Lawful interception of application functionality activity

Abstract

The invention relates to a method for enabling lawful interception of a User Equipment UE activity by means of an application capability AF associated with a bootstrapping technique, said activity using an AF key, while the UE is in a roaming situation with a Visited Public Land Mobile Network vPLMN using a Generic Universal Temporary Identifier GUTI, said vPLMN being provided with said provided application capability key by a third party controlling the AF for lawful interception.

Description

[Technical field]

[0001] The present invention relates to a method for enabling lawful interception of activities of a user equipment UE by an application function AF associated with a bootstrapping technique.

[0002] The invention also relates to a User Equipment UE implementing said method and to a Bootstrapping Anchor Function implementing said method. [Background technology]

[0003] A bootstrapping technique allows sharing of keys between the User Equipment UE and the Application Function AF. Such a bootstrapping technique is usually the Generic Bootstrapping Architecture (GBA) or the Authentication and Key Management for Applications (AKMA) based on 3GPP credentials in the 5G System. GBA is specified in 4G, while AKMA is specified in 5G Rel-17.

[0004] These technologies are gaining new applications, notably with the development of Edge Computing and Proximity Services, known under the acronym ProSe. V2X applications, especially those involving vehicles, are examples of services based on ProSe enablers.

[0005] Their use also increases the use cases when having application functions outside of currently used Public Land Mobile Networks (PLMNs), which gives rise to specific situations regarding access to UE activities using the application functions.

[0006] In particular, the roaming use case has been excluded from Rel-17 by the LI group (3GPP SA3-LI) until a solution can be provided to ensure that the VPLMN is receiving adequate material to ensure lawful intercept LI.

[0007] A solution may be to use certificate-based TLS, but this solution is not privileged for newly developed applications. The bootstrapping technique has relatively practical advantages and needs to meet lawful interception requirements for all deployment scenarios, typically even for roaming UEs for those techniques.

[0008] A bootstrapping technique, typically GBA and AKMA, allows the establishment of a key shared between the UE and the AF. 3GPP does not prevent the AF from being operated outside the visited public land mobile network VPLMN. The AF may be operated in the Home Network HPLMN or in a visited network, or by a third party. During 3GPP Rel-17, the 3GPP SA3 LI group responsible for Lawful Intercept raised the following issue:

[0009] In most cases, the shared key may be used for encryption across the VPLMN by creating an encrypted tunnel between the UE and a point outside the VPLMN, e.g., a point in the Home PLMN or in a third party, thereby preventing lawful interception within the VPLMN, if necessary.

[0010] With respect to encryption that the MNO has helped to establish, there are lawful intercept requirements to monitor the decrypted traffic or to provide the means for law enforcement to decrypt the traffic.

[0011] This requirement applies to mechanisms such as AKMA where the MNO participates in the establishment and distribution of keying material for encryption. Thus, lawful intercept requirements exist for AKMA and GBA.

[0012] Furthermore, when roaming, LI needs to be able to be performed independently in each of the jurisdictions involved, including the jurisdiction of the roaming country. In particular, activation of LI in the VPLMN needs to be performed without explicit support from the Home PMLN, since otherwise it would lead to information that the inbound roamer is a LI target in the VPLMN. In particular, the problem to be solved applies to the AKMA and GBA.

[0013] To date, there are no known solutions to address the above problems, and alternative and advantageous solutions are accordingly desired in the art. Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention aims to enable lawful interception for any application using bootstrapping techniques and in roaming situations. [Means for solving the problem]

[0015] The invention is defined in its broadest sense as a method for enabling lawful interception of a user equipment UE activity by means of an application capability AF associated to a bootstrapping technique, said activity using an AF key, while the UE is in a roaming situation with a visited PLMN with at least one parameter known by both the UE and the visited public land mobile network PLMN, said visited PLMN being provided with said provided application capability key for lawful interception, said method comprising the steps of: - transmitting parameters encrypted by an AF key or the provided AF key, respectively, known by both the UE and the visited PLMN or the UE, respectively; For each visited PLMN or UE from which encrypted parameters are received: - decrypting the encrypted parameters by the or each of the provided AF keys; - comparing the decrypted parameters with parameters known by the visited PLMN or UE, respectively, which received the encrypted parameters; - authorizing the use of AF only if the comparison indicates that both parameters are the same.

[0016] The lawful interception feasibility of the present invention is based on the provision of a shared AF key to the visited PLMN by the home PLMN (hereafter HPLMN) or by any third party responsible for a given application function AF. It should be noted here that the AF belongs to the HPLMN or to a third party. For the moment, the provisioning of the shared AF key is under the sole responsibility of the HPLMN, since the HPLMN is the owner of the anchor function, typically the AAnF for the AKMA anchor function, and the AF key is derived there. However, the present invention also applies to the situation where such a key is provided by a third party that monitors the application function. The present invention applies to both cases.

[0017] The present invention further ensures that the HPLMN or a third party responsible for providing the Application Capabilities Key cannot lie to the Visited PLMN (hereafter VPLMN) about the value of the shared key, otherwise the provision of the AF key could not be of any value for the requirements of lawful interception.

[0018] In the context of the bootstrapping technique, when the UE is in a roaming state and the AF belongs to the HPLMN or to another party, a scenario arises where the HPLMN may lie to the VPLMN regarding the value of the shared AF key.

[0019] The present invention includes a method for verifying that the correct AF key that meets the requirements of lawful interception has been provided when the AF key is systematically provided to the VPLMN. In other words, the present invention enables the VPLMN to verify the AF key provided by the HPLMN when the UE is in a roaming state and the AF is operated by the HPLMN or by a third party in the visited PLMN.

[0020] The principle of the invention is therefore to perform a parallel cryptographic operation with the AF key to be verified in order to enable the provided AF key to be correct. It should therefore be noted that in this document the term encrypt / decrypt refers to any kind of cryptographic operation that allows to verify that the correct AF key has been provided by the HPLMN. The calculation of the parameter integrity value calculated with the AF key would therefore be considered as encryption within the meaning of the invention.

[0021] Thus, in a particular embodiment, the encrypted parameters are parameter integrity values ​​calculated by the AF key or the provided AF key, respectively, the decryption step consists in calculating an integrity value by the provided AF key or the AF key, respectively, of the parameters known by the visited PLMN or the UE, respectively, which received the encrypted parameters, and the comparison step consists in comparing the calculated integrity value with the received integrity value, the use of AF being authorized only if the comparison indicates that both integrity values ​​are the same.

[0022] In this particular embodiment, a Message Authentication Code is typically used, calculated using the AF key.

[0023] The present invention prevents the HPLMN or any PLMN from lying to any other PLMN, typically the VPLMN, about the shared key used between the UE and the AF by hosting an application function that implements a bootstrapping technique.

[0024] The present invention therefore relies on the use of an AF key provided to the VPLMN by the HPLMN or by another entity associated with the AF, and the use of parameters known by the UE and the VPLMN. The present invention includes parameters known by the UE and the VPLMN.

[0025] In the preferred embodiment, this parameter is a Generic Universal Temporary Identifier, GUTI.

[0026] This embodiment is the simpler and therefore preferred embodiment since it uses the main parameters used for the UE's connection to the visited PLMN.

[0027] The present invention makes it possible to verify the authenticity of application capability keys in a user equipment roaming context where user equipment using the application capability keys is connected to a visited public land mobile network.

[0028] The present invention ensures that the GBA and AKMA solutions can be used in any deployment scenario where, in addition to generally relying on the presence of a USIM, there is an interest in securing the interface with Pre-share key-TLS PSK-TLS.

[0029] According to an advantageous feature, an application capability identifier for identifying the involved AF is included in the exchange between the UE and the visited PLMN.

[0030] Such an AF identifier allows obtaining the appropriate application function key and authorizing the use of the correct, verified application function. Such an identifier is minimally associated with messages containing encrypted parameters and authorization-related messages.

[0031] According to one particular feature, the UE has a home public land mobile network PLMN, and the provisioning of the application feature key is performed by the home PLMN.

[0032] This situation corresponds to the case where the Home PLMN owns the AF, but also to the case where the Home PLMN is central to the management of a bootstrapping scenario involving a third party. This is currently the scheme that is mostly implemented when a third party in the sense of 3GPP standardization is involved in the management of the AF. Therefore, in such a case, the Home PLMN receives the necessary keying information, including the application capability key, from such a third party for the implementation of the bootstrapping.

[0033] According to another particular feature of the invention, the bootstrapping technique implements an anchor function in the PLMN, said anchor function stores the application capability keys resulting from the bootstrapping technique, and the steps performed by the visited PLMN are performed by the anchor function of the visited PLMN.

[0034] This feature represents the simplest implementation of the present invention in a visited PLMN. The centralization of the bootstrapping requirements in the anchor function of the visited PLMN and the execution of the steps of the present invention within the anchor function is a simple and efficient way to implement the present invention.

[0035] According to one implementation, in a roaming situation using an access management function, for an entity that encrypts parameters known by both the UE and the visited PLMN, the step of transmitting the encrypted parameters to another entity includes the sub-steps of the encrypting entity transmitting the encrypted parameters to the access management function, which forwards them to the other entity.

[0036] This implementation implies an Access Management Function AMF, which is typically active in a roaming situation, which will be involved in the method of the present invention. It should be noted that in this specification, when an AF identifier is used, it follows the same method as via the AMF.

[0037] The invention also relates to a User Equipment UE having a roaming capability with a visited PLMN with parameters known by both the UE and the visited PLMN and tasked with enabling lawful interception of its activities by an application function AF associated to a bootstrapping technique, said activities using an AF key stored in the UE, said UE comprising: - an encryption / decryption module adapted to encrypt parameters known by both the UE and the visited PLMN using the stored AF key and / or to decrypt received encrypted parameters using the stored AF key; - a receiving / transmitting module adapted to transmit the encrypted parameters to a visited PLMN and / or to receive the encrypted parameters from the visited PLMN; - a processing module adapted to, if the parameters are decoded, compare the decoded parameters with parameters known by the UE, the receiving / transmitting module being further adapted in this case to transmit a result of the comparison to an access management function, which authorises the use of the AF only if the comparison indicates that both parameters are the same.

[0038] Such a user equipment is adapted to the implementation of the method of the present invention according to both embodiments of the method, i.e. in the direction from the UE to the visited PLMN or from the visited PLMN to the UE. Of course, these two embodiments may be implemented in one direction for a certain AF and in the other direction for another AF. The two embodiments may coexist or one of them may be implemented exclusively so that it also performs the method of the present invention. The use of the terms "or" and "and / or" in the claims is intended to cover both embodiments, either together or independently, within the definition of the scope of the present invention. The term "respectively" allows the two embodiments to be covered in parallel.

[0039] The invention also relates to a PLMN adapted to attach a User Equipment UE in a roaming situation as a visited PLMN with parameters known by both the UE and by itself as a visited PLMN, and adapted to enable lawful interception of the activities of the UE by means of an Application Function AF associated with a bootstrapping technique, said AF being owned by a third party of the PLMN, said activities being monitored using an AF key, the PLMN is adapted to be provided with an application capability key; The PLMN: - an encryption / decryption module adapted to encrypt parameters using a provided AF key and / or to decrypt received encrypted parameters using a provided AF key; - a receiving / transmitting module adapted to transmit encrypted parameters to a UE and / or to receive encrypted parameters from the UE; - further comprising a processing module adapted to, if the parameters are decoded by the PLMN, compare the decoded parameters with parameters known by the PLMN, the receiving / transmitting module being in this case further adapted to transmit a result of the comparison to an access management function, which authorises the use of the AF only if the comparison indicates that both parameters are the same.

[0040] Such a PLMN is adapted to perform both embodiments of the method of the present invention. Moreover, the implementation of only one embodiment without the second embodiment is within the scope defined in the claims.

[0041] Herein, generally, and elsewhere in this patent application, the term "third party" refers to what it generally is designated in 3GPP, i.e., to an entity that is separate / independent from an operator that is a home PLMN or a visited PLMN. However, in the above definition of the PLMN of the present invention in the last paragraph, these terms also refer to all third parties of the PLMN, including the home PLMN here.

[0042] According to one advantageous implementation, the PLMN comprises a bootstrapping anchor function adapted to carry out the steps of the method of the invention.

[0043] As noted above, this implementation is a simple and efficient way of practicing the present invention.

[0044] To the accomplishment of the foregoing and related ends, the one or more embodiments comprise the features hereinafter fully described and particularly pointed out in the claims.

[0045] The following description and the accompanying drawings set forth in detail certain illustrative aspects, while also illustrating some of the various ways in which the principles of the embodiments may be utilized. Other advantages and novel features will become apparent from the following detailed description when considered in conjunction with the drawings, and the disclosed embodiments are intended to include all such aspects and their equivalents. [Brief description of the drawings]

[0046] [Figure 1] FIG. 2 shows a time flow chart of a first embodiment of the method of the present invention. [Diagram 2] FIG. 4 shows a time flow chart of a second embodiment of the method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] For a more complete understanding of the present invention, the present invention will now be described in more detail with reference to the accompanying drawings. The detailed description illustrates and describes what are considered to be preferred embodiments of the present invention. It is, of course, understood that various modifications and changes in form or detail can be easily made without departing from the scope of the present invention. Thus, the present invention cannot be limited to the exact form and to what has been specifically shown and described herein, nor to anything less than the entirety of the invention disclosed herein and hereinafter claimed. The same elements are designated by the same reference numerals in different drawings. For the sake of clarity, only those elements and steps that are helpful in understanding the present invention are shown and described in the drawings.

[0048] FIG. 1 shows a schematic flow chart of the method of the present invention. The method of the invention device 10 of the type to which the present invention is applied as an embodiment. The present invention relates to GBA and AKMA as bootstrapping techniques implemented in 5G. The following exemplary description is for AKMA bootstrapping, but similar functional entities exist in GBA or in other bootstrapping techniques, and the implementation of the present invention will be similar.

[0049] In this example flow chart, the user equipment UE is in a roaming situation with a visited public land mobile network VPLMN having a visited AKMA anchor function vAAnF. While attached to the VPLMN, the UE is provided with a generic universal temporary identity GUTI.

[0050] As a prerequisite of the present invention, in step S0, the UE has registered and derived a bootstrapping AF key for the use of an application function AF using a bootstrapping technique, typically an AKMA-based AF key for the use of some AFs. This prerequisite can be performed before or during a roaming situation as soon as the UE is ready to associate with an AF. During this registration, the UE is in communication with the Access and Mobility Management Function AMF in 5G and the Authentication Server Function AUSF.

[0051] The registration is made for the use of an application function AF managed by the home PLMN of the UE or another entity. In such a situation, this may be the anchor function hAAnF of the home PLMN that derives the keys related to the bootstrapping technique, but the AF keys may also be managed and therefore provided by any other third party trained to manage such AFs.

[0052] Thus, a primary authentication and establishment of the keys useful for the bootstrapping technique is performed in a preliminary step S0. The useful keys, including at least the master bootstrapping key mKBS from which the application function keys are to be derived, are then stored in an anchor function hAAnF, here belonging to the home PLMN. It may also be an anchor function belonging to a third party that manages the application functions AF. This step in the prerequisites of the method of the invention.

[0053] Then, in step S1, the UE requests an application session establishment with the AF while in a roaming situation, which implies the transmission of the AKMA key identifier of the UE A-KID in the AKMA infrastructure. The identifier used in the GBA infrastructure is the B-TID.

[0054] In step S2, the AF then sends a request for an application key KAF together with the A-KID and the AF identifier AF_ID to the anchor function hAAnF in charge of managing the AF, with which the UE has previously initiated the primary authentication and establishment of the master bootstrapping key mKBS.

[0055] In step S3, the hAAnF derives an application function key KAF from the previously stored master bootstrapping key mKBS. Then, in step S4, the hAAnF replies to the AF, transmitting at least the key KAF and advantageously the key expiry time.

[0056] In step S5, the hAAnF, once it has been informed of the visited PLMN of the UE, also sends the key KAF to the Visited Anchor Function vAAnF, which is the entity that receives the KAF from the home PLMN of the UE or from a third party that manages application functions. It should therefore be noted here that it is not the hAAnF but another third party that is informed of the visited PLMN of the UE in order to be able to provide the required AF key.

[0057] Step S4 triggers a reply in step S6 of the AF to the UE informing the UE that the application session is established.

[0058] In the first embodiment of the present invention, after the application session establishment response, in a roaming situation, messages are exchanged in the direction from the UE to the AMF, and then the AMF communicates with the vAAnF.

[0059] In step S10, the UE encrypts the GUTI using the KAF. Alternatively, the UE can also use the KAF to calculate an integrity value of the GUTI as the encrypted GUTI. Then, in step S11, the UE sends the encrypted GUTIe together with the identifier to the AMF, so that the appropriate KAF in the target VAAnF can be obtained. In step S12, the AMF, knowing the GUTI, forwards both the encrypted GUTIe and the clear text GUTI together with the identifier to the vAAnF, so that the appropriate KAF in the target VAAnF can be obtained. In step S13, the vAAnF then decrypts the encrypted GUTIe using the KAFp received from the hAAnF of the home PLMN or from a third party managing the AF. Alternatively, the vAAnF calculates an integrity value GUTId of the received clear text GUTI using the KAFp received from the hAAnF of the home PLMN or from a third party managing the AF.

[0060] The decrypted GUTId is compared with the clear text received GUTI in step S14. Alternatively, the calculated integrity value GUTId is compared with the received integrity GUTI value. In step S15, the vAAnF sends a message to the AMF indicating whether the verification of the GUTI was successful or not together with the identifier, so that the appropriate KAF in the UE can be obtained. Then, as shown by step S16, the AMF sends a message to the UE indicating whether the verification of the GUTI was successful or not. The UE then uses the application function AF only if the verification is successful.

[0061] In the second embodiment shown in FIG. 2, after the application session establishment response in step S6, messages are exchanged in the direction from vAAnF to AMF, and then the messages are forwarded to the UE.

[0062] In a first step S20, the vAAnF contacts the AMF to obtain the GUTI in step S21. Then, in step S22, the vAAnF encrypts the GUTI using the key KAFp received from the hAAnF.

[0063] The vAAnF then sends the encrypted GUTIe together with the identifier to the AMF in step S23, so that the appropriate KAF in the UE can be obtained. The AMF forwards the encrypted GUTIe together with the identifier to the UE in step S24, so that the appropriate KAF can be obtained. In step S25, the UE decrypts the GUTI using the appropriate key KAF. The UE then compares the decrypted value GUTId with the GUTI stored in the UE in step S26. The UE sends a message to the AMF in step S27 indicating whether the verification of the GUTI was successful or not. The AMF then forwards an indication to the vAAnF in step S28. The UE uses the application functions only if the verification was successful.

[0064] According to the present invention, as soon as the UE is in roaming state, the UE checks whether a verification of the GUTI has been performed while requesting any use of any application function AF. Thus, the application step using AF occurs only if the verification of the GUTI has occurred. This solution applies to any application using the bootstrapping technique, typically AKMA and GBA.

[0065] In the above detailed description, reference is made to the accompanying drawings, which show by way of example specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Therefore, the above detailed description is not to be taken in a limiting sense, and the scope of the invention is defined only by the appended claims and interpreted accordingly. In particular, the use of an integrity value as an encrypted value is within the scope of the invention. In this case, the decryption step is in fact the calculation of the integrity value with the AF key, which does not depart from the principles of the invention, thereby solving the problem of enabling lawful interception of the application by being able to verify that the correct application key has been provided.

Claims

1. A method for enabling lawful interception of activities of a user equipment UE by an application function AF associated with a bootstrapping technique, said activities using an AF key while the UE is in a roaming situation with a visited public land mobile network PLMN with at least one parameter known by both the UE and the visited public land mobile network PLMN, the visited PLMN being provided with the provided application function key for lawful interception, the method comprising the steps of: sending to the visited PLMN or the UE, respectively, parameters encrypted by an AF key or the provided AF key, respectively, known by both the UE and the visited PLMN; For each visited PLMN or UE that received the encrypted parameters: decrypting the encrypted parameters by the provided AF key or AF keys, respectively; comparing the decrypted parameters with parameters known by the visited PLMN or UE, respectively, which received the encrypted parameters; authorizing the use of AF only if the comparison indicates that both parameters are the same. A method comprising:

2. 2. The method of claim 1, wherein the parameter known by both the UE and the visited PLMN is a Generic Universal Temporary Identifier GUTI.

3. The method according to claim 1 or 2, wherein an application capability identifier for identifying the involved AF is included in the exchange between the UE and the visited PLMN.

4. The method according to any one of claims 1 to 3, wherein the UE has a home public land mobile network (PLMN) and the provisioning of the application capability key is performed by the home PLMN.

5. 5. The method according to claim 1, wherein the bootstrapping technique implements an anchor function in the PLMN, the anchor function stores an application capability key resulting from the bootstrapping technique, and the steps performed by the visited PLMN are performed by the anchor function of the visited PLMN.

6. 6. A method according to claim 1, wherein in a roaming situation an access management function is used and for an entity encrypting parameters known by both the UE and the visited PLMN, the step of transmitting the encrypted parameters to the other entity comprises the sub-step of the encrypting entity transmitting the encrypted parameters to the access management function and the access management function forwarding it to the other entity.

7. A User Equipment UE having roaming capability with a visited PLMN using parameters known by both the UE and the visited PLMN and tasked with enabling lawful interception of its activities by an Application Function AF associated with a bootstrapping technique, said activities using an AF key stored in the UE, said UE comprising: an encryption / decryption module adapted to encrypt parameters known by both the UE and the visited PLMN using the stored AF key and / or to decrypt received encrypted parameters using the stored AF key; a receiving / transmitting module adapted to transmit the encrypted parameters to a visited PLMN and / or receive the encrypted parameters from the visited PLMN; A user equipment UE comprising a processing module adapted to, if the parameters are decoded, compare the decoded parameters with parameters known by the UE, the receiving / transmitting module being further adapted in this case to transmit a result of the comparison to an access management function, which authorizes the use of the AF only if the comparison indicates that both parameters are the same.

8. 1. A public land mobile network (PLMN) adapted to attach a user equipment (UE) in a roaming situation as a visited PLMN (PLMN) with parameters known by both the UE and itself as the visited PLMN (PLMN), and adapted to enable lawful interception of the UE's activities by an application function (AF) associated with a bootstrapping technique, said AF being owned by a third party in the PLMN, said activities using an AF key, the PLMN is adapted to be provided with an application capability key; The PLMN: an encryption / decryption module adapted to encrypt parameters using the provided AF key and / or to decrypt received encrypted parameters using the provided AF key; a receiving / transmitting module adapted to transmit the encrypted parameters to the UE and / or to receive the encrypted parameters from the UE; The PLMN further comprises a processing module adapted to, if the parameters are decoded by the PLMN, compare the decoded parameters with parameters known by the PLMN, the receiving / transmitting module being further adapted in this case to transmit a result of the comparison to an access management function, which authorises the use of the AF only if the comparison indicates that both parameters are the same, the access management function authorising the use of the AF.

9. 9. The PLMN of claim 8, wherein the PLMN has a bootstrapping anchor function adapted to perform the steps of the method according to any one of claims 1 to 6.

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