a method and apparatus is disclosed for confirming the identify a mobile station in a mobile telephone system ( mts ). the disclosed method and apparatus ensures that each mobile station ( ms ) can use a particular set of security values ( such as a “ rand ” or an authentication signature generated from a particular set of information , including a rand ) only once within a predetermined time . by ensuring that each ms can only use a particular security value once within a predetermined time , the risk of “ replay attacks ” is eliminated . the disclosed method and apparatus includes the claimed present invention . however , the scope of the invention should be determined exclusively by the appended claims . [ 0026 ] fig2 illustrates a challenge / response dialog between infrastructure components 312 of an mts 300 and an authorized ms 320 ( e . g ., an ms that has a valid billing account with the service provider who operates the mts 300 ). an ms 321 is an intruder ( i . e ., an unauthorized user ). in one embodiment of the disclosed method and apparatus , the infrastructure components 312 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 . the mts 300 is preferably capable of performing both unique and broadcast challenges . the infrastructure components 312 transmit ( via the bs 310 ) a broadcast security value ( such as a “ broadcast rand ”) to all mss 320 over an air link 340 . the broadcast security value is preferably a randomly generated value that is used in a “ broadcast authentication ” process , as is described below . from time to time , the broadcast security value changes , and the new broadcast security value is broadcast to all ms &# 39 ; s 320 . as will become apparent from the following description , there is a tradeoff between changing the broadcast security value more frequently to reduce the number of unique challenges required and changing the broadcast security value less frequently to reduce the overhead required to generate and broadcast new broadcast security values . in the case in which the broadcast security value is a rand , the disclosed method and apparatus preferably operates in compliance with any industry standards that dictate how often a rand is to be changed . when a particular ms 320 attempts to access telephone service for the first time through the infrastructure components 312 , the ms 320 must first receive the broadcast security value . the broadcast security value is provided as one of several inputs to a signature generation (“ sg ”) algorithm , such as a cave ( cellular authentication and voice encryption ) algorithm , to generate an authentication signature . the other inputs to the sg algorithm preferably include the mobile identification number (“ min ”), the electronic serial number (“ esn ”), and the shared secret data (“ ssd - a ”) values associated with the ms 320 . each particular pair of esn and min values identifies a particular ms . the ssd - a value that is generated from a “ key ” value using a secret algorithm . the key value and the ssd - a value are never transmitted over the air . once the ms 320 has generated the authentication signature , the ms 320 transmits over the air to the infrastructure components 312 , a set of security values . in accordance with one embodiment of the disclosed method and apparatus , the set of security values include : ( 1 ) the authentication signature , ( 2 ) either the entire broadcast security value used as input to the sg , a portion of that broadcast security value , or some value which represents that broadcast security value , ( 3 ) the esn , and ( 4 ) the min used to generate that authentication signature . since the ssd - a value and the particular sg algorithm are not known to anyone who might intercept this information , there is no possibility that an intruder would be able to use this information in the future to independently generate an authentication signature when the security value changes . the infrastructure components 312 note at least some of the values within the set of the security values transmitted . for example , in one embodiment , the infrastructure components 312 note which broadcast security value was used by the ms 320 to generate the authentication signature . alternatively , the security value noted by the infrastructure components 312 is the authentication signature itself . in one embodiment of the disclosed method and apparatus , the infrastructure components 312 store a portion of the security information , such as the broadcast security value or the authentication signature . in a particular embodiment of the disclosed method and apparatus , the infrastructure components 312 are equipped with sufficient memory capacity to store several security values ( or values representing the value of the security value ) for each ms 320 . alternatively , the infrastructure components 312 may only have memory allocated for one storing one security value ( or value representing the value of the security value ) for each ms 320 . the next time the ms 320 attempts to access telephone service , the ms 320 uses the then current broadcast security value and the min , esn , and ssd - a to calculate an authentication signature . if the broadcast security value has changed since the last attempt to access the system , then the ms 320 will transmit the esn and min with the new broadcast security value ( or representative value ) and authentication signature . in this case , the process will be essentially identical to the case in which the ms 320 makes its first attempt to access the system . however , if the broadcast security value has not changed since the mobile &# 39 ; s last attempt to access the system , then the values of the computed authentication signature and broadcast security value will be the same as those values used for the previous attempt to gain access to the system . that is , given the same input to the sg , the output from the sg will be the same for the second access attempt . the ms 320 transmits the broadcast security value ( or representative value ), the calculated authentication signature , and esn and min to the infrastructure components 312 over the air link 340 a . the infrastructure components 312 compare one or more of the received set of security values with stored security values ( or representative values ) previously received by the infrastructure components 312 from that ms 320 . for example , in one embodiment of the disclosed method and apparatus , the infrastructure components 312 compare the broadcast security value received with broadcast security values previously received from that ms 320 . alternatively , the infrastructure components 312 can check the entire set of information that is sent by the ms 320 . in yet another alternative some portion of that information other than the security value or representative value ( such as the authentication signature ) is checked , as long as the information that is checked changes each time the ms 320 uses a different broadcast security value in the access attempt . since , in this case , the infrastructure components 312 have previously received the same security information from the ms 320 ( e . g ., a rand or authentication signature having the same value ), the infrastructure components 312 will require additional verification of the identity of the ms 320 before that ms 320 will be allowed to access the system . in accordance with one embodiment of the disclosed method and apparatus , additional verification is performed by having the infrastructure components 312 initiate a unique challenge authentication procedure . alternatively , the infrastructure components 312 could force a change in the broadcast security value and require the ms 320 to respond to the broadcast challenge using the new security value value . in yet another embodiment , another method may be used to force the ms 320 to verify its identity . if the additional verification procedure indicates that the ms 320 is authorized ( e . g ., a successful outcome results from the unique challenge ) the ms 320 is considered to be a legitimate subscriber and not an intruder ( e . g ., ms 321 ). accordingly , the infrastructure components 312 grants the ms 320 access to telephone service . however , if an unauthorized ms 321 captures authentication data ( e . g ., a rand , authentication signature , and esn and min ) by monitoring transmissions from an authorized ms 320 , that unauthorized ms 321 would fail the additional verification process . for example , if the infrastructure components 312 requested that the ms 321 respond to a unique challenge , that ms 321 could not respond properly , since the ms 321 would have to independently generate a new authentication signature from the unique challenge security value that is provided from the infrastructure components 312 . alternatively , if the infrastructure components 312 changed the broadcast security value and then requested the ms 321 to respond to the broadcast challenge using the new broadcast security value , the ms 321 could not do so successfully . this is because the broadcast challenge would now require independent generation of a new authentication signature based upon the new broadcast security value . it should be understood that the functions of each of the particular components within the infrastructure components 312 may vary from one embodiment of the disclosed method and apparatus to another . however , each such component is essentially conventional with the exception of the functions that are performed to determine whether an ms 320 has previously attempted to access the system , and the process of requesting a further verification from the ms 320 , if so . in one embodiment of the disclosed method and apparatus in which the infrastructure components 312 include the base station 310 , the msc 330 , the hlr 350 , the ac 360 , and the vlr 355 , the msc 330 generates a broadcast security value . this broadcast security value is communicated to the bs 310 . the bs 310 transmits the broadcast security value to the ms 320 . when the ms 320 attempts to access communication services from the network 300 , the ms 320 sends the following information back to the bs 310 . the ms 320 sends a portion of the broadcast security value ( or a value that is generated based upon the value of the security value ), a copy of the min , the esn , and the authentication signature that was generated by the ms 320 using these parameters . each of these parameters are communicated to the hlr 350 . the hlr 350 determines whether the ms 320 is registered in the system 300 . if the hlr 350 determines that the ms 320 is registered , then the parameters communicated to the hlr 350 are communicated to the ac 360 . the ac 360 checks whether the ms 320 ( which is identified by the min and esn ) has previously attempted to access the system using the same broadcast security value . if not , then the ac 360 uses the min , the esn , the ssd - a , and the broadcast security value to independently generate the authentication signature . the ac 360 then checks to ensure that the authentication signature that it generated is the same as the authentication signature that was received from the ms 320 . if the authentication signature generated by the ac 360 does not match the authentication signature that was received from the ms 320 , or if the ac 360 determines that the ms 320 has already attempted to access service from the network using the same broadcast security value , then the ac will generate a unique challenge security value . the ac 360 will use the unique challenge security value to generate a new authentication signature ( a “ unique authentication signature ”). the unique challenge security value and the unique authentication signature are both communicated to the msc 330 . the msc 330 communicates only the unique challenge security value to the bs 310 . the bs 310 transmits the unique challenge security value to the ms 320 . the ms 320 then responds with a unique authentication signature that the ms 320 has independently calculated using the min , esn , unique challenge security value , and ssd - a . the bs 310 receives the unique authentication signature from the ms 320 . the bs 310 then communicates the signature to the msc 330 . the msc 330 compares the unique authentication signature received from the ms 320 with the unique authentication signature that was provided to the msc 330 from the ac 360 . if they match , then the ms 320 is assumed to be legitimate . if the msc 330 determines that the ms - 320 is a visitor , then the vlr 355 is used to perform the functions that would otherwise be performed by the hlr 350 . however , it should be clear that the functions that are described above as being performed by one component , such as the ac 360 , may be performed equally well by another component , such as the hlr 350 , vlr 355 , or msc 330 . [ 0040 ] fig3 is an illustration of the components of the msc 330 . as shown in fig3 the msc preferably includes a processor 301 , a receiver 303 , and a memory 305 . the receiver is any type of receiving device that can receive signals from an external source . in accordance with one embodiment of the disclosed method and apparatus , the receiver is a conventional receiver , such as is commonly found in equipment that is coupled to a base station via land lines . the processor 301 is coupled to the receiver 303 . the processor is shown here as a single processor . however , it will be understood by those skilled in the art that the processor merely represents processing functions may be either performed by a single processing entity , such as a microprocessor , or which is performed by a plurality of processing entities distributed throughout the infrastructure components 312 . nonetheless , the processing required is such that a conventional microprocessor and / or digital signal processor can perform all of the necessary functions of the disclosed method and apparatus . [ 0041 ] fig4 is a flow chart describing the steps executed during an authentication process in one embodiment of the disclosed method and apparatus . the system described in fig2 may be used to implement the steps of fig4 . as shown in fig4 the process begins at step 400 . at step 410 , when a particular ms 320 attempts to access telephone service , the ms 320 transmits a set of security values , including identification data ( e . g ., min / esn ), a previously received security value , and an associated authentication signature . the ms 120 may also transmit other data , if desired . typically , the ms 320 obtains the previously received broadcast security value from the infrastructure components 312 during a previous broadcast by the msc 330 , or during a previous unique challenge procedure with the infrastructure components 312 . at step 430 , the infrastructure components 312 determine whether the ms 320 has previously obtained service from the infrastructure components 312 using the same set of security values . in an alternatively embodiment , the infrastructure components 312 check whether some portion of the set of security value was previously used by the ms 320 to access service . if the infrastructure components 312 determine that the ms 320 has not previously accessed service using the same set of security values , then at step 440 , the infrastructure components 312 store the security value received from the ms 320 . at step 450 , the infrastructure components 312 verify the value of the authorization signature received from the ms 320 . that is , a check is made of the value of the authorization signature that is expected ( e . g ., the value calculated independently by the infrastructure components 312 using the same inputs to the sg as were used by the ms 320 ). after verifying the authorization signature , the process proceeds to step 470 . if , on the other hand , the infrastructure components 312 determine at step 430 that the ms 320 has previously accessed service using the same security value , then the process proceeds to step 460 . at step 460 the infrastructure components 312 perform an additional verification of the ms 320 , such as by requesting a response from the ms 320 to a unique challenge procedure . as noted above , the unique challenge procedure involves the exchange of at least a unique security value from the infrastructure components 312 to the ms 320 , and a unique challenge signature from the ms 320 to the infrastructure components 312 . at step 470 , the infrastructure components 312 determine whether the ms 320 has passed the authentication procedures performed at the step 450 or 460 . this determination is accomplished by executing the same sg algorithm ( e . g ., the cave algorithm ) as that executed by the ms 320 to compute an expected authentication signature . the infrastructure components 312 compare the expected authentication signature with the authentication signature computed by the ms 320 . if the two signatures match , then the process proceeds to step 480 and the ms 320 is granted access to telephone service . if the two signatures do not match , then the process proceeds to step 490 and the ms 320 is denied access to service . the process terminates at step 499 . in view of the foregoing , it will be appreciated that the invention overcomes the long - standing need for a wireless system and method having an intrusion - resistant authentication procedure . by performing the authentication process of this invention , the probability of intrusion is minimized . to defeat the authentication process of this invention , an intruder would have to obtain not only the authentication data , but acquire the ssd - a which is not transmitted over the air . the invention may be embodied in other specific forms without departing from its spirit or essential characteristics . the described embodiment is to be considered in all respects only illustrative and not restrictive . the scope of the invention is , therefore , indicated by the appended claims rather by the foregoing description . all changes which fall within the meaning and range of equivalency of the claims are to be embraced within their scope .