METHOD FOR MANAGING A USER PARTICIPATING IN A GROUP COMMUNICATION

Abstract

The invention relates to a method for managing a user (13) in a group communication, said group communication comprising a plurality of other users (11), the user (13) and the plurality of other users (11) being able to communicate securely with each other in said group communication using a symmetric encryption key (KS). The management method comprises a step (E5) of receiving an exclusion request (ReqExclu) from the user (13), said user to be excluded, and a step (E8) of transmitting to the other users (11) a new symmetric encryption key (New KS) and a notification (I-message) for the use of said new symmetric encryption key (New KS) in place of the symmetric encryption key (KS) used before receiving the exclusion request from user (13). Figure for the abstract: Fig. 1

Description

Title of the invention: Method for managing a user participating in a group communication Technical field

[0001] The present invention lies in the field of secure telecommunications. More particularly, it addresses the issues of authentication, confidentiality and integrity of critical communications of the intervention group type of protection services, such as civil protection services. Prior art

[0002] During an event, such as an attack, a natural disaster or a mass accident, different intervention groups may be in action to provide assistance to the victims (firefighters, law enforcement, emergency medical services, civil protection, etc.). Intervention operations require strong assurance in terms of security, availability and implementation time, and each of the intervention groups has the means to dynamically establish secure exchange channels specific to each group. By exchange channels, we understand the addressing parameters such as IP (Internet Protocol) addressing and the connection functions such as the Push-to-Talk speech controllers commonly used in intervention groups. The terminals used can be managed in a pool, that is to say that the user takes a free terminal at the time of his mission, for example, a firefighter leaving for the intervention site.The initial secret elements are carried not by prior enrollment but by a user authentication procedure. This procedure can be multi-factor, that is to say, comprising several elements of proof, including, for example, the presentation of a contactless smart card held by the user. Therefore, a flexible mechanism for establishing group communications is required which guarantees the identity and authentication of the actors and which maintains the integrity and confidentiality of the exchange channels.

[0003] The ETSI 3GPP standard (for "European Telecommunications Standards Institute" in English and "3rd Generation Partnership Project" in English) is a standard that defines standards for critical services provided on 4G public communications networks and beyond. This standard is based on a key distribution mechanism called MIKEY-SAKKE described by the RFCs (for "Request For Comments" in English) of 1TETF. This mechanism is based on the properties of elliptic curve cryptographic techniques and in particular the principles of asymmetric encryption keys called Identity-based Encryption or IBE where the public part of the pair is deduced from the identity of the holder of the private part.

[0004] The major drawback in the 3GPP standard is the difficulty in revoking IBE asymmetric encryption key pairs since the public part is by construction directly deduced from the identity of the holder of the private part without the possibility for the user of said public part to detect the revocation of the key pair. This revocation may be due to the compromise of the private part or the banishment of the holder of this private part. By compromise or banishment, we understand that a user of one of the communication networks becomes malicious and provides erroneous information that can disrupt all rescue operations. The user is considered malicious, for example, when the terminal used falls into the hands of a harmful person external to the intervention group who provides false information.It is therefore necessary to change all the keys of an intervention group to exclude the malicious user. This change, provided for by the standard, consists of modifying the parameters of a security domain. However, such a change significantly disrupts the service by generating communication interruptions during encryption key changes.

[0005] There is therefore a need to limit the unavailability of critical services during a procedure for excluding a malicious user in a communications network. Presentation of the invention

[0006] The present invention aims to at least partially address this need.

[0007] More particularly, the present invention aims to improve the revocation security keys when excluding a user.

[0008] For this purpose, a first object of the invention relates to a method for managing a user in a group communication. Said group communication comprises a plurality of other users. The user and the plurality of other users are able to communicate with each other securely in said group communication using a symmetric encryption key. The management method comprises a step of receiving a request to exclude the user, called the user to be excluded, a step of determining the other users able to intervene in said group communication, a step of generating a new symmetric encryption key.The method also comprises a step of transmitting to the other users the new symmetric encryption key and a notification for the use of said new symmetric encryption key instead of the symmetric encryption key used before receiving the user's exclusion request, said new symmetric encryption key not being transmitted to the user to be excluded.

[0009] The method thus makes it possible to revoke, in a simple and practical manner, the key of Symmetric encryption used in the communications network. A new symmetric encryption key is transmitted to network users except for the user to be excluded. The malicious user will be effectively excluded from all communications with other network users. The other users are then active authorized users. Establishing group communication will allow these other users in action on the ground to provide the exchange channels.

[0010] In a particular embodiment, the user to be excluded participates in several group communications and the method comprises a step of determining the group communications in which the user to be excluded participates. For each group communication in which the user to be excluded participates, the method comprises a step of determining the other users able to participate in said group communication and a step of generating a new symmetric encryption key. The method also comprises a step of transmitting to the other users the new symmetric encryption key and a notification for the use of said new symmetric encryption key instead of the symmetric encryption key used before receiving the user's exclusion request, said new symmetric encryption key not being transmitted to the user to be excluded.

[0011] The method thus makes it possible to exclude the malicious user from all of the exchange channels in which he or she intervenes. Indeed, the malicious user intervenes in several secure group communications and therefore has knowledge of several symmetric encryption keys which, as a result, become compromised.

[0012] In a particular embodiment, the symmetric encryption keys having a predetermined validity period, the new symmetric encryption key has a validity period identical to that of the symmetric encryption key that it replaces.

[0013] The new symmetric encryption key thus replaces the original symmetric encryption key over time.

[0014] In a particular embodiment, the new symmetric encryption key is compatible with an AES algorithm.

[0015] In a particular embodiment, prior to the step of transmitting the new symmetric encryption key, the new symmetric encryption key is encrypted using a public asymmetric encryption key to form an encrypted symmetric encryption key. The encrypted symmetric encryption key is capable of being decrypted by one of the other users holding a private asymmetric encryption key associated with said public asymmetric encryption key.

[0016] In a particular embodiment, a key pair comprising the public asymmetric encryption key and the private asymmetric encryption key is specific to each user of the other users.

[0017] In a particular embodiment, the key pair is generated from an identifier of the user of the other users.

[0018] In a particular embodiment, the method comprises a step of determining a security domain in which all or part of the public asymmetric encryption key is produced from a hash function of the user identifier and a sequence number.

[0019] The use of a sequence number facilitates the management of asymmetric encryption keys by a KMS management server, in particular when the logic of said KMS management server is distributed over several nodes of the communication network.

[0020] In a particular embodiment, the user and the plurality of other users communicate via a centralized 4G and / or 5G compatible radio network.

[0021] In a particular embodiment, the user to be excluded intervenes in a first group communication using a centralized radio network and intervenes in a second group communication using a decentralized radio network, said user to be excluded being the initiator of establishing said second group communication, the exclusion of said user results in a release of this second group communication as soon as the other users intervening in the second group communication can access the centralized radio network.

[0022] The user to be excluded is the initiator of establishing the second group communication secured by a symmetric encryption key. He was able to securely provide the users of the second group communication with the symmetric encryption key using the IBE asymmetric public keys of the other users and a signature by his IBE asymmetric private key. The exclusion of the user to be excluded results in the release of this second group communication as soon as the other users can access the services of the centralized radio network to verify that this initiator has not been banned.

[0023] Another object of the invention relates to a key management server for transmitting a symmetric encryption key to users in a group communication in order to communicate securely in said group communication. The key management server comprises the following elements: a central data processing unit, an input / output interface, an asymmetric encryption key generation module, a symmetric encryption key generation module, a database listing the users belonging to the communication group, said elements being configured to implement the steps of a method for managing a user to be excluded from the group communication according to the invention.

[0024] In a particular embodiment, the user to be excluded intervenes in a plurality of group communications, said database being able to list the users participating in said plurality of group communications.

[0025] In a particular embodiment, the management server is distributed over several nodes of a communication network.

[0026] The present invention will be better understood on reading the detailed description of embodiments taken as non-limiting examples and illustrated by the appended drawings in which:

[0027] [Fig-1] [Fig.l] illustrates the steps of a management method in a communication group;

[0028] [Fig.2] [Fig.2] illustrates a first embodiment in which the method of management of [Fig.l] is implemented in group communication;

[0029] [Fig.3] [Fig.3] illustrates a second embodiment in which the method of management of [Fig.l] is implemented in two group communications;

[0030] [Fig.4] [Fig.4] illustrates a third embodiment in which the method of management of [Fig.l] is implemented in two group communications, one of which operates according to a decentralized radio network;

[0031] [Fig.5] [Fig.5] details the different elements of a key management server for the implementation of the steps of the management process of [Fig.l].

[0032] The invention is not limited to the embodiments and variants presented and other embodiments and variants will become clear to those skilled in the art.

[0033] [Fig.2] illustrates a group communication GC1 comprising a plurality of users 10, 11, 12, 13. These users 10-13 communicate with each other securely via a centralized radio network represented in the form of an antenna 1. This centralized network is, for example, a 4G and / or 5G compatible network.

[0034] [Fig.l] illustrates the steps of a management method in a group communication. These steps are carried out between a control server Control, a user 13 becoming malicious, a KMS key management server and another user 11.

[0035] The control server is adapted to authorize / prevent access of users 10-13 to secure group communications.

[0036] Users 11 and 13 have terminals adapted to participate in group communication via the communication network. In the remainder of the description, it is understood that user and user terminal are synonymous.

[0037] The KMS key management server is adapted to generate and deliver symmetric encryption keys Ks to the different users of a group communication. This KMS management server is physically centralized on a node of the communication network. Alternatively, the logic of the KMS management server is distributed over several nodes of the communication network so as to have on each of these nodes an operation seen by the users identical to the case where the KMS management server is physically centralized.

[0038] In a first authentication step E1, the user 13, who is not yet identified as being malicious, seeks to be contactable by secure communications. For this, an authentication request Reqid is transmitted to the control server Control. This authentication request Reqident includes the identification ID13 of the user 13. In return, the control server Control provides in a response R epid an OIDC (for “Open ID Connect” in English) token to the user 13.

[0039] In a second step E2, the user 13 seeks to obtain a private asymmetric encryption key KAPriv in order to be able to securely exchange with other users symmetric encryption keys previously allocated to a secure communication. To do this, the user 13 sends a ReqKA request to the KMS key management server. This ReqKA request comprises a public asymmetric key KAPub and the OIDC token. The public asymmetric key KAPub is associated with the user 13. In a preferred embodiment, the public asymmetric key KAPub corresponds to the identifier ID13 of the user 13. In return, the KMS server sends a RepKA response comprising the private asymmetric key KAPriv associated with the public asymmetric key KAPub.

[0040] In a third step E3, the user seeks to join a group communication GC1 and therefore needs a symmetric encryption key Ks. To do this, the user 13 sends a request ReqKs to the key management server KMS. This request ReqKs includes the identifier ID13 of the user 13. In return, the KMS server sends a response ReqKs including the symmetric encryption key Ks. This symmetric encryption key Ks has been previously encrypted using the public asymmetric encryption key KAPub associated with the user 13. This user 13 is thus able to decrypt the encrypted symmetric encryption key using the private asymmetric encryption key KAPriv that he possesses.

[0041] In a fourth step E4, the user 13 communicates securely with the other user 11 using the symmetric encryption key Ks. Thus, all of the messages Mcrypt sent by the user 13 to the other user 11 are encrypted by the symmetric encryption key Ks. In the same way, all of the messages sent by the other user 11 to the user 13 are encrypted by the symmetric encryption key Ks. It will be noted that the other user 11a previously received the same symmetric encryption key Ks. in a step E'3. It will also be noted that the symmetric encryption key Ks has a limited duration, so that a new symmetric encryption key Ks is automatically generated and transmitted to the user 13 and to the other user 11 when the symmetric encryption key Ks expires.

[0042] In the case where it is identified that the user 13 is a malicious user, the management method comprises a step E5 of receiving an exclusion request Req Exdu of user 13 by the KMS server. This request is sent by the control server Control. This control server Control has identified the maliciousness of user 13, for example, by analyzing the user's communications. Alternatively, the control server Control has been notified by another user of a problem concerning user 13. The exclusion request ReqExciu includes the identifier ID13 of user 13.

[0043] In a step E6 (not shown in [Fig.l]), the KMS server determines the other users 10, 11, 12 involved in the group communication GC1 because, in a step E'3, the KMS server has given them a symmetric encryption key Ks

[0044] In a step E7 (not shown in [Fig.l]), the KMS server generates a new symmetric encryption key New Ks.

[0045] In a step E8, the KMS server transmits to the other user 11 the new symmetric encryption key New Ks as well as a notification I_Message of use of said new symmetric encryption key New Ks instead of the symmetric encryption key Ks. This new symmetric encryption key New Ks is transmitted in encrypted manner using the public asymmetric encryption key associated with the user 11. In the same way, this new symmetric encryption key New Ks is transmitted encrypted to all the other users 10, 12, from the respective public asymmetric encryption keys of these users. However, the new symmetric encryption key New Ks is not transmitted to the user 13, which automatically excludes him from any communication with the other users 10, 11, 12.

[0046] [Fig.5] details the different elements of the KMS key management server. This server includes: - a central data processing unit 100; - an FO input / output interface; - an MA module for generating asymmetric encryption keys; - a Ms module for generating symmetric encryption keys; - a BD database.

[0047] The central data processing unit 100 is adapted to process the data in the KMS server. This central unit is connected to the input / output interface I / O, to the key generation module MG, and to the database BD.

[0048] The input / output interface I / O is adapted to receive and transmit messages. This input / output interface I / O is thus able to receive the request ReqKA for obtaining the private asymmetric encryption key KAPriv, the request ReqKs for obtaining the symmetric encryption key Ks, the exclusion request ReqExciu of the user 13. The input / output interface I / O is also able to transmit the private asymmetric encryption key KAPriv, the symmetric encryption key Ks as well as the new symmetric encryption key New Ks.

[0049] The asymmetric encryption key generation module MA is adapted to generate private / public asymmetric encryption key pairs. These key pairs enable secure distribution of symmetric encryption keys.

[0050] The generation module Ms is adapted to generate symmetric encryption keys Ks, New Ks. These encryption keys are generated when a new user enters the communication group Gcl, when the symmetric encryption key is renewed, or when a user is requested to be excluded from the group communication Gcl. Preferably, the symmetric encryption keys are compatible with an AES algorithm (for “Advanced Encryption Standard” in English).

[0051] The BD database is adapted to list active users who have requested symmetric encryption keys to join group communications. It is thus possible to trace a possible compromise and revoke potentially compromised keys.

[0052] [Fig. 3] illustrates a second embodiment in which the user to be excluded 13 intervenes in a first group communication GC1 and in a second group communication Gc2. As already specified, the first group communication GC1 comprises users 10 to 13. The second group communication Gc2 comprises users 11, 13, 14 and 15. Users 11 and 13 are therefore common to both communications Gc1, Gc2. The different users 10-15 communicate with each other securely via the centralized radio network represented in the form of antenna 1.More precisely, users 10 to 13 communicate with each other securely using a first symmetric encryption key provided by the KMS server at the time each of the users wanted to join the GCL group communication. Users 11, 13, 14 and 15 communicate with each other securely using a second symmetric encryption key provided by the KMS server at the time each of the users wanted to join the Gc2 group communication. Users 11 and 13 common to both communications Gcl, Gc2 are therefore in possession of two symmetric encryption keys.

[0053] In the case where the KMS server receives an exclusion request ReqExciu from the user 13. The management method comprises a step E'5 of determining the group communications in which the user to be excluded intervenes. In the case of the embodiment of [Fig.3], the user to be excluded 13 intervenes both in the first group communication GC1 and in the second group communication Gc2. The management method then comprises for each group communication Gc 1, Gc2 in which the user to be excluded intervenes: - a step E'6 of determining the other users involved in said communication group communication; - a step E'7 for generating the new symmetric encryption key New Ks; - a step E'8 of transmitting to the other users the new symmetric encryption key and a notification I_Message' for the use of said new symmetric encryption key instead of the symmetric encryption key used before receiving the user's exclusion request, said new symmetric encryption key not being transmitted to the user to be excluded.

[0054] The method then generates the creation of two new symmetric encryption keys New Ks, one for each group communication Gcl, Gc2.

[0055] It will be noted that in this embodiment, the database BD of [Fig.5] is capable of listing the users 10-16 involved in the two group communications Gcl, Gc2.

[0056] [Fig. 4] illustrates a third embodiment of the invention. In this embodiment, the user to be excluded 13 intervenes in a first group communication GC1 using a centralized radio network and in a second group communication Gc2 using a decentralized radio network, also called an ad hoc network in which the users are autonomous and do not have access to the KMS server. This user 13 is here at the initiative of the second group communication and was able to provide an encryption key to the other users who do not have access to the KMS server via the centralized radio network. This key provision was able to be done securely thanks to the encryption of the symmetric encryption keys by the public key IBE of each user.The exclusion of user 13 then results in the release of each of the other users 14, 15, 16 from the second group communication Gc2 as soon as they regain connectivity with the centralized radio network and can verify with the KMS server the validity of the public key IBE of the initiator of the second group communication which protected the symmetric key.

[0057] It will be noted that the method can be applied to group communications limited to two users, an initiating user and a requested user, the initiating user securely transmitting by the asymmetric keys IBE the symmetric encryption key of the communication called point-to-point communication.

[0058] The invention makes it possible to implement the following steps at the level of the KMS key management server: - a distribution of users into one or more security domains, a user being able to belong to several security domains and a security domain being able to take into account a connection mode; - the creation of lists of active users by secure communication to whom a symmetric encryption key has been given; - the generation and storage of IBE asymmetric encryption key pairs for all security domains so that each user can have one or more pairs of asymmetric encryption keys. In a sub-step, it is possible to determine a security domain where the construction of the public parts of IBE asymmetric encryption keys is done from a hash function on the user's identity and a sequence number generated exclusively by the KMS server. This security domain will allow strong security of users in connected mode to the radio infrastructure (centralized radio network); - the allocation of one or more pairs of asymmetric IBE encryption keys to each user who opens a session with authentication; - the generation of symmetric encryption keys valid for a given period of time for each group communication with encryption of said symmetric encryption keys by a public asymmetric key; - the creation of lists per user of symmetric encryption keys provided since the start of an authenticated session; - the exploitation of these lists to revoke symmetric encryption keys when the user is blacklisted (compromised user); - the revocation of a symmetric encryption key by generating a new symmetric encryption key whose validity period covers the validity period of the revoked key; - notification of the revocation of the key to each affected user.

[0059] In the case where the KMS server logic is distributed in several nodes of the network, the sequence number used for the construction of the public part of an IBE key pair for a user is shared by all the nodes. The symmetric encryption keys are shared between the nodes involved in a group communication by taking the same principle of distribution and secure storage as for the users. Each node has a secure dedicated structure which encapsulates and encrypts the shared symmetric encryption key.

[0060] The invention is thus based on: - IBE asymmetric encryption keys dedicated to the distribution and storage of certain symmetric encryption keys where a strong coupling between the two types of keys allows simple and immediate operations of revocation of group keys, banning of participants and all actions controllable from a KMS server; - a division into security domains taking into account the users' connection mode. A user changes security domain depending on the connection mode they use. This mode can include ad hoc mode and the Radio infrastructure connection mode. The security domain is then a subset of participants and connection mode; - a logically centralized KMS server but whose secure algorithms are distributable on the Radio Access Network.

[0061] The invention then provides the following advantages: - the process allows symmetric encryption keys to be revoked in the event of a symmetric encryption key being compromised or a participant being banned; - the process follows strong authentication of a user and must ensure the integrity and confidentiality of the information that it exchanges mainly with groups of stakeholders. This process has both strong flexibility and a high degree of security; - the process allows backward compatibility with a 3GPP standard; - the process can be done without manual action by users or service administrators; - the process is in long-term persistence on terminal equipment; - the process is easily integrated with a strong authentication device based on tokens; - the method is compatible with different operating modes, for example, a mode connected to a radio infrastructure or an ad hoc mode where the user groups are autonomous; - the process is compatible with recording and playback functions; - the process is compatible with the use of identity federation and divisions into multiple security domains; - the method is compatible with tactical bubble deployment situations where KMS key servers can be easily deployed at the edge of the network; - the simple sharing of an order number between edge nodes makes it possible to manage in a distributed manner the generation of IBE asymmetric encryption keys necessary for the distribution of symmetric encryption keys in a tactical bubble environment; - the process allows for an immediate effect to repudiate an intervener who could constitute a threat to the smooth running of a mission, which avoids any butterfly effect; - the process makes it possible to limit the time during which security flaws can be exploited; - the key management server manages both communication groups and IBE keys.

Claims

Claims

1. A method of managing a user (13) in a group communication (Gcl), said group communication comprising a plurality of other users (10, 11, 12), the user (13) and the plurality of other users (10, 11, 12) being able to communicate with each other securely in said group communication (Gcl) using a symmetric encryption key (Ks), said management method comprising - a step (E5) of receiving an exclusion request (ReqExciu) from the user (13), called the user to be excluded, said exclusion request (Req Exciu) having been sent by a control server (Control) to a key management server (KMS); - a step (E6) of determining the other users (10, 11, 12) able to intervene in said group communication; - a step (E7) of generating a new symmetric encryption key (New Ks); - a step (E8) of transmitting to the other users (10, 11, 12) the new symmetric encryption key (New Ks) and a notification (I-message) for the use of said new symmetric encryption key (New Ks) instead of the symmetric encryption key (Ks) used before receiving the exclusion request from the user (13), said new symmetric encryption key (New Ks) not being transmitted to the user to be excluded (13), said steps of determination (E6), generation (E7) and transmission (E8) being carried out by the key management server (KMS); according to which prior to the step of transmitting the new symmetric encryption key (New KS), said new symmetric encryption key (New KS) is encrypted using a public asymmetric encryption key (KAPub) to form an encrypted symmetric encryption key, said encrypted symmetric encryption key being capable of being decrypted by one of the other users holding a private asymmetric encryption key (KAPriv) associated with said public asymmetric encryption key (KAPub); according to which a key pair comprising the public asymmetric encryption key (KAPub) and the private asymmetric encryption key (KAPriv) is specific to each user; whereby the key pair is generated from an identifier of the user; and said method comprises a step of determining a security domain in which all or part of the public asymmetric encryption key (KAPub) is produced from a hash function of the user identifier and a sequence number.

2. Management method according to claim 1, in which the user (10-15) to be excluded intervenes in several group communications (Gcl, Gc2), said method comprises: - a step (E'5) of determining the group communications in which the user to be excluded intervenes (13); - for each group communication in which the user to be excluded participates (13): - a step (E'6) of determining the other users able to intervene in said group communication; - a step (E'7) of generating a new symmetric encryption key; - a step (E'8) of transmitting to the other users the new symmetric encryption key and a notification for the use (I-message') of said new symmetric encryption key instead of the symmetric encryption key used before receiving the user's exclusion request, said new symmetric encryption key not being transmitted to the user to be excluded (13).

3. Management method according to any one of claims 1 to 2, in which, the symmetric encryption keys having a predetermined validity period, the new symmetric encryption key (New Ks) has a validity period identical to that of the symmetric encryption key (Ks) which it replaces.

4. Management method according to any one of claims 1 to 3, in which the new symmetric encryption key (New Ks) is compatible with an AES algorithm.

5. Management method according to any one of claims 1 to 4, in which the user (13) and the plurality of other users (10, 11, 12, 14, 15) communicate via a centralized 4G and / or 5G compatible radio network.

6. Management method according to any one of claims 1 to 5, in which the user to be excluded (13) intervenes in a first group communication (Gcl) using a centralized radio network and intervenes in a second group communication (Gc2) using a decentralized radio network, said user to be excluded (13) being the initiator of establishing said second group communication (Gc2), the exclusion of said user (13) results in a release of this second group communication (Gc2) as soon as the other users (14, 15, 16) involved in the second group communication (Gc2) can access the centralized radio network.

7. Management method according to any one of claims 1 to 6, in which the user to be excluded (13) intervenes in a group communication limited to two users, an initiating user and a requested user, the initiating user securely transmitting by the asymmetric keys IBE the symmetric encryption key of the communication called point-to-point communication 8. Key management server for transmitting a symmetric encryption key to users in a group communication for the purpose of communicating securely in said group communication, said key management server (KMS) comprising the following elements: - a central data processing unit (100); - an input / output (I / O) interface; - an asymmetric encryption key generation module (MA); - a module (Ms) for generating symmetric encryption keys; - a database (DB) listing the users belonging to the communication group, said elements being configured to implement the steps of a method for managing a user to be excluded from the group communication, according to any one of claims 1 to 7.

9. Management server according to claim 8, the user to be excluded intervening in a plurality of group communications (GC1, GC2), said database (BD) is capable of listing the users intervening in said plurality of group communications.

10. Management server according to any one of claims 8 or 9, wherein said management server is distributed over several nodes of a communication network.

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