Identity management process by an issuing entity in a 3GPP MCS network

Abstract

TITLE: Method for Managing Encryption by a Sending Entity in a 3GPP MCS Network. One aspect of the invention relates to a method implemented by a sending client entity within a network conforming to the 3GPP MCS standard (3rd Generation Partnership Program Mission Critical Services). The sending client entity is configured to send multiple contents intended for at least one receiving client entity within the network. The sending and receiving client entities are affiliated with the same communication group. The method comprises at least one step of generating a Group User Key Identifier (GUK-ID) by the sending client entity. The GUK-ID is specific to the communication group and is used to encrypt the content. The generation step is repeated each time a predetermined event occurs. Figure to be published with the abstract: Figure 2

Description

Title of the invention: Method for identity management by an issuing entity in a 3GPP MCS network TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of telecommunications.

[0002] The present invention relates to a method for identity management by an issuing entity in a 3GPP MCS network, and in particular making it possible to resolve security problems not resolved by the standard. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] The PMR radiocommunication standards (according to the Anglo-Saxon term "Professional Mobile Radio") TETRAPOL®, TETRA® or P25® allow the implementation of secure professional networks. These narrowband networks are national or local networks: they are implemented for example within an organization such as a company, within a country for example for communications between firefighters, law enforcement, the military, etc.

[0004] These networks are evolving towards support for broadband exchanges. The 3GPP standard governing mobile networks of the “GSM” type according to the Anglo-Saxon term “Global System for Mobile Communications” and more particularly in deployments using critical communications services defined by the 3GPP called “MCS” according to the Anglo-Saxon term “Mission Critical Services” allows these secure broadband exchanges.

[0005] The encryption of MCPTT (Mission Critical Push To Talk) or MCVideo voice media in a group communication is defined in the technical specification TS 33.180. It notably implements endpoint diversity.

[0006] Hereinafter, any Mission-Critical service defined by the 3GPP MCS standard will be called "MCX", such as the MCVideo, MCData (for "Data" in French) and MCPTT services. A "client" and a server are devices comprising at least one processor and one memory, the memory comprising instructions which, when executed by the processor, cause the user device to implement at least the actions assigned to it. Preferably, a client is a user device. Similarly, a "server" can be a user device. An "MCX client" and an "MCX server" are therefore user devices configured to implement Mission-Critical services.

[0007] When transmitting media from an MCX client, the transmitted media can be encrypted in a way that does not depend on the transmitter. In such a case, the concept of "endpoint diversity" is not implemented. On the contrary, the implementation of endpoint diversity requires the encryption of the transmitted media by a key specific to the transmitting MCX client. For this, the MCX ID identity of the user of this transmitting MCX client is used to generate a group user key identifier (GUK-ID for "Group User Key Identifier" in English). This GUK-ID identifier is used for: • encrypt a media of the SRTP stream (from the English “Secure Real-time Protocol” for “Protocol Temps Réel Sécurisé” in French) sent by the MCX client sender and • decrypt this SRTP media stream by the receiving MCX clients.

[0008] The procedures of the technical specification TS 33.180 (clause 7.4.2) require the sending MCX client to include this GUK-ID identifier in a 64-bit SRTP MKI (Master Key Identifier) ​​field transmitted with each SRTP packet. The long format (64-bit) MKI master key identifier actually includes a group master key identifier (GMK-ID) concatenated with the group user key identifier GUK-ID. To create the security association of the communication group within which the media is exchanged, a group master key (GMK) and its associated identifier (GMK-ID) are distributed to the MCX clients in the group by a group management server (GMS).

[0009] This procedure also provides the possibility, when the identity of the user of the sending MCX client (identity also called "User Sait" in English) is known to the receiving MCX clients, to reduce the SRTP MKI to 32 bits by omitting its GUK-ID component of the sender, that is to say by only including the group master key identifier GMK-ID. The group user key identifier GUK-ID is then calculated locally by the receiving MCX clients by performing an "exclusive OR" XOR operation between the known identity of the sending MCX client user ("User sait") and the group master key identifier GMK-ID. In the same way, the group master key identifier GMK-ID can be calculated from the group user key identifier GUK-ID and the known identity of the sending MCX client user ("User sait").On the other hand, the identity of the sending MCX client user cannot be obtained from the group master key identifier GMK-ID and the group user key identifier GUK-ID, in order to maintain a certain confidentiality.

[0010] The identity of the user of the sending MCX client can be obtained because it is included in the floor control messages in MCPTT voice service, messages called “Floor Control”. In MCVideo video service, this information is obtained because it is included in the transmission control messages, messages called "transmission control". In MCData service, there is no endpoint diversity in the 3GPP specifications. In MCData, however, it is possible to recover the identity of the user of the sending MCX client in the payload of SIP and / or HTTP messages. SIP is a well-known Session Initiation Protocol and HTTP (for "HyperText Transfer Protocol") is a well-known communication protocol. In MCData, this payload is end-to-end encrypted but without endpoint diversity.

[0011] In the 3GPP MCS standard, the user identity of the MCX client is transmitted in all call setup requests and in all floor requests and transmission requests.

[0012] This poses a security problem, particularly when the 3GPP MCS network extends over several security domains, because it is then possible for a receiving MCX client to identify the user of the sending MCX client via its group user key identifier GUK-ID, this identifier being used in the standard to encrypt the content sent with endpoint diversity. By "identifier" we mean the ability for a receiving client to track the user of the sending client, that is to say, when it speaks several times or communicates several times, to link all its speeches and communications to the same sending client. This principle is called "linkability" in English and allows a receiving client to obtain key information on the 3GPP MCS network and the users that compose it.It is also possible, if the receiving client knows a list of potential sending client identities, to know if the transmission comes from one of these users, by testing the different known identities.

[0013] There is therefore a need to be able to ensure, in a 3GPP MCS network, that a receiving MCX client cannot identify a sending MCX client via its group user key identifier GUK-ID while being able to decrypt the sent content encrypted with its group user key identifier GUK-ID. Summary of the invention

[0014] The invention provides a solution to the problems mentioned above, by allowing a sending client, in a 3GPP MCS network, to change user identity so that a receiving client can decrypt the transmitted content without being able to link several communications from the sending client to said sending client.

[0015] One aspect of the invention relates to a method implemented by a transmitting client entity included in a network according to the 3GPP MCS “3rd Generation Partnership Program Mission Critical Services” standard, the transmitting client entity being configured to transmit a plurality of contents intended for at least one receiving client entity included in the network, the transmitting client entity and the receiving client entity being affiliated with the same communication group, the method comprising at least one step of generation, by the transmitting client entity, of a group user key identifier GUK-ID, the group user key identifier GUK-ID being specific to the communication group and being used to encrypt the content, the generation step being repeated each time a predetermined event takes place.

[0016] Thanks to the invention, it is ensured that the entity receiving a content transmitted and encrypted by a transmitting entity is capable of decrypting the content, without being able to link the communication comprising the content to other communications of the same transmitting entity. For this, the invention comprises a random generation of a group user key identifier GUK-ID of the transmitting entity. Thus, the transmitting entity cannot be "traced", that is to say cannot be linked to its different communications so as to identify that it is a single transmitter, but the 3GPP MCS standard remains respected, in that the encryption of the content is carried out, with endpoint diversity, with the group user key identifier GUK-ID of the transmitting entity.

[0017] In addition to the characteristics which have just been mentioned in the preceding paragraphs, the method according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations: • the method further comprises the steps of: • Encryption of the content to be transmitted, the content being encrypted by the transmitting client entity, the encryption of the content being based on a master key according to the SRTP protocol (Secure Real Time Protocol), the master key comprising a group master key identifier (GMK-ID) and the generated group user key identifier (GUK-ID). • Transmission of at least one frame to the receiving entity, according to the SRTP protocol, the at least one frame comprising the encrypted content. • a plurality of frames is transmitted, each frame of the plurality of frames comprising a portion of the encrypted content, the master key being included in the header of a first frame of the plurality of frames. • the predetermined event is the start and / or end of a predetermined time interval, the group user key identifier (GUK-ID) being used to encrypt each of a plurality of contents transmitted during the predetermined time interval. • the predetermined event is the emission of new content. • the group user key identifier (GUK-ID) is randomly generated. • the communication group is an MCPTT group and the content is a voice communication or an MCVideo group and the content is a video or an MCData group and the content is a text data set or a file.

[0018] Another aspect of the invention relates to a communication network according to the 3GPP MCS “3rd Generation Partnership Program Mission-Critical System” standard, the communication network comprising at least: • an issuing client entity configured to implement the method according to the invention, • a receiving client entity configured to receive the encrypted content and the master key issued by the sending entity.

[0019] Yet another aspect of the invention relates to a computer program product comprising instructions which cause the client entity transmitting the network according to the invention to execute the steps of the method according to the invention.

[0020] Yet another aspect of the invention relates to a computer-readable medium, on which the computer program according to the invention is recorded.

[0021] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0022] The figures are presented for information purposes only and in no way limit the invention. • [Fig.l] shows a schematic representation of a network comprising entities configured to implement the method according to the invention, • [Fig.2] shows an example of implementation of the process according to the invention, • [Fig.3] shows a schematic representation of a process according to the invention, • Figures 4A and 4B show a schematic representation of a first embodiment of the method according to the invention, • [Fig.4C] shows a schematic representation of a second embodiment of the method according to the invention. DETAILED DESCRIPTION

[0023] Unless otherwise specified, the same element appearing in different figures presents a unique reference.

[0024] [Fig.l] shows a schematic representation of a network comprising entities configured to implement the method according to the invention.

[0025] In particular, the network represented in [Fig. 1] comprises a transmitting entity E configured to implement the method according to the invention, and a receiving entity R.

[0026] The network shown in [Fig.l] is a network according to the 3GPP MCS standard, that is to say it is implemented following the specifications defined by the 3GPP MCS standard.

[0027] [Fig. 3] shows a schematic representation of the method according to the invention. The method shown in [Fig. 3] is an identity management method according to the invention within the network of [Fig. 1].

[0028] The network of [Fig.l] comprises a communication group G. The transmitting entity E is affiliated with the communication group G. The receiving entity R is also affiliated with the same communication group G. The group G is an MCPTT, MCVideo or MCData communication group as defined in the state of the art.

[0029] The sending entity E and the receiving entity R may be client or server entities, participating or non-participating, or any other entity defined by the 3GPP MCS standard. The sending entity E and the receiving entity R are devices comprising at least one processor and a memory, the memory comprising instructions which, when executed by the processor, cause the processor to implement an action attributed to the entity. For example, the entities may be user devices such as mobile phones, tablets, computers, or any other device usable by a user, or may also be computers or devices having the role of server within the meaning of the 3GPP MCS standard.

[0030] The method 1 according to the invention represented in [Fig. 3] allows the transmitting entity E to dynamically modify its identity, identity which will be used to encrypt at least one content intended for the receiving entity R. For this, the transmitting entity E comprises at least one identity generation module Gen, making it possible to implement the generation step 11 of the method 1 according to the invention represented in [Fig. 3]. This module is preferably a software module, implemented by the processor of the transmitting entity.

[0031] The invention uses the following key identifiers: • Group user key identifier GUK-ID: this identifier is a key identifier specific to a user of the sending entity E and specific to the communication group G. Thus, this key can be seen as a “session key” in the SRTP protocol, as defined in RFC 3711. An identifier of this key, which does not have to remain secret, makes it possible to retrieve this key, which must remain secret. This user key is used to encrypt content in the 3GPP MCS standard in the presence of endpoint diversity. • Group master key identifier GMK-ID: This identifier is a group master key identifier specific to the communication group G. In the presence of endpoint diversity, this group master key GMK is used in combination with the group user key GUK to encrypt content as defined in point 7.4.2 of the technical specification TS 33.180. • MKI Master Key Identifier: This identifier is a master key identifier comprising, in the presence of endpoint diversity, the group user key identifier GUK-ID, and the group master key identifier GMK-ID.

[0032] The method 1 according to the invention shown in [Fig.3] comprises at least one step 11 of generating a group user key identifier GUK-ID. This group user key identifier GUK-ID is generated, according to the invention, each time a predetermined event occurs. Thus, it is not possible for a receiving entity R to link the different communications sent by the sending entity E to the same sending entity E, since its group user key identifier GUK-ID, normally fixed, is regularly modified.

[0033] For example, as shown in [Fig.2], a frame T1 will be sent comprising a content C1 encrypted with a first group user key identifier GUK-ID 1 and then a frame T2 will be sent comprising a content C2 encrypted with another group user key identifier GUK-ID2. The two frames T1 and T2 cannot be linked, by the receiving entity R, to the sending entity E since the group user key identifiers GUK-ID 1 and GUK-ID2 used to encrypt the contents C1 and C2 respectively and transmitted respectively in the frames T1 and T2 are different and not linked to the identity of the sending entity E.

[0034] Preferably, the group user key identifier GUK-ID generated in step 11 is generated randomly. The group user key identifier GUK-ID can also be generated according to a predetermined data set, the important thing being that this data is not linked to the sending entity E so as not to be able to identify it as the sender of the content encrypted with the group user key identifier GUK-ID.

[0035] The method according to the invention also comprises a step 12 of encrypting the content C included in the frame T sent to the receiving entity R. The encryption 12 of the content C is carried out by the sending entity E. The encryption is based on the group user key identifier GUK-ID generated last, i.e. during the last implementation of the generation step 11, and on the group master key identifier GMK-ID. The encryption 12 is carried out using a master key according to the SRTP (Secure Real Time Protocol) protocol in RFC3711 and according to the technical specification TS 33.180 point 7.5.1, the master key being identified by its master key identifier MKI.

[0036] The method 1 according to the invention then comprises a step 13 of transmitting at least one frame T according to the SRTP protocol, by the transmitting entity E to the receiving entity R, the frame T comprising the content C encrypted in step 12 with the group user key identifier GUK-ID generated in step 11. The frame T also comprises in the header the master key identifier MKI comprising the group user key identifier GUK-ID generated in step 11 and the group master key identifier GMK-ID. The frame T is then transmitted to the receiving entity R, which uses the information included in the master key identifier MKI and the information that it has at its disposal thanks to the topology and the context of the network to decrypt the content C.

[0037] In one variant, the encrypted content C is split into several parts and distributed and sent in a plurality of frames. In this variant, the master key identifier MKI may only be included in the header of the first frame of the plurality of frames. This saves bandwidth, while still allowing the content to be decrypted.

[0038] Step 11 is repeated each time a predetermined event occurs. Steps 12 and 13 are repeated when a content C must be transmitted. The invention only makes sense in the case of transmission of a plurality of contents C. Indeed, in the case of transmission of a single content C, the security problem does not exist.

[0039] According to the invention, the event leading to a new generation 11 can be: • the beginning or end of a predetermined time interval, or • a speech or the start of a communication.

[0040] The first case is shown in Figures 4A and 4B and the second case is shown in [Fig.4C].

[0041] Figures 4A and 4B represent a first embodiment, that is to say the case where the predetermined event is a function of a predetermined time interval. This time interval has for example a duration At, the duration of the interval being predetermined, that is to say fixed in advance by configuration, for example thanks to a parameter included in the memory of the transmitting entity E or recovered from another remote device. The predetermined interval has a duration expressed for example in seconds, minutes, hours or days.Preferably, the predetermined interval is chosen so as to limit the possibilities of identifying the same transmitting entity E, therefore so as not to cover, with the same group user key identifier GUK-ID, more than a few content broadcasts, for example no more than two content broadcasts C, or no more than ten content broadcasts, or no more than a percentage of the average number of content broadcasts over a given period. for example 10%, so as to change the group user key identifier GUK-ID ten times for sending all C content over the given period.

[0042] When, as shown in Figures 4A and 4B, the event is a function of a time interval, step 11 of generating a group user key identifier GUK-ID can be carried out for each new interval, for example at the beginning or at the end of each interval. Step 11 of generation is then carried out periodically.

[0043] In [Fig.4A], step 11 of generating the group user key identifier GUK-ID is carried out four times at times T0 to T3 while the steps 12 of encrypting the content with the group user key identifier GUK-ID and of transmitting 13 the frame comprising the encrypted content and the master key identifier MKI comprising the group user key identifier GUK-ID are carried out only twice.

[0044] In [Fig.4B], step 11 of generating the group user key identifier GUK-ID is performed twice at times T0 and T1 while steps 12 of encrypting the content with the group user key identifier GUK-ID and of transmitting 13 the frame comprising the encrypted content and the master key identifier MKI comprising the group user key identifier GUK-ID are performed twice, with the same group user key identifier GUK-ID. These two communications can be linked to the same transmitting entity E, without however having knowledge of its identity. The group user key identifier GUK-ID then acts as a “pseudonym”. A new group user key identifier GUK-ID is then generated in step 11 performed at time T1, and the following communications (not shown) will not be linkable to the first two communications.

[0045] In this first embodiment, the generation 11 of the group user key identifier GUK-ID is not directly linked to the transmission of content from the transmitting entity E to the receiving entity R, since it is carried out according to a time condition.

[0046] In a variant of the first embodiment, the duration of the predetermined interval may be variable, i.e. At is not fixed.

[0047] [Fig.4C] represents a second embodiment in which the predetermined event is a function of the initiation of a communication. In this second embodiment, the generation 11 of the group user key identifier GUK-ID is carried out at each speech in MCPTT, at each transmission of video content in MCVideo, or at each transmission of textual data or file in MCData. Thus, in this second embodiment, the receiving entity R cannot group any communication with others and cannot link them with the transmitting entity E. The receiving entity R can still decrypt the content since it receives, in the master key identifier MKI, the group user key identifier GUK-ID used to encrypt the content with the group master key identifier GMK-ID.

Claims

Claims

1. Method (1) implemented by a transmitting client entity (E) included in a network according to the 3GPP MCS “3rd Generation Partnership Program Mission Critical Services” standard, the transmitting client entity (E) being configured to transmit a plurality of contents (C) intended for at least one receiving client entity (R) included in the network, the transmitting client entity (E) and the receiving client entity (R) being affiliated to the same communication group (G), the method (1) comprising at least one step of generation (11), by the transmitting client entity (E), of a group user key identifier (GUK-ID), the group user key identifier (GUK-ID) being specific to the communication group (G) and being used to encrypt the content (C), the generation step (11) being repeated each time a predetermined event occurs.

2. Method (1) according to the preceding claim further comprising the steps of: - Encryption (12) of the content (C) to be transmitted, the content (C) being encrypted by the transmitting client entity (E), the encryption of the content (C) being based on a master key according to the SRTP protocol "Secure Real Time Protocol", the master key comprising a group master key identifier (GMK-ID) and the generated group user key identifier (GUK-ID), - Transmission (13) of at least one frame (T) to the receiving entity (R), according to the SRTP protocol, the at least one frame (T) comprising the encrypted content (C).

3. Method (1) according to the preceding claim according to which a plurality of frames (T) is transmitted, each frame (T) of the plurality of frames comprising a part of the encrypted content (C), the master key being included in the header of a first frame (T) of the plurality of frames.

4. Method (1) according to any one of the preceding claims, wherein the predetermined event is the start and / or the end of a predetermined time interval, the group user key identifier (GUK-ID) being used to encrypt each content (C) of a plurality of contents transmitted during the predetermined time interval.

5. Method (1) according to any one of claims 1 to 3 according to which the predetermined event is the emission of new content.

6. Method (1) according to any one of the preceding claims wherein the group user key identifier (GUK-ID) is randomly generated.

7. Method (1) according to any one of the preceding claims wherein the communication group (G) is - an MCPTT group and the content (C) is a voice communication or - an MCVideo group and the content (C) is a video or - an MCData group and the content (C) is a text data set or a file.

8. Communication network according to the 3GPP MCS “3rd Generation Partnership Program Mission-Critical System” standard, the communication network comprising at least: - a transmitting client entity (E) configured to implement the method (1) according to any one of claims 1 to 7, - a receiving client entity (R) configured to receive the encrypted content (C) and the master key transmitted by the transmitting entity (E).

9. Computer program product comprising instructions which cause the client entity transmitting the network according to claim 8 to execute the steps of the method according to one of claims 1 to 7

10. / . Computer-readable medium, on which the computer program according to claim 9 is recorded.

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