WO1997007613A1

WO1997007613A1 - Method for managing ciphering keys for a symmetric cryptography system and device generating the ciphering keys pour implementing the method

Info

Publication number: WO1997007613A1
Application number: PCT/FR1996/001287
Authority: WO
Inventors: Christine France Isabelle Routier; Franck Jean Pierre André Roland LEFEVRE; Jean Pierre Roland Paul Lefevre
Original assignee: Routier Christine France Isabe; Lefevre Franck Jean Pierre And; Lefevre Jean Pierre Roland Pau
Priority date: 1995-08-17
Filing date: 1996-08-14
Publication date: 1997-02-27
Also published as: AU6877796A; FR2737929A1; FR2737929B1; EP0845179A1

Abstract

The present invention relates to a method for the management of ciphering keys for a symmetric crypography system comprising the following steps: the initial communication, through an authority common to entities susceptible of exchanging ciphered information, of a private key Fi(arg) = F(cs;UTILi; arg) comprised of a bijective function, parametered specifically for each of the addressees UTILi, and, at the time when each of the ciphered transactions is performed, by the data user sender: a) constructing a key CLEi = Fi(UTILj; VAR); b) by the data user addressee: b) calculating the key CLEj = Fj(UTILi; VAR). It also relates to a device for implementing said method.

Description

ENCRYPTION KEY MANAGEMENT METHOD FOR SYSTEM

SYMMETRIC CRYPTOGRAPHY AND KEY GENERATING DEVICE

OF ENCRYPTION OF IMPLEMENTATION OF THE PROCESS

The invention relates to a method for managing encryption keys and / or authentication for a symmetric cryptography system and to a device for generating encryption keys and / or authentication codes for implementing the method.

The field of the invention is more generally that of cryptology, that is to say of the science of secret writings, of encrypted documents.

Nowadays, with the continuous development of: - electronics (miniaturization and acceleration of the operating speed of components),

- information technology (large and medium computer systems, mini / microcomputers, software, files and databases, etc.), the protection of information requires, in order to guarantee the confidentiality and integrity of data, to use cryptographic techniques.

Indeed, cryptography, that is to say all the techniques relating to text encryption, applies well to the protection of computer files stored on magnetic media or routed electronically by specialized data transmission networks. or public.

In this context, encrypting a computer file consists of transforming the file to be protected, known as a "clear file", into another file, unintelligible for a third party, known as an "encrypted file", in order to ensure the secrecy of its transmission or of its conservation.

The operation performed on the "clear file" to obtain the "encrypted file" is ensured by a transformation law, generally mathematical, the encryption algorithm.

Conversely, decrypting a computer file consists of transforming the protected file, known as an "encrypted file" into another file, known as a "clear file", intelligible to the designated recipient, in order to restore previous processing possibilities on the file. The operation performed on the "encrypted file" to obtain the "clear file" again is also ensured by a transformation law (generally the same mathematical law), the decryption algorithm. The encryption / decryption algorithms fall into two categories: private algorithms (for example banking) and standardized algorithms (for example the American system DES (Data Encryption Standard).

To obtain a satisfactory level of security, it is essential to configure the operation of the encryption / decryption algorithm. This setting is made using an "encryption key".

In all cryptographic systems (except the most basic), the role of the encryption key is crucial. Indeed, keyless encryption algorithms, which always behave in a predictable manner, are of academic interest only. The security of such systems relies on the secrecy of design details, and when secrecy is exposed, a new design is needed to replace the lost figure.

In key encryption algorithms, the encryption process is performed under the control of the encryption key, which influences the behavior of the encryption algorithm. This property applies equally to substitution, transposition and dialed digits. This is particularly important in the case of encryption machines. Indeed the capture of the machine can allow the opponent to know all the details of construction of the encryption algorithm. However, if the adversary does not know the key used, then the knowledge of the only encryption algorithm is totally insufficient to authorize the decryption of an encrypted message. Hence a healthy principle, very often observed today: the security of a cryptography system should not rest on the secret of the encryption algorithm but on the secret of the encryption key. This principle gives great responsibility to the person who manages: generates, distributes, uses and destroys the encryption keys after use. In the past, a messenger was used to send encryption keys to users of the cryptography system, but this method is generally too slow and impractical for current applications. Methods are therefore needed to transport the encryption keys more quickly and efficiently. This often implies that the encryption keys are routed through transmission channels which are themselves protected by a cryptographic system.

Most cryptographic systems in use today use a secret encryption key known to both the sender and the recipient of the information. These are "symmetrical" cryptography systems since the knowledge of the secret key by A and B allows the secret of the communication from A to B or from B to A. Nothing distinguishes A from B in such a cryptographic system which, by Therefore, provides a protected channel in both directions. An example of a widely used symmetric cryptography system is the Data Encryption Standard (DES), sometimes referred to as the Data Encryption Algorithm (DEA).

In order to solve the thorny problem posed by the routing of secret encryption keys to users of a cryptography system, cryptologists (Diffie and Hellmann) proposed in 1976 (New directions in cryptography) a new type of system. cryptography, in which the sender and the recipient use separate but linked encryption keys, only one of which requires secrecy. The recipient of the information has a "secret" encryption key which allows him to decrypt, but the sender encrypts with a different encryption key which can be made public without risk of compromise for the cryptography system. This constitutes an "asymmetric" cryptography system providing secure communication in a direction only. Establishing secure communication in the other direction requires a second pair of encryption keys. An example of an asymmetric public key cryptography system is the RSA system (Rivest, Shamir, Adlman).

A public key cryptography system has the advantage of not requiring the transport of a secret key between A and B to establish a protected channel. The transport of a secret key indeed involves risks and, because of the many essential precautions to be taken, can prove to be inconvenient and costly. The storage of a secret key also involves risks and, in certain applications of public key encryption, these risks are considerably reduced. When a key has to be stored in different places, getting rid of the need for secrecy is a huge step forward.

From a theoretical point of view, an asymmetric cryptography system (with public key) should therefore prevail over a symmetric cryptography system (with secret key). In practice, it has proven extremely difficult to design satisfactory public key cryptographic systems. Testing the security level of a system is similar to that of symmetric cryptography systems. It consists of proposing all kinds of attacks which we manage (in favorable cases) to show ineffectiveness. The RSA system algorithm (Rivest, Shamir, Adlman) has passed the tests, although absolute certainty is still out of reach. As a result, organizations that demand the highest level of security (for example, defense agencies in the United States or many foreign countries) have generally decided to use only symmetric cryptographic systems, despite the difficulty of routing and management of encryption keys to users. The security of a cryptography system therefore rests on the protection of encryption keys. This is why key management is the strategic element of a symmetric (secret key) cryptography system. 5 In practical terms, the needs for managing encryption keys in a computer file protection system are different from those existing in a communication system between computers: in a communication system between

10 computers, the encryption and decryption operations are carried out by specialized equipment placed at the two terminations of the link; therefore two copies of the encryption key are required in different geographic locations. In a system of

15 protection of computer files, encryption and decryption operations can be performed in the same premises.

- a communication system between computers usually involves two interlocutors, whereas

Many users can access a computer file protection system, which therefore results in the need to share the secret encryption key.

- in a communication system between 25 computers, the message remains encrypted for a short period of time and is exposed to interception only during this period. In a computer file protection system, encrypted files are exposed indefinitely. 30 - changing the encryption key in a communication system between computers is a simple operation, while changing the encryption key in a computer file protection system requires that all> files be used to be encrypted with the new

35 encryption key.

These differences affect the management of encryption keys because the key management needs in a Computer file protection system are different from that of a communication system between computers. In a file protection system it is necessary to keep the encryption keys secret for long periods and to use them frequently, which tends to decrease the level of security of the encryption keys used.

The present invention which aims to provide a solution to the management of encryption keys and 1 'authentication of stakeholders in a symmetric cryptography system (secret key) provides a method for managing encryption keys and / or authentication system for symmetric cryptography and a device for generating encryption keys and / or authentication codes, the operation of which is closely associated with this method.

The invention relates more particularly to a method for managing encryption and / or authentication keys for a symmetric cryptography system comprising the following steps:

- the initial communication, by a common authority to the entities likely to exchange encrypted information, of a private key Fi ( _ar g ₎ = F (cs, -UTILi _; arg) constituted by a bijective function, configured specifically for each of the UTILi recipients, the parameter consisting of UTILi public information linked to said recipient, then, at the time of each encrypted transaction, to authenticate the interlocutor: - By the user sending the data: a) Build a CLEi = Fi key (UTIL j; VAR) which is the result of the private key of the sending user applied to the argument formed by the public name UTILj of the user receiving the encrypted data, and of a public VAR variable; b) to transmit to the recipient user the key CLEi _; - By the user receiving the data: c) calculating the key CLEj - Fj (UTILi; VAR) which is the result of the private key of the recipient user applied to the argument formed by the public name UTILj of the sender user, and the public variable VAR; d) check 1 'identitée between CLEJ _e t Clei. Advantageously, the UTIL parameter is constituted by public information identifying its owner unique in the organization comprising the users capable of communicating, such as his email address, the variable VAR being a public random variable.

According to a particular embodiment, the public key F (es; UTILi _; arg) is a matrix function parameterized by the parameter UTILi _# delivering a character string depending on the argument arg, said matrix being defined so that F ( cs; UTILi _; UTILj _; VAR) = F (es; UTILj _;

UTILi; VAR).

According to an advantageous application, the key F (es; UTILi _; UTILj_ ^ VAR) is intended for one authentication of the entity UTILj by the entity UTILi.

According to a particular mode of implementation, the function F (es; UTILi _; UTILj _L VAR) is a matrix formed by forty-five or two hundred and fifty-six digital matrices (respectively four or eight groups of two, three or four digits ) registered in the device generating encryption keys and / or authentication codes.

The method also makes it possible in a simple, secure and inexpensive manner: to manage and obtain the encryption keys required within the framework of the implementation and operation of a symmetric cryptography system, by eliminating the constraint to have to distribute the secret encryption key by a secure channel, - to bring the same advantages as those usually obtained by the implementation and operating an asymmetric cryptography system (public key), benefiting from the higher level of security widely recognized by symmetric cryptography systems (secret key) over asymmetric cryptography systems (public key).

Due to the completely autonomous operating mode of the device for generating encryption keys and / or authentication codes, the method for managing encryption keys and / or authentication for a symmetric cryptography system can be integrated without particular difficulty into existing cryptography systems or in specialized IT equipment or software.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows of the method for managing encryption keys and / or authentication for a symmetric cryptography system and the device for generating encryption keys and / or codes. which implements it, in which FIG. 1 represents a device generating an encryption key and / or authentication codes.

The device for generating encryption keys and / or authentication codes shown in FIG. 1 comprises a box having a keyboard (1) consisting of: - twenty-six keys making it possible to compose the twenty-six characters of the latin alphabet,

- ten keys for dialing the ten Arabic numbers,

- ten keys for composing special characters, for example the characters: space, period, comma, percent, equal, plus, minus, en dash, fraction bar, asterisk,

- eleven function keys: Fl, F2, F3, F4, F5, F6, F7, F8, Enter, J, Backspace, - four positioning keys: up arrow, down arrow, left arrow, right arrow, - a key: Shift, allowing the user to select the special characters which can appear on the upper part of certain keys of the keyboard.

- an activation or deactivation key, which can also allow a temporary restoration of the data previously entered,

In the housing of the device for generating an encryption key and / or authentication codes shown in FIG. 1 are incorporated standard electronic components from an industrial point of view and in particular:

- a liquid crystal display screen (2) allowing the display of 24 characters,

a microprocessor (3) in which a specific program is recorded, responsible for managing all of the functions of the device generating encryption keys and / or authentication codes and for executing the algorithm for generating encryption keys and / or authentication codes.

- A memory (4) in which is kept the code specific to each device generating encryption keys and / or authentication codes. This code of 16 alphanumeric characters is accessible for reading by the microprocessor of the device generating encryption keys and / or authentication codes. This code, recorded during the manufacturing of the equipment, cannot be modified by the user.

- A memory (5) in which is kept the identifier code assigned to each user. This code of 16 alphanumeric characters is accessible for reading by the microprocessor of the device generating encryption keys and / or authentication codes. This code, saved during configuration, cannot be modified by the user, but it can be modified by a manager who has the specific code corresponding to the device generating encryption keys and / or authentication codes, - a memory (6) in which a secret code is kept. This code of 16 alphanumeric characters is accessible by the microprocessor of the device generating encryption keys and / or authentication codes. This code, recorded during the manufacturing of the equipment, can be modified by the user. a memory module (7) in which the forty-five or two hundred and fifty-six digital matrices are respectively stored (respectively four or ^• eight groups of two, three or four digits) corresponding to the values of the matrices of the generation algorithm encryption keys and / or authentication codes. This information initiated during the manufacture of the memory module is accessible by the microprocessor of the device generating encryption keys and / or authentication codes and can be modified by a specially authorized user, that is to say having:

- the specific code corresponding to the device generating encryption keys and / or authentication codes, the secret code kept in the device generating encryption keys and / or authentication codes. The explanation given below recalls the different steps for encrypting and decrypting information in a common symmetric cryptography system.

Suppose that the user DUPONT, of a computer (in which a symmetric cryptography system is available), wishes to proceed to the encryption of the computer file: FICHPAIE for example, in order to send it encrypted to the user DURAND.

In this secret key cryptographic system, the DUPONT user must (in order):

- choose a secret encryption key, for example PENELOPE, encrypt the FICHPAIE file by communicating, as a parameter, the secret encryption key PENELOPE to the algorithm of the encryption / decryption software,

- transmit the encrypted FICHPAIE file to the user DURAND,

- transmit the PENELOPE secret encryption key to the DURAND user via a secure channel (carrier, secret mail, different encrypted link, etc.).

Upon receipt, in order to be able to use the encrypted FICHPAIE file, the DURAND user must (in order) -:

- be in possession of the encrypted file FICHPAIE, be in possession of the secret encryption key PENELOPE (routed through the secure channel),

- decrypt the encrypted FICHPAIE file by communicating the secret encryption key as a parameter

PENELOPE to the algorithm of the encryption / decryption software.

The following explanation explains the different steps for encrypting and decrypting information in a symmetric cryptography system which uses the method of managing encryption keys and / or authentication codes for symmetric key cryptography system and the device. generator of encryption keys and / or authentication codes to implement it. Let us again suppose that the user DUPONT, of a computer (in which a symmetric cryptography system is available), wishes to proceed to the encryption of the computer file: FICHPAIE for example, in order to send it encrypted to the user DURAND. In this case, the DUPONT and DURAND users each have a device for generating encryption keys and / or authentication codes suitably configured.

In this secret key cryptographic system, which uses the method for managing encryption keys and / or authentication codes and the device for generating encryption keys and / or authentication codes, the user DUPONT must (in order): ask its device generating encryption keys and / or authentication codes to generate a secret encryption key, for example ZB2XK3FGS8DR. We will see later how the DUPONT user proceeds to implement his device generating encryption keys and / or authentication codes in order to obtain the encryption key.

- encrypt the FICHPAIE file by communicating as a parameter the secret encryption key ZB2XK3FGS8DR to the algorithm of the encryption / decryption software,

- transmit the encrypted FICHPAIE file to the user DURAND,

Upon receipt, in order to be able to use the encrypted FICHPAIE file, the user DURAND must (in order) -: - ask his device, which generates encryption keys and / or authentication codes, to generate the secret encryption key which was used to encrypt the FICHPAIE file, therefore in our example ZB2XK3FGS8DR. We will see below how the DURAND user proceeds to implement his device generating encryption keys and / or authentication codes in order to obtain the encryption key allowing him to decrypt.

ZB2XK3FGS8DR to the encryption / decryption software algorithm.

It can be seen that the method of managing encryption keys and / or authentication for a symmetric cryptography system with the device generating encryption keys and / or authentication codes eliminates the step which consists in transmitting over a secure channel. , the secret encryption key chosen by the user at the origin of the encryption operation, to the recipient of the encrypted file.

Another advantage of the method for managing encryption keys and / or authentication codes for a system of symmetric cryptography with device generating encryption keys and / or authentication codes is that the level of security is considerably reinforced because: the choice of encryption keys is no longer the responsibility of a user, who very often chooses weak encryption keys to attack by adversaries, but is the result of the execution of an encryption key generation algorithm that works with strict mathematical construction rules.

- the encryption key is no longer routed to the recipient of the encrypted file, there is no risk of there being an accidental or fraudulent revelation of the encryption key during the routing. - the encryption key no longer risks being lost or even forgotten, resulting in the irreversible loss of the computer file due to the permanent impossibility of decrypting it.

Indeed, there is no longer any need to manage the encryption keys; the user limits himself to asking his device for generating encryption keys and / or authentication codes, the encryption key when he needs it.

In our example, the implementation by the user DUPONT of the device generating encryption keys and / or authentication codes, in order to obtain a secret key for encrypting the FICHPAIE file, before transmitting it to the recipient DURAND s '' performs the following steps: - the DUPONT user dials the secret code stored in the memory of his device generating encryption keys and / or authentication codes in order to unlock the operation of the device.

- the message IDENTIFYING? is displayed on the liquid crystal display of the device generating encryption keys and / or authentication codes. - the DUPONT user composes the identifier of the recipient to whom he wishes to send the FICHPAIE file. In our example, he dials the DURAND identifier using the keyboard of the device generating encryption keys and / or authentication codes.

- the message PUBLIC WORD? is displayed on the liquid crystal display of the device generating encryption keys and / or authentication codes.

- the DUPONT user composes on the keyboard of the device generating encryption keys, and / or authentication codes, a public word to be taken into account, that is to say for example the name of the file to be encrypted (the name which will be indicated on the shipping label), in our example FICHPAIE. - the program stored in the microprocessor of the device generating encryption keys and / or authentication codes executes the algorithm for generating encryption keys, then displays the secret encryption key obtained, ie in our example ZB2XK3FGS8DR, on l display of the appliance.

At this stage, the user DUPONT can proceed to encrypt the computer file FICHPAIE with the encryption key ZB2XK3FGS8DR displayed by his device by transmitting this encryption key as a parameter to the specialized encryption / decryption software of the cryptography system in use.

When the recipient DURAND, after receiving the encrypted computer file FICHPAIE decides to decrypt it, he must in turn ask his device for generating encryption keys and / or authentication codes to provide him with the encryption key that has been used to encrypt the FICHPAIE file. This operation is carried out according to the steps: the DURAND user dials the secret code recorded in the memory of his device, generating encryption keys and / or authentication codes in order to unlock the operation of the device. - the message IDENTIFYING? is displayed on the liquid crystal display of the device generating encryption keys and / or authentication codes.

- the DURAND user composes the identifier of the sender who sent him the FICHPAIE file.

In our example, it composes the DUPONT identifier using the keyboard of the device generating encryption keys and / or authentication codes.

- the message PUBLIC WORD? is displayed on the liquid crystal display of the device generating encryption keys and / or authentication codes. the DURAND user dials the public word to be taken into account using the keyboard of the device generating encryption keys and / or authentication codes, i.e. in the example the name of the file to be decrypted (the name which appears on the shipping label), therefore in our example FICHPAIE. the program stored in the microprocessor of the device generating encryption keys and / or authentication codes executes the algorithm for generating encryption keys, then displays the secret encryption key obtained, that is in our example ZB2XK3FGS8DR, on the device's liquid crystal display.

At this stage, the user DURAND can proceed to decrypt the computer file FICHPAIE with the encryption key ZB2XK3FGS8DR displayed by his device by transmitting this encryption key as a parameter to the specialized encryption / decryption software of the cryptography system in use. The algorithm for generating encryption keys and / or authentication codes uses the forty-five or two hundred and fifty-six digital matrices (four or eight groups of two, three or four digits) recorded in the module as input. of memory. This information is organized in the form of a table. Each matrix in the table corresponds to one of the forty-five or two hundred and fifty-six different characters likely to be composed by the user using the keyboard of the device generating encryption keys and / or authentication codes when entering the IDENTIFIING and PUBLIC WORD information.

For example, the matrix function F (es; UTILi; UTILj; VAR) can be constituted by a matrix product type function where:

C (0) = (UTILi (2) * UTILj (2) + (UTILi (5) * UTILj (6i) +

UTILi (1 * UTILj (1) + UTILi (4 * 'τUTILj (7) + UTILi (0 * UTILJ (5) + UTILi (6' UTILj (0) + UTILi (7 * UTILj (3) + UTILi (3 * UTILj (4) mod251

C (l (UTILi () * UTILj (5) + (UTILi (0) * UTILj (0 + UTILi (7 * UTILj (2) + UTILi (1 * UTILj (6) + UTILi (2 * UTILj (4) UTILi (3 * UTILj (7) + UTILi (5 * UTILj (1) + UTILi (4 * UTILj (3) mod251

C (2) = (UTILi (l) * UTILj (1) + (UTILi (2) * UTILj (7 + UTILi (4 * UTILj (4) + UTILi (0 * UTILj (5) + UTILi (5 * UTILj ( 3) + UTILi (7 * UTILj (6) + UTILi (3 * UTILJ (0) + UTILi (6 * UTILj (2) mod251

C (3 (UTILi (7) * UTILj (4) + (UTILi (6) * UTILj (1 + UTILi (5 * UTILj (0) + UTILi (2 * UTILj (2) UTILi (3 * UTILj (7) UTILi (4 * UTILj (3) UTILi (0 * UTILj (6) + UTILi (1 * UTILj (5) mod251

C (4 (UTILi (5) * UTILj (0) + (UTILi (4) * UTILj (2 + UTILi (3) * UTILj (5) + UTILi (7 * UTILj (3) + UTILi (1) 1) + UTILi (2 * UTILj (4) + UTILi (6) * UTILJ (7) + UTILi (0 * UTILj (6) mod251

C (5; (UTILi (0) * UTILj (6) + (UTILi (7) * UTILj (3 + UTILi (6 * UTILj (7) + UTILi (3 * UTILj (4) + UTILi (4 * UTILj (2 ) + UTILi (1 * UTILj (1) + UTILi (2 * UTILj (5) + UTILi (5 * UTILj (0) mod251 c (6: (UTILi (3) * UTILj (7) + (UTILi (1) UTILj (5 + UTILi (0 * UTILJ (3) + UTILi (6 * UTILj (0) + UTILi (7 * UTILj (6) + UTILi (5 * UTILj (2) + UTILi (4 * UTILj (4) (2 * UTILj (1) mod251

C (7 (UTILi (4) * UTILj (3) + (UTILi (3) * UTILj (4) UTILi (2) * UTILj (6) + (UTILi (5) * UTILj (1) (UTILi (6) * UTILj (0)) + (UTILi (0) * UTILj (5)) + (UTILi (l) * UTILj (2)) + (UTILi (7) * UTILj (7))) mod251

For a random variable VAR providing the following matrix:

VAR (O) (2; 2) (5 6) (1; 1) (4; 7) (0; 5) (6; 0) (7; 3) (3; 4) VAR (1) (6; 5) (0 0) (7; 2) (1; 6) (2; 4) (3; 7) (5; 1) (4; 3) VAR (2) (1; D (2 7) (4 ; 4) (0; 5) (5; 3) (7; 6) (3; 0) (6; 2) VAR (3) (7; 4) (6 1) (5; 0) (2; 2 ) (3; 7) (4; 3) (0; 6) {1; 5) VAR (4) (5 0) (4 2) (3; 5) (7; 3) (1; 1) (2 ; 4) (6; 7) (0; 6) VAR (5) (0 6) (7 3) (6; 7) (3; 4) (4; 2) (1; 1) (2; 5) (5; 0) VAR (6) (3 7) (1 5) (0; 3) (6; 0) (7; 6) (5; 2) (4; 4) (2; 1) VAR (7 ) (4 3) (3 4) (2; 6) (5; 1) (6; 0) (0; 5) (1; 2) (7; 7)

The execution of the algorithm for generating encryption keys and / or authentication codes consists in searching for each of the characters composed by the user, the corresponding matrix in the table, then in carrying out the products of each chain. matrix obtained, using an arithmetic based on the greatest prime number of two, three or four digits, as a function of the content of the array of matrices recorded in the device generating encryption keys and / or authentication codes. The result obtained is then processed by: the standardized DES (Data Encryption Standard) algorithm, or any other equivalent algorithm,

- then by a routine in order to produce, according to the configuration of the device generating encryption keys and / or authentication codes, encryption keys which can be according to the user's choice: numeric, alphabetical, alphanumeric, hexadecimal, in the form of three-character syllables, etc.

After processing, the result (the encryption key, in our example ZB2XK3FGS8DR), is communicated to the user on the device's liquid crystal display.

It should be specified that the method for managing encryption keys and / or authentication for a symmetric cryptography system and the device for generating encryption keys and / or authentication codes for implementing the method can operate with an algorithm for generating encryption keys and / or authentication codes different from that just explained in the previous paragraph. What is essential in the method for managing encryption keys and / or authentication codes for a symmetric cryptography system and the device for generating encryption keys and / or authentication codes for implementing the method, is that the algorithm used closely associates the information to generate the encryption key and / or the authentication code:

- TABLE of matrices,

- IDENTIFIER of the sender, - IDENTIFIER of the recipient,

- PUBLIC WORD attributed to the file to be encrypted or decrypted or public variable VAR.

This explanation has exposed the secure exchange of the encrypted file: FICHPAIE between the two users DUPONT and DURAND. An exchange of encrypted information via a communication system between computers can also be ensured by using the encryption key management and / or authentication method for symmetric cryptography system and the key generator device. encryption and / or authentication codes for implementing the method.

Suppose now that the DUPONT user, by means of a network of terminals, wishes to exchange sensitive information with the DURAND user. In a common symmetric cryptography system, the DUPONT user should: define an encryption key for the encrypted communication session, for example the ARISTOTE encryption key, introduce, at the start of the encrypted communication session, the ARISTOTE encryption key in the encryption equipment connected to its own terminal.

- communicates the ARISTOTE encryption key to the DURAND user via a secure channel,

And that the user DURAND: - receives the ARISTOTE encryption key from the secure channel, introduces, at the start of the encrypted communication session, the ARISTOTE encryption key into the encryption equipment connected to his own terminal. In a symmetric cryptography system using the encryption key management and / or authentication method for symmetric cryptography system and the device for generating encryption keys and / or authentication codes for the implementation of the method, the DUPONT user must at the start of the session:

- ask its device generating encryption keys and / or authentication codes to generate a secret encryption key for the communication session, for example the encryption key KAG5B6RPS2LF. - introduce the KAG5B6RPS2LF encryption key into the encryption equipment connected to its own terminal.

Conversely, the DURAND user must also at the start of the session: - ask their device for generating encryption keys and / or authentication codes to generate the secret encryption key to decrypt the communication session, for example the KAG5B6RPS2LF encryption key. - introduce the KAG5B6RPS2LF encryption key into the encryption equipment connected to its own terminal. In this example, the implementation by the user DUPONT of the device generating encryption keys and / or authentication codes, in order to obtain a secret encryption key for encrypting the communication session is carried out according to the steps :

- the DUPONT user dials the secret code stored in the memory of his device, which generates encryption keys and / or authentication codes in order to unlock the operation of the device. - the message IDENTIFYING? is displayed on the liquid crystal display of the device generating encryption keys and / or authentication codes.

- the DUPONT user dials the identifier of the recipient with whom he wishes to establish a communication session. In our example, he dials the DURAND identifier using the keyboard of the device generating encryption keys and / or authentication codes.

- the DUPONT user composes on the keyboard of the device generating encryption keys and / or authentication codes, the public word to be taken into account, that is to say the variable information that the operating system of the computer displays on the terminal screen at the start of the session, for example: ΞESSION228A.

- the program stored in the microprocessor of the device generating encryption keys and / or authentication codes executes the algorithm for generating encryption keys, then displays on the liquid crystal display of the device the secret key of encryption obtained for the communication session, in our example the KAG5B6RPS2LF encryption key.

Conversely, the implementation by the user DURAND of the device generating encryption keys and / or authentication codes, in order to obtain the secret encryption key to decrypt the communication session is carried out according to the steps:

- the DURAND user dials the secret code recorded in the memory of his device, which generates encryption keys and / or authentication codes in order to unlock the operation of the device.

- the message IDENTIFYING? is displayed on the liquid crystal display of the device generating encryption keys and / or authentication codes. - the user DURAND dials the identifier of the requestor of the communication session. In our example, it composes, using the keyboard of the device generating encryption keys and / or authentication codes, the DUPONT identifier. - the message PUBLIC WORD? is displayed on the liquid crystal display of the device generating encryption keys and / or authentication codes.

- the DURAND user composes on the keyboard of the device generating encryption keys and / or authentication codes, the public word to be taken into account, that is to say the variable information that the operating system of the computer displays on the screen of its terminal, in the example: SESSION228A. the program stored in the microprocessor of the device for generating encryption keys and / or authentication codes executes the algorithm for generating encryption keys, then displays the secret encryption key on the liquid crystal display of the device allowing to decrypt the communication session, in our example the encryption key KAG5B6RPS2LF.

In this second example, it can also be seen that the method of managing encryption keys and / or authentication for a symmetric cryptography system with the device generating encryption keys and / or authentication codes eliminates the step which consists of to be transmitted by a secure channel to the partner of the session communication, the secret encryption key chosen for this encrypted session.

One can also imagine that the PUBLIC WORD necessary for the execution of the algorithm for generating encryption keys and / or authentication codes, for example the public word CHARLEMAGNE, could be communicated by telephone by the user. DUPONT to the user DURAND. Indeed, this is public information, the interception of which by an adversary does not make it possible to determine the encryption key which will be used to encrypt and then decrypt the communication session.

The encryption key management and / or authentication method for symmetric cryptography system uses a device for generating encryption keys and / or authentication codes, as shown in FIG. 1, for its implementation. However, a complementary and advantageous characteristic of the method of managing encryption keys and / or authentication for a symmetric cryptography system consists in that the device generating encryption keys and / or authentication codes can be produced with media. different. For example, the logic used for the device generating encryption keys and / or authentication codes can be transcribed in software. With the ultimate aim of being executed by a general computer, or by a specialized computer, this software can itself be recorded in one of the following media:

- a specialized electronic component such as a RAM or EPROM or EEPROM memory or even a memory of a future technology.

- a magnetic medium, for example a personal computer diskette in the standard format of 5 1/4 inches, 3 1/2 inches, or 2 1/2 inches, or a future standard. - an optical type support for personal computer, a photographic type support, for example a laser card,

- a microcomputer,

- a microcircuit card (memory card), - a new support for future technology, etc.

Indeed, from a functional point of view, what is important for the device generating encryption keys and / or authentication codes is its capacity to preserve the content of the forty-five or two hundred and fifty-six matrices of the table used as input to an encryption key generation algorithm.

However, from the user's point of view, the operating mode, which presides over the implementation of the media, remains identical to that of the device generating encryption keys and / or authentication codes, which is transposed in its entirety. .

It is also obvious that any method of managing encryption keys and / or authentication, whether or not implemented by a device generating encryption keys and / or authentication codes, would be deemed to be carried out in the same spirit as that of the invention, and therefore would not depart from the scope of the said invention, if one or more of the technical specifications were modified by: the quantity of digital matrices kept in the specialized table, the size of the digital matrices kept in the specialized table, - the operating mode of the algorithm for dynamic generation of encryption keys and / or authentication codes,

- the number of elements (IDENTIFIER (S), VAR = PUBLIC WORD (S)) taken into account in the algorithm for generating encryption keys and / or authentication codes, - the nature of the elements (IDENTIFIER (S), VAR = PUBLIC WORD (S)) taken into account in the algorithm for generating encryption keys and / or authentication codes, ^" - the presentation sequence elements taken into account in the algorithm for generating encryption keys and or authentication codes,

- the characteristics ^" of the processing relating to the display of the result (the encryption key generated), The invention proposes a method for managing encryption keys and / or authentication for symmetric cryptography system and a key generator device encryption and / or authentication codes for implementing the process, acceptable to all and which, due to the perfect autonomy of the device generating encryption keys and / or authentication codes, does not present any difficulties particular for integrating it into existing symmetric cryptographic systems or for implanting it in new products. The encryption key management and / or authentication method for symmetric cryptography system and the encryption key generator device and / or authentication codes for implementing the method, makes it simple, secure and inexpensive to generate the keys encryption and / or authentication codes required in the context of the implementation and operation of a symmetric cryptography system.

The method for managing encryption keys and / or authentication for a symmetric cryptography system and the device for generating encryption keys and / or authentication codes for implementing the method relates to the security level cryptology means. Student.

Claims

1 - Method of authentication and / or management of encryption keys for a symmetric cryptography system characterized in that it consists of carrying out the following steps:

- the initial communication, by a common authority to the entities likely to exchange encrypted information, of a private key Fi (arg) = F (cs; UTILi _; arg) constituted by a bijective function, configured specifically for each of the UTILi recipients , the parameter being constituted by public information UTILi linked to said recipient, then, at the time of each transaction,

- By the user sending the data: a) Construct a sequence CLEi = Fi (UTILj; VAR) which is the result of the private key of the sending user applied to the argument formed by the public name UTILj of the recipient user encrypted data, and a public VAR variable; b) to transmit to the recipient user the CLEi sequence _;

- By the user receiving the data: c) calculating the key CLEj = Fj (UTILi; VAR) which is the result of the private key of the recipient user applied to the argument formed by the public name UTILj of the user sender, and the public variable VAR; d) check 1 'identitée between CLEJ _e t Clei.

2 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to claim 1 characterized in that the UTIL parameter is constituted by public information identifying its owner unique in the organization comprising the users likely to communicate, such as their email address. 3 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to claim 1 or 2 characterized in that the variable VAR is a public random variable.

4 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to any one of the preceding claims, characterized in that the public key F (cs; UTILi _; arg) is a matrix function parameterized by the parameter UTILi, delivering a character string depending on the argument arg, said matrix being defined so that F (es; UTILi _; UTILj; VAR) = F (es; UTILj _; UTILi; VAR).

5 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to any one of the preceding claims, characterized in that the key F (cs; UTILi _; UTILj; VAR) is intended for authentication. of the UTILj entity by the UTILi entity.

6 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to claim 5 characterized in that the function F (cs; UTILi; UTILj; VAR) is a matrix formed by forty-five or two one hundred and fifty-six digital matrices (respectively four or eight groups of two, three or four digits) recorded in the device generating encryption keys and / or authentication codes.

7 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to any one of the preceding claims, characterized in that it consists, for managing the encryption keys necessary for the encryption and decryption operations sensitive computer data, during the transmission to third parties, by carrying out the following steps:

By the user sending the computer data: a) Build a character string of variable size, consisting of the following information:

- UTIj, identifier of the user receiving the encrypted data.

- VAR, public name assigned to the computer data to be encrypted, b) Have an encryption key produced, by the algorithm for generating encryption keys and / or authentication codes which is recorded in the device generating the encryption keys and / or authentication codes, by exploiting:

- the character string constructed in step a),

- UTI_i, identifier of the sending user, coming from the specialized memory of the device generating encryption keys and / or authentication codes. through :

- the function F (cs; UTILi _; UTILj; VAR) c) Display, on the liquid crystal screen of the device generating encryption keys and / or authentication codes, the encryption key resulting from the processing carried out at 'step b). d) Encrypt the computer data with the specialized encryption / decryption software of the cryptographic system, by communicating to it as a parameter the encryption key displayed in step c) by the device generating encryption keys and / or code authentic ication.

By the recipient user of the encrypted computer data: e) Construct a character string of variable size, consisting of the following information:

- UTIi, identifier of the sending user. - VAR, public name assigned to encrypted computer data; f) Have an encryption key produced by the algorithm for generating encryption keys and / or authentication codes which is recorded in the device generating encryption keys and / or authentication codes, by using:

- the character string constructed in step e),

- UTI j, identifier of the recipient user, coming from the specialized memory of the device generating encryption keys and / or authentication codes. through :

- function F (es; UTILi _; UTILj; VAR), g) Display, on the liquid crystal screen of the device generating encryption keys and / or authentication codes, the encryption key resulting from the processing carried out at step f). h) Have the encrypted computer data decrypt with the specialized encryption / decryption software of the cryptographic system, by communicating to it as a parameter the encryption key displayed in step g) by the device generating encryption keys and / or d codes. 'authentication.

8 - Method for managing encryption keys and / or authentication for a symmetric cryptography system according to claim 7 characterized in that step a) relating to the construction of the character string of variable dimension, is carried out by a manual entry operation performed by the user using the keyboard keys. of the device generating encryption keys and / or authentication codes, successively entering the alphanumeric and special characters corresponding to the information: - UTIi, identifier of the sending user,

- PUBLIC NAME assigned to computer data. 9 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to claim 7 characterized in that step b) relating to the generation of the encryption key by the specialized algorithm recorded in the device for generating encryption keys and / or authentication codes.

- research, by exploring the forty-five or two hundred and fifty-six digital matrices of the table recorded in the device generating encryption keys and / or authentication codes, the matrix corresponding to each character (by exploiting the character string from left to right and character by character) of the character string resulting from step a), - then chain the products of each matrix obtained, using an arithmetic based on the largest prime number of two , three or four digits, depending on the content of the matrixes of the table recorded in the device generating encryption keys and / or authentication codes.

The result obtained is then processed by:

- the standardized DES (Data Encryption Standard) algorithm, or any other algorithm,

- then by a routine in order to translate, according to the configuration of the device generating encryption keys and / or authentication codes, encryption keys which can be according to the user's choice: numeric, alphabetical, alphanumeric, hexadecimal, in the form of three-character syllables.

10 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to claim 7 characterized in that step e) relating to the construction of the character string of variable dimension, is carried out by a manual entry operation performed by the user using the keys on the keyboard of the encryption key generator device and / or authentication codes, successively entering the alphanumeric and special characters corresponding to the elements:

- UTIj, identifier of the recipient user,

- PUBLIC NAME assigned to computer data.

11 - Method for managing encryption keys and / or authentication for symmetric cryptography system according to claim 7 characterized in that step f) relating to the generation of the encryption key by the specialized algorithm recorded in the device for generating encryption keys and / or authentication codes: - research, by exploring the forty-five or two hundred and fifty-six digital matrices of the table recorded in the device for generating encryption keys and / or code authentication, the matrix corresponding to each character (by exploiting the character string from left to right and character by character) of the character string resulting from step e),

then chain the products of each matrix obtained, using an arithmetic based on the greatest prime number of two, three or four digits, depending on the content of the matrixes of the table recorded in the device generating encryption keys and / or authentication codes, the result obtained then being processed by: the standardized DES (Data Encryption Standard) algorithm, or any other equivalent algorithm,

- then by a routine in order to produce, according to the configuration of the device generating encryption keys and / or authentication codes, encryption keys which can be according to the user's choice: numeric, alphabetical, alphanumeric, hexadecimal, in the form of three-character syllables. 12 - Device for generating encryption keys and / or authentication codes, of the type comprising a keyboard (1), a display screen (2), a microprocessor (3) in which a specific program is loaded, responsible for manage all the functions of the device generating encryption keys and / or authentication codes and execute the specialized algorithm for generating keys and / or authentication codes, for implementing the method according to the at least one of the preceding claims, characterized in that it further comprises a memory (4) in which the code F (es; UTIi; arg) is kept which is specific to each device generating encryption keys and / or codes authentication, this code being recorded during the manufacture of the equipment and cannot be modified by the user, a memory (5) in which is kept a UTIi identification code assigned to each user, this code being recorded during the manufacturing of the material and cannot be modified by the user, but can be modified by a manager who has the specific code corresponding to the device generating encryption keys and / or authentication codes.

13 - Device generating encryption keys and / or authentication codes according to claim 12 characterized in that it further comprises a memory (6) in which is kept a secret code modifiable by the user, a module memory (7) in which the key F (es; UTIi; arg) is stored, consisting of forty-five or two hundred and fifty-six digital matrices (respectively four or eight groups of two, three or four digits) corresponding to the matrices of l key generation algorithm, this information initiated during the manufacture of the memory module being accessible by the microprocessor of the device generating encryption keys and / or authentication codes and being able to be modified by a specially authorized user, i.e. having:

. specific code corresponding to the device for generating encryption keys and / or authentication codes, the secret code kept in the device for generating encryption keys.

14 - Device generating encryption keys and / or authentication codes according to claim 12 or 13 characterized in that a specialized function key is used to direct the program loaded in the microprocessor to the instruction sequence responsible for managing the functional unit intended to generate an encryption key.

15 - Device generating encryption keys and / or authentication codes according to claim 12 or 13 characterized in that a specialized function key allows to direct the program loaded in the microprocessor to the instruction sequence responsible for managing the functional unit intended to generate an authentication code.

16 - Device for generating encryption keys and / or authentication codes according to claim 12 or 13 characterized in that the function key referenced J makes it possible to trigger the execution of the program loaded in the microprocessor in order to generate a key encryption and / or authentication code.

17 - Device for generating encryption keys and / or authentication codes according to any one of claims 12 to 16 characterized in that the encryption key and / or the authentication code depends on a computerized processing method algorithmic of a character string, which is executed in the microprocessor of the device generating encryption keys and / or authentication codes. 18 - Device for generating encryption keys and / or authentication codes according to any one of claims 12 to 17 characterized in that the character string which makes it possible to obtain the encryption key by executing the algorithm for generating encryption keys and / or authentication codes is composed of the information:

- IDENTIFIER of the sending user, - PUBLIC NAME assigned to the computer data.

- IDENTIFIER of the recipient user,

- TABLE of forty-five or two hundred and fifty-six digital matrices recorded in each device generating encryption keys and / or authentication codes,

19 - Device generating encryption keys and / or authentication codes according to any one of claims 12 to 17 characterized in that the character string which makes it possible to obtain the authentication code by executing the The algorithm for generating encryption keys and / or authentication codes is made up of information: - IDENTIFIER of the sending user,

- value of the public variable VAR,

- IDENTIFIER of the recipient user,

- TABLE of two hundred and fifty-six digital matrices recorded in each device generating encryption keys and / or authentication codes,

20 - Device for generating encryption keys and / or authentication codes according to any one of claims 12 to 19 characterized in that the specialized algorithm for generating encryption keys and / or authentication codes, to exploit the character string:

- search, in the forty-five or two hundred and fifty-six digital matrices of the table recorded in the device generating encryption keys and / or authentication codes, the matrix corresponding to each character (by exploiting the character string of left to right and character by character),

- then chain the products of each matrix - obtained, using an arithmetic based on the largest prime number of two, three or four digits, depending on the type of matrix of the table recorded in the device generating encryption keys and / or authentication codes, the result obtained is then processed by:

- then by a routine in order to produce, as a function of the configuration of the device generating encryption keys and / or authentication codes, encryption keys and / or authentication codes which may be according to the choice of the user: numeric, alphabetical, alphanumeric, hexadecimal, in the form of three-character syllables.