Patent Publication Number: US-7721106-B2

Title: Transitive authentication authorization accounting in the interworking between access networks

Description:
This application claims the benefit, under 35 U.S.C. § 365 of International Application PCT/US03/07623, filed Mar. 12, 2003, which was published in accordance with PCT Article 21(2) on Nov. 6, 2003 in English and which claims the benefit of U.S. Provisional Patent Application No. 60/376,160, filed Apr. 26, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to networking and, more particularly, to method for transitive Authentication Authorization and Accounting (AAA) in the interworking between access networks. 
     2. Background of the Invention 
     Typically, Authentication, Authorization and Accounting (AAA) are required to access and utilize networks such as cellular networks and Wireless Local Area Networks (WLANs). In an environment in which a mobile terminal has multiple network access mechanisms, providing AAA interworking among these networks is of great importance. However, it is generally the case that one or more of the involved networks have a closed AAA scheme and it is difficult for one of the networks to use the AAA structure of another one of the networks and vice versa. For example, cellular networks have an AAA infrastructure that is not compatible with Internet based AAA and cannot be easily accessed through Internet protocols, even though the involved networks (including the cellular networks) have external IP connectivity. 
     Convention approaches for providing AAA interworking all require a special interworking function between the networks, even for AAA interworking between networks that have pre-established trust relationships amongst themselves. Using this interworking function, e.g., network B will then access network A&#39;s AAA infrastructure to authenticate a user which has already been authenticated by network A (through a closed network AAA mechanism). The conventional approaches do not take advantage of the fact that the user has already been authenticated by network A which has pre-established trust relationship with network B. 
     Accordingly, it would be desirable and highly advantageous to have a method for transferring the trust that is attributed to a user by one network from that network to another network, particularly without requiring any special interworking function to accomplish the same. 
     SUMMARY OF THE INVENTION 
     The problems stated above, as well as other related problems of the prior art, are solved by the present invention, a method for transitive Authentication Authorization and Accounting (AAA) in the interworking between access networks. 
     According to an aspect of the present invention, there is provided a method for allowing a user device that has already been authenticated by a first network to gain access to a second network. The first network and the second network have a pre-established trust relationship there between. A packet is received from the user device that includes a user device public key, by the second network. A session key is sent from the second network to the user device when a source Internet Protocol (IP) address associated with the packet falls into a range allocated to the first network. The session key is encrypted with the user device public key. The session key is for permitting the user device to access the second network. 
     These and other aspects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments, which is to be read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a computer system  100  to which the present invention may be applied, according to an illustrative embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating a transitive AAA structure to which the present invention may be applied, according to an illustrative embodiment of the present invention; 
         FIG. 3  is a flow diagram illustrating an AAA method for allowing a user device that has been authenticated by a 3G cellular network to gain access to a Wireless Local Area Network WLAN, according to an illustrative embodiment of the present invention; and 
         FIG. 4  is a flow diagram illustrating an accounting method for performing an accounting for the user of the user device of the method of  FIG. 3 , according to an illustrative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a transitive Authentication Authorization and Accounting (AAA) scheme for an interworking between access networks. It is to be appreciated that the present invention is applicable to any combination of access networks. However, the present invention is particularly applicable to cellular network and Wireless Local Area Network (WLAN) interworking. 
     The present invention transfers the trust on a user by a first access network to a second access network where the first and the second access networks have a pre-established trust relationship. In contrast to the prior art, the present invention does not require any special interworking function between the two networks, but rather relies on IP addressing and routing schemes to verify user access right. It is to be appreciated that the present invention is also referred to herein as transitive AAA. 
     It is to be understood that the present invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. Preferably, the present invention is implemented as a combination of hardware and software. Moreover, the software is preferably implemented as an application program tangibly embodied on a program storage device. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU), a random access memory (RAM), and input/output (I/O) interface(s). The computer platform also includes an operating system and microinstruction code. The various processes and functions described herein may either be part of the microinstruction code or part of the application program (or a combination thereof) which is executed via the operating system. In addition, various other peripheral devices may be connected to the computer platform such as an additional data storage device and a printing device. 
     It is to be further understood that, because some of the constituent system components and method steps depicted in the accompanying Figures are preferably implemented in software, the actual connections between the system components (or the process steps) may differ depending upon the manner in which the present invention is programmed. Given the teachings herein, one of ordinary skill in the related art will be able to contemplate these and similar implementations or configurations of the present invention. 
       FIG. 1  is a block diagram illustrating a computer system  100  to which the present invention may be applied, according to an illustrative embodiment of the present invention. The computer processing system  100  includes at least one processor (CPU)  102  operatively coupled to other components via a system bus  104 . A read only memory (ROM)  106 , a random access memory (RAM)  108 , a display adapter  110 , an I/O adapter  112 , a user interface adapter  114 , a sound adapter  199 , and a network adapter  198 , are operatively coupled to the system bus  104 . 
     A display device  116  is operatively coupled to system bus  104  by display adapter  110 . A disk storage device (e.g., a magnetic or optical disk storage device)  118  is operatively coupled to system bus  104  by I/O adapter  112 . 
     A mouse  120  and keyboard/keypad  122  are operatively coupled to system bus  104  by user interface adapter  114 . The mouse  120  and keyboard/keypad  122  are used to input and output information to and from system  100 . 
     At least one speaker (herein after “speaker”)  185  is operatively coupled to system bus  104  by sound adapter  170 . 
     A (digital and/or analog) modem  196  is operatively coupled to system bus  104  by network adapter  198 . 
       FIG. 2  is a block diagram illustrating a transitive AAA structure to which the present invention may be applied, according to an illustrative embodiment of the present invention. In the illustrative embodiment of  FIG. 2 , the transitive AAA structure includes: a first network  210 ; a second network  220 ; the Internet  230 , and a user device  240 . The second network  220  includes an AAA server  230   a . The user device  240  includes a first network interface  240   a  and a second network interface  240   b . It is to be appreciated that while the present invention is described herein with respect to two networks, the present invention may be applied with any number and any types of networks, while maintaining the spirit and scope of the present invention. 
     For the purpose of illustrating the present invention, the following description thereof is made with respect to two networks, a 3G cellular network and a Wireless Local Area Network (WLAN). However, it is to be appreciated that the present invention may be applied to any number of networks in combination as well as any type of network, while maintaining the spirit and scope of the present invention. 
     In the illustrative example, user device  240  has dual radio interfaces for accessing the 3G network and the WLAN. According to the present invention, user device  240  is able to access WLAN  220  via the AAA mechanism of the 3G network  210  as follows. Upon detection of WLAN  220 , user device  240  determines whether WLAN  220  supports transitive AAA. If so, user device  240  sends a registration message to the 3G network via path  214 . The registration message includes a user public key. The registration message is transmitted to WLAN server  230   a  via the Internet as indicated by paths  216  and  222 . Upon receiving the registration message, WLAN server  230   a  checks the source IP address to determine whether the received address is within a range of address for which transitive AAA is supported. If so, WLAN server  230  provides a session key that is encrypted with the user device public key and transmits the session key to 3G network  210  via the Internet as indicated by paths  224  and  218 . The 3G network than transmits the session key to user device  240  as indicated by path  212 . User device  240  then decrypts the session key using a user device private key and is able to gain access to WLAN  220  using the session key. 
     In this manner, user device  240  is able to gain access to WLAN  220  via the AAA mechanism of 3G network  210 , as long as WLAN  220  supports transitive AAA and has a pre-existing trust relationship with 3G network  210 . The present invention provides a mechanism for allowing a user device  240  to “roam” between WLANs that have a pre-existing relationship with the 3G network by directly using the AAA mechanism of the 3G network rather than having the WLAN contact the 3G AAA services for authentication or using the AAA mechanism associated with each WLAN. 
     The 3G cellular network is allocated a range of IP addresses; when the user uses the 3G cellular network for IP access, the source IP address will fall into this range. Given the routing scheme of the Internet, while any snooper can fake such a source IP address, when a return IP packet is sent, it can only be received by the user that actually has the IP address, unless the snooper can break into the routers that forward the IP packets. Thus, the present invention may provide an additional measure of security. 
       FIG. 3  is a flow diagram illustrating an AAA method for allowing a user device that has been authenticated by a 3G cellular network to gain access to a Wireless Local Area Network WLAN, according to an illustrative embodiment of the present invention. The user device has two radio access interfaces (3G cellular and WLAN). The 3G cellular network and the WLAN have a pre-established trust relationship there between. 
     Upon the user device moving into an area under the coverage of the WLAN, it is determined (e.g., by the WLAN interface of the user device) whether the WLAN supports transitive MA and whether the 3G cellular network has a pre-established trust relationship with the WLAN (e.g. through broadcasting or Dynamic Host Configuration Protocol (DHCP)) (step  302 ). If not, then the method is terminated. Otherwise, step  304  is performed as described herein below and then the method proceeds to step  305 . At step  305 , the IP address of an AAA server of the WLAN (hereinafter WLAN AAA server) is obtained by the user device (step  305 ). 
     A User Datagram Protocol (UDP) packet that includes a registration message is sent from the user device to the WLAN AAA server, e.g., through the 3G cellular interface of the user device (step  310 ). It is to be appreciated that while step  310  is described with respect to a UDP packet, any type of packet may be employed including, but not limited to, a Transmission Control Protocol (TCP) packet. The registration message includes the WLAN address (e.g. Medium Access Control (MAC) address or IP address of the WLAN interface) of the user device, and the public key of the user device. 
     Upon receiving the registration message, the WLAN AAA server determines whether the source IP address of the registration message (e.g., an IP address of the 3G interface) falls into a range allocated to the 3G cellular network with which the WLAN network has a pre-established relationship (step  315 ). If not, then the method is terminated. Otherwise, the WLAN AAA server sends back a confirmation message to the 3G cellular interface of the user device (step  320 ). The confirmation message includes a session key that is to be used between the user device and the WLAN (session key permits the user device to access the WLAN); the session key is encrypted with the public key of the user device. The WLAN AAA server also registers a mapping between the WLAN address of the user device and the (assigned) session key (step  325 ). Step  325  is performed so that a given session key is associated with a corresponding user. 
     Upon receiving the confirmation message (e.g., via the 3G cellular interface of the user device), the session key is decrypted using a private key of the user device (step  328 ). Using the session key, access to the WLAN is obtained by the user device (step  330 ). 
     A description will now be given of a possible collaborative hacker attack on the method of  FIG. 3 . It is to be appreciated that the following attack is possible due to the use of IP addressing and IP routing without additional authentication support from the 3G cellular network. A hacker sends a registration message with a fake IP address that falls into the range of the 3G cellular network. The hacker then intercepts the confirmation message somewhere along the route between the WLAN and the 3G cellular core network. The hacker notifies another hacker within the WLAN coverage about the discovered key. 
     However, it is very difficult to accomplish the above attack, especially the step of intercepting the confirmation message. The hacker has to gain access to a router along the route between the WLAN and the 3G network, just for the purpose of obtaining a session key, and the two hackers have to collaborate to carry out the attack (assuming that a hacker within the coverage of the WLAN cannot get access to any of the routers discussed above because if the hacker could obtain access, then there would have been no point of carrying out the attack since the hacker would already have had Internet access). 
     To prevent the preceding collaborative hacker attack, step  304  is performed in the method of  FIG. 3 . At step  304 , a secure IP channel (e.g. an Internet Protocol (IP) Security (IPSec) tunnel) is established between the WLAN AAA server and a Gateway General Packet Radio Service (GPRS) Serving/Support Node (GGSN) of the 3G cellular network. Since the path is also secure between the user and the GGSN of the 3G cellular network (as ensured by the 3G network security), the above attack can be thwarted. 
     A description will now be given of an accounting method that may be employed along with the method of  FIG. 3 , according to an illustrative embodiment of the present invention.  FIG. 4  is a flow diagram illustrating an accounting method for performing an accounting for the user of the user device of the method of  FIG. 3 , according to an illustrative embodiment of the present invention. 
     It is determined whether the IP address of the 3G cellular interface of the user device is a static IP address (step  405 ). If so, the identity of the user is determined based upon the IP address of the 3G cellular interface, (step  410 ), and the method proceeds to step  450 . Otherwise (the IP address is dynamic), the identity of the user is determined from a mapping between the (temporary) IP address of the 3G cellular interface and the actual ID of the user (step  415 ), and the method proceeds to step  450 . At step  450 , an accounting step is performed with respect to the user based on the IP address of the 3G cellular interface (static IP address) or the mapping (dynamic IP address). 
     It is to be appreciated that for the purposes of the present invention, Network Address Translation (NAT) is treated the same as if the IP address of the 3G cellular interface were dynamic. Moreover, with respect to the mapping referred to at step  415  above, such mapping may be stored, e.g., at a DHCP server or a NAT server if NAT is used. It is to be further appreciated that the present invention is not limited to the use of mappings to determine user identity in the case of non-static IP address and, thus, other approaches may be employed, while maintaining the spirit and scope of the present invention. 
     Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.