Mobile communication N1N2 interface security protection device and method

Abstract

The present invention discloses a mobile communication N1N2 interface security protection device and method, the device includes an underlying protocol stack, a north-south interface and a security protection processing unit, the underlying protocol stack provides the corresponding layer message receiving and parsing functions, the security protection processing unit provides the communication system with a compliance check function and a NAS signaling decryption function, and the north-south interface provides the operation instructions of each underlying protocol stack and the operation instructions of the security protection processing unit. The present invention can not only perform compliance checks on state machines, signaling messages, terminal identities and base station identities, but also cope with the situation where NAS signaling itself is encrypted, and will not affect communication services.

Description

Technical Field

[0001] The present invention belongs to the field of communication security technology, and in particular relates to a mobile communication N1N2 interface security protection device and method. Background Art

[0002] The traditional 5G private network security solution model includes mobile terminal-base station-core network-VPN gateway-mobile application. The 3GPP standard specifies the corresponding security mechanism for the network attachment signaling process of the mobile terminal, such as Figure 1 The figure shows the security mechanism specified in the standard for signaling of network attachment in mobile communications.

[0003] The existing security mechanisms specified in the 3GPP standards have the following security risks:

[0004] (1) The main authentication of the 3GPP standard is actually aimed at the SIM module on the mobile terminal, and the user plane authentication of industry applications is actually aimed at the security module on the mobile terminal. Neither of them performs identity compliance verification on the mobile terminal itself or the base station itself. Attackers can exploit vulnerabilities in mobile terminals and base stations, or malicious terminals and base stations, to launch attacks on the core network.

[0005] (2) The base station will unconditionally forward NAS signaling messages sent to the terminal. Once an attacker obtains a legitimate USIM module, he can still use an illegal mobile terminal to launch an attack on the core network by sending illegal NAS signaling messages before the user plane service channel is established.

[0006] (3) In addition to sending illegal NAS signaling messages, attackers can also use illegal mobile terminals to construct and replay legal NAS signaling messages, and use legal NAS signaling messages in unauthorized processes and state machines, thereby attacking the availability of the core network.

[0007] (4) NAS signaling before SMC security mode negotiation does not support integrity protection, and attackers can tamper with NAS messages before SMC;

[0008] (5) 3GPP does not provide a security mechanism for the NG-AP layer (5G) / S1-AP layer (4G) signaling carried by the NAS protocol. Attackers can forge, tamper with, and replay NG-AP / S1-AP layer messages.

[0009] To address the above security risks, the current solution is to connect a signaling security protection device in series between the base station and the core network. However, the following problems may arise during use:

[0010] (1) After the SMC security mode is negotiated, NAS signaling may be encrypted, making it impossible to perform compliance checks on the format and content of NAS signaling;

[0011] (2) The signaling security protection device in the serial deployment mode will increase the overhead of the mobile terminal's network attachment process, and once it fails, it will cause the mobile communication service to be unavailable. Summary of the invention

[0012] The purpose of the present invention is to overcome the defects of the prior art and provide a mobile communication N1N2 interface security protection device and method, which can perform compliance checks on state machines, signaling messages, terminal identities and base station identities, and perform compliance checks on encrypted NAS (Network Attached Storage) signaling after decryption.

[0013] The object of the present invention is achieved through the following technical solutions:

[0014] A mobile communication N1N2 interface security protection device, the device is applied to a communication system composed of a mobile terminal, a base station and a core network AMF (Access and Mobility Management Function), and obtains uplink and downlink signaling traffic from the core network AMF in a mirroring manner. The device includes:

[0015] The underlying protocol stack includes IP bearer, SCTP (Stream Control Transmission Protocol) protocol stack, S1-AP / NG-AP protocol stack and NAS protocol stack, providing the reception and parsing functions of the corresponding layer messages;

[0016] A security protection processing unit, the security protection processing unit including a state machine compliance check submodule, a signaling message compliance check submodule, a terminal identity compliance check submodule, a base station identity compliance check submodule and a NAS signaling decryption submodule, providing a compliance check function and a NAS signaling decryption function for the communication system;

[0017] A north-south interface, wherein the north-south interface includes a callback function set and an API interface set, wherein the callback function set includes operation instructions of each underlying protocol stack, and the API interface set includes operation instructions of a security protection processing unit.

[0018] On the other hand, the present invention also provides a mobile communication N1N2 interface security protection method, which is implemented based on the above-mentioned security protection device. The method includes decrypting the encrypted NAS signaling and performing compliance checking, specifically including:

[0019] The uplink and downlink NAS signaling messages are obtained in the NAS callback function;

[0020] Extracting and tracking the main authentication process of each mobile terminal from the uplink and downlink NAS signaling messages;

[0021] Obtain the NAS signaling decryption key from the primary authentication subsequent signaling process;

[0022] Obtain the NAS encryption algorithm used by both the mobile terminal and the AMF network element from the NAS security mode negotiation process, and decrypt the NAS signaling according to the NAS signaling decryption key;

[0023] After decryption, the format and content of the NAS signaling are checked for compliance.

[0024] Further, the obtaining of the NAS signaling decryption key from the subsequent signaling process of the primary authentication specifically includes:

[0025] If the core network is customizable, the decryption key of each mobile terminal NAS signaling is obtained directly from the core network AMF network element;

[0026] If the core network is not customizable, the derived key information of the interaction between network elements is obtained and tracked from the mirrored signaling flow, and the decryption key of the NAS signaling is calculated.

[0027] Further, decrypting the NAS signaling according to the NAS signaling decryption key specifically includes:

[0028] If the NAS security mode negotiation uses the null algorithm, no decryption processing is required;

[0029] If the encryption algorithm is enabled in the NAS security mode negotiation, the encryption algorithm and decryption key of the NAS signaling are obtained.

[0030] On the other hand, the present invention also provides a mobile communication N1N2 interface security protection method, which is implemented based on the above-mentioned security protection device, and the method includes base station identity compliance check, specifically including:

[0031] Get the source and destination IP addresses and port numbers in the upstream SCTP message from the SCTP callback function;

[0032] Use the source IP address to match the base station compliance check policy, and use the destination IP address to match the core network elements that the base station can access. When an abnormal situation occurs, perform protection operations on the core network.

[0033] Check whether the destination port number matches the port number corresponding to the S1-AP or NG-AP protocol, and perform protection operations on the core network if an abnormality occurs;

[0034] Get the base station ID and base station name in the uplink S1-AP or NG-AP message from the S1-AP or NG-AP callback function, and perform protection operations to the core network when an abnormal situation occurs.

[0035] On the other hand, the present invention also provides a mobile communication N1N2 interface security protection method, which is implemented based on the above-mentioned security protection device. The method includes terminal identity compliance check, specifically including:

[0036] Obtaining user identification information of the mobile terminal from an uplink network attachment request NAS message;

[0037] If the mobile terminal carries an unencrypted SUCI (Subscription concealed identifier), the SUPI (subscription identifier) / IMSI (International Mobile Subscriber Identity) is directly parsed from it, and the mobile terminal identity compliance check is performed based on the SUPI / IMSI, and protection operations are performed for the access of unauthorized mobile terminals;

[0038] If the mobile terminal carries an encrypted SUCI, the SUPI / IMSI identifier of the mobile terminal is obtained through a subsequent process;

[0039] If the mobile terminal carries a GUTI and the core network is customizable, the SUPI / IMSI corresponding to the GUTI is obtained from the AMF network element through the GUTI, and the mobile terminal identity compliance check is performed based on the SUPI / IMSI, and protection operations are performed for the access of unauthorized mobile terminals;

[0040] If the mobile terminal carries the GUTI and the core network is not customizable, the SUPI / IMSI identifier of the mobile terminal is obtained through the subsequent process;

[0041] Get the various elements of the uplink NAS security mode complete SMC message from the NAS callback function;

[0042] According to the IMEI / PEI identification carried in the element, the compliance check policy of the mobile terminal identity is matched, and protection operations are performed on the access of unauthorized mobile terminals;

[0043] Obtain the SUPI / IMSI passed by the core network AUSF (Authentication Server Function) network element to the AMF network element from the subsequent process of the main authentication, perform mobile terminal identity compliance check based on the SUPI / IMSI, and perform protection operations for the access of unauthorized mobile terminals.

[0044] On the other hand, the present invention also provides a mobile communication N1N2 interface security protection method, which is implemented based on the above-mentioned security protection device. The method includes message compliance checking, specifically including:

[0045] Get the message fields in the upstream SCTP message from the SCTP callback function;

[0046] Determine whether the formats of each field in the upstream SCTP message are compliant;

[0047] If there are fields in an uncompliant format in the upstream SCTP message, protection operations are performed;

[0048] If the formats of all fields in the uplink SCTP message are compliant, obtain all elements in the uplink S1-AP or NG-AP message from the S1-AP or NG-AP callback function, and if there are non-compliant elements in the elements, perform protection operations;

[0049] If all elements are compliant, obtain all elements in the uplink NAS message from the NAS callback function. If there are non-compliant elements in the uplink NAS message, perform protection operations. If all elements are compliant, it is determined to be a legal message.

[0050] Furthermore, the elements include optional elements and mandatory elements. When both the optional elements and the mandatory elements are compliant, the elements are determined to be compliant; otherwise, it is determined that non-compliant elements exist.

[0051] Further, the obtaining of each mandatory element in the uplink NAS message from the NAS callback function includes:

[0052] If the NAS message is a ciphertext message, it is first decrypted and then each element is obtained.

[0053] On the other hand, the present invention also provides a mobile communication N1N2 interface security protection method, the method is implemented by the aforementioned security protection device, the method includes a state machine compliance check, specifically including:

[0054] Maintaining the session management state machine for each user and the uplink and downlink NAS signaling messages related to the user, including:

[0055] Perform compliance checks on each event input into the session management state machine and perform protection actions on non-compliant NAS signaling messages.

[0056] The beneficial effects of the present invention are:

[0057] The present invention provides a mobile communication N1N2 interface security protection device and method, which can not only solve the security risks existing in the standard 3GPP security mechanism, but also cope with the situation where the NAS signaling itself is encrypted, and will not affect the communication business, so as to meet the security requirements of key industries for mobile communication private networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a security mechanism specified in the mobile communication standard for network attachment signaling;

[0059] Figure 2 Schematic diagram of a mobile communication N1N2 interface security protection device according to an embodiment of the present invention;

[0060] Figure 3 This is a flow chart of a security protection method in a 4G private network application according to an embodiment of the present invention;

[0061] Figure 4 It is a flow chart of the security protection method of an embodiment of the present invention in 5G private network applications. DETAILED DESCRIPTION

[0062] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0063] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0064] The traditional solution uses a method of connecting a signaling security protection device in series between the base station and the core network to solve the security risks of the security mechanism specified by the 3GPP standard. This has the following disadvantages:

[0065] (1) After the SMC security mode is negotiated, NAS signaling may be encrypted, making it impossible to perform compliance checks on the format and content of NAS signaling;

[0066] (2) The signaling security protection device in the serial deployment mode will increase the overhead of the mobile terminal's network attachment process, and once it fails, it will cause the mobile communication service to be unavailable.

[0067] In order to solve the above technical problems, the following embodiments of the mobile communication N1N2 interface security protection device and method of the present invention are proposed.

[0068] Example 1

[0069] Reference Figure 2 ,like Figure 2 The figure shows a schematic diagram of the mobile communication N1N2 interface security protection device of this embodiment. The device is applied to a communication system composed of a mobile terminal, a base station and a core network AMF, and obtains uplink and downlink signaling traffic from the core network AMF in a mirroring manner.

[0070] Specifically, the device includes three parts: underlying protocol stack, north-south interface, and security protection processing.

[0071] Among them, the underlying protocol stack includes IP bearer, SCTP protocol stack, S1-AP (4G) / NG-AP (5G) protocol stack and NAS protocol stack, which mainly provide the reception and parsing functions of the corresponding layer messages. The north-south interface includes a callback function set and an API interface set. The callback function set is mainly the event notification and related operations at each time point after the reception and parsing of each layer of the protocol stack in the underlying protocol stack. The API interface set is mainly the various operations performed by the security protection processing itself and the control processing of each layer of the protocol stack in the underlying protocol stack. The security protection processing includes five sub-modules: NAS signaling decryption, base station identity compliance check, terminal identity compliance check, message compliance check, and state machine compliance check.

[0072] Among them, the specific method of NAS signaling decryption is as follows:

[0073] S1. Get the uplink and downlink NAS signaling messages from the NAS callback function;

[0074] S2, extract and track the main authentication process of each mobile terminal from the uplink and downlink NAS signaling messages;

[0075] S2. Obtain the NAS signaling decryption key from the subsequent signaling process of the primary authentication;

[0076] S2-1. If the core network is customizable, the decryption key K of each mobile terminal NAS signaling is obtained directly from the core network AMF network element. NASenc ;

[0077] S2-2. If the core network is not customizable, obtain and track the derived key information of the interaction between network elements from the mirror signaling flow, and calculate the decryption key K of the NAS signaling NASenc ;

[0078] S3, obtain the NAS encryption algorithm used by the mobile terminal and the AMF network element from the NAS security mode negotiation process;

[0079] S3-1. If the NAS security mode negotiation uses the null algorithm (i.e. no encryption), no decryption is required;

[0080] S3-2, if the NAS security mode negotiation enables the encryption algorithm (one of AES, Snow-3G, Zuc), according to the encryption algorithm and decryption key K of the obtained NAS signaling NASenc , complete the decryption of NAS signaling.

[0081] The specific method of base station identity compliance check is as follows:

[0082] S1. Get the source and destination IP addresses and port numbers in the upstream SCTP message from the SCTP callback function;

[0083] S2. Use the source IP address to match the base station compliance check policy, and use the destination IP address to match the core network elements that the base station can access. If any abnormal situation occurs, a security alarm will be sent to the core network in a timely manner.

[0084] S3. Check whether the destination port number matches the port number corresponding to the S1-AP or NG-AP protocol it carries (the default port number for S1-AP is 36412, and the default port number for NG-AP is 38412). If any abnormality occurs, promptly send a security alarm to the core network;

[0085] S4. Obtain the base station ID and base station name in the uplink S1-AP or NG-AP message from the S1-AP or NG-AP callback function, and promptly send a security alarm to the core network in case of abnormal conditions.

[0086] The specific method of terminal identity compliance check is as follows:

[0087] S1. Obtain user identification information of the mobile terminal from an uplink network attachment request NAS message;

[0088] S1-1. If the mobile terminal carries an unencrypted SUCI, the SUPI / IMSI is directly parsed from it, and the mobile terminal identity compliance check is performed based on the SUPI / IMSI, and a security alarm is issued for the access of unauthorized mobile terminals;

[0089] S1-2. If the mobile terminal carries an encrypted SUCI, the SUPI / IMSI identifier of the mobile terminal is obtained through a subsequent process;

[0090] S1-3. If the mobile terminal carries a GUTI and the core network is customizable, the SUPI / IMSI corresponding to the GUTI is obtained from the AMF network element through the GUTI, and the mobile terminal identity compliance check is performed based on the SUPI / IMSI, and a security alarm is issued for the access of unauthorized mobile terminals;

[0091] S1-4. If the mobile terminal carries the GUTI and the core network cannot be customized, the SUPI / IMSI identifier of the mobile terminal is obtained through a subsequent process;

[0092] S2. Obtain the various elements of the uplink NAS security mode completion SMC message from the NAS callback function;

[0093] S3. Complete the IMEI / PEI identification carried in each element of the SMC message according to the uplink NAS security mode, match the compliance check strategy of the mobile terminal identity, and issue a security alarm for the access of unauthorized mobile terminals;

[0094] S4. Obtain the SUPI / IMSI transmitted by the core network AUSF network element to the AMF network element from the subsequent process of the main authentication, and perform a mobile terminal identity compliance check based on the SUPI / IMSI, and issue a security alarm for the access of unauthorized mobile terminals.

[0095] The specific method of message compliance check is as follows:

[0096] S1. Get the message fields in the uplink SCTP message from the SCTP callback function;

[0097] S2. Determine whether the formats of each field in the uplink SCTP message are compliant;

[0098] S2-1. If there are fields in an uncompliant format in the upstream SCTP message, a security alarm is issued;

[0099] S2-2. If the formats of all fields in the uplink SCTP message are compliant, continue with the subsequent processing;

[0100] S3. Obtain each mandatory element and optional element in the uplink S1-AP or NG-AP message from the S1-AP or NG-AP callback function;

[0101] S3-1. If there are mandatory elements in the uplink S1-AP or NG-AP message that do not conform to the format, a security alarm is issued;

[0102] S3-2: If there are optional elements in an uncompliant format in the uplink S1-AP or NG-AP message, a security alarm is issued;

[0103] S3-3. If the formats of all mandatory and optional elements in the uplink S1-AP or NG-AP message are compliant, continue with the subsequent processing;

[0104] S4. Obtain each optional element and mandatory element in the uplink NAS message from the NAS callback function;

[0105] S4-1. If the NAS message is a ciphertext message, decrypt it first;

[0106] S4-2: If there are non-compliant mandatory elements in the uplink NAS message, a security alarm is issued;

[0107] S4-3. If there are non-compliant optional elements in the uplink NAS message, a security alarm is issued;

[0108] S4-4. If the formats of all mandatory and optional elements in the uplink NAS message are compliant, it is determined to be a legal message.

[0109] The specific method of state machine compliance check is as follows:

[0110] S1. Maintain the mobility management and session management state machines for each UE and its related uplink and downlink NAS signaling messages;

[0111] S2. For the current specific state of the mobility management state machine, an access control mechanism that implements a whitelist strategy based on the state input trigger event is used to issue a security alert for illegal NAS signaling messages of the state machine to prevent subsequent NAS signaling disguised as legal formats from attacking the core network through abnormal state machines;

[0112] S3. For the current specific state of the session management state machine, an access control mechanism that implements a whitelist strategy based on the state input trigger event is used to issue a security alert for illegal NAS signaling messages of the state machine to prevent subsequent NAS signaling disguised as a legal format from attacking the core network through an abnormal state machine.

[0113] The mobile communication N1N2 interface security protection device provided in this embodiment can not only solve the security risks existing in the standard 3GPP security mechanism, but also cope with the situation where the NAS signaling itself is encrypted, and will not affect the communication business, so as to meet the security requirements of key industries for mobile communication private networks.

[0114] Example 2

[0115] This embodiment provides an application example in a 4G private network. Figure 3 ,like Figure 3 Shown is a flow chart of the security protection method of this embodiment in 4G private network applications.

[0116] The relevant functional entities include 4G mobile terminal UE, 4G base station eNB, 4G core network EPC, 4G private network application and signaling security protection device. It should be noted that the N1N2 interface in the 4G system is the LTE-Uu and S1-MME interfaces.

[0117] The specific steps include:

[0118] S1. Provide security protection for SCTP bearer connections;

[0119] S1-1, perform compliance check on the base station identity and access destination according to the SCTP IP and port number;

[0120] S1-2, perform message compliance check according to the SCTP message format;

[0121] S1-3. Perform proxy transfer on compliant SCTP bearer connections.

[0122] S2, provide security protection for S1-AP bearer connection;

[0123] S2-1, based on the base station ID and base station name in the S1-AP message, perform compliance check on the base station identity and access destination;

[0124] S2-2. Perform message compliance check based on the mandatory and optional element formats in the S1-AP message.

[0125] S2-3. Issue security alerts for non-compliant S1-AP bearer connections.

[0126] S3, provide security protection for NAS signaling;

[0127] S3-1. If the NAS signaling is encrypted, it is first decrypted;

[0128] S3-2, perform compliance check on the mobile terminal identity according to the IMEI in the NAS message;

[0129] S3-3, performing compliance check on the mobile terminal identity based on the acquired IMSI;

[0130] S3-4. Check the compliance of the message according to the required and optional element formats in the NAS message;

[0131] S3-5. According to the mobility management and session management state machines, a compliance check is performed on the input events of the current state machine of each UE;

[0132] S3-6. Issue security alerts for non-compliant NAS signaling messages.

[0133] Example 3

[0134] This embodiment provides an application example in a 5G private network. Figure 4 ,like Figure 4 Shown is a flow chart of the security protection method of this embodiment in 5G private network applications.

[0135] Relevant functional entities include 5G mobile terminal UE, 5G base station gNB, 5G core network 5GC, 5G private network applications and signaling security protection devices.

[0136] The specific steps include:

[0137] S1. Provide security protection for SCTP bearer connections;

[0138] S1-1, perform compliance check on the base station identity and access destination according to the SCTP IP and port number;

[0139] S1-2, perform message compliance check according to the SCTP message format;

[0140] S1-3. Issue security alerts for non-compliant SCTP bearer connections.

[0141] S2. Provide security protection for NG-AP bearer connections;

[0142] S2-1, perform compliance check on the base station identity and access destination according to the base station ID and base station name in the NG-AP message;

[0143] S2-2. Perform message compliance check based on the mandatory and optional element formats in the NG-AP message.

[0144] S2-3. Issue security alerts for non-compliant NG-AP bearer connections.

[0145] S3, provide security protection for NAS signaling;

[0146] S3-1. If the NAS signaling is encrypted, it is first decrypted;

[0147] S3-2, perform compliance check on the mobile terminal identity according to the PEI in the NAS message;

[0148] S3-3. Perform compliance check on the mobile terminal identity based on the obtained SUPI;

[0149] S3-4. Check the compliance of the message according to the required and optional element formats in the NAS message;

[0150] S3-5. According to the mobility management and session management state machines, a compliance check is performed on the input events of the current state machine of each UE;

[0151] S3-6. Issue security alerts for non-compliant NAS signaling messages.

[0152] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A mobile communication N1N2 interface security protection device, characterized in that: The device is applied to a communication system consisting of a mobile terminal, a base station and a core network AMF, and obtains uplink and downlink signaling traffic from the core network AMF in a mirroring manner. The device includes: The underlying protocol stack includes IP bearer, SCTP protocol stack, S1-AP / NG-AP protocol stack and NAS protocol stack, and provides the reception and parsing functions of corresponding layer messages; A security protection processing unit, the security protection processing unit including a state machine compliance check submodule, a signaling message compliance check submodule, a terminal identity compliance check submodule, a base station identity compliance check submodule and a NAS signaling decryption submodule, providing a compliance check function and a NAS signaling decryption function for the communication system; The NAS signaling decryption submodule includes: Get the uplink and downlink NAS signaling messages from the NAS callback function; Extracting and tracking the main authentication process of each mobile terminal from the uplink and downlink NAS signaling messages; Obtain the NAS signaling decryption key from the primary authentication subsequent signaling process; Obtain the NAS encryption algorithm used by both the mobile terminal and the AMF network element from the NAS security mode negotiation process, and decrypt the NAS signaling according to the NAS signaling decryption key; The process of obtaining the NAS signaling decryption key from the subsequent signaling process of the primary authentication specifically includes: If the core network is customizable, the decryption key of each mobile terminal NAS signaling is obtained directly from the core network AMF network element; If the core network is not customizable, obtain and track the derived key information exchanged between network elements from the mirrored signaling flow, and calculate the decryption key of the NAS signaling; A north-south interface, wherein the north-south interface includes a callback function set and an API interface set, wherein the callback function set includes operation instructions of each underlying protocol stack, and the API interface set includes operation instructions of a security protection processing unit.

2. The mobile communication N1N2 interface security protection method according to claim 1, characterized in that: The decrypting the NAS signaling according to the NAS signaling decryption key specifically includes: If the NAS security mode negotiation uses the null algorithm, no decryption processing is required; If the encryption algorithm is enabled in the NAS security mode negotiation, the encryption algorithm and decryption key of the NAS signaling are obtained.

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