Abstract:
A system and method for strong authentication achieved in a single round trip is disclosed, which reduces the amount of time needed for a mobile node to be authenticated by the network. In an embodiment of the present invention, the, authentication time is approximately three times faster than for  3 GPP.

Description:
RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/271,143 filed Feb. 23, 2001, the benefit of the earlier filing date of which is hereby claimed under 35 U.S.C. §119 (e). 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to mobile networks, and more particularly to authentication in for mobile networks.  
         BACKGROUND OF THE INVENTION  
         [0003]    Mobile IP enables a mobile node to move freely from one point of connection to another. During the movement of the mobile node from one connection point to another there should be no disruption of the TCP end-to-end connectivity. In order to extend Mobile IP for use by cellular telephone companies and check the mobile node&#39;s identity, an authentication, authorization, and accounting (“AAA”) mechanism may be used. AAA may be used to provide the authentication of a mobile node (“MN”) when mobile node is connected to the point of the agent on the foreign domain (foreign agent).  
           [0004]    Authentication in 3GPP and GSM is typically done by first asking the identity of the mobile node to the network. The mobile node sends an attach request to the foreign domain&#39;s MSC or SGSN or 3GSGSN. The 3GSGSN asks the identity of the mobile node to the home authentication server (the HLR). When the identity is verified, the SGSN asks for authentication quintuplets or triplets in GSM. When the SGSN receives the quintuplets or triplets it sends an authentication request to the mobile node. The mobile node uses its local algorithms to sign the random number received in the quintuplet from the SGSN. The mobile node may then verify the network identity when in 3GPP and send back a signature to the visited SGSN. The foreign SGSN verifies the signature by comparing it to the expected result received in the quintuplet. When this matches, then the three entities (the mobile node, the foreign authentication server and the home authentication server) are authenticated and trust each other.  
           [0005]    This authentication process, however, requires many steps and communications from the foreign domain to the home domain. Not only is this time consuming, but the communications may be costly.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is directed at addressing the above-mentioned shortcomings, disadvantages and problems, and will be understood by reading and studying the following specification.  
           [0007]    According to aspects of the invention, a system and method for strong authentication in a single round trip within a GPRS network is disclosed, which reduces the amount of time needed for a mobile node (MN) to be authenticated by the network.  
           [0008]    According to an aspect of the invention, a random number is generated by the base station in the foreign network. The random number may be sent directly to the MN or the random number may be broadcast on a common channel. The MN receives the random number generated at the base station much faster as compared to a random number generated by the home domain.  
           [0009]    According to another aspect of the invention, the MN generates a signature using the random number to authenticate itself to the network. Any algorithm for signature generation may be used. The home authentication server (AAAH), typically the HLR, authenticates the signature. When the signature is authenticated, the AAAH generates a signature to authenticate the network to the MN. The AAAH sends this signature to the MN. When the MN authenticates the signature, strong authentication has occurred. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 illustrates an exemplary mobile IP network in which the invention may operate;  
         [0011]    [0011]FIG. 2 is a schematic diagram that shows an exemplary AAA server that is operative to provide authentication, authorization, and accounting rules;  
         [0012]    [0012]FIG. 3 illustrates a mobile IP/AAA model;  
         [0013]    [0013]FIG. 4 illustrates authentication functions; and  
         [0014]    [0014]FIG. 5 shows a process for a single round trip authentication, in accordance with aspects of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanied drawings, which form a part hereof, and which is shown by way of illustration, specific exemplary embodiments of which the invention may be practiced. Each embodiment is described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.  
         [0016]    Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The term “node” refers to a network element, such as a router. The term support node refers to both “GGSN” and “SGSN” nodes. The term “user” refers to any person or customer such as a business or organization that employs a mobile node to communicate or access resources over a mobile network. The term “operator” refers to any technician or organization that maintains or services an IP based network. The term “AAA” refers to authentication, authorization, and accounting. The term “AAAH” refers to a home domain AAA server for a mobile node. The term “AAAF” refers to a foreign domain AAA server relative to a mobile node. The term “HA” refers to a home agent. The term “FA” refers to a foreign agent. The term “home agent” refers to a node, such as a router, on the home network which serves as the point of communications with the mobile node. The term “foreign agent” refers to a node, such as a router, on the mobile node&#39;s point of attachment when it travels to a foreign network. The term “HLR” refers to a home location register. The term “VLR” refers to visitor location register. The term “MN” refers to a mobile node.  
         [0017]    Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or is inconsistent with the disclosure herein.  
         [0018]    Illustrative Operating Environment  
         [0019]    With reference to FIG. 1, an exemplary mobile IP network in which the invention may operate is illustrated. As shown in the figure, mobile IP network  100  includes mobile node (MN)  105 , SIM  150 , radio access network  110 , base station (BS)  155 , Serving GPRS Support Node (SGSN)  115 , core network  120 , routers  125   A-C , AAA server  200 , General Packet Radio Service Nodes (GGSNs)  135   A-B , data network  140 , and data network  145 .  
         [0020]    The connections and operation for mobile IP network  100  will now be described. MN  105  is coupled to radio access network  110 . Generally, MN  105  may include any device capable of connecting to a wireless network such as radio access network  110 . Such devices include cellular telephones, smart phones, pagers, radio frequency (RF) devices, infrared (IR) devices, integrated devices combining one or more of the preceding devices, and the like. MN  105  may also include other devices that have a wireless interface such as Personal Digital Assistants (PDAs), handheld computers, personal computers, multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCs, wearable computers, and the like. As illustrated, MN  105  is coupled to Subscriber Identity Module (SIM)  150 . SIM  150  is a smart card that may be used in MN  105  to store information. This information may include a key that is only known to MN  105  and the home authority to which the user belongs. A User Services Identity Module (USIM) or other software/hardware may also be used to provide the same functionality. The secret key is used for authenticating MN  105 . For example, the secret key that is stored in SIM  150  and is associated with MN  105  is used for authentication when MN  105  is roaming and is not within its home authority. SIM  150  may also store algorithms to generate a signature used for authentication as well as other data.  
         [0021]    Radio access network (RAN)  110  transports information to and from devices capable of wireless communication, such as MN  105 . Radio access network  110  may include both wireless and wired components. For example, radio access network  110  may include a cellular tower that is linked to a wired telephone network. Typically, the cellular tower carries communication to and from cell phones, pagers, and other wireless devices, and the wired telephone network carries communication to regular phones, long-distance communication links, and the like. As shown in the figure, RAN  110  includes BS  155  that is arranged to receive signals from MN  105  and send signals to MN  105 . Depending on the specific architecture of the mobile network a base station controller (BSC) or radio network controller (RNC) may also be coupled to BS  155 . Generally, the BSC/RNC manages advanced radio-related functions, handovers from one cell to another, radio channel assignments, Quality of Service (QoS) issues, load-balancing, and the like.  
         [0022]    Some nodes may be GPRS nodes. For example, SGSN  115  may send and receive data from mobile stations, such as MN  105 , over radio access network  110 . SGSN  115  also maintains location information relating to MN  105 . SGSN  115  communicates between MN  105  and GGSNs  135   A-B  through core network  120 .  
         [0023]    Core network  120  is an IP packet based backbone network that includes routers, such as routers  125   A-C , to connect the support nodes in the network. Some of the routers may act as a HA or a FA for a MN. Generally, an agent (HA or FA) communicates with AAA server  200  to maintain a secure connection with the mobile node. Routers are intermediary devices on a communications network that expedite message delivery. On a single network linking many computers through a mesh of possible connections, a router receives transmitted messages and forwards them to their correct destinations over available routes. On an interconnected set of LANs, including those based on differing architectures and protocols, a router acts as a link between LANs, enabling messages to be sent from one to another. Communication links within LANs typically include twisted wire pair, fiber optics, or coaxial cable, while communication links between networks may utilize analog telephone lines, full or fractional dedicated digital lines including T1, T2, T3, and T4, Integrated Services Digital Networks (ISDNs), Digital Subscriber Lines (DSLs), wireless links, or other communications links.  
         [0024]    GGSNs  135   A-B  are coupled to core network  120  through routers  125   A-C  and act as wireless gateways to data networks, such as network  140  and network  145 . Networks  140  and  145  may be the public Internet or a private data network. GGSNs  135   A-B  allow MN  105  to access network  140  and network  145 .  
         [0025]    AAA server  200  is coupled to core network  120  through communication mediums. AAA server  200  may be programmed by an operator to contain the authentication, authorization, and accounting rules associated with the operator&#39;s network. AAA server  200  may be programmed differently under different operator&#39;s networks. AAA server  200  may also be programmed such that is can communicate with foreign AAA servers (not shown).  
         [0026]    Utilizing an AAA server helps to enforce authentication, authorization, and accounting rules to help ensure end-to-end quality of service (QoS) for users. Operators have the flexibility to provide different AAA rules. For example, conversational traffic may be mapped into either the Expedited Forwarding (EF) class or Assured Forwarding (AF) class at the core network. The operator may employ a different charging structure for each class. Also, AAA rules may be established between a foreign authority and a home authority. An exemplary AAA server is described in more detail in conjunction with FIG. 2.  
         [0027]    Furthermore, computers, and other related electronic devices may be connected to network  140  and network  145 . The public Internet itself may be formed from a vast number of such interconnected networks, computers, and routers. Mobile IP network  100  may include many more components than those shown in FIG. 1. However, the components shown are sufficient to disclose an illustrative embodiment for practicing the present invention.  
         [0028]    The media used to transmit information in the communication links as described above illustrates one type of computer-readable media, namely communication media. Generally, computer-readable media includes any media that can be accessed by a computing device. Communication media typically embodies computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, communication media includes wired media such as twisted pair, coaxial cable, fiber optics, wave guides, and other wired media and wireless media such as acoustic, RF, infrared, and other wireless media.  
         [0029]    [0029]FIG. 2 is a schematic diagram that shows an exemplary AAA server that is operative to provide authentication, authorization, and accounting rules. Accordingly, AAA server  200  may receive and transmit data relating to the AAA rules and authentication procedures. For instance, AAA server  200  may transmit AAA rules and receive data from the nodes on the mobile IP network.  
         [0030]    AAA server  200  may include many more components than those shown in FIG. 2. However, the components shown are sufficient to disclose an illustrative embodiment for practicing the present invention. As shown in FIG. 2, AAA server  200  is connected to core network  120 , or other communications network, via network interface unit  210 . Network interface unit  210  includes the necessary circuitry for connecting AAA server  200  to core network  120 , and is constructed for use with various communication protocols including the Common Open Policy Services (COPS) protocol that runs on top of the Transmission Control Protocol (TCP). Other communications protocols may be used, including, for example, User Datagram Protocols (UDP). Typically, network interface unit  210  is a card contained within AAA server  200 .  
         [0031]    AAA server  200  also includes processing unit  212 , video display adapter  214 , and a mass memory, all connected via bus  222 . The mass memory generally includes RAM  216 , ROM  232 , and may include one or more permanent mass storage devices, such as hard disk drive  228 , a tape drive, CDROM/DVD-ROM drive  226 , and/or a floppy disk drive. The mass memory stores operating system  220  for controlling the operation of policy server  200 . This component may comprise a general purpose server operating system  220  as is known to those of ordinary skill in the art, such as UNIX, LINUX™, or Microsoft WINDOWS NT®. Basic input/output system (“BIOS”)  218  is also provided for controlling the low-level operation of AAA server  200 .  
         [0032]    The mass memory as described above illustrates another type of computer-readable media, namely computer storage media. Computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computing device.  
         [0033]    The mass memory also stores program code and data for AAA server program  230 , and programs  234 . AAA server program  230  includes computer executable instructions which, when executed by AAA server computer  200 , maintain authentication, authorization, and accounting rules and procedures. AAA server  200  may include a JAVA virtual machine, an HTTP handler application for receiving and handing HTTP requests, JAVA applets for transmission to a WWW browser executing on a client computer, an IPsec handler, a Transport Layer Security (TLS) handler and an HTTPS handler application, and a secure protocol AAA handler, for handling secure connections.  
         [0034]    AAA server  200  also comprises input/output interface  224  for communicating with external devices, such as a mouse, keyboard, scanner, or other input devices not shown in FIG. 2. Likewise, AAA server  200  may further comprise additional mass storage facilities such as CD-ROM/DVD-ROM drive  226  and hard disk drive  228 . Hard disk drive  228  is utilized by AAA server  200  to store, among other things, application programs, databases, and program data used by AAA server program  230 . For example, AAA rules, user databases, relational databases, and the like, may be stored.  
         [0035]    Authentication in a Single Round Trip  
         [0036]    [0036]FIG. 3 illustrates a mobile IP/AAA model, in accordance with aspects of the invention. As shown in the figure, IP/AAA trust model  300  includes foreign authority  305 , home authority ( 310 ), mobile node  335 , AAAF  315 , AAAH  320 , and SIM  370 , and base station (BS)  375 .  
         [0037]    Connections may be established between the MN, AAAH, and AAAF nodes to help ensure secure communication. SIM  370  is coupled to MN  335  and to home authority  310 . SIM  370  is used to store a secret key that is used to authenticate MN  335 . The secret key is only known to the home authority and to the MN. Additionally, SIM  370  may store algorithms to create a signature as well as keep track of counters relating to the MN to support authentication. SIM  370  may also be a USIM or some other software/hardware device.  
         [0038]    In order to authenticate mobile nodes while roaming, a model, as shown in FIG. 3, may be used. In this exemplary figure, MN  335  belongs to home authority, or home domain  310  within a GPRS network. An authority is able to validate a user&#39;s credentials and is used to maintain and establish security relationships with authorities that are external to the mobile node&#39;s home network. The authority may be a single node, such as a computer or router, on the network, or the authority may include several nodes that are used to make up the authority. Connection  355  between AAAF  315  and AAAH  320  may be arranged to handle the authentication, authorizations, and possibly the accounting data, between home authority  310  and foreign authority  305 . Connection  365  may be established between AAAF  315  and MN  335 . Connections within a single domain may be achieved by local management or static configuration. However, secure connections, or authentications for a MN in a foreign authority is more difficult as there may be many hops between the AAAF and the AAAH. Additionally, a secure association does not typically exist between AAA&#39;s located within different authorities.  
         [0039]    When MN  335  moves from home authority  310  to foreign authority  305 , MN  335  an authentication process begins. The authentication of MN  335  is achieved in a single round trip from MN  335  to AAAF  315  to AAAH  320  and back. The system and method for strong authentication achieved in a single round trip has many advantages. For example, the time required for authentication of a mobile node is faster than when using traditional methods. MN  335  receives a random number that it uses to generate a signature. The algorithm used for the signature generation could be any algorithm. An example of such an algorithm is the one used in the 3GPP recommendation 3GPP TS 33.102 V3.6.0 (2000-10) Technical Specification 3 rd  Generation Partnership Project. According to one embodiment, base station  375  associated with foreign authority  305  sends the random number to mobile node  335  when MN  335  is roaming in foreign authority  305 . By generating the random number at the base station local to MN  335 , the random number is received much faster by the MN than having to wait for it to be generated in home authority  310 . This results in a significant time reduction for a MN that frequently roams. A unicast connection established between the mobile node and base station may be used to send the random number or the mobile node may receive the random number from a broadcast message. When the signature is prepared, MN  335  sends the signature to AAAF  315 . Any algorithm for signature generation may be used. AAAF  315  forwards the signature to AAAH  320 . According to one embodiment, the home location register (HLR) receives the signature. AAAH  320  authenticates the signature by comparing the identity of MN  335  to the signature received. When the signature is not authentic, the authentication process fails. When the signature is authentic, AAAH  320  prepares its own signature which is used to verify the network to MN  335 . AAAH  320  sends the signature to AAAF  315 . Along with the signature, AAAH  320  can proceed as in the 3GPP specification and return a set of quintuplets for further authentications. AAAF  315  forwards the signature to MN  335  for authentication. MN  335  then authenticates the signature prepared by AAAH  320 . When the signature is not authentic, the authentication process fails. When the signature is authentic, a strong authentication has occurred. Strong authentication is achieved when the signature created by MN  335  is authenticated by AAAH  320  and when the signature created by AAAH  320  is authenticated by MN  335 .  
         [0040]    Strong authentication achieved in a single round trip has many advantages. The time required for authentication of a mobile node is faster than when using traditional methods. Also, network messages are reduced, thereby reducing cost. Authentication is also achieved in a single round trip.  
         [0041]    [0041]FIG. 4 illustrates authentication functions. Once the random number RAND is generated it is used by the MN and the home authentication server (AAAH) to generate a set of variables including a ciphering key (CK), an integrity check key (IK) a signature response (RES) and the authentication token AUTN which is used to authenticate the network to the MN. AUTN is based on the secret key K common to the MN and the AAAH and a sequence number SQN. The authentication vector may include a random number RAND, the authentication part AUTN, an expected result part XRES, key CK, and key IK. K is the secret key stored locally in the SIM card (USIM) associated with the MN. As mentioned previously, the MN and the AAAH use the same secret key for authentication. SQN is a sequence number. AK is an anonymity key.  
         [0042]    Functions f1-f5 are keyed one way functions that are used to produce authentication data and key material for confidentiality and integrity. Functions f1-f5 each have an input coupled to key K and an input coupled to random number RAND. Function f1 also includes an input for sequence SQN and authentication management field (AMF). Function f1 produces the expected message authentication code (XMAC). Function f2 produces response RES. Function f4 produces cipher key CK. Function f4 produces integrity key IK. Function f5 produces anonymity key AK. As mentioned above, the AAAH may send the authentication vectors AV (quintuplets which is the equivalent of a GSM “triplet”) to the MN.  
         [0043]    The computed RES value may be compared with the XRES value included in an authentication vector to determine if the AKA exchange was successful. Sequence number SQN is a synchronized counter between the MN and the AAAH. By using this synchronized SQN and other parameters the AAAH can compute using function f1 a MAC value that can be checked by the USIM associated with the MN. This way the USIM authenticates that the secret key K, known only by the home authority and the MN, was used when constructing AUTN. The AMF field may be used to carry information about the used AKA algorithms and used secret key K if there are several. The AK is used to conceal the sequence number as the sequence number if not keyed may expose the identity and location of the user.  
         [0044]    In the network authentication process the expected message authentication code (XMAC) is first computed and compared to the received message authentication code (MAC). When XMAC equals MAC and the sequence number is fresh (SQN &gt;SQN HE ) the network authentication is successful. To compute the XMAC value the encrypted Sequence Number SQN is first recovered. After this, function f1 is used to compute XMAC from K, SQN, AMF and RAND.  
         [0045]    In the process used to authenticate USIM to the network, response value RES is computed from RAND and K using function f2. Resulting RES value is then transmitted to the network. Used CK and IK are computed from RAND and K using functions f3 and f4 respectively. Actual encryption over the air link may be performed using a stream cipher mode of a block cipher KASUMI with ciphering key CK.  
         [0046]    [0046]FIG. 5 shows a process for a single round trip authentication within a GPRS network. After a start block, the process moves to block  502  where a random number is generated. According to one embodiment, the random number is generated in the local authority relative to the MN. Moving to block  505 , the random number is sent to a mobile node. According to one embodiment, the base station sends the random number to the mobile node. A unicast connection established between the mobile node and base station may be used to send the random number or the mobile node may receive the random number from a broadcast message. Stepping to block  510 , the mobile node prepares a signature relating to the random number. Any algorithm for signature generation may be used. Transitioning to block  515 , the MN sends the signature to the base station from which it received the random number. Flowing to block  520 , the base station forwards the signature to its associated AAAF. Moving to block  525 , the AAAF forwards the signature to the MN&#39;s AAAH. Typically, the home location register (HLR) receives the signature. Stepping to block  530 , the signature is authenticated. The signature is authenticated by comparing the identity of the MN to the signature received. Transitioning to decision block  540 , a determination is made as to whether the signature is authentic. When the signature is not authentic, the process flows to block  537  where the authentication process is ended. The process then steps to an end block and returns to processing other actions. When the signature is authentic, the process flows to block  545  where the AAAH prepares its own signature. Moving to block  550 , the AAAH sends the signature to the AAAF associated with the MN. Next, at block  555 , the AAAF forwards the signature to the MN for authentication. Transitioning to block  560 , the MN authenticates the signature prepared by AAAH. Moving to decision block  565 , the process determines when the signature is authentic. When the signature is not authentic, the process moves to block  537  where the authentication process is terminated. The process then steps to an end block and returns to processing other actions. When the signature is authentic, the process moves to block  570  at which point a strong authentication has occurred. A strong authentication occurs when the MN to the network is authenticated and when the network to the MN is authenticated. In other words, strong authentication is achieved when the signature created by the MN is authenticated by the AAAH and when the signature created by the AAAH is authenticated by the MN. The process then transitions to an end block and returns to processing other actions.  
         [0047]    The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended and their equivalents.