Abstract:
A method for enabling a mobile telephone to operate in a communications network, including: generating a random authentication number and an expected response to the random authentication number, and transmitting a forward short message service (SMS) message incorporating the random authentication number to the mobile telephone. The method further includes generating at the mobile telephone, responsive to the random authentication number, an authentication response, and receiving from the mobile telephone a return SMS message incorporating the authentication response. The method also includes performing a comparison between the authentication response in the return SMS message and the expected response, and authenticating the mobile telephone to operate in the communications network responsive to the comparison.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/332,117, filed Nov. 21, 2002, which is incorporated herein by reference.  
           [0002]    I. Field Of The Invention  
           [0003]    The present invention relates generally to methods of verification, and specifically to a method for authenticating a mobile telephone operating in a cellular communication network.  
           [0004]    II. Background Of The Invention  
           [0005]    Mobile telephones operating within a cellular communication network undergo a process of authentication before being able to place or receive calls. The authentication, inter alia, prevents fraudulent use of the mobile. Two types of networks wherein authentication is performed are a Code Division Multiple Access (CDMA) network, and a Global System for Mobile Communications (GSM) network, which operates in a Time Division Multiple Access (TDMA) format.  
           [0006]    [0006]FIG. 1 is a schematic diagram illustrating a process of authentication in a cellular network  10 , as is known in the art. A mobile telephone  12  in network  10  transmits an initial signal to a mobile switching center (MSC)  16  communicating with a base-station system (BSS)  14 . In order to be authenticated for operation in the network, MSC  16  instructs an authentication center (AUC)  18  to generate a random authentication number  20 , typically as a triplet. Authentication number  20  is transmitted to mobile telephone  12  within an authentication packet  22 . The generation is performed using data derived from a home location register (HLR)  29 . MSC  16 , AUC  18 , and HLR  29  are comprised in a backbone of network  10 , to which BSS  14  is coupled. The mobile telephone processes the number through an authentication algorithm comprised in the mobile in order to generate a reply value  24 . The reply value is transmitted in an authentication response packet  26  to the MSC. The MSC checks, with AUC  18  and HLR  29 , if random number  20  and reply  24  satisfy authentication criteria of the network. If the criteria are satisfied, the mobile telephone is allowed to continue operating within the network.  
           [0007]    Network  10  also comprises a short message service center (SMS-C)  28  in the backbone of the network, which is able to transmit and receive short alphanumeric messages. Mobile telephone  12  may be implemented to receive and transmit such SMS messages. Typically, alphanumeric messages transmitted and received by an SMS-C consist of approximately 128 characters, although higher numbers of characters may be transferred.  
           [0008]    If network  10  comprises a CDMA network operating according to an industry-standard protocol, such as a TIA/EIA/IS-2000-A-1 standard published by the Telecommunications Industry Association, Arlington, Va., mobile  12  comprises a CDMA mobile. AUC  18  implements an ANSI-41 protocol, published by the 3rd Generation Partnership Project 2, which may be found at http://www.3gpp2.org, and which is incorporated herein by reference. In this case, random authentication number  20  sent from the authorization center is a 32-bit number, and reply value  24  generated by the CDMA mobile is an 18-bit number. In order to perform the authentication, the CDMA mobile thus needs to be able to transmit its authentication reply as an 18-bit number.  
           [0009]    If network  10  comprises a GSM network operating according to an industry-standard protocol, such as an ETSI TS 100 940 V7.8.0 technical specification, published by the European Telecommunications Standards Institute, Sophia Antipolis Cedex, France, mobile  12  comprises a GSM mobile. Section 4.3 of the specification, incorporated herein by reference, describes the authentication procedure followed in a GSM network. In this case, the random authentication number sent from the authorization center is a 128-bit number, and the reply value generated by the GSM mobile is a 32-bit number. In order to perform the authentication in the GSM network, the GSM mobile needs to be able to transmit its authentication reply as a 32-bit number.  
           [0010]    If a CDMA mobile is to operate in a GSM network, however, the authentication reply which the mobile needs to generate, a 32-bit number, is larger than the 18-bit capability of the CDMA mobile. Methods known in the art for overcoming the limited capability of the CDMA mobile include changing software in both the GSM authentication center and the CDMA mobile. When the CDMA mobile is to operate in its native CDMA environment, the software is replaced by the original software. An alternative procedure which is known in the art is to change software in the GSM center so that only “CDMA-type” authentication is performed on CDMA mobiles operative in the GSM network. It will be appreciated that both methods are problematic.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of some aspects of the present invention to provide a method and apparatus for authenticating a mobile telephone to operate in a communications network.  
           [0012]    In a preferred embodiment of the present invention, a mobile telephone is to be operated within a cellular communications network. A base station or a switching center in the network authenticates the mobile telephone by transmitting an authentication request in the form of a message, most preferably a short messaging system (SMS) message, to the mobile. The SMS message comprises a first identifier defining the SMS message as the authentication request, together with a random number which is used as part of an authentication procedure. By analyzing the first identifier, the mobile telephone recognizes the SMS message as the authentication request and processes the accompanying random number through an authentication algorithm comprised in the mobile telephone, so as to generate an authentication response. The response is sent in a return SMS message transmitted from the mobile to the network. The return SMS message comprises a second identifier defining the return message as including the authentication response. The network recovers the response from the return message, and compares the recovered response with an expected response, in order to authenticate the mobile telephone. Using SMS messages as delivery systems for authentication requests and responses avoids limitations on sizes of the random number and of responses in systems known in the art.  
           [0013]    In some preferred embodiments of the present invention, the mobile telephone is able to operate in more than one communications network. Each network comprises a different authentication protocol, each protocol defining a different size for the random number and response. The mobile can be authenticated in its “native” network, or in a network operating under a different protocol, without software or hardware changes in the mobile as it moves from network to network.  
           [0014]    In an alternative preferred embodiment of the present invention, where the network within which the mobile operates supports data burst messages (DBMs), the authentication request message to the mobile, and the authentication response message from the mobile, are sent as DBMs. Most preferably, the DBMs are of a type already supported by a communications protocol under which the network is operating.  
           [0015]    The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a schematic diagram illustrating a process of authentication in a cellular communications network, as is known in the art;  
         [0017]    [0017]FIG. 2 is a schematic diagram illustrating a process of authentication of a mobile telephone, according to a preferred embodiment of the present invention; and  
         [0018]    [0018]FIG. 3 is a sequence diagram showing steps involved in authentication of the mobile telephone of FIG. 2 operating in a communications network, according to a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]    Reference is now made to FIG. 2, which is a schematic diagram illustrating a process of authentication of a mobile telephone  32 , according to a preferred embodiment of the present invention. Mobile telephone  32  is adapted to operate in a cellular communications network  30 , which functions according to a first industry-standard cellular communications protocol. The mobile comprises circuitry  35  enabling the mobile to operate. Most preferably, mobile  32  is adapted to operate according to the first protocol, as well as being operative according to a second industry-standard cellular communications protocol. For example, the first protocol comprises a Global System for Mobile Communications (GSM) protocol, such as an ETSI TS 100 940 V7.8.0 technical specification referred to in the Background of the Invention, and the second protocol comprises a Code Division Multiple Access (CDMA) protocol, such as a TIA/EIA/IS-2000-A-1 standard also referred to in the Background of the Invention. Alternatively, mobile  32  is operative according to either a GSM or a CDMA industry-standard protocol, or according to another protocol known in the art.  
         [0020]    A base-station system (BSS)  34  is coupled to a mobile switching center (MSC)  40 , which is in turn coupled to an authentication center (AUC)  36 , and a home location register (HLR)  38 . Optionally, a short message service center (SMS-C)  42  may also be coupled to MSC  40 . One or more of BSS  34 , AUC  36 , HLR  38 , and MSC  40  act as a network control center  37 , controlling transmissions within network  30 . Except for the differences described below, AUC  36 , HLR  38 , MSC  40 , and SMS-C  42  respectively operate generally as AUC  18 , HLR  29 , MSC  16 , and SMS-C  28 , described with reference to FIG. 1 in the Background of the Invention.  
         [0021]    Mobile  32  wishes to operate in network  30 , and transmits an initial signal to BSS  34 . In order to authenticate the mobile, BSS  34  transmits a random authentication number  44 , encapsulated in a first, forward, message  48 , to mobile  32 . Except where otherwise stated hereinbelow, message  48  is assumed to comprise an SMS message. Message  48  incorporates an identifier  46  within the message, so that mobile  48  is able to recognize SMS message  48  as a special message conveying the random authentication number. On receipt of SMS message  48 , mobile  32  decodes the message, recovers the value of random authentication number  44 , and applies the recovered value to an authentication algorithm comprised in the mobile, to generate an authentication response. Preferably, software for decoding message  48 , recovering number  44 , and the authentication algorithm is incorporated as a separate replaceable element  31 , most preferably as a subscriber identity module (SIM) within mobile  32 . Alternatively, the software is incorporated integrally within a memory  33  of the mobile.  
         [0022]    Mobile  32  incorporates the authentication response in a second, return, message  54 , as a reply value  50 , and transmits the message to BSS  34 . Except where otherwise stated hereinbelow, message  54  is assumed to comprise an SMS message. Mobile  32  incorporates an identifier  52  in message  54 , so that the message may be recognized as a special message conveying the authentication reply. SMS message  54  is routed by BSS  34  to MSC  40 , which, from identifier  52 , recognizes the message as comprising the authentication reply, and extracts reply value  50  from the message. MSC  40  checks that value  50  corresponds with an expected response to random number authentication  44 , and if there is a correspondence, authenticates mobile  32 . By incorporating random number authentication  44  and reply value  50  in SMS messages, limitations on sizes of the random number authentication and the reply value, as defined by the different protocols under which mobile  32  operates, are overcome. The limitations are overcome since SMS messages are able to transmit 128 or more 8-bit characters.  
         [0023]    [0023]FIG. 3 is a sequence diagram  60  showing steps involved in authentication of mobile telephone  32  operating in network  30 , according to a preferred embodiment of the present invention. By way of example, network  30  is assumed to operate according to a GSM protocol. Sequence diagram  60  illustrates steps performed before and after mobile  32  has made an initial transmission, received by BSS  34 , and is awaiting authentication. The initial transmission incorporates an international mobile subscriber identity (IMSI), typically the telephone number of mobile  32 , which has been allocated to the mobile when it is initially registered in the network, and which is also stored in AUC  36 . Also at registration, mobile  32  is allocated a subscriber authentication key (Ki), which is stored both in the mobile and in AUC  36 .  
         [0024]    In a first step  62 , AUC  36  generates a random number (RAND), and uses RAND to calculate an identification parameter, termed signal response (SRES), which is a function of RAND and Ki. AUC  36  also calculates an encryption key (Kc) which is a function of Ki and RAND. IMSI, Kc, RAND, and SRES are transferred and stored in HLR  38 .  
         [0025]    In a second step  64 , HLR  38  transfers the values of IMSI, Kc, RAND, and SRES to MSC  40 , after the MSC has received the initial transmission via BSS  34 . MSC  40  stores IMSI, Kc, RAND, and SRES for later comparison purposes.  
         [0026]    In a third step  66 , MSC  40  incorporates the RAND value, corresponding to random authentication number  44  (FIG. 2) into SMS message  48 . The SMS message is transferred to BSS  34  via either a traffic or a control channel. Alternatively, if network  30  comprises a CDMA  2000  network, the transfer may be made using an Application Data Delivery Service (ADDS).  
         [0027]    In a fourth step  68 , BSS  34  adds identifier  46  to the message and transmits the message to mobile  32 .  
         [0028]    In a fifth step  70 , mobile  32  identifies SMS message  48 , by identifier  46 , as a message comprising number  44 , using software comprised in SIM  31  or memory  33  of the mobile. The mobile uses number  44 , and the mobile&#39;s stored values of IMSI and Ki, to generate reply value  50  as a signal response to number  44 . The mobile then constructs SMS message  54 , incorporating reply value  50  and identifier  52 .  
         [0029]    In a sixth step  74  the mobile transmits SMS message  54  to BSS  34 .  
         [0030]    In a final step  76 , BSS  34  transfers SMS message  54  to MSC  40 , which identifies the SMS message, from identifier  52 , as a response to the authentication SMS message  48 . MSC  40  then recovers the value of reply value  50 , as a signal response, from message  54 , and compares the recovered value with an expected value of SRES received from HLR  38  in second step  64 . If the two signal responses tally, MSC  40  authenticates the mobile; if the responses do not tally, the mobile is not authenticated.  
         [0031]    It will be appreciated that the descriptions above with respect to FIGS. 2 and 3 apply to substantially any mobile transceiver operating in a cellular communication network, wherein the transceiver is capable of transmitting and receiving SMS messages. Thus, the scope of the present invention is not limited to any specific protocol or method of transmission utilized by the transceiver and/or the network.  
         [0032]    In an alternative preferred embodiment of the present invention, wherein BSS  34  and mobile  32  are able to communicate via a spread spectrum system such as a code division multiple access (CDMA) system, messages  48  and  54  (FIG. 2) comprise short data burst messages. Data burst messages are described and characterized in TIA/EIA/IS-2000-A-1 standard, referred to in the Background of the Invention. The data burst messages are preferably implemented according to one of the predefined types incorporated in the standard, or alternatively via a custom-defined type. If messages  48  and  54  are in the form of data burst messages, then in sixth step  74  and final step  76  BSS  34  identifies the data burst message as an authentication response, recovers reply value  50 , and provides the value to MSC  40 . The MSC then performs the comparison between the recovered value and the expected value of SRES.  
         [0033]    By incorporating random authentication numbers and responses to these numbers in SMS or data burst messages, limitations on sizes of the numbers and of the responses are avoided. Such size limitations, i.e., respective numbers of bits for the random authentication number and its response, are typically defined by a specific protocol. Using SMS or data burst messages as delivery systems thus enables a mobile telephone to be authenticated in a variety of protocols, without changing software or hardware in the mobile telephone.  
         [0034]    It will be appreciated that the preferred embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.