KR100545512B1 - System and method for preventing replay attacks in wireless communication - Google Patents

Abstract

A method and apparatus are provided for verifying the identity of a mobile station in a communication network. The mobile station transmits a security value to obtain a connection to the network. The system authenticates the mobile station before granting the mobile station access to the network. If the security value sent by the mobile station matches the security value previously sent, the system performs an additional process before granting access to the system. Using the present invention, the system prevents reuse intrusion attempts by intruders.

Reuse Intrusion Prevention

Description

Reusable intrusion prevention system and method in wireless communication {SYSTEM AND METHOD FOR PREVENTING REPLAY ATTACKS IN WIRELESS COMMUNICATION}

The present invention generally relates to a wireless communication system, such as a mobile telephone system. In particular, the present invention relates to an authentication procedure in a mobile telephone system.

When the telephone company first introduced mobile communications to the market, its main purpose was to establish capacity and coverage and attract new customers. As the network grows, telephone companies expect customers to benefit from using their equipment. However, fraudulent use of mobile phones, in particular cloning, can significantly impact the ability to operate a communications system to benefit. Cloning attempts to steal the identity of a legitimate subscriber terminal and obtain unauthorized telephone service by duplicating the legitimate subscriber terminal. These actions create problems and practical inconveniences for system users. According to the Cellular Telecommunications Industry Association (CTIA), global annual revenue losses from cloning exceed $ 100 million.

Authentication procedures are currently used to combat fraudulent access to mobile phone services. As used herein, authentication refers to the exchange and processing of stored information to verify the identity of the user terminal. The authentication process is performed by the network and is to approve the identity of a telephone that conforms to standards such as an IS-54B, IS-136, IS-91, or IS-95 standard telephone. Typically, the authentication procedure is independent of the air-interface protocol (ie CDMA or TDMA) used.

1 is a diagram of an exemplary mobile communication system having one or more mobile stations. Mobile telephone system (MTS) 100 typically includes infrastructure components 112 that communicate with a plurality of mobile stations (MS) 120 using radio frequency (RF) channels. do. The base components may include a base station (BS) 110, a mobile switching center (MSC) 130, a home location register (HLR) 150, an authentication center (AC) 160, and a visitor. It includes a location location register (VLR) 155. BS 110 provides an air interface between MS 120 and MSC 130. The MSC 130 coordinates all communication channels and processes and allows the BS 110 to connect to the public switched telephone network (PSTN) 140. HLR 150 has subscriber database 152. Subscriber database 152 manages each subscriber's mobile identification number (MIN) and electronic serial number (ESN). The MIN and ESN together uniquely identify each MS.

Typically, MSC 130 also includes a visitor location register (VLR) 155. However, VLR 155 may be an independent component of the system. VLR 155 has a temporary subscriber database 157 similar to the permanent subscriber database in HLR 150. Information from HLR 150 and VLR 155 is used to authorize system access and to approve billing for a particular billing account. MSC 130 also interfaces with AC 160 via HLR 150.

The VLR 155 and the MS 120 each access three or more pieces of information constituting data used for authentication: the MIN of the mobile station, the ESN of the mobile station, and the shared secret data (SSD-A) associated with the mobile station. ). SSD-A is typically derived from an A-Key. Each MIN and associated ESN represent a unique combination that may be used to identify a particular legitimate subscriber. A-Key is a secret value unique to each individual subscription. For example, the A-Key may be a 64-bit cryptographic variable key stored in the memory of the MS 120. For example, the A-Key may be entered once from the keypad of the MS 120 when the mobile station first begins providing service to a particular subscriber. Typically, the A-Key remains unchanged unless its value is compromised. The MIN and ESN can be transmitted over the airwaves, but the A-Key is not transmitted over the airwaves.

In North American systems, authentication of MS uses a process commonly referred to as "cellular authentication and voice encryption" (CAVE) algorithm. The CAVE algorithm is a software-compatible nonlinear mixing function with a 32-bit linear-feedback shift register (LFSR), 16 8-bit mixing registers, and a lookup table of 256 entries. For more details on the CAVE algorithm, see the Common Cryptographic Algorithms cellular standard. Authentication is a procedure whereby MS 120 and the underlying components 112 of a system execute a CAVE algorithm with a common set of data to generate an authentication signature. If the authentication signature generated by the MS 120 matches the authentication signature generated by the underlying components, then the identity of the MS 120 is authenticated and access to the telephone service is granted. Otherwise, attempts by the MS 120 for network connection are denied.

The authentication procedure may be performed by a unique challenge or a broadcast challenge. At the unique challenge, the " RAND " requesting the system connection is sent to the MS 120. RAND is a value generated by a random number typically used in the authentication procedure. RAND for unique challenges is typically a 24-bit digital value. MS 120 receives the RAND and calculates the authentication signature by executing the CAVE algorithm using the received RAND, SSD-A, and other data. The authentication signature is usually an 18 bit value. MS 120 transmits the RAND and the calculated authentication signature to base components 112. Similarly, the base components 112 use the CAVE algorithm to calculate the authentication signature based on the stored values of SSD-A, MIN, and ESN. If the authentication signature received from the MS 120 matches the authentication signature calculated independently by the base components 112, then a service connection to the MS 120 is granted. Otherwise, the service connection of the MS 120 is denied.

In contrast, in a broadcast challenge, the underlying components do not send a RAND to only one MS 120 that has requested a connection to a dedicated broadcast channel (e.g., a cellular paging channel). Broadcast RAND). Broadcast challenges are sometimes referred to as "global challenges". Normally, sometimes a new RAND is generated and transmitted. When the MS 120 requests a connection to the service, the MS 120 calculates an authentication signature based on the most recent broadcast RAND before communicating with the underlying components 112. As an example, MS 120 transmits the eight most significant bits of the RAND and the calculated authentication signature to underlying components 112 for authentication. Since the underlying components 112 send an authentication signature with the service request, verification of the authentication signature can begin immediately as the MS 120 requests a service connection, thereby minimizing delay in call processing. Can be.

While broadcast challenges result in faster call setup than unique challenges, clone calls, or other intruders, can gain unauthorized access to the system in a way commonly known as "reuse intrusion." Reuse intrusions allow an intruder to appear as a legitimate subscriber. As a result, the intruder can make calls that are billed to legitimate subscribers. According to the reuse attack, the attacker monitors the information sent between the authorized MS 120 and the underlying components 112. The attacker would store the RAND and authentication signature sent by the authorized MS 120 to the underlying components 112. At the end of the call, the attacker sends a request for the service with the same RAND and authentication signature as previously sent by the legitimate subscriber. If the RAND does not change because the authorized MS 120 has calculated the stolen authentication signature, the subscriber owning the authorized MS 120 would have to pay for the attacker's use of the service.

Prior efforts such as using dialed digits as input to the CAVE algorithm to prevent reuse intrusion have not been successful. In calls using mobile phones, a subset of dial numbers was used as input to the CAVE algorithm instead of MIN. Since dial numbers typically change with each call, using dial numbers as input to the CAVE algorithm results in a unique authentication signature for each call, unless two calls use the same number. However, the normal authentication procedure uses a predetermined number of last digits among the dial digits, which are the most unique digits for each call. In many cases, the dial number of an authorized call can be added to the dial number of an unauthorized call without adversely affecting the call. Thus, the underlying components will generate the same authentication signature as that generated for the call made by the authorized MS 120. In addition, unauthorized access to the system is possible when an unauthorized MS steals a call through an operator-assisted call or through a directory-assisted operator and uses the information stolen to access the system (ie, RAND and authentication signature). . Many wireless service providers currently provide directory assistance services that connect users directly to the requested number, so many users only need to press "411" to gain access to the system. Thus, by waiting for an operator assisted call made by an authorized user, a fraudulent user can gain unauthorized access to the system.

Thus, there is a need for an authentication procedure in wireless communication technology that allows less unauthorized access to the system.

Summary of the Invention

A method and apparatus for authenticating the identity of a station in a communication network, such as a mobile telephone system, is disclosed. The disclosed methods and apparatus allow less reuse intrusion. In addition, the disclosed methods and apparatus implement an authentication procedure with a relatively short delay. The disclosed methods and apparatus include the invention as defined by the appended claims.

The disclosed method and apparatus includes a first station (eg, mobile station) that communicates a first “security parameter” (eg, RAND) and an authentication signature with a second station (eg, an underlying component) within a communication network. ). For the purposes of the present disclosure, a security parameter is defined as any signal, pattern, or value that can be used as input to a signature generation ("SG") algorithm, such as a conventional CAVE algorithm that generates an authentication signature. The authentication signature is defined as a signal, pattern, or value output from the SG algorithm in response to one or more security parameters entered. Each particular set of input security parameters preferably produces a certificate signature that is different from the certificate signature that is output as a result of any other set of input security parameters.

The second station receives the first security parameter and the authentication signature from the first station. If the first security parameter is different from each of the predetermined number of first security parameters previously received from the first station, the second station performs a conventional procedure to authenticate the first station (ie, the identity of the first station). Certified). If the second station authenticates the first station, the first station is granted access to the communication network. If the first security parameter is equal to one of the first security parameters transmitted by the first station in the most recent attempt attempted by the first station to obtain a connection, the second station performs a "unique challenge". do.

In another embodiment of the disclosed method and apparatus, it is determined whether the first station has previously connected to the communication network. If the first station has previously connected to the communication network, the unique challenge procedure is initiated by the second station before the first station is allowed to connect.

Brief description of the drawings

These and other aspects, features and advantages of the present invention will be more readily understood with reference to the following detailed description in conjunction with the accompanying drawings.

1 is a diagram of an exemplary mobile communication system having one or more mobile stations.

2 is a diagram of a challenge / response dialog between a mobile switching center and a mobile station.

3 illustrates the components of an MSC.

4 is a flow diagram illustrating steps performed during the operation of an authentication procedure.

Detailed Description of the Invention

A method and apparatus for authenticating the identity of a mobile station in a mobile telephone system (MTS) is disclosed. The disclosed methods and apparatus enable the use of a particular set of security values (eg, "RAND", or an authentication signature generated from a particular set of information, including RAND) only once within a given time. By having each MS use a particular security value only once within a predetermined time, the risk of "reuse intrusion" is eliminated. The disclosed methods and apparatus include the claimed invention. However, the scope of the invention is to be determined entirely by the appended claims.

2 shows the challenge / between the underlying components 312 of the MTS 300 and the authorized MS 320 (eg, an MS having a valid billing account for the service provider operating the MTS 300). The response dialog is shown. MS 321 is an intruder (ie, unauthorized user). In one embodiment of the disclosed method and apparatus, the base components 312 may include a base station (BS, 310), a mobile switching center (MSC, 330), a home location register (HLR, 350), an authentication center (AC, 360). , And a visitor location register (VLR) 355. MTS 300 is preferably capable of performing unique and broadcast challenges. The underlying components 312 transmit a broadcast security value (such as "broadcast RAND") (via BS 310) to all MSs 320 over an air link 340. The broadcast security value is preferably a value generated with a random number used in the "broadcast authentication" procedure described below. Occasionally, the broadcast security value changes and a new broadcast security value is broadcast to all MSs 320. As will be apparent from the following discussion, changing the broadcast security value more often to reduce the required number of unique challenges, and less broadcast to reduce the overhead required to generate and broadcast new broadcast security values. There is a tradeoff between changing security values. When the broadcast security value is RAND, the disclosed method and apparatus preferably operates in accordance with any industry standard indicating how often the RAND changes.

When a particular MS 320 first attempts to access a telephony service through the underlying components 312, the MS 320 must first receive a broadcast security value. The broadcast security value is provided as one of several inputs to the signature generation ("SG") algorithm, such as the CAVE algorithm that generates the authentication signature. Other inputs to the SG algorithm preferably include mobile identification number ("MIN"), electronic serial number ("ESN"), and shared secret data ('SSD-A') values associated with MS 320. . Each particular pair of ESN and MIN values identifies a particular MS. The SSD-A value is generated from the "key" value using a secret algorithm. Key values and SSD-A values are not transmitted over the air.

When the MS 320 generates an authentication signature, the MS 320 sends a set of security values to the base components 312 over the airwaves. According to one embodiment of the disclosed method and apparatus, the set of security values includes (1) an authentication signature, (2) an overall broadcast security value used as an input to the SG, a portion of this broadcast security value, or this broadcast security Some value representing the value, (3) the ESN, and (4) the MIN used to generate the authentication signature. Since the SSD-A value and the specific SG algorithm are not known to anyone wishing to steal the information, there is no possibility that an intruder can use the information in the future to independently generate an authentication signature when the security value changes.

The base components 312 note at least some of the values in the set of transmitted security values. For example, in one example, the base components 312 note which broadcast value was used by the MS 320 to generate an authentication signature. Optionally, the security value noted by the underlying components 312 is the certificate signature itself. In one embodiment of the disclosed method and apparatus, the base components 312 store a portion of security information, such as broadcast security values or authentication signatures. In certain embodiments of the disclosed method and apparatus, the foundation components 312 have sufficient memory capability to store several security values (or values indicative of the value of the security value) for each MS 320. Optionally, the base components 312 may have memory allocated to store one security value (or a value representing the value of the security value) for each MS 320.

The next time MS 320 attempts to connect to the telephone service, MS 320 calculates the authentication signature using the current broadcast security value, MIN, ESN, and SSD-A. If the broadcast security value has changed since the last connection attempt to the system, the MS 320 sends the ESN and MIN with the new broadcast security value (or representative value) and the authentication signature. In this case, the procedure is essentially the same as when the MS 320 makes the first connection attempt to the system.

However, after the last connection attempt of the mobile station's system, if the broadcast security value has not changed, the computed authentication signature and the computed values of the broadcast security value are the same as the values used for the previous connection to obtain a connection to the system. . In other words, given the same input to the SG, the output from the SG for the second connection attempt is the same.

The MS 320 sends the broadcast security value (or representative value), the calculated authentication signature, and the ESN and MIN to the base components 312 via the air link 340a. The base components 312 compare one or more of the set of received security values with the stored security values (or representative values) previously received by the base components 312 from the MS 320. For example, in one embodiment of the disclosed method and apparatus, the base components 312 may receive the received broadcast security value and the stored security value previously received by the base components 312 from the MS 320. To (or representative values). Optionally, the foundational components 312 can check the entire set of information sent by the MS 320. In another optional example, whenever the information being checked is different from the MS 320 using different broadcast security values in the connection attempt, a portion of the information other than the security value or representative value (eg, an authentication signature) is checked. In this case, the base components 312 have previously received the same security information (eg, RAND or an authentication signature with the same value) from the MS 320, so that the MS 320 grants access to the system. Before receiving, the base components 312 require further verification of the identity of the MS 320. According to one embodiment of the disclosed method and apparatus, additional verification is performed by causing the base components 312 to initiate a unique challenge authentication procedure. Optionally, the base components 312 force a change in the broadcast security value and require the MS 320 to respond to the broadcast challenge using the new security value. In another embodiment, other methods may be used to force the MS 320 to verify its identity.

If additional verification procedures indicate that the MS 320 is authoritative (ie, a successful result is obtained from a unique challenge), then the MS 320 is considered to be a legitimate subscriber and not an intruder (eg, MS 321). Thus, the underlying components 312 allow the MS 320 to connect to the telephone service.

However, if the unauthorized MS 321 captures authentication data (e.g., RAND, authentication signature, and ESN and MIN) by monitoring the transmission from the authorized MS 320, the unauthorized MS 321 may additionally. The verification procedure will fail. For example, if the base components 312 request that the MS 321 respond to a unique challenge, then the MS 321 independent of the new certificate signature from the unique challenge security values provided from the base components 312. MS 321 cannot respond appropriately. Optionally, the MS 321 responds successfully if the underlying components 312 change the broadcast security value and request the MS 321 to respond to the broadcast security value using the new broadcast security value. Can not. This is because broadcast challenges now require independent generation of new authentication signatures based on new broadcast security values.

It is to be understood that the functionality of each of the specific components in the foundational components 312 may vary among embodiments of the disclosed method and apparatus. However, each component is inherently conventional except for the functions that determine whether the MS 320 has previously attempted to connect to the system, and the procedure for requesting further verification from the MS 320 if connected.

In one embodiment of the disclosed method and apparatus, the base components 312 include a base station 310, an MSC 330, an HLR 350, an AC 360, and a VLR 355. Generates a broadcast security value. This broadcast security value is passed to BS 310. BS 310 transmits the broadcast security value to MS 320. When the MS 320 attempts to access a communication service from the network 300, the MS 320 sends the following information to the BS 310. The MS 320 sends a portion of the broadcast security value (or value generated based on the value of the security value) and the MIN, ESN, and authentication signatures generated by the MS 320 using these parameters. Each of these parameters is passed to the HLR 350. HLR 350 determines whether MS 320 has been registered in system 300. If the HLR 350 determines that the MS 320 is registered, the parameters passed to the HLR 350 are passed to the AC 360. AC 360 checks if MS 320 (identified by MIN and ESN) has previously attempted to connect to the system using the same broadcast security value. Otherwise, AC 360 uses the MIN, ESN, SSD-A, and broadcast security values to independently generate an authentication signature. AC 360 then checks whether the generated certificate signature is the same as the certificate signature received from MS 320.

The authentication signature generated by the AS 360 does not match the authentication signature received from the MS 320, or the AC 360 has already established a service connection from the network by the MS 320 using the same broadcast security value. If determined to attempt, AC 360 generates a unique challenge security value. AC 360 uses the unique challenge security value to generate a new certificate signature (“unique certificate signature”). The unique challenge security value and the unique certificate signature are both passed to the MSC 330. The MSC 330 merely passes the unique challenge security value to the BS 310. BS 310 transmits a unique challenge security value to MS 320. MS 320 then responds with a unique authentication signature that was independently calculated using MIN, ESN, unique challenge security value, and SSD-A. BS 310 receives a unique certificate signature from MS 320. Next, BS 310 passes the authentication signature to MSC 330. The MSC 330 compares the unique certificate signature received from the MS 320 with the unique certificate signature provided from the AC 360 to the MSC 330. If they match, MSC 320 is considered legitimate.

If the MSC 330 determines that the MS 320 is a visitor, the VLR 355 is used to perform the functions, otherwise it is performed by the HLR 350.

However, it is apparent that the functions described above performed by one component, such as AC 360, are equally well performed by other components, such as HLR 350, VLR 355, or MSC 330. .

3 is a diagram illustrating the components of the MSC 330. As shown in FIG. 3, the MSC preferably includes a processor 301, a receiver 303, and a memory 305. The receiver is any type of receiving device capable of receiving a signal from an external source. In one embodiment of the disclosed methods and apparatus, the receiver is a conventional receiver as commonly found in an apparatus connected to a base station via land lines. Processor 301 is coupled to receiver 303. The processor is shown as a single processor. However, those skilled in the art will understand that the processor merely represents processing functions performed by a single processing device, such as a microprocessor, or by a plurality of processing devices distributed throughout the base components 312. Nevertheless, the required processing functions may be handled by conventional microprocessors and / or digital signal processors as conventional microprocessors and / or digital signal processors may perform all the necessary functions of the disclosed methods and apparatus. Can be.

4 is a flow diagram illustrating steps executed during an authentication procedure in one embodiment of the disclosed method and apparatus. The system of FIG. 2 can be used to implement the steps of FIG. 4. As shown in FIG. 4, the procedure begins at step 400. In step 410, when a particular MS 320 attempts to access the telephone service, the MS 320 includes identification data (e.g., MIN / ESN), a previously received security value, and an associated authentication signature. Send a set of security values. The MS 320 may also transmit other data if necessary. Typically, MS 320 is a broadcast security previously received from base components 312 during a previous broadcast by MSC 330 or during a previous unique challenge procedure by base components 312. Get the value. At step 430, the base components 312 determine whether the MS 320 previously received a service from the base components 312 using the same set of security values. In an alternative embodiment, the base components 312 check whether a portion of the security value set was previously used by the MS 320 to access the service.

The base components 312 determine that the MS 320 has not previously connected to the service using the same set of security values, and then, in step 440, the base components 312 determine the MS 320. Save the security value received from In step 450, the base components 312 verify the value of the authentication signature received from the MS 320. That is, a check is made on the value of the expected authentication signature (eg, a value calculated independently by the base components 312 using inputs to the SG, such as used by the MS 320). Is done. After verifying the authentication signature, the procedure continues to step 470.

On the other hand, if the base components 312 determine in step 430 that the MS 320 previously accessed the service using the same security value, the procedure proceeds to step 460. In step 460, the underlying components 312 perform further verification of the MS 320, for example by requesting a response from the MS 320 for the unique challenge procedure. As described above, the unique challenge procedure involves the exchange of at least one unique security value from the base components 312 to the MS 320 and the exchange of the unique challenge signature from the MS 320 to the base components 312. Include.

At step 470, the base components 312 determine whether the MS 320 has passed the authentication procedure performed at step 450 or 460. This determination is accomplished by executing the same SG algorithm (eg, the CAVE algorithm) as executed by the MS 320 to calculate the expected authentication signature. The foundational components 312 compare the expected authentication signature with the authentication signature calculated by the MS 320. If the two signatures match, the procedure continues to step 480, and the MS 320 is granted a telephone service connection. If the two signatures do not match, the procedure proceeds to step 490 and the MS 320 is denied service access. The procedure ends at step 499.

In view of the foregoing, the present invention addresses the long need for a wireless system and method having an intruder protection authentication procedure. By performing the authentication procedure of the present invention, the probability of intrusion is reduced. In order to break the authentication procedure of the present invention, the attacker must obtain SSD-A, which is not transmitted over the air, with authentication data. The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are merely illustrative in all respects and not restrictive. Accordingly, the scope of the invention is indicated by the appended claims rather than by the foregoing description. All variations that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims (14)

A station in a communication network, A receiver for receiving transmissions from at least one mobile station operating within range of the station; A comparator in response to a challenge sent by the station, comparing a first received transmission with a second received transmission, each carrying authentication information of the mobile station; And Processing the authentication information in the first received transmission and the authentication information in the second received transmission and if the authentication information in the second received transmission matches the authentication information in the first received transmission as a result of the comparison; 2 a processor for re-challenge to the mobile station that has received the received transmission Station comprising a. A method for verifying the identity of a mobile station in a communication network, Transmitting a challenge from the base station to the mobile station; Comparing, at a base station, a first received transmission with a second received transmission that includes authentication information identifying the mobile station in response to the challenge; And Sending a challenge from the base station to the mobile station where the second received transmission occurred if the authentication result in the second received transmission matches the authentication information in the first received transmission as a result of the comparison. step How to verify the identity of the mobile station that includes A system for preventing a replay attack in a communication network, Receive a public security parameter from the mobile station and an authentication signature generated using both the public and private security parameters; Compare the public security parameter communicated by the mobile station with at least one public security parameter previously used by the mobile station; And If the public security parameter communicated by the mobile station was previously used, send a new public security parameter to the mobile station, generate a new authentication signature based on the private security parameter and the new security parameter, and send it to at least one station Configured to require the mobile station to And at least one station. delete The method of claim 3, wherein And the at least one station is a combination of infrastructure components. The method of claim 5, The combination of the base components is, Base station; Mobile switching center; And Home location register System for preventing reuse intrusion, characterized in that it comprises a. The method of claim 5, Certification center; And Visitor Location Register The system for preventing reuse intrusion further comprising. A system for authenticating a mobile station in a communication network, Receive a public security parameter and an authentication signature generated using both public and private security parameters from the mobile station; Compare the public security parameter communicated by the mobile station with at least one public security parameter previously received by the mobile station; And Configured to require additional verification of an identity from the mobile station if the public security parameter communicated by the mobile station matches a previously received public security parameter of the mobile station. 10. A system for authenticating a mobile station, comprising at least one station. A station for authenticating a mobile station in a communication network, Means for receiving a public security parameter and an authentication signature generated using both a public security parameter and a private security parameter from the mobile station; And Means for comparing the public security parameter communicated by the mobile station with at least one public security parameter previously received by the mobile station. And a station for authenticating the mobile station. A system for authenticating a mobile station in a communication network, At least one base station for receiving signals from said mobile station and for authenticating said mobile station prior to granting access to said communication network, If the mobile station attempts to connect to the communication network using the same public security parameters as those used in previous attempts to connect to the network by a similarly identified mobile station, each base station is unique. A system for authenticating a mobile station, characterized by performing a challenge challenge procedure. The method of claim 10, And the public security parameter comprises at least one RAND. A method of authenticating subscribers in a communication network, the method comprising: Determining whether the subscriber has previously accessed the network; And Performing a unique challenge procedure when the subscriber has previously connected to the network using the broadcast security parameter used in the previous attempt How to authenticate the subscriber comprising a. A method of authenticating subscribers in a communication network, the method comprising: Determining whether the subscriber has previously accessed the network; And Performing a unique challenge procedure if the subscriber previously connected to the network using the authentication signature used in the previous attempt to access the network How to authenticate the subscriber comprising a. A method of authenticating subscribers in a communication network, the method comprising: Receiving a broadcast security parameter and an authentication signature from the subscriber; Determining whether the broadcast security parameter sent by the subscriber matches a previously transmitted parameter; And Generating an authentication signature using the broadcast security parameter sent by the subscriber as an input of a signature generation algorithm if the broadcast security parameter is different from the previously transmitted parameter; Performing a unique challenge procedure if the broadcast security parameter matches a broadcast security parameter previously sent by the subscriber How to authenticate the subscriber comprising a.

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