Abstract:
Disclosed is a method and apparatus for providing authentication for a subscriber of a wireless communication system employing one type of authentication technology roaming into a wireless communication system employing a second type of authentication technology. The method and apparatus involves transmitting (or receiving) a first message to a first system comprising a mobile identifier for a subscriber of the first and a second system indicator indicating that the subscriber is attempting to gain access to a second system that uses an authentication process different than an authentication process used by the first system; determining shared secret data for the subscriber using the mobile identifier; receiving (or transmitting) a second message from the first system having shared secret data associated with the subscriber; generating an expected response to a unique challenge using the shared secret data and an encryption algorithm, and transmitting the expected response to the second system.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to wireless communication systems and, in particular, to roaming among wireless communication systems. 
   BACKGROUND OF THE RELATED ART 
   Subscribers to wireless communication systems employing the well-known ANS-41 signaling protocol standard may, at times, roam outside their home system and into wireless communication systems employing the well known GSM standard. Assuming that the subscribers have user equipment or mobile-stations operable to function in either wireless communication system, some form of authentication needs to be performed before the GSM based wireless communications system can provide any type of service to the subscribers of the ANS-41 based wireless communication systems. However, the manner in which authentication is performed in GSM and ANS-41 based wireless communication systems are different. Accordingly, there exists a need for providing authentication for a subscriber to a ANS-41 based wireless communication system roaming into a GSM based wireless communication system, and vice-versa. 
   SUMMARY OF THE INVENTION 
   The present invention is a method and apparatus for providing authentication for a subscriber of a wireless communication system employing one type of authentication technology roaming into a wireless communication system employing a second type of authentication technology. The present invention involves transmitting (or receiving) a first message to a first system comprising a mobile identifier for a subscriber of the first and a second system indicator indicating that the subscriber is attempting to gain access to a second system that uses an authentication process different than an authentication process used by the first system; determining shared secret data for the subscriber using the mobile identifier; receiving (or transmitting) a second message from the first system having shared secret data associated with the subscriber; generating an expected response to a unique challenge using the shared secret data and an encryption algorithm, and transmitting the expected response to the second system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1  depicts an example of an IIF of the present invention positioned between the edges of a GSM system and an ANS-41 system; 
       FIG. 2  depicts an example of a successful authentication of a subscriber of ANS-41 system in GSM system in an initial access attempt; 
       FIG. 3  depicts an example of an unsuccessful authentication of a subscriber of ANS-41 system in GSM system in an initial access attempt; and 
       FIG. 4  depicts an example of a successful authentication of a subscriber of ANS-41 system in GSM system in an initial access attempt in which a Registration Notification INVOKE with a SYSACCTYPE parameter value indicating GSM access with successful authentication is used. 
   

   DETAILED DESCRIPTION 
   The present invention uses an Interoperability/Interworking Function (IIF) as a logical network entity between the edges of two wireless communication systems based on different technologies to map or convert operations, messages and/or procedures from one signaling protocol to another (e.g., ANS-41 to GSM). For purposes of discussion, the present invention will be described herein with reference to a subscriber of an ANS-41 based wireless communication system (ANS-41) roaming or visiting in a GSM based wireless communication (GSM system). It should be understood that the present invention can also be applied for a subscriber of a GSM based wireless communication system roaming or visiting in an ANS-41 based wireless communication system. 
     FIG. 1  depicts an example of an IIF  10  of the present invention positioned between the edges of a GSM system  12  and an ANS-41 system  14 , wherein ANS-41 system  14  includes enhanced authentication and mobility management capabilities to support roaming of its subscribers to GSM system  12 , as will be described herein. 
   A subscriber of ANS-41 system  14  is equipped with user equipment  16 . User equipment  16  is either an ANS-41 based user equipment capable of roaming into GSM system  12  or a GSM based user equipment having a User Identity Module (UIM) of the subscriber. Regardless of the type of user equipment  16 , a Mobile-station Identification Number (MIN) based on an International Mobile-station Subscriber Identification (IMSI) is programmed in user equipment  16  for use in GSM system  12 . User equipment  16  (or the UIM inserted therein) is capable of generating Shared Secret Data (SSD) for the subscriber, and to use the SSD and the well-known CAVE algorithm (or some other encryption algorithm) to generate a response (RES) to random challenges (RAND) issued by GSM system  12  and to generate a cipher key K c . 
   Preferably, IIF  10  requires no or little changes to standard network protocol in its interactions with either systems  12  or  14 . IIF  10  functions as a Visitor Location Register (VLR) in its interactions with ANS-41 system  14  to support roaming of the subscriber in GSM system  12 . IIF  10  functions as a GSM Home Location Register (HLR) and Authentication Center (AC) in its interactions with GSM system  12 . IIF  10  supports the enhanced operations required for authentication of user equipment  16  in GSM system  12 . IIF  10  provides GSM triplets needed for authentication and privacy in GSM system  12  using the CAVE algorithm and the SSD provided by an HLR of the wireless communication system to which user equipment  16  belongs, wherein the GSM triplets include the RAND, K c  and an expected response (XRES). IIF  10  is operable to convert an IMSI into a MIN to be used by ANS-41 system  14 , and a MIN into an IMSI to be used by GSM system  12 . 
   ANS-41 system  14  shares SSD with IIF  10  for roaming subscribers of ANS-41 system  14  into GSM system  12 . Note that the AC should not be able to update SSD or a COUNT value for the subscriber when the subscriber is being served by GSM system  12 . The subscriber&#39;s SSD is updated when the user returns to ANS-41 system  12  or leaves GSM system  14 . IIF  10  is capable of providing a secure method of storing SSD received from ANS-41 system  14 . IIF  10  does not transmit or otherwise disclose the SSD to any other network entity. 
   For illustration purposes, the following example of a subscriber of ANS-41 system  14  roaming or visiting GSM system  12  is provided. User equipment  16  presents itself to GSM system  12  for service. GSM system  12  records the presence of user equipment  16  in its VLR and will attempt to authenticate user equipment  16  via the HLR of ANS-41 system  14 . Since the VLR of GSM system  12  and the HLR of ANS-41 system are of different technologies, IIF  10  is needed to assist in the authentication process, including translating messages between the two systems  12  and  14 . 
   In IIF  10 &#39;s interactions with GSM system  12 , IIF  10  appears to GSM system  12  as a HLR of the same technology as GSM system  12 . By contrast, in IIF  10 &#39;s interactions with ANS-41 system  14 , IIF  10  appears to ANS-41 system  14  as a VLR of the same technology as ANS-41 system  14 . When IIF  10  receives a message from GSM system  12  for authentication of user equipment  16 , IIF converts the message to a format based on ANS-41. The converted message is then transmitted to ANS-41 system  14 . 
   Preferably, IIF does not need to be provisioned with any subscriber specific data, such as Mobile-Station Identification (MSID) in the form of a MIN or IMSI. Subscriber specific data can also include an Electronic Serial Number (ESN) of the subscriber associated with the MIN. A common identifier is preferably used by GSM system  12  and ANS-41 system  14  for user equipment  16 . For example, the IMSI is used in both systems  12  and  14  to identify user equipment  16 . However, when different identifiers are used by both systems  12  and  14  to identify a subscriber, IIF  10  needs to convert identifiers used in one system to identifiers used in the other system. In this situation, either a database for converting identifiers (e.g., from IMSI to MIN, and vice-versa) would be required or a change to the receiving system may be required. For example, the ESN is required to authenticate a subscriber of ANS-41 system  14  but not in GSM system  12 . When user equipment  16  of the subscriber presents itself to GSM system  12 , GSM system  12  does not require the ESN of user equipment  16 . Thus, GSM system  12  does not present to IIF  10  the ESN since it thinks its interacting with a GSM based VLR. When IIF  10  attempts to use the information provided to it by GSM system  12  to authenticate user equipment  16  with ANS-41 system  14 , IIF  10  does not have an ESN to provide the HLR of ANS-41 system  14  as required in an ANS-41 authentication request operation (AUTHREQ). To compensate for this lack of ESN and appear to ANS-41 system  14  as a ANS-41 based VLR, the present invention requires IIF  10  to present a default or mull value in place of an ESN in the AUTHREQ. In response to the AUTHREQ, the HLR of ANS-41 system  14  responds with the subscriber&#39;s real ESN. IIF  10  stores the subscriber&#39;s real ESN in its temporary memory to present to ANS-41 system  14  in future operations where it is required. The subscriber&#39;s real ESN is preferably not saved by IIF  10  after the subscriber leaves GSM system  12 . 
   The above described exchange of ESN (between IIF  10  and ANS-41 system  14 ) is not normally acceptable to the HLR of ANS-41 system  14 . In the present invention, an exception for exchanging the ESN is allowed at the HLR of ANS-41 system  14 . That is, for subscribers of ANS-41 system  14  roaming into GSM system  12 , the HLR of ANS-41 system  14  will permit an exchange of ESN with IIF  10 . IIF  10  will provide an indication to ANS-41 system  14  that the subscriber is roaming in GSM system  12 . For example, the indication is a unique value in a system capability (SYSCAP) parameter. A GSM system access type may also be indicated through a unique value in a System Access Type (SYSACCTYPE) parameter. 
   SSD is typically provided by ANS-41 system  14  to the system currently serving its subscriber (i.e., GSM system  12 ) to authenticate the subscriber. The SSD provided by the home ANS-41 system is used to produce authentication vectors usable by the VLR of GSM system  12  to authenticate the subscriber. 
     FIG. 2  depicts an example  20  of a successful authentication of a subscriber of ANS-41 system  14  in GSM system  12  in an initial access attempt, wherein user equipment  16  associated with the subscriber uses a MIN-based IMSI as its identifier in GSM system  12 . In step a, the mobile-station (MS) or user equipment determines that a new serving system, i.e., GSM system  12  has been entered. MS registers at GSM system  12  and requests for system access by providing its MIN-based IMSI to GSM system  12  in a location area update message. 
   In step b, GSM system  12  sends a SEND_AUTHENTICATION_INFO to IIF  10 , wherein the SEND_AUTHENTICATION_INFO is an authentication information message having the IMSI. In step c, IIF  10  sends an AUTHREQ to the HLR of the subscriber&#39;s home system, i.e., ANS-41 system  14 . The AUTHREQ includes a MSCID, SYSCAP, MIN, ESN, and SYSACCTYPE, wherein MSCID identifies IIF  10 , SYSCAP indicates that the subscriber is roaming in GSM system  12 , ESN is a default value and SYSACCTYPE indicates GSM system access. The MIN is set to a value derived from the MIN-based IMSI. 
   In step d, the HLR forwards the AUTHREQ to an authentication center (AC), which may be a part of ANS-41 system  12  or a separate entity. In step e, the AC determines that the subscriber is roaming in GSM system  12  based on the SYSCAP and responds with an authreq to the HLR, wherein the authreq includes the SSD associated with the subscriber. Note that the ESN, SYSCAP or SYSACCTYPE in the AUTHREQ may alone, or in combination, indicate to the HLR or AC that the associated subscriber (as indicated by the MIN) is attempting to gain access in a system that uses a different authentication process than the AC of the present system. In step f, the HLR forwards the authreq to IIF  10 . Note that the SYSACCTYPE would indicate to the AC that the ESN generated by IIF  10  (i.e., default value) is not the real ESN of the subscriber, whereas the SYSCAP indicates that a serving MSC is using GSM authentication and privacy procedures. When the AC sees these indications, AC knows its okay to provide the SSD of the subscriber. 
   In step g, IIF  10  determines one or more groups of GSM triplets using the subscriber&#39;s SSD and the CAVE algorithm. IIF  10  sends a SEND_AUTHENTICATION_INFO acknowledgement (or ack) to GSM system  12 , wherein the SEND_AUTHENTICATION_INFO ack includes an AuthenticationSetList having the one or more groups of GSM triplets. 
   In step h, GSM system  12  issues a RAND or Unique Challenge to the MS. In step i, the MS responds to the RAND with its response or RES. In step j, GSM system  12  compares the RES received from the MS with the expected response or XRES in one of the GSM triplets. In this example, the RES is identical to the XRES. Accordingly, GSM system  12  sends an UPDATE_LOCATION to IIF  10 , wherein the UPDATE_LOCATION includes the IMSI. 
   Note that, in one embodiment, TR-45 AHAG is used to determine a manner of computing the XRES in response to the RAND in GSM system  12  by IIF  10  and the MS. The TR-45 AHAG may also be used to determine how the cipher key K c  is computed. 
   In step k, IIF sends an authentication status report (ASREPORT) to the HLR of ANS-41 system  14 , wherein the ASREPORT includes the MSCID, MIN and a UCHALRPT for indicating that the RAND (or Unique Challenge) was successful. In step  1 , the HLR forwards the ASREPORT to the AC. In step m, the AC responds with an asreport to the HLR. In step n, the HLR forwards the asreport to IIF  10 . In step o, IIF  10  sends a registration notice (REGNOT) to the HLR, wherein the REGNOT includes the MSCID, SYSCAP, MIN, ESN, SYSACCTYPE and a TRANSCAP. The SYSCAP indicates that the subscriber is roaming in GSM system  12  and the SYSACCTYPE indicates GSM system access. 
   In step p, the HLR sends a regnot to IIF  10 , which includes a profile of the subscriber. In step q, IIF  10  sends an INSERT_SUBSCRIBER_DATA to GSM system  12 . In step r, GSM system  12  responds with an INSERT_SUBSCRIBER_DATA ack to IIF  10 . In step s, IIF  10  sends an UPDATE_LOCATION ack to GSM system  12 . In step t, GSM system  12  sends a location area update ack to the MS. 
     FIG. 3  depicts an example  30  of an unsuccessful authentication of a subscriber of ANS-41 system  14  in GSM system  12  in an initial access attempt, wherein user equipment  16  associated with the subscriber uses a MIN-based IMSI as its identity in GSM system  12 . Steps a 1 -i 1  of  FIG. 3  corresponding to steps a-i of FIG.  2 . In step j 1 , GSM system  12  compares the RES received from the MS with the XRES in one of the GSM triplets. In this example, the RES is not identical to the XRES. Thus, authentication fails and GSM system  12  sends an Authentication_Failure to IIF  10 , wherein the Authentication_Failure indicates the IMSI. 
   In step k 1 , IIF  10  sends an ASREPORT to the HLR of ANS-41 system  14 . The MIN being derived from the IMSI and the UCHALRPT indicating the RAND (or Unique Challenge) was a failure. In step  1   1 , the HLR forwards the ASREPORT to the AC. In step m 1 , the AC sends an asreport to the HLR, wherein the asreport includes DENACC and NOSSD parameters. In step n 1 , the HLR forwards the asreport to IIF  10 . In step o 1 , IIF removes the SSD received for the MS from the AC and any other information for the MS from its memory. IIF  10  sends an Authentication_Failure ack to GSM system  12 . In step p 1 , GSM system  12  rejects the MS′ request for system access. 
     FIG. 4  depicts an example  40  of a successful authentication of a subscriber of ANS-41 system  14  in GSM system  12  in an initial access attempt, wherein user equipment  16  associated with the subscriber uses a MIN-based IMSI as its identity in GSM system  12 . In this example, IIF  10  would not send an ASREPORT to indicate a successful Unique Challenge. Rather, IIF  10  sends a Registration Notification INVOKE with a SYSACCTYPE parameter value indicating GSM access with successful authentication. 
   Steps a 2 -j 2  of  FIG. 4  being identical to steps a-j of FIG.  2 . In step k 2 , IIF  10  sends a REGNOT to the HLR. SYSACCTYPE is set to indicate GSM access with successful authentication, and SYSCAP is set to indicate GSM system  12 . In step l 2 , the HLR determines the subscriber is authorized for service in GSM system  12 . The HLR sends an ASREPORT to the AC, wherein the ASREPORT includes an UCHALRPT indicating that the RAND or unique challenge was successful and a MSCID set to indicate IIF  10 . 
   In step m 2 , the AC sends an asreport to the HLR. In step n 2 , the HLR sends a regnot to IIF  10 . In step o 2 , IIF  10  sends an INSERT_SUBSCRIBER_DATA to GSM system  12 . In step p 2 , GSM system  12  sends an INSERT_SUBSCRIBER_DATA ack to IIF  10 . In step q 2 , IIF  10  sends an UPDATE_LOCATION ack to GSM system  12 . In step r 2 , GSM system  12  sends a location area update ack to the MS. 
   Although the present invention has been described in considerable detail with reference to certain embodiments, other versions are possible. Therefore, the spirit and scope of the present invention should not be limited to the description of the embodiments contained herein.