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 line. Furthermore, since each of these intermediate lines depends only on one term of the original signal, it is not necessary to wait for the complete signal to be available before elaborating these intermediate lines, allowing time coding. real. This results in greater speed, making this coding entirely 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 meaning, in a telecommunications network for example; it can also be used for error correction (calculation lag). It allows, by entering particular keys to break codes, depending on the concealment, or not, of the drags of messages. 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 having reached its destination.

According to a particular preferred characteristic, the said intermediate sequence is shifted in full, 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 offset and by applying an offset only in 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 that we want 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 one is ready to accept).

According to another preferred particular characteristic, for each integer i between 1 and N, the offset value Uj associated with the (i + l) ^th line is determined from a certain part of the key. In the following, the key is denoted K and the part of the key that can be used to determine the offset value uι 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 line index i and possibly other binary elements contained in the key K. Thus, as an advantageous example, 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 the key K is determined from the value of the line index i and from 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 provides a device for transforming a sequence of N binary data of origin representative of a message, using at least a key, N being an integer greater than 1, this device being characterized in that it comprises means for developing a sequence (uj, ..., UN) of N algebraic offset values and:

(a) means for filling an array with N + 1 lines, comprising: - means for writing the original sequence on the first line 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 Uj columns with respect to the written sequence on the first line, Uj being a chosen offset value, said intermediate sequence being either a predetermined sequence contained in the key if the i ^th binary datum of the original sequence is worth 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 above comments concerning the process 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 also relates to an apparatus for processing digital signals, comprising a transformation device as above. The present invention also relates to a telecommunications network, comprising means suitable for implementing a transformation method as above.

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

The present invention also relates to a device for processing speech representative signals, comprising means suitable for implementing a transformation method as above.

The present invention also relates to a device for processing speech representative signals, comprising a transformation device as above. These digital signal processing devices, telecommunications networks, mobile and / or base stations and devices for processing speech representative signals having characteristics and peculiarities similar to those of the transformation method according to the invention, these are not not repeated here. Other aspects and advantages of the invention appear from the following detailed description of particular embodiments, given by way of nonlimiting 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 encryption technique known in Figure 1;

- Figure 3 illustrates how to use the commutative property of addition in the present invention; - Figure 4 is a flowchart illustrating steps of a transformation method according to the present invention, in a particular embodiment;

- Figure 5 schematically illustrates the transformation technique according to the present invention, in a particular embodiment; - Figure 6 schematically illustrates a digital example of application of the transformation technique of Figure 5, in a particular embodiment; FIG. 7 schematically illustrates how to obtain offset values for transforming an original sequence in accordance with the present invention, in a particular embodiment;

- Figure 8 is a block diagram illustrating a transformation device according to the present invention, in a particular embodiment;

- Figure 9 schematically shows an electronic device comprising a processing device according to the present invention, in another particular embodiment; and - Figure 10 is a simplified schematic view of a wireless telecommunications network capable of implementing the invention.

We consider in what follows a sequence of N original binary data (bi, ..., b _n ), N being an integer greater than 1, these data being representative of a message, and a key is also provided 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 designate either the horizontal dimension or the vertical dimension of this table.

A relationship between the coding of the invention and that known, described with reference to FIGS. 1 and 2, results from the observation that, in FIG. 2, each diagonal (see the sequences of binary data surrounded) consists of the coding key when the corresponding term in the original sequence is 1, or zeros when the corresponding term in this sequence is zero. However, in the intermediate lines which are added to give the encrypted signal, it is possible to replace each diagonal sequence by a line, as shown 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 of the key or of a succession of zeros. The table in FIG. 6 is thus obtained, which will be commented on later in connection with the method of the invention. In any case, it can be seen that the transformation with respect to the table in FIG. 2 has not modified the encrypted signal. Very generally, the method of the invention, shown schematically in FIG. 4, consists in providing the following steps:

- starting from the original sequence, an array is initialized at 10 by copying this original sequence on the first row (or column); - An intermediate sequence (see below) offset from line 1 by an offset u, the value of which depends on i, is then produced at 14 on the following line, 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 worth N + 1 (which means that as many intermediate lines have been worked out as there are terms in the original sequence), we proceed in 20 to the summation , column by column, binary values of all the intermediate lines, which gives a transformed digital signal (encrypted), otherwise we proceed for this value of i in operations 14 and 16.

Step 12 of developing offset values (in practice between 1 and 256) can be carried out in parallel with step 10 of initialization, or beforehand. The sequence of these values can simply be preestablished 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 it is the same 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 developed as being:

- or a sequence contained in the key K, such as the predetermined sequence ci, ..., CM of the key of the prior art, described above in conjunction with FIG. 1, if the i ^th binary data b, of the original sequence is worth 1, - i.e. a sequence of zeros if b, = 0.

As a variant, we can of course decide inversely that if b, = 1, the intermediate sequence is a sequence of zeros, and if b, = 0, the sequence intermediate is a sequence contained in the key K, such as the predetermined sequence ci, ..., CM-

FIG. 5 is a diagram representing the table filled in according to the flow diagram of FIG. 4: in this particular embodiment, each intermediate line is defined as being the product of the key by the value of the considered term 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 line is equal to the corresponding value of i. This amounts to a configuration where each intermediate line is shifted one column to the right with respect to the previous intermediate line. 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 manner of developing these offset values: in the key K are provided values (di, ..., d _P ) with 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 we deduce the offset values (ui, ..., UN). The values in memory are advantageously chosen with maximum entropy, that is to say that they are chosen as being as different as possible. For example, the aforementioned P values are part of the M values ci, ..., c _M (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 offset 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 needs, and the number of terms that we are ready 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 offset values (it may be a simple memory, if these values have been completely predefined),

a processing block 82 adapted to receive the original data and to process it as a function of the key K, of the values v (i, K) and of the offset values Uj (by deducing them, if necessary, from the key K), - a writing area 84, for example formed of register memories, where the original and intermediate sequences can be written and temporarily stored, and

an addition module 86 adapted to add the content of the columns written in the area 84. This add-on module 86 modulo 2 may include at least one OR-exclusive gate.

FIG. 9 schematically illustrates the constitution of a network station or computer coding station, in the form of a block diagram. This station includes 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; - RAM 94;

- ROM ROM 93; 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. The information source 90 is, for example, an interface device, a sensor, a modulator, an external memory or another information processing system (not shown), and is preferably adapted to supply sequences of signals representative of speech, images, service messages or multimedia data, in the form of sequences of binary data.

The term "register" used below designates, in each of the memories 93 and 94, both a low-capacity memory area (some binary data) and a high-capacity memory area (allowing an entire program to be stored).

The random access memory 94 is adapted to store data, variables and intermediate processing results in memory registers bearing, in the description, the same names as the data whose values they store. The random access memory 94 comprises in particular: - a "data_source" 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 bi sequence, ..., bu,

- a register "/", which keeps an integer corresponding to the line index of the table described above,

- a register "v (i, K) 'in which the values v (i, K) described above are kept,

- a register "u", in which the offset values described above are stored, and - a register "data_transformed" (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 adapted to keep 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 - a predetermined sequence contained in the key K, in a register "K".

The central processing unit 92 is adapted to implement the present invention, and in particular the flow diagram of FIG. 4. As shown in FIG. 10, a network according to the invention consists of a station called base station SB designated by the reference 180, and several peripheral stations SPi, i = 1, ..., F, where F is an integer greater than or equal to 1, respectively designated by the references 200ι, 200 ₂ , ..., 200 _F. The peripheral stations 200-ι, 200 ₂ , ..., 200 _F are distant from the base station SB, each linked 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 adapted to implement the present invention, and in particular the flow diagram of FIG. 4.

Claims

1. Method for transforming a sequence of N original binary data (bi, ..., b) representative of a message, using at least one key (K), N being a higher integer at 1, this method being characterized in that a sequence (ui, ..., UN) of N algebraic offset values is worked out and steps are carried out according to which:

(a) we fill in an array with N + 1 lines as follows:

- the original sequence (bi bu) is written on the first line of the table;

- for each integer i between 1 and N, we write on the (i + 1) ^th row of the table an intermediate sequence of binary elements shifted in whole or by parts of Uj columns compared to the sequence written on the first line , said intermediate sequence being either a predetermined sequence contained in the key (K) if the i ^th binary datum (bj) of the original sequence is 1, or a sequence of zeros otherwise; and

2. Method according to claim 1, characterized in that the said entire intermediate sequence is shifted and a non-identical offset value u _f is chosen for all the lines.

3. Method according to claim 1, characterized in that the said intermediate sequence is shifted by parts and a non-identical offset value Uj is chosen for all the parts.

4. Method according to claim 1, 2 or 3, characterized in that, for each integer i between 1 and N, the offset value Uj associated with the (i + 1) ^th line is determined 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).

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 line index i and said specific sequence (di, ..., dp).

7. Device for transforming a sequence of N original binary data (bi, ..., b _N ) representative of a message, using at least one key (K), N being an integer greater than 1, this device being characterized in that it includes means for developing a sequence (ui, ..., UN) of N algebraic offset values and:

(a) means for filling an array with N + 1 lines, comprising:

- means for writing the original sequence (bi, ..., b _N ) on the first line 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 by parts of u, columns relative to the sequence written on the first line, Uj being a chosen offset value, said intermediate sequence being either a predetermined sequence contained in the key (K) if the i ^th binary datum (bj) of the original sequence is 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 offset value Uj is not identical for all the lines.

9. Device according to claim 7, characterized in that it comprises means for shifting said intermediate sequence by parts and in that the offset value Uj is not identical for all the parts.

10. Device according to claim 7, 8 or 9, characterized in that it further comprises means for determining, for each integer i included between 1 and N, the offset value Uj 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 line 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 for 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 line index i and from said specific sequence (di, ..., dp). • -

13. Apparatus for processing digital signals, characterized in that it includes means suitable for implementing a transformation method according to any one of claims 1 to 6.

14. Digital signal processing apparatus, 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 adapted to implement a transformation process 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 suitable for implementing 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.

19. Base station in a telecommunications network, characterized in that it includes means suitable for implementing 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. Device for processing representative speech signals, characterized in that it includes means suitable for implementing a transformation method according to any one of claims 1 to 6.

22. Device for processing representative speech signals, characterized in that it comprises a transformation device according to any one of claims 7 to 12.