Methods, systems, and computer readable media for preventing unauthorized use of certificate management protocol (CMP) client identity private key and public key certificates associated with network functions

Abstract

A method for preventing unauthorized use of a CMP client identity private key and a CMP public key certificate associated with an NF includes receiving, by a CMP CA agent, a first CMP certificate request for resuming a security certificate associated with a first NF, the CMP certificate request including a public key certificate associated with the first NF and protected by a CMP client identity private key associated with the first NF. The method further comprises: determining that the first NF has registered with the NRF; and in response to determining that the first NF has registered with the NRF, checking, by the CMP CA agent, whether the first CMP certificate request includes an NRF issued access token for the first NF; determining that the CMP credential request does not include an NRF issued access token for the first NF; and in response to determining that the first CMP credential request does not include the NRF issued access token for the first NF, performing a network security action with respect to the first CMP credential request.

Description

[0001] Priority claim

[0002] This application claims the benefit of priority to U.S. patent application serial number 18 / 113,041, filed on February 22, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The subject matter described herein relates to protecting against the unauthorized use of credentials that could be used to impersonate a network function (NF), such as a 5G NF in a 5G network. More particularly, the subject matter described herein relates to methods, systems, and computer-readable media for preventing the unauthorized use of CMP client identity private keys and public key certificates associated with an NF. Background Art

[0004] In 5G telecommunications networks, a network function that provides a service is called a producer NF or NF service producer. A network function that consumes a service is called a consumer NF or NF service consumer. A network function can be a producer NF, a consumer NF, or both, depending on whether the network function is consuming, producing, or both consuming and producing services. The terms "producer NF" and "NF service producer" are used interchangeably herein. Similarly, the terms "consumer NF" and "NF service consumer" are used interchangeably herein.

[0005] A given producer NF may have many service endpoints, where a service endpoint is the contact point for one or more NF instances hosted by the producer NF. A service endpoint is identified by a combination of an Internet Protocol (IP) address and port number, or a fully qualified domain name (FQDN) that resolves to the IP address and port number of the network node hosting the producer NF. An NF instance is an instance of the producer NF that provides a service. A given producer NF may include more than one NF instance. It should also be noted that multiple NF instances can share the same service endpoint.

[0006] NFs register with the Network Function Repository Function (NRF). NRF maintains profiles of available NF instances that identify the services supported by each NF instance. The profile of an NF instance is referred to as an NF profile in 3GPP TS29.510. An NF instance can obtain information about other NF instances that have registered with the NRF through an NF discovery service operation. According to the NF discovery service operation, a consumer NF sends an NF discovery request to the NRF. The NF discovery request includes query parameters, which the NRF uses to locate the NF profile of a producer NF that can provide the service identified by the query parameters. An NF profile is a data structure that defines the type of service provided by an NF instance and contact and capacity information about the NF instance.

[0007] The Service Communication Proxy (SCP) can also invoke NF Discovery service operations to learn about available producer NF instances. The use of NF Discovery service operations by the SCP to obtain information about producer NF instances on behalf of a consumer NF is called delegated discovery. The consumer NF connects to the SCP, which load balances traffic between the producer NF service instances that provide the required service or routes the traffic directly to the destination producer NF instance.

[0008] In addition to the SCP, another example of an intermediate proxy that forwards traffic between producer and consumer NFs is the Security Edge Protection Proxy (SEPP). The SEPP is a network function used to protect control plane traffic exchanged between different 5G Public Land Mobile Networks (PLMNs). Thus, the SEPP performs message filtering, policing, and topology hiding on all application programming interface (API) messages transmitted between PLMNs.

[0009] One concern in 5G and other types of networks is that the NF client identity private key and public key certificate could be stolen and used without authorization to obtain the NF's Transport Layer Security (TLS) certificate. The NF's TLS certificate includes the NF's NF Instance ID in the TLS certificate's Subject Alternative Name. This TLS certificate could then be used to impersonate the NF and perform malicious actions in the network.

[0010] The Third Generation Partnership Project (3GPP) specifies the use of the Certificate Management Protocol (CMP) for automated certificate management. CMP messages are protected using a CMP client private key and public key certificate, which can be manually configured by the network operator on the Certificate Manager (CM). If the CMP client private key and CMP public key certificate are stolen, a hacker can successfully obtain the TLS certificate of a registered NF and use it to impersonate the NF and perform malicious actions within the network.

[0011] Therefore, in light of these and other difficulties, there is a need to prevent unauthorized use of CMP client identity private keys and public key certificates to prevent hackers from obtaining and using NF TLS certificates. Summary of the Invention

[0012] A method for preventing unauthorized use of a Certificate Management Protocol (CMP) client identity private key and a CMP public key certificate associated with a network function (NF) includes receiving, by a CMP certificate authority (CA) agent, a first CMP certificate request for renewing a security certificate associated with a first NF, the CMP certificate request including a public key certificate associated with the first NF and protected by a CMP client identity private key associated with the first NF. The method also includes checking, by the CMP CA agent, whether the first NF is registered with a NF repository function (NRF), and determining that the first NF is registered with the NRF. The method also includes, in response to the CMP CA agent determining that the first NF is registered with the NRF, checking, by the CMP CA agent, whether the first CMP certificate request includes an access token issued by the NRF for the first NF, and determining that the CMP certificate request does not include an access token issued by the NRF for the first NF. The method also includes performing a network security action with respect to the first CMP certificate request in response to the CMP CA agent determining that the first CMP certificate request does not include an access token issued by the NRF for the first NF.

[0013] According to another aspect of the subject matter described herein, receiving the first CMP certificate request includes receiving the first CMP certificate request from a hacker impersonating the first NF.

[0014] According to another aspect of the subject matter described herein, performing a network security action for the first CMP certificate request includes preventing the CMP CA from providing the security certificate to a hacker.

[0015] According to another aspect of the subject matter described herein, preventing the CMP CA from providing a security certificate to a hacker includes preventing a first CMP certificate request from reaching the CMP CA.

[0016] According to another aspect of the subject matter described herein, receiving the first CMP certificate request at the CMP CA proxy includes receiving the first CMP certificate request at the CMP CA proxy that is a component of the NRF or at a CMP CA proxy that is separate from the NRF.

[0017] According to another aspect of the subject matter described herein, receiving the first CMP certificate request includes intercepting the first CMP certificate request.

[0018] According to another aspect of the subject matter described herein, receiving the first CMP certificate request includes receiving the first CMP certificate request for a Transport Layer Security (TLS) or Client Credential Assertion (CCA) certificate for the first NF.

[0019] According to another aspect of the subject matter described herein, checking whether the first CMP certificate request includes an NRF-issued access token for the first NF includes checking whether the first CMP request includes an OAuth 2.0 access token issued by the NRF to the first NF.

[0020] According to another aspect of the subject matter described herein, a method for preventing unauthorized use of a CMP client identity private key and a CMP public key certificate associated with a NF includes: receiving, by a CMP CA agent, a second CMP certificate request for renewing a security certificate associated with a second NF, the request including a public key certificate associated with the second NF and protected by the CMP client identity private key associated with the second NF. The method also includes: checking, by the CMP CA agent, whether the second NF is registered with an NRF, and determining that the second NF is not registered with the NRF. The method also includes: in response to determining that the second NF is not registered with the NRF, allowing processing of the second CMP certificate request by forwarding the second CMP certificate request to the CMP CA. The method for preventing unauthorized use of a CMP client identity private key and a CMP public key certificate associated with a NF includes: generating, at the CMP CA, a CMP certificate response including the security certificate associated with the second NF, and forwarding the CMP certificate response to an initiator of the second CMP certificate request.

[0021] According to another aspect of the subject matter described herein, a method for preventing unauthorized use of a CMP client identity private key and a CMP public key certificate associated with an NF includes: transmitting, by a second NF, a second CMP certificate request for renewing a second security certificate associated with the second NF to a CMP CA agent, the second CMP certificate request including a public key certificate, protected by the CMP client identity private key associated with the second NF, and including an access token issued by an NRF associated with the second NF; receiving, by the CMP CA agent, the second CMP certificate request; checking, by the CMP CA agent, whether the second NF has been registered with the NRF, and determining that the second NF has been registered with the NRF; in response to the CMP CA agent determining that the second NF has been registered with the NRF, checking, by the CMP CA agent, whether the second CMP certificate request includes an access token issued by the NRF associated with the second NF, and determining that the second CMP certificate request includes the access token issued by the NRF associated with the second NF; and in response to the CMP CA agent determining that the second CMP certificate request includes the access token issued by the NRF associated with the second NF, allowing processing of the second CMP certificate request by forwarding the second CMP certificate request to the CMP CA agent.

[0022] According to another aspect of the subject matter described herein, a system for preventing unauthorized use of a CMP client identity private key and a CMP public key certificate associated with a NF. The system includes a CMP CA agent, the CMP CA agent including at least one processor and a memory. The system also includes a CMP certificate request validator implemented by the at least one processor, configured to: receive a first CMP certificate request for renewing a security certificate associated with a first NF, the CMP certificate request including a public key certificate associated with the first NF and protected by a CMP client identity private key associated with the first NF; check whether the first NF is registered with an NF repository function (NRF), and determine that the first NF is registered with the NRF; in response to determining that the first NF is registered with the NRF, check whether the first CMP certificate request includes an access token issued by the NRF for the first NF, and determine that the CMP certificate request does not include an access token issued by the NRF for the first NF; and in response to determining that the first CMP certificate request does not include an access token issued by the NRF for the first NF, perform a network security action with respect to the first CMP certificate request.

[0023] According to another aspect of the subject matter described herein, the first CMP certificate request originates from a hacker impersonating the first NF.

[0024] According to another aspect of the subject matter described herein, in performing a network security action for the first CMP certificate request, the CMP certificate request validator is configured to prevent the CMP CA from providing a security certificate to a hacker by preventing the first CMP certificate request from reaching the CMP CA.

[0025] According to another aspect of the subject matter described herein, the CMP CA agent comprises a component of the NRF or is separate from the NRF.

[0026] According to another aspect of the subject matter described herein, a CMP certificate request validator is configured to receive a first CMP certificate request by intercepting the first CMP certificate request.

[0027] According to another aspect of the subject matter described herein, the security certificate includes a Transport Layer Security (TLS) or Client Credential Assertion (CCA) certificate of the first NF.

[0028] According to another aspect of the subject matter described herein, an access token issued by an NRF for a first NF includes an OAuth 2.0 access token issued by the NRF to the first NF.

[0029] According to another aspect of the subject matter described herein, a CMP certificate request validator is configured to receive a second CMP certificate request for renewing a security certificate associated with a second NF, the request including a public key certificate associated with the second NF and protected by a CMP client identity private key associated with the second NF. The CMP certificate request validator is further configured to check whether the second NF is registered with an NRF and to determine that the second NF is not registered with the NRF. The CMP certificate request validator is further configured to, in response to determining that the second NF is not registered with the NRF, allow processing of the second CMP certificate request by forwarding the second CMP certificate request to a CMP CA.

[0030] According to another aspect of the subject matter described herein, a system for preventing a CMP client identity private key and a CMP public key certificate includes a second MF for transmitting a second CMP certificate request for renewing a second security certificate associated with a second NF to a CMP CA agent, the second CMP certificate request including a public key certificate associated with the second NF, protected by a CMP client identity private key associated with the second NF, and including an access token issued by an NRF associated with the second NF. A CMP certificate request validator is configured to receive the second CMP certificate request; check whether the second NF is registered with the NRF, and determine that the second NF is registered with the NRF; in response to determining that the second NF is registered with the NRF, check whether the second CMP certificate request includes an access token issued by the NRF associated with the second NF, and determine that the second CMP certificate request includes an access token issued by the NRF associated with the second NF; and in response to determining that the second CMP certificate request includes an access token issued by the NRF associated with the second NF, allow processing of the second CMP certificate request by forwarding the second CMP certificate request to the CMP CA.

[0031] According to another aspect of the subject matter described herein, a non-transitory computer-readable medium is provided having executable instructions stored thereon that, when executed by a processor of a computer, control the computer to perform steps. The steps include: receiving, by a Certificate Management Protocol (CMP) certificate authority (CA) agent, a first CMP certificate request for renewing a security certificate associated with a first network function (NF), the CMP certificate request including a public key certificate associated with the first NF and protected by a CMP client identity private key associated with the first NF. The steps also include: checking, by the CMP CA agent, whether the first NF has been registered with an NF repository function (NRF), and determining that the first NF has been registered with the NRF. The steps also include: in response to the CMP CA agent determining that the first NF has been registered with the NRF, checking, by the CMP CA agent, whether the first CMP certificate request includes an access token issued by the NRF for the first NF, and determining that the CMP certificate request does not include an access token issued by the NRF for the first NF. The steps also include performing a network security action with respect to the first CMP certificate request in response to determining by the CMP CA agent that the first CMP certificate request does not include an access token issued by the NRF for the first NF.

[0032] The subject matter described herein can be implemented in software in combination with hardware and / or firmware. For example, the subject matter described herein can be implemented with software executed by a processor. In an exemplary embodiment, the subject matter described herein can be implemented using a non-transitory computer-readable medium having computer-executable instructions stored thereon, which control the computer to perform steps when executed by the processor of a computer. Exemplary computer-readable media suitable for implementing the subject matter described herein include non-transitory computer-readable media, such as disk memory devices, chip memory devices, programmable logic devices, and application-specific integrated circuits. In addition, the computer-readable medium that implements the subject matter described herein can be located on a single device or computing platform, or can be distributed across multiple devices or computing platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Exemplary embodiments of the subject matter described herein will now be explained with reference to the accompanying drawings, in which:

[0034] Figure 1 is a network diagram illustrating an exemplary 5G system network architecture;

[0035] Figure 2 is a network diagram illustrating an example security architecture for certificate management of a 5G NF;

[0036] Figure 3 The diagram is in use Figure 2 A message flow diagram of exemplary messages exchanged in obtaining a TLS certificate in the security architecture shown in FIG.

[0037] Figure 4 is a message flow diagram illustrating exemplary messages exchanged in an NFRegister service operation;

[0038] Figure 5 is a message flow diagram illustrating exemplary messages exchanged when a hacker uses a stolen CMP client identity private key and certificate to obtain a TLS certificate for a NF;

[0039] Figure 6A is a network diagram illustrating an example of a security architecture in which a CA proxy intercepts a CMP certificate request and requires an OAuth 2.0 access token issued by the NRF of the registered NF before providing the NF's TLS certificate to the querying entity;

[0040] Figure 6B is a network diagram illustrating an alternative security architecture in which a CA proxy intercepts CMP certificate requests and requires an OAuth 2.0 access token issued by the NRF of the registered NF before presenting the NF's TLS certificate to the querying entity;

[0041] Figure 6C is a network diagram illustrating yet another alternative security architecture in which a CA proxy intercepts CMP certificate requests and requires an OAuth 2.0 access token issued by the NRF of the registered NF before presenting the NF's TLS certificate to the querying entity;

[0042] Figure 7 is a message flow diagram illustrating exemplary messages exchanged using a CMP CA agent to validate a CMP certificate request;

[0043] Figure 8 is a block diagram illustrating an exemplary architecture for a CMP CA agent; and

[0044] Figure 9 is a flow chart illustrating an exemplary process for preventing unauthorized use of a CMP client identity private key and a CMP public key certificate associated with a NF. DETAILED DESCRIPTION

[0045] Figure 1 is a block diagram illustrating an exemplary 5G system network architecture. Figure 1The architecture in FIG includes an NRF 100 and an SCP 101, which can be located in the same Home Public Land Mobile Network (HPLMN). As described above, the NRF 100 can maintain a profile of available NF instances and the services they support, and allow consumer NFs or SCPs to subscribe and be notified of registrations of new / updated NF instances. The SCP 101 can also support NF instance selection and service discovery. The SCP 101 can perform load balancing of connections between consumer and producer NFs.

[0046] The NRF 100 is a repository for profiles of NF instances. To communicate with a producer NF instance, a consumer NF or SCP must obtain the producer NF instance's NF profile from the NRF 100. The NF profile is a JavaScript Object Notation (JSON) data structure defined in 3GPP TS 29.510. The NF profile includes attributes indicating the type of service provided, the capabilities of the NF instance, and information for contacting the NF instance.

[0047] exist Figure 1 In the example, any network function can be a consumer NF, a producer NF, or both, depending on whether they are requesting a service, providing a service, or requesting and providing a service. In the example shown, the NFs include a policy control function (PCF) 102 that performs policy-related operations in the network, a unified data management function (UDM) 104 that manages user data, and an application function (AF) 106 that provides application services.

[0048] Figure 1 The NF shown in FIG1 also includes a session management function (SMF) 108, which manages sessions between an access and mobility management function (AMF) 110 and PCF 102. AMF 110 performs mobility management operations similar to those performed by a mobility management entity (MME) in a 4G network. Authentication server function (AUSF) 112 performs authentication services for user equipment (UE) such as user equipment (UE) 114 seeking to access the network.

[0049] The Network Slice Selection Function (NSSF) 116 provides network slicing services to devices seeking to access specific network capabilities and features associated with network slices. The NSSF 116 provides the NSSelection service that allows NFs to request information about network slices, and the NSSAIReachability service that enables NFs to update and subscribe to receive notifications of updates to Network Slice Selection Assistance Information (NSSAI) reachability information.

[0050] The Network Exposure Function (NEF) 118 provides an Application Programming Interface (API) for application functions seeking to obtain information about Internet of Things (IoT) devices and other UEs attached to the network. The NEF 118 performs functions similar to the Service Capability Exposure Function (SCEF) in 4G networks.

[0051] Radio Access Network (RAN) 120 connects User Equipment (UE) 114 to the network via wireless links. gNB ( Figure 1 1) or other wireless access points to access the radio access network 120. A user plane function (UPF) 122 may support various proxy functions for user plane services. An example of such a proxy function is a Multipath Transport Control Protocol (MPTCP) proxy function. UPF 122 may also support performance measurement functions that UE 114 may use to obtain network performance measurements. Figure 1 Also illustrated in FIG. 1 is a data network (DN) 124 through which the UE accesses data network services, such as Internet services.

[0052] SEPP 126 filters incoming traffic from another PLMN and performs topology hiding for traffic leaving the home PLMN. SEPP 126 can communicate with a SEPP in a foreign PLMN, which manages the security of the foreign PLMN. Thus, traffic between NFs in different PLMNs can traverse two SEPP functions: one for the home PLMN and one for the foreign PLMN. Unified Data Repository (UDR) 128 stores subscription data for the UE. Binding Support Function (BSF) 130 manages the binding between PDU sessions and PCFs.

[0053] As mentioned above, one issue that can arise in 5G and other types of networks is that the NF client identity private key and public key certificate could be stolen and used without authorization to obtain the NF's TLS certificate. This TLS certificate could then be used to impersonate the NF and gain unauthorized access to other NFs and information in the network.

[0054] According to one aspect of the subject matter described herein, instead of issuing a TLS certificate to an entity that merely presents a request with a signature generated using a CMP client identity private key and public key certificate, an access token (such as an OAuth 2.0 access token) issued by an NRF may be required as an additional credential before issuing the NF's TLS certificate. In the context of a 5G communication network, the NF service consumer acts as an OAuth 2.0 resource client, the NF service producer acts as an OAuth2.0 resource server, and the NRF acts as an authorization server. Thus, an NF service consumer seeking access to a service provided by the NF service producer signals the NRF to obtain an access token for accessing resources provided by the NF service producer. After the NF service consumer obtains the access token from the NRF, the NF service consumer sends a service request to the NF service producer, wherein the service request includes the access token. The NF service producer verifies the access token and provides access to the service requested by the NF service consumer. The subject matter described herein does not simply use an OAuth 2.0 access token to allow a consumer NF to access services provided by a producer NF. Instead, it includes using the NF's OAuth 2.0 access token as a mandatory credential for the requesting entity to obtain the NF's TLS certificate. By providing the OAuth 2.0 access token in addition to a signature generated using the CMP client identity private key and public key certificate in the CMP certificate request, the NF utilizes multi-factor authentication (MFA), which enhances the security of the CMP protocol. In the example described herein, the multi-factor authentication is two-factor authentication, i.e., verification of the OAuth 2.0 access token as the first factor and verification of the signature generated using the CMP client identity private key as the second factor.

[0055] When an entity requests renewal of a NF's TLS certificate, the access token issued by the NRF can be a mandatory credential. Using the access token issued by the NRF as an additional mandatory credential reduces the likelihood that a hacker will be able to obtain the TLS certificate of a registered NF, even if the CMP client identity private key and public key certificate are compromised. In one example, a CA agent is provided in front of the CMP CA to verify that the OAuth 2.0 access token issued by the NRF for the NF requesting its TLS certificate is embedded in the HTTP-based CMP certificate renewal request. In order to successfully renew the TLS certificate, the requesting entity needs to provide the OAuth 2.0 access token issued by the NRF when renewing the TLS certificate. The CA agent queries the NRF to check whether the NF is registered. If the NF is registered, the CA agent uses the NRF public key corresponding to the private key used for token generation to verify the OAuth 2.0 access token. The certificate request must contain the OAuth 2.0 access token issued by the NRF of the NF to successfully retrieve the NF's TLS certificate.

[0056] 3GPP TS 33.501 Section 13.3.1 specifies the use of mutually authenticated TLS and HTTPS, and further uses the identity embedded in the end-entity certificate for authentication and policy checking. If a hacker can gain access to the private key and public key certificate of the CMP client identity, then the hacker can obtain a TLS certificate issued in the name of the NF and can use the TLS certificate to impersonate the NF to access the NRF or other NFs.

[0057] TLS certificates and private keys can be stolen by hackers and used in SBI requests (e.g., requests for the NFRegister service operation). TLS / Public Key Infrastructure (PKI) provides the concept of revoking certificates that are stolen with the owner's knowledge using Certificate Revocation Lists (CRLs) or the Online Certificate Status Protocol (OCSP). However, when TLS certificates and private keys are stolen without the owner's knowledge, there are no mitigations available at the transport layer. Even with CRLs and OCSP, the owner must notify the authority of the certificate theft, and the authority must update its database regarding the theft and mark the certificate as stolen. There is a time delay between the theft and revocation of the certificate, which provides an opportunity for hackers to conduct attacks. The subject matter described in this article mitigates the problem of certificates being stolen without the owner's knowledge. The proposed solution is also useful when a certificate is stolen but there is a delay in revoking the stolen certificate.

[0058] In one possible security architecture, a certificate manager (CM) can be used to automate certificate management for NFs. Figure 2 An example of such an architecture is shown in Figure 2 In 5G, CM 200 is configured with CMP client identity private key and CMP public key certificate for one or more NFs 202. The CMP client identity private key and CMP public key certificate are used to authenticate to CMP Certificate Authority (CA) 204. The communication between 5G NF 202 and CM 200 can be secured using a service mesh or other similar solutions. Figure 2 In the example architecture shown in , NF 202 and CM 200 are implemented in a Kubernetes cluster 206.

[0059] Figure 3 Illustrated using Figure 2 The security architecture shown in the example messages exchanged in TLS certificates is shown in the example. Figure 3In step 1, NF 202 sends a request to CM 200 for a TLS key and certificate. In step 2, CM 200 generates a key pair for the TLS certificate request and, in step 3, generates a CMP certificate request to send to CA 204. The key pair generated by CM 200 includes the private and public keys of the CMP client identity for NF 202. CM 200 uses a signature generated using the CMP client identity private key for PKI message protection. In step 4, CM 200 sends the CMP certificate request to CA 204. The CMP certificate request includes a public key certificate (containing NF 202's public key and key metadata). The CMP certificate request also includes a signature generated using the CMP client identity private key. In step 5, CA 204 verifies the request using the public key used to verify the signature in the request and generates a certificate response including NF 202's TLS key and certificate. The response is then sent to CM 200. In step 6, CM 200 sends the TLS key and certificate to NF 202. A hacker with access to the CMP client identity private key can impersonate CM 200 and obtain the NF TLS certificate from CA 204.

[0060] As indicated above, it is desirable to prevent hackers from impersonating registered NFs. A registered NF is an NF that has registered with the NRF using the NFRegister service operation. The NFRegister service operation is described in 3GPP TS 29.510, Section 5.2.2.2.1. Figure 4 Figure 1 shows example messages exchanged during NFRegister service operations. Figure 4 In line 1, NF Service Consumer 202 sends an NFRegister request to NRF 100. This NFRegister request includes the NF profile of NF Service Consumer 202. This NFRegister request is also protected using the TLS certificate of NF Service Consumer 202. NRF 100 receives the NFRegister request, verifies the TLS certificate, processes the request, and if the processing is successful, responds with a 201Created message, as indicated in line 2a. The 201Created message includes the NF profile of the NF being registered. If the processing of the NFRegister request is unsuccessful, then NRF 100 responds with an NF 4xx or 5xx message specifying the details of the problem, as indicated in line 2b.

[0061] Figure 5 is a message flow diagram illustrating exemplary messages exchanged when a hacker uses a stolen CMP client identity private key and public key certificate to obtain a NF's TLS certificate. Figure 5In line 1, NF 202 sends an NF Certificate Request to CM 200. In line 2, CM 200 sends a CMP Certificate Request to CMP CA 204. In line 3, CMP CA 204 sends a CMP Certificate Response to CM 200. The CMP Certificate Response includes the TLS certificate of NF 202. In line 4, CM 200 provides the TLS certificate to NF 202 in the NF Certificate Response message. In line 5, NF 202 uses Figure 4 The NFRegister service operation shown in FIG. registers with the NRF 100. The NFRegister service operation is secured using the TLS certificate of the NF 202.

[0062] In line 6, the hacker obtains the CMP client identity private key and public key certificate of NF 202. In line 7, the hacker sends a CMP Certificate Request to CMPCA 204. In line 8, CMP CA 204 responds with a CMP Certificate Response that includes the TLS certificate of NF 202. In line 9, the hacker uses the stolen TLS certificate to initiate a service operation impersonating NF 202.

[0063] To reduce the likelihood of a hacker successfully obtaining a NF TLS certificate, the subject matter described herein includes a CA proxy that intercepts CMP requests and forces an NRF-issued OAuth 2.0 access token for TLS certificate renewal. In addition to the CMP client identity private key and certificate, the hacker also requires an NRF-issued OAuth 2.0 access token for requesting TLS certificate renewal. The NF needs to provide an NRF-issued OAuth 2.0 access token for TLS certificate renewal or creation. If the NF is not yet registered, then an NRF-issued OAuth 2.0 access token is not required for TLS certificate requests. In one embodiment of the subject matter described herein, direct access to the CMP CA is only available to the CA proxy.

[0064] Figure 6A Figure 1 illustrates an example of a security architecture where a CA proxy intercepts CMP certificate requests and requires an OAuth 2.0 access token issued by the NRF for the registered NF before presenting the NF's TLS certificate to the querying entity. Figure 6A, CM 200 issues a CMP certificate request to CA 204 on behalf of 5GNF 202. The certificate requests each include the NF public key certificate and are each protected by the CMP client identity private key associated with the NF. In addition, if the certificate request is for a NF that has previously registered with NRF 100, the certificate request also includes an OAuth 2.0 access token. CA agent 600 receives or intercepts the certificate request, checks whether the NF has been registered with NRF 100, and in response to determining that the NF has been registered with NRF, checks the certificate request for the presence of an OAuth 2.0 access token for the registered NF. If the certificate request includes an OAuth 2.0 access token for the registered NF (together with the public key certificate of the NF), CA agent 600 allows the request to be passed to CMP CA 204. CMPCA 204 renews the TLS certificate for the NF and provides the TLS certificate to the CM that made the request in a TLS certificate response.

[0065] If the NF is already registered, and the CMP certificate request does not include an OAuth 2.0 access token for the NF, the CA agent 600 may perform network security actions, such as preventing further processing of the CMP certificate request by the CA 204 by dropping the request.

[0066] Figure 6B An alternative security architecture is illustrated where a CA proxy intercepts CMP certificate requests for registered NFs and requires an OAuth 2.0 access token issued by the NRF of that NF before presenting the NF’s TLS certificate to the querying entity. Figure 6B In the architecture in FIG, each NF 202 includes its own CM 200 and communicates directly with the CA agent 600. The CA agent 600 communicates directly with the CA agent 600. Figure 6A , to validate a CMP certificate request based on the presence of an NRF-issued OAuth 2.0 access token.

[0067] Figure 6C Yet another alternative security architecture is illustrated, where the CA proxy intercepts CMP certificate requests and requires an OAuth 2.0 access token issued by the NRF for a registered NF before providing the TLS certificate of that NF to the querying entity. Figure 6C In the architecture of Figure 6B Similar to the architecture in FIG, each NF 202 includes its own CM 200 and communicates directly with the CA agent 600. In addition, the CA agent 600 is not separated from the NRF 100, but is a component of the NRF 100. Figure 6A Authenticating a CMP certificate request based on the presence of an NRF-issued OAuth 2.0 access token operates identically to that shown in , with the following differences: Figure 6C Instead of querying a separate NRF, the CA agent 600 shown in FIG can access the internal NF profile database of the NRF 100 to determine whether the NF is registered, and can also obtain the OAuth 2.0 access token of the registered NF from the internal database of the NRF.

[0068] Figure 7 is a message flow diagram illustrating exemplary messages exchanged using a CMP CA agent to verify a CMP certificate request. Figure 7 In line 1, NF 202 sends an NF certificate request to CM 200. In line 2, CM 200 sends a CMP certificate request to CA 204. CMP CA agent 600 intercepts the request and, in line 3, queries NRF 100 to determine whether the NF identified in the CMP certificate request is registered. In one example, the query used to determine whether the NF is registered may be an NFDiscover request. In line 4, NRF 100 responds, indicating that NF 202 is not registered. Because NF 202 is not registered, CA agent 600 forwards or allows the CMP certificate request to pass to CMP CA 204 in line 5. CMP CA 204 renews the TLS certificate for NF 202 and, in line 6, sends a CMP certificate response including NF 202's TLS certificate to CMP CA agent 600. In line 7, CMP CA agent 600 sends the CMP certificate response to CM 200. In line 8 , CMP CA 204 sends a NF Certificate Response to NF 202 .

[0069] In line 9, NF 202 registers with NRF 100 using the NFRegister service operation. In line 10, a hacker who has obtained the CMP client identity private key and public key certificate of NF 202 sends a CMP certificate request to CA 204. The CMP certificate request includes the public key certificate of NF 202 but does not include the OAuth 2.0 access token of NF 202. CMP CA agent 600 intercepts the CMP certificate request, determines that the request is for the TLS certificate of an already registered NF, determines that the request does not include the OAuth 2.0 access token, and performs a network security action in step 11, such as blocking the request.

[0070] Figure 8 is a block diagram illustrating an exemplary architecture for a CMP CA agent 600. Figure 8, the CMP CA agent 600 includes at least one processor 800 and memory 802. The CMP CA agent 600 may also include a CMP certificate request validator 804 for performing the steps described herein for validating a CFP certificate request before allowing the request to proceed to the CMP CA 204. The CMP certificate request validator 804 may be implemented using computer-executable instructions stored in the memory 802 and executed by the processor 800. The CMP CA agent 600 may be a standalone entity or may be a component of the NRF.

[0071] The CMP CA agent 600 may register as a custom NF with the NRF 100. Registration of the CMP CA agent 600 with the NRF 100 may be necessary for the CMP CA agent 600 to be allowed to query the NRF 100 to determine whether the NF is registered. The scope of the OAuth 2.0 access token issued by the NRF for the CA agent 600 may be limited to the CA agent service.

[0072] Figure 9 is a flow chart illustrating an exemplary process for preventing unauthorized use of a CMP client identity private key and a CMP public key certificate associated with a NF. Figure 9 In step 900, the process includes receiving, by a CMP Certificate Authority (CA) agent, a first CMP certificate request for renewing a security certificate associated with a first NF, the CMP certificate request including a public key certificate associated with the first NF. For example, the CMP CA agent 600 may receive a CMP certificate request requesting a TLS or other security certificate for the NF. If the request is legitimate, then the request likely originated from a CM associated with the first NF. If the request is illegitimate, then the request likely originated from a hacker who has stolen the CMP client identity private key and public key certificate associated with the first NF.

[0073] In step 902, the process also includes checking, by the CMP CA agent, whether the first NF is registered with the NF repository function (NRF), and determining that the first NF is registered with the NRF. For example, the CMP CA agent 600 may query the NRF using, for example, an NFDiscover request or other type of query message to determine whether the first NF is registered with the NRF. The CMP CA agent 600 may determine that the first NF is registered with the NRF by receiving an NFDiscover or other response message indicating that the first NF is registered with the NRF.

[0074] In step 904, the processing also includes: in response to the CMP CA agent determining that the first NF has registered with the NRF, the CMP CA agent checks whether the first CMP certificate request includes an access token issued by the NRF for the first NF, and determines that the CMP certificate request does not include an access token issued by the NRF for the first NF. For example, the CMP CA agent 600 can determine whether the CMP certificate request includes an OAuth 2.0 access token in addition to the public key certificate of the first NF and a signature generated using the CMP client identity private key associated with the first NF. The CMP CA agent 600 can extract the OAuth 2.0 access token from the request and verify the OAuth 2.0 access token using the public key of the NRF. In step 904, the CMP CA agent 600 determines that the OAuth 2.0 access token is not present in the CMP certificate request.

[0075] In step 906, the process further includes: in response to the CMP CA agent determining that the first CMP certificate request does not include an access token issued by the NRF for the first NF, performing a network security action with respect to the first CMP certificate request. For example, the CMP CA agent 600 may prevent the CMP CA request from reaching the CA, thereby preventing the initiator of the CMP certificate request from obtaining a TLS certificate for the first NF.

[0076] While the above examples relate to reducing the likelihood of a hacker successfully impersonating an NF to renew the NF's TLS certificate, the subject matter described herein is not limited to preventing unauthorized renewal of TLS certificates. The same protections and protocols can be used to reduce the likelihood of a hacker successfully renewing or obtaining a Client Credential Assertion (CCA) certificate associated with an NF. The message flow for preventing unauthorized renewal of a CCA certificate is similar to the message flow described above, with the following exceptions: the CMP certificate request will identify the request as a request for a CCA certificate, rather than a request for a TLS certificate. An OAuth 2.0 access token will be a mandatory parameter of the CMP certificate request used to obtain the NF's CCA certificate.

[0077] Exemplary advantages of the subject matter described herein include preventing hackers from using stolen CMP client identity private keys and public key certificates to obtain NF TLS certificates. This further prevents hackers from impersonating NFs to access 5G entities that rely on transport-based security mechanisms to authenticate NFs. The CMP CA agent can be used to authenticate NFs for any NF, including Figure 1The CMP CA Proxy functionality, which validates the certificate request using an OAuth 2.0 access token issued by the NRF, is extensible to enhance the security / protection of the certificate management protocol for other types of certificates, in addition to TLS certificates, that may be used for future 5G or subsequent generation deployments. The CMP CA Proxy can be used in combination with any 5G or other generation network function, including but not limited to the NRF, SCP, SEPP, PCF, BSF, NEF, NSSF, UDR, Equipment Identity Register (EIR), or Network Data Analysis Function (NWDAF).

[0078] The disclosure of each of the following references is hereby incorporated by reference in its entirety.

[0079] References

[0080] 1.3 rd Generation Partnership Project; Technical Specification GroupServices and System Aspects for the 5G System(5GS); Stage 2; (Release 17)3GPPTS23.501V17.7.0(2022-12)

[0081] 2.3 rd Generation Partnership Project; Technical Specification GroupServices and System Aspects; Procedures for the 5G System(5GS); Stage 2(Release17)3GPP TS23.502V17.7.0(2022-12)

[0082] 3.3 rd Generation Partnership Project; Technical Specification GroupCore Network and Terminals; 5G System; Network Function Repository Services; Stage 3(Release 18)3GPP TS29.510V18.1.0(2022-12)

[0083] 4.3 rdGeneration Partnership Project; Technical Specification GroupCore Network and Terminals; 5G System; Technical Realization of Service BasedArchitecture; Stage 3(Release 18)3GPP TS29.500V18.0.0(2022-12)

[0084] 5.3 rd Generation Partnership Project; Technical Specification GroupCore Network and Terminals; 5G System; Principles and Guidelines for ServicesDefinition; Stage 3(Release 18)3GPP TS 29.501V18.0.0(2022-12)

[0085] 6.3 rd Generation Partnership Project; Technical Specification GroupServices and System Aspects; Security architecture and procedures for 5Gsystem(Release 18)3GPP TS 33.501V18.0.0(2022-12)

[0086] It should be understood that various details of the subject matter described herein may be changed without departing from the scope of the subject matter described herein. Furthermore, the foregoing description is for the purpose of illustration only and not for the purpose of limitation, as the subject matter described herein is defined by the claims set forth hereinafter.

Claims

1. A method for preventing unauthorized use of a Certificate Management Protocol (CMP) client identity private key and a CMP public key certificate associated with a Network Function (NF), the method comprising: Receiving, by a CMP certificate authority (CA) agent, a first CMP certificate request for renewing a security certificate associated with a first NF, the CMP certificate request including a public key certificate associated with the first NF and protected by a CMP client identity private key associated with the first NF; Checking, by the CMP CA agent, whether the first NF has been registered with the NF repository function (NRF), and determining that the first NF has been registered with the NRF; In response to determining, by the CMP CA agent, that the first NF has registered with the NRF, checking, by the CMP CA agent, whether the first CMP certificate request includes an access token issued by the NRF for the first NF, and determining that the CMP certificate request does not include the access token issued by the NRF for the first NF; as well as In response to determining by the CMP CA agent that the first CMP certificate request does not include an access token issued by the NRF for the first NF, a network security action is performed with respect to the first CMP certificate request. 2 . The method of claim 1 , wherein receiving the first CMP certificate request comprises receiving the first CMP certificate request from a hacker impersonating the first NF. 3 . The method of claim 2 , wherein performing a network security action with respect to the first CMP certificate request comprises preventing the CMP CA from providing a security certificate to a hacker. 4 . The method of claim 3 , wherein preventing the CMP CA from providing the security certificate to the hacker comprises preventing the first CMP certificate request from reaching the CMP CA.

5. The method of any of the preceding claims, wherein receiving the first CMP certificate request at the CMP CA proxy comprises receiving the first CMP certificate request at a CMP CA proxy that is a component of the NRF or at a CMP CA proxy that is separate from the NRF.

6. The method of any of the preceding claims, wherein receiving the first CMP certificate request comprises intercepting the first CMP certificate request.

7. The method according to any one of the preceding claims, wherein receiving the first CMP certificate request comprises receiving a first CMP certificate request for a Transport Layer Security (TLS) or Client Credential Assertion (CCA) certificate of the first NF.

8. The method according to any one of the preceding claims, wherein checking whether the first CMP certificate request includes an access token issued by an NRF for the first NF comprises: Check whether the first CMP request includes an OAuth2.0 access token issued by the NRF to the first NF.

9. The method according to any one of the preceding claims, comprising: receiving, by the CMP CA agent, a second CMP certificate request for renewing a security certificate associated with the second NF, the request including a public key certificate associated with the second NF and protected by a CMP client identity private key associated with the second NF; The CMP CA agent checks whether the second NF is registered with the NRF and determines that the second NF is not registered with the NRF; as well as In response to determining that the second NF is not registered with the NRF, processing of the second CMP certificate request is permitted.

10. The method of claim 9, wherein allowing processing of the second CMP certificate request comprises: Submitting the second CMP certificate request to the CMP CA; generating, at the CMP CA, a CMP certificate response including a security certificate associated with the second NF; and forwarding the CMP certificate response to the initiator of the second CMP certificate request.

11. The method according to any one of the preceding claims, comprising: The second NF transmits a second CMP certificate request for renewing a second security certificate associated with the second NF to the CMP CA agent, the second CMP certificate request including a public key certificate associated with the second NF and an access token issued by the NRF; Receiving, by the CMP CA agent, a second CMP certificate request; The CMP CA agent checks whether the second NF has been registered with the NRF and determines that the second NF has been registered with the NRF; In response to determining, by the CMP CA agent, that the second NF is registered with the NRF, checking, by the CMP CA agent, whether the second CMP certificate request includes an access token issued by the NRF associated with the second NF, and determining that the second CMP certificate request includes the access token issued by the NRF associated with the second NF; as well as In response to determining by the CMP CA agent that the second CMP certificate request includes an access token issued by an NRF associated with the second NF, processing of the second CMP certificate request is enabled by forwarding the second CMP certificate request to the CMP CA agent.

12. A system for preventing unauthorized use of a Certificate Management Protocol (CMP) client identity private key and a CMP public key certificate associated with a Network Function (NF), the system comprising: A CMP certificate authority (CA) agent comprising at least one processor and memory; as well as a CMP certificate request validator implemented by the at least one processor, the CMP certificate request validator configured to: receive a first CMP certificate request for renewing a security certificate associated with a first NF, the CMP certificate request including a public key certificate associated with the first NF and protected by a CMP client identity private key associated with the first NF; check whether the first NF is registered with an NF repository function (NRF), and determine that the first NF is registered with the NRF; In response to determining that the first NF has registered with the NRF, checking whether the first CMP certificate request includes an access token issued by the NRF for the first NF, and determining that the CMP certificate request does not include the access token issued by the NRF for the first NF; and in response to determining that the first CMP certificate request does not include an access token issued by the NRF for the first NF, performing a network security action with respect to the first CMP certificate request.

13. The system of claim 12, wherein the first CMP certificate request originates from a hacker impersonating the first NF.

14. The system according to claim 13, wherein: When performing the network security action for the first CMP certificate request, the CMP certificate request validator is configured to prevent the CMP CA from providing the security certificate to the hacker by preventing the first CMP certificate request from reaching the CMP CA.

15. The system according to claims 12 to 14, wherein the CMP CA agent comprises a component of the NRF or is separate from the NRF.

16. The system according to any one of claims 12 to 15, wherein the CMP CA agent is configured to receive the first CMP certificate request by intercepting the first CMP certificate request.

17. The system according to any one of claims 12 to 16, wherein the security certificate comprises a Transport Layer Security (TLS) or Client Credential Assertion (CCA) certificate of the first NF.

18. The system according to any one of claims 12 to 17, wherein the access token issued by the NRF for the first NF comprises an OAuth 2.0 access token issued by the NRF to the first NF.

19. The system according to any one of claims 12 to 18, wherein the CMP certificate request validator is configured to: receiving a second CMP certificate request for renewing a security certificate associated with the second NF, the request including a public key certificate associated with the second NF and protected by a CMP client identity private key associated with the second NF; checking whether the second NF is registered with the NRF, and determining that the second NF is not registered with the NRF; and In response to determining that the second NF is not registered with the NRF, processing of the second CMP certificate request is permitted.

20. The system according to any one of claims 12 to 19, comprising a second NF, the second NF being configured to transmit a second CMP certificate request for renewing a second security certificate associated with the second NF to the CMP CA agent, the second CMP certificate request comprising a public key certificate associated with the second NF, protected by a CMP client identity private key associated with the second NF, and comprising an access token issued by an NRF associated with the second NF, wherein the CMP certificate request validator is configured to: receiving a second CMP certificate request; Check whether the second NF has been registered with the NRF, and confirm that the second NF has been registered with the NRF; In response to determining that the second NF has registered with the NRF, checking whether the second CMP certificate request includes an access token issued by the NRF associated with the second NF, and determining that the second CMP certificate request includes the access token issued by the NRF associated with the second NF; as well as In response to determining that the second CMP certificate request includes an access token issued by the NRF associated with the second second NF, processing of the second CMP certificate request is permitted by forwarding the second CMP certificate request to the CMP CA.

21. A non-transitory computer-readable medium having executable instructions stored thereon, wherein when the executable instructions are executed by a processor of a computer, the computer is controlled to perform the following steps: receiving, by a Certificate Management Protocol (CMP) certificate authority (CA) agent, a first CMP certificate request for renewing a security certificate associated with a first network function (NF), the CMP certificate request including a public key certificate associated with the first NF and protected by a CMP client identity private key associated with the first NF; Checking, by the CMP CA agent, whether the first NF has been registered with the NF repository function (NRF), and determining that the first NF has been registered with the NRF; In response to determining, by the CMP CA agent, that the first NF has registered with the NRF, checking, by the CMP CA agent, whether the first CMP certificate request includes an access token issued by the NRF for the first NF, and determining that the CMP certificate request does not include the access token issued by the NRF for the first NF; as well as In response to determining by the CMP CA agent that the first CMP certificate request does not include an access token issued by the NRF for the first NF, a network security action is performed with respect to the first CMP certificate request.

Images