CN103152731A - 3G accessed IMSI (international mobile subscriber identity) privacy protection method - Google Patents

Abstract

The invention discloses a 3G accessed IMSI (international mobile subscriber identity) privacy protection method. The method comprises the following steps that a VLR (visitor location register) sends a subscriber identity request, an MS (mobile subscriber) replies the subscriber identity response; the VLR/SGSN (serving GPRS supported node) sends an authentication data request to an HLR (home location register), and the HLR replies the authentication data response; and when the MS is authorized, the VLR/SGSN sends a subscriber authorization request to the MS, and the MS replies the subscriber authorization response. Through the method, the confidentiality of the IMSI is protected by means of key identifiers and key groups; and after the user transmitted IMSI information is encrypted, the information is transmitted by means of cipher texts, so that the IMSI is avoided from being leaked. At the same time, when the HLR generates an authentication vector for the user, an encryption key which is updated in real time is distributed, so that the representation forms are different after the user encrypts the IMSI information for each time, and the user can be avoided from being tracked.

Description

A 3G Access IMSI Privacy Protection Method

technical field

The invention relates to the technical field of 3G network communication security, in particular to an IMSI privacy protection method for 3G access.

Background technique

In the 3G network, the identity of a mobile subscriber (Mobile Subscriber, MS) is uniquely determined globally by the International Mobile Subscriber Identification Number (IMSI). The identity authentication phase of MS accessing the 3G network is completed by using the authentication and key distribution protocol (AKA). Through the exchange of authentication information between the core network and the MS, the mutual authentication and negotiation of communication keys between the MS and the network are realized. During the entire verification process, the IMSI It is transmitted in the form of plain text. Therefore, although the AKA protocol has effectively improved the security loopholes of the GSM system, it also has the problem of MS identity leakage. For this reason, in the 3GPP specification, the 3G network uses a temporarily assigned Temporary Mobile Subscriber Identity (TMSI) instead of the IMSI to protect the user's identity. However, in some cases, the system cannot determine the identity of the user through the TMSI, such as: when the user performs initial registration in the service network, or when the service network cannot retrieve the IMSI from the MS's TMSI, the service network still requires the MS to Provide the IMSI. At this time, the MS will respond with the IMSI information in plain text.

The IMSI protection methods of some MSs are realized by encrypting IMSI information or assigning aliases, but the practicability is not strong, such as: using the public key of the Home Location Register (Home Location Register, HLR) to encrypt the IMSI information, and regularly updating the IMSI information of the HLR Public-private key pair, which will bring a large calculation burden to network equipment and increase the delay of authentication; HLR shares a key with all MSs belonging to it, and uses this shared key to generate a The encryption key is used to symmetrically encrypt the IMSI information, but this method has the risk of key exposure, and it is easy to attack all MSs belonging to the same HLR due to the key leakage of a certain MS; each MS uses It encrypts with its own key K _i , and traverses all (IMSI, K _i ) records stored in the HLR on the network side until the correct IMSI information is found. This method uses its own key for encryption, although it can avoid the disadvantages of sharing the key and ensure the confidentiality of the MS identity, but it requires a large amount of calculation on the network side and has low efficiency.

Contents of the invention

Purpose of the invention: the present invention provides a 3G access IMSI privacy protection method, which uses key identification and symmetric key group to protect IMSI information, prevent MS identity from leaking, and at the same time ensure that HLR can easily decrypt IMSI ciphertext Find the decryption key for fast authentication.

Technical solution: an IMSI privacy protection method for 3G access, comprising the following steps:

(1) The VLR initiates an identity request to the user, requesting the user's permanent identity IMSI;

(2) The MS responds to the encrypted MSIN information, forms the encrypted IMSI information together with the routing information HLR_ID of the HLR, and submits the encryption key identification number K_ID _old at the same time; the MS needs to use the assigned symmetric key to encrypt the MSIN, and then communicate with the MCC|| The MNCs are combined together to form the encrypted information of the IMSI;

(3) After receiving the user identity response message, the VLR/SGSN sends an authentication data request message to the HLR according to the routing information HLR_ID of the HLR, that is, MCC||MNC, and the content includes the encrypted IMSI information and the encryption key identification number K_ID _old ;

(4) HLR finds the corresponding encryption key K _old from the key store according to the received K_ID _old , and decrypts the IMSI; then changes the record state corresponding to K_ID _old to FREE; then generates an authentication vector group for the IMSI, and distributes it at the same time The new key identifier K_ID _new and the new encryption key K _new ; obtain the authentication vector embedded in the key information, and then transmit the new authentication vector group AV _s together with the IMSI information to the VLR/SGSN;

(5) VLR/SGSN stores the authentication vector group AV _s and IMSI information from HLR, and sends the authentication information RAND _IN (i)||AUTN(i) to MS;

(6) MS uses the inverse function F′ of the embedded function F to extract random numbers RAND and K_ID _new ||K _new from RAND _IN ; calculate XMAC=f1 _k (SQN||RAND||AMF), and determine the equation MAC= Whether XMAC is set up, if set up then calculate response value RES=f2 _k (RAND) and send to VLR/SGSN, and store K_ID _new and K _new as new IMSI encryption key identification number and encryption key;

(7) After the VLR/SGSN obtains the RES sent by the MS, it judges whether the equation XRES=RES is established. If it is established, the authentication succeeds, otherwise the authentication fails.

Among them, HLR needs to maintain a key store, its size is determined according to the number of MSs to which HLR belongs, and each record includes four attributes, namely: key identification number KEY_ID, encryption key KEY, key usage status STATUS and update time TIME .

The present invention adopts the above technical scheme and has the following beneficial effects: in the present invention, since the IMSI information is transmitted in encrypted form each time the HLR is provided, the attacker cannot obtain the plaintext form of the IMSI. Secondly, when the HLR generates the authentication vector for the user, it will redistribute an encryption key to the user, that is, the expression form of the user's encrypted IMSI information is different every time, so as to avoid the user from being tracked.

Description of drawings

FIG. 1 is a schematic structural diagram of an IMSI in an embodiment of the present invention;

Fig. 2 is a schematic diagram of a key storehouse structure according to an embodiment of the present invention;

Fig. 3 is the key identification processing flowchart of the HLR of the embodiment of the present invention;

FIG. 4 is an AKA protocol diagram for protecting user privacy according to an embodiment of the present invention;

Fig. 5 is the process figure that the embedding function F of the embodiment of the present invention produces RAND _IN ;

FIG. 6 shows the process of obtaining K_ID _new ||K _new by the embedding function F of the embodiment of the present invention.

Detailed ways

Below in conjunction with specific embodiment, further illustrate the present invention, should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention, after having read the present invention, those skilled in the art will understand various equivalent forms of the present invention All modifications fall within the scope defined by the appended claims of the present application.

The implementation process of an IMSI privacy protection method for 3G access is as follows:

1. System initialization

FIG. 1 is a schematic diagram of an IMSI structure in an embodiment of the present invention, and each MS has a different IMSI. Each HLR generates a keystore composed of multiple records. The size of the keystore is determined according to the number of MSs that the HLR belongs to. Each record includes four attributes, namely the key identification number KEY_ID, the encryption key KEY, and the encryption key. Key usage status STATUS, update time TIME. The key usage status refers to whether the key is currently assigned to the user for IMSI encryption. If it is not used, it is marked as FREE, otherwise it is marked as USED; the update time TIME refers to the latest time when the record status is changed. Randomly select a key K _i and key identification number K_ID _i from the key storehouse and save it on the USIM (Universal Subscriber Identity Module) card of the MS. FIG. 2 is a schematic structural diagram of a key store according to an embodiment of the present invention. Fig. 3 is a flow chart of the key identification processing of the HLR according to the embodiment of the present invention.

2. The steps of the IMSI privacy protection method for 3G access, as shown in Figure 4:

(1) VLR (Visitor Location Register) initiates an identity request to the user, requesting the user's permanent identity IMSI;

(2) The MS replies with encrypted MSIN (Mobile Subscriber Identification Number, mobile subscriber identification number) information, which forms encrypted IMSI information together with HLR routing information HLR_ID. At the same time, submit the encryption key identification number K_ID _old , the size is 128bit; the MS response information is:

HLR_ID||K_ID _old ||f ₁₁ (K _old ,MSIN), where f ₁₁ is the function of encrypting IMSI information,

An initial key identification number and encryption key will be stored in the USIM card, which is randomly assigned by the HLR key store when the USIM card is generated;

(3) VLR/SGSN (Visitor Location Register/Serving GPRS SUPPORT NODE Visitor Location Register/GPRS Service Support Node) receives the user identity response message from MS, according to the HLR routing information HLR_ID, that is, MCC||MNC, to HLR Send an authentication data request message, the content includes the encrypted IMSI information and the key identification number K_ID _old ;

(4) HLR finds the corresponding encryption key K _old from the key store according to the received K_ID _old , the size of which is 128bit. Among them, use this key to decrypt to get the IMSI, and then change the status record corresponding to K_ID _old to FREE; The authentication vector set AV _s is then generated for the IMSI:

AV=RAND||XRES||CK||IK||AUTN

MAC＝f1 _K (SQN||RAND||AMF)

XRES＝f2 _K (RAND) AK＝f5 _K (RAND)

CK＝ _f3K (RAND)IK＝ _f4K (RAND)

Among them, RAND is a random number, XRES is an expected response value, CK is an encryption key, IK is an integrity key, and AUTN is an authentication token;

At the same time, assign a new key identification number K_ID _new and a new encryption key K _new (both 128 bits in size), and embed them into the random number RAND of AV _s , and the embedding function is F, as shown in Figure 5. Get the authentication vector with embedded key information: AV _IN ＝RAND _IN ||XRES||CK||IK||AUTN, and then send the new authentication vector group and IMSI information to VLR/SGSN: AV _s ||IMSI ;

(5) VLR/SGSN stores the authentication vector group AV _s and IMSI information from the HLR, takes out an unused authentication vector when it needs to authenticate the MS, and then sends a user authentication request message to the MS, including the RAND _IN ( i)||AUTN(i);

(6) MS uses the inverse function F' of the embedded function F to extract the random number RAND and K_ID _new ||K _new from RAND _IN , as shown in Figure 6. Calculate XMAC=f1 _k (SQN||RAND||AMF), and judge whether the equation MAC=XMAC holds true. If it is established, continue to verify whether the SQN belongs to the normal range, if the SQN does not belong to the normal range, then send a synchronization failure message to the VLR/SGSN and end the verification process, otherwise the user successfully authenticates the network identity. Then the MS calculates the response value RES=f2 _k (RAND), sends this value to the VLR/SGSN, and calculates CK=f3 _K (RAND) and IK=f4 _K (RAND) as the encryption key and complete unique key, and store K_ID _new and K _new as a new IMSI encryption key identifier and encryption key at the same time;

(7) After the VLR/SGSN obtains the RES sent by the MS, it judges whether the equation XRES=RES is established. If established, the network authenticates the user successfully, and the VLR/SGSN takes out CK and IK from the authentication vector as the encryption key and integrity key when communicating with the MS; otherwise, the network fails to authenticate the user.

Claims (3)

1. the IMSI method for secret protection of a 3G access, is characterized in that, comprises the steps:

(1) VLR initiates the identify label request to the user, request user's permanent identification IMSI;

(2) the MS response MSIN information of encrypting consists of the IMSI information of encryption jointly with the routing iinformation HLR_ID of HLR, submits simultaneously encryption key identification number K_ID to _old

(3) after VLR/SGSN received the user identity response message, according to the routing iinformation HLR_ID of HLR, namely MCC||MNC, sent authentication data request message to HLR, and content comprises IMSI information and the encryption key identification number K_ID after encryption _old

(4) HLR is according to the K_ID that receives _oldFind corresponding encryption key K from cipher key store _old, deciphering IMSI; Then with K_ID _oldCorresponding recording status changes FREE into; Then for this IMSI produces the Ciphering Key group, distribute simultaneously new encryption key sign K_ID _newWith new encryption key K _newObtain the Ciphering Key of embedded key information, subsequently with new Ciphering Key group AV _sSend VLR/SGSN to together with IMSI information;

(5) the VLR/SGSN storage is from the Ciphering Key group AV of HLR _sWith IMSI information, and with authentication information RAND _IN(i) || AUTN (i) sends to MS;

(6) MS utilizes the inverse function F ' of imbedding function F from RAND _INIn extract random parameter RAND and K_ID _new|| K _newCalculate XMAC=f1 _k(SQN||RAND||AMF), judge whether equation MAC=XMAC sets up, calculate response RES=f2 if set up _k(RAND) send to VLR/SGSN, and with K_ID _newAnd K _newBe stored as new IMSI encryption key identification number and encryption key;

(7) after VLR/SGSN obtains the RES of MS transmission, judge whether equation XRES=RES sets up, and sets up authentication success, otherwise authentification failure.

2. the IMSI method for secret protection of a kind of 3G access as claimed in claim 1; it is characterized in that: described HLR need to safeguard a cipher key store; its size determines according to the quantity of MS under HLR; every record comprises four attributes, that is: encryption key identification number KEY_ID, encryption key KEY, key use state STATUS and update time TIME.

3. the IMSI method for secret protection of a kind of 3G access as claimed in claim 1, it is characterized in that: in described step (2), MS need to utilize the symmetric key encryption MSIN that is assigned to, and then combines the enciphered message of common formation IMSI with MCC||MNC.

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