Abstract:
Apparatus for eavesdropping within an area layer adjacent to and surrounding a LAN area periphery for potential wireless transmissions of an intruder having a lower frequency within a level below the LAN frequency; and an implementation responsive to said eavesdropping apparatus for changing the encryption code of said encrypted wireless transmission upon the eavesdropping detection of a wireless transmission of said lower frequency addressed to a network location of one of the terminals in said LAN.

Description:
TECHNICAL FIELD 
   The present invention relates to the protection of wireless communications and particularly Local Area Network (LAN) communications from unauthorized intrusion through eavesdropping devices. 
   BACKGROUND OF RELATED ART 
   Local Area Networks that use radio waves for the unguided transmission of data and protocols come to be known as wireless LANs. The term “wireless” is not completely descriptive since these networks merely reduce the quantity of wire needed to construct a LAN. Wireless LANs may more adequately be described as local area networks in which a portion of the communications are wireless. This follows the tremendous growth in wireless communication products including cellular telephones, wireless personal computers and like devices. Thus, the wireless LAN is conventionally a geographically defined facility, such as a business and manufacturing site, a university site or a government facility within which the workers can unhook from the network connections and move about without restriction to access the Wireless LANs from virtually anywhere within the facility. Car rental facilities use wireless LANs to facilitate check-ins; traders on stock exchange floors use mobile wireless LANs for entering trades; students on university campuses may access lectures, books and notes from any point; medical professionals making rounds may access medical data wirelessly from any point in the hospital plant. Some good background on wireless LANs may be found in the text,  Peter Norton&#39;s Complete Guide to Networking,  SAMS Division of MacMillan Computer Publishing, Indianapolis, Ind., 1999, pp. 49–62. 
   A wireless LAN may be as simple as two laptop computers with radio signal sending and receiving capabilities forming an ad-hoc network on the fly. However, most business networks use a wireless station connectivity enabling a mobile user with a laptop to set up a wireless connection to a hub. The laptop computers still have to be connected to an antenna for transmission to and from the hub. A portable radio antenna may be connected to the laptop through its PCMCIA (Personal Computer Memory Card International Association) slot. The hub that communicates via its own antenna is associated with a server for the client wireless computers. 
   The IEEE Industry Standard 802.11B Architecture (IEEE 802.11B) extensively used for wireless LAN transmissions in the frequency range of 2.4–2.4835 GHz of spread spectrum radio transmission. 
   A major problem with these spread spectrum wireless LAN transmissions is that they are not very secure. They are vulnerable to eavesdropping done with relatively simple radio equipment. Anyone equipped with a suitable transceiver within the range of transmission can eavesdrop. In a simple eavesdropping operation, any intruder may circle the perimeter of the target facility in a car or truck equipped with a transceiver and pick up messages since the 2.4 GHz signals must have a range extending for at least a short distance beyond the perimeter of the LAN area. Normally, this type of eavesdropping is not detectable since the sender or the intended receiver has no way of knowing whether the transmission has been intercepted. 
   A conventional way that users of wireless LANs have defended themselves against the eavesdropping intruders is through encryption of the transmissions with the LAN area. The wireless messages may be encrypted by the client computers in the LAN as well as by the LAN server, e.g. the LAN server associated with the hub. This has presented a problem to the eavesdropping intruders. However, the intruders have been attempting to decipher the encryption keys by a process that involves addressing a message to one of the client wireless client computers in the target LAN. The intruder then expects that the message will be encrypted through the LAN server so that it will be wirelessly transmitted to the addressee client computer in the LAN. The intruder then eavesdrops for the encrypted message which he sent. Now, the intruder has both the unencrypted and encrypted message and can break the secret encryption key. Then all encrypted wireless transmissions within the LAN may be eavesdropped and decrypted. 
   SUMMARY OF THE PRESENT INVENTION 
   The present invention involves the recognition that since the eavesdropper is likely to be mobile and operating on a short time cycle, he himself is likely to be wirelessly transmitting his test message. 
   Consequently, the present invention involves the combination of means for eavesdropping within an area layer adjacent to and surrounding the LAN area periphery for wireless transmissions having a lower frequency within a level below the LAN frequency and addressed to the network location of any one of the computer terminals in the LAN; and means responsive to said eavesdropping means for changing the encryption code of said encrypted wireless transmission upon the eavesdropping detection of a wireless transmission of said lower frequency addressed to a network location of one of the terminals in said LAN. 
   The invention recognizes that there are several factors contributing to the success of the process of the invention. It is likely that the intruder must send his message at a lower frequency than the 2.4 GHz frequency of the LAN area transmissions because the intruder will probably have to reach a base station tower over a longer distance or range than the adjacent target wireless LAN facility. This insures that the eavesdropping of the present invention will be at a lower frequency and, thus, not interfered with by the transmissions within the LAN. This will make the detection of the lower frequency intruder messages much easier. For best results, when the Wireless LAN is operating under an IEEE Standard 802.11B frequency, the eavesdropping by the system for the intruder test messages must be in the order of 902 MHz. 
   The means for changing the encryption code preferably dynamically reconfigures the secret key encryption upon said eavesdropping detection without interruption in transmissions within the LAN. Also, the secret key encryption is reconfigured independently of the previous secret key which is being changed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood and its numerous objects and advantages will become more apparent to those skilled in the art by reference to the following drawings, in conjunction with the accompanying specification, in which: 
       FIG. 1  is a generalized diagrammatic view of a wireless LAN and a communicating Internet portion to illustrate the elements of the present invention; 
       FIG. 2  is a block diagram of a data processing system including a central processing unit and network connections via a communications adapter that is capable of functioning as the LAN servers for encrypting and dynamically reconfiguring the secret encryption keys upon the detection of wireless transmissions of test messages indicative of an intruder; 
       FIG. 3  is an illustrative flowchart describing the setting up of the elements of a program according to the present invention for protecting the wireless LAN from eavesdroppers; and 
       FIG. 4  is a flowchart of an illustrative run of the program set up in  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , there is provided a generalized view of a wireless LAN and its interconnections to a network, such as the Internet or World Wide Web (Web), so as to illustrate the present invention. The wireless LAN is confined to a facility area  11 . 
   The LAN includes wireless devices, such as PCs  13  or personal digital assistants  130  sending and receiving wireless radio frequency communications  15  through their respective antennae  23  received and sent via corresponding antenna  23  of IEEE 802.11B protocol wireless hub  19  having an associated network server containing secrecy key encryption routine (ENC)  21  that encrypts and decrypts the wireless communications within the LAN so that the routines are encrypted during the wireless transmissions within the LAN. The LAN server in hub  19  may communicate with the Internet  50 , for example through appropriate communication linkage  49 . Let us assume that intruder truck  25  is cruising on path  27  around a peripheral street surrounding the LAN facility eavesdropping via RF detection waves  33  from antenna  31 . The LAN transmissions intercepted by antenna  31  are encrypted, intruder will try to find the encryption key as follows: a signal  37  will be sent via antenna  35  that will contain a test message addressed to one of the client computers  13  in the LAN  11 . Since the truck  25  is mobile, the test message signal is wireless and must be sent to a tower antenna  44  of a base station  45  in a wired communication network. The distance from the truck to the tower is greater than the distances between the devices in the wireless LAN, then the transmissions from the truck antenna to the tower  44  have to be a lower frequency than the wireless LAN transmissions. 
   For example, with the wireless IEEE 802.11B protocols having a frequency of 2.4 GHz, the wireless transmissions of the test message from the truck to the tower  44  are likely to be at a frequency of 902 MHz. Following the intruder&#39;s test message through, it may proceed from the Base Station  45  through a standard PSTN (Public Switching Telephone Network)  46 , then via wired connection  47  through a network, such as Internet  50 , back to hub via interconnection  49  back to encryptor  21  of the server in the hub  19  of the LAN. The message from the truck will now be encrypted. Thus, if the truck through the detection waves  33  from antenna  31  now intercepts the encrypted test message to a particular wireless client address, the intruder will now have both the unencrypted and encrypted versions. From this pair, the intruder may be able to decipher the secret encryption key. 
   As will be subsequently described in greater detail, the present invention sets up an eavesdropping system  48  that sends detection waves “??????????????”  52  via antenna  51 . With the knowledge that the intruder truck is probably sending the test message initially wirelessly at a lower frequency of 902 MHz, the system of this invention tries to detect such transmissions. In  FIG. 1 , there is such an illustrative interception of a lower frequency transmission by the systems eavesdropping implementation at point  53 . In response, as will hereinafter be described in greater detail, the system thus determines that there is an intruder and begins a dynamic reconfiguration of the secret encryption key in the wireless LAN. This reconfiguration should be completed before the intruder can decipher the initial secret encryption. Thus, the intruder fails. 
   Referring now to  FIG. 2 , a typical generalized data processing system display terminal is shown that may function as the computer server for controlling the wireless LAN of this invention, as well as the client PC computers. A central processing unit (CPU)  10 , such as any PC microprocessor in a PC available from International Business Machines Corporation (IBM) or Dell Corp., is provided and interconnected to various other components by system bus  12 . An operating system  41  runs on CPU  10 , provides control and is used to coordinate the functions of the various components of  FIG. 1 . Operating system  41  may be one of the commercially available operating systems such as Microsoft&#39;s Windows98™ or WindowsNT™, as well as the UNIX or AIX operating systems. An application program that includes routines of the present invention for eavesdropping on the eavesdroppers, to be subsequently described in detail, runs in conjunction with operating system  41  and provides output calls to the operating system  41 , which in turn implements the various functions to be performed by the application  40 . A Read Only Memory (ROM)  16  is connected to CPU  10  via bus  12  and includes the Basic Input/Output System (BIOS) that controls the basic computer functions. Random Access Memory (RAM)  14 , I/O adapter  18  and communications adapter  34  are also interconnected to system bus  12 . It should be noted that software components, including operating system  41  and application  40 , are loaded into RAM  14 , which is the computer system&#39;s main memory. I/O adapter  18  may be a Small Computer System Interface (SCSI) adapter that communicates with the disk storage device  20 , i.e. a hard drive. Communications adapter  34  interconnects bus  12  with an outside network linkage  43  in the case of the LAN server enabling the data processing system to communicate with other such systems over a network includes, of course, the Internet or Web. In the server that is associated with the hub shown in  FIG. 1 , encryption applications are stored with applications  40  and loaded into RAM during encryption/decryption. I/O devices are also connected to system bus  12  via user interface adapter  22  and display adapter  36 . Keyboard  24  and mouse  26  are all interconnected to bus  12  through user interface adapter  22 . Mouse  26  operates in a conventional manner insofar as user movement is concerned. There may be a display associated with the LAN server. In such a set up, display adapter  36  includes a frame buffer  39 , which is a storage device that holds a representation of each pixel on the display screen  38 . Images may be stored in frame buffer  39  for display on monitor  38  through various components, such as a digital to analog converter (not shown) and the like. By using the mouse or related devices, a user is capable of inputting information to the system through the keyboard  24  or mouse  26  and receiving output information from the system via display  38 . 
   Now, with reference to the programming shown in  FIG. 3 , there will be described how the system and programs of the present invention are set up. 
   The invention involves the protection of a wireless LAN with a hub for receiving and sending wireless transmissions to and from wireless client computers under protocol IEEE 802.11B, step  61 . These 802.11 protocols, which are widely used in the wireless LAN technology, are discussed in greater detail at pp. 60–62 in the above-referenced  Peter Norton&#39;s Complete Guide to Networking  text, as well as in the article,  A Wireless Local Area Network Protocol That Improves Throughput Via Adaptive Control,  B. E. Mullins et al.,  Proceedings of the IEEE International Conference on Communications,  pp. 1427–1431, June 1997. The Hub is controlled and the client computers in the LAN are served by a server computer that has conventional program routines for encrypting and decrypting transmissions so that all wireless transmissions within the LAN are encrypted, step  62 . The system uses secret or shared key encryption/decryption, for example as set forth in the  Internet Key Exchange  ( IKE ) protocols as published 1998, by the  Internet Society  and publicly available as  RFC  2409, Harkins et al. November 1998. The encrypted LAN transmissions are at a frequency of 2.4 GHz, step  63 . An eavesdropping implementation is provided for scanning an area surrounding the periphery of the LAN area to intercept wireless transmissions having a lower frequency in the order of 902 MHz, step  64 . Eavesdropping equipment to scan for such transmissions is readily available and inexpensive to set up. Any modified off-the-shelf device may be used to scan for the 902 MHz transmissions. In other words, the same eavesdropping equipment used by the intruders to eavesdrop may be used against the intruders when they transmit wirelessly. Reference may be made to the article,  Intercepting Mobile Communication, The Insecurity of  802.11, M. Borisov et al., published by the 7th Annual International Conference of Mobile Computing and Networking, July 2001, for illustrative examples of eavesdropping equipment that may be used. Accordingly, an implementation is provided for determining if an intercepted wireless transmission is addressed to any client computer terminal in the LAN, step  65 . Then, a routine is provided for reconfiguring the secret encryption key whenever the intercepted wireless transmission is found to be addressed to a client terminal in the Wireless LAN, step  66 . Conventional routines for dynamically reconfiguring secret encryption keys are described in the above-mentioned  Internet Key Exchange  ( IKE ) protocols as part of “Perfect Forward Secrecy” routines, referenced in Sections 3.3 and 5.5 “Quick Mode”. This dynamic reconfiguration of the secret key is done without interrupting the Wireless LAN operations and without any reliance on the discarded previous key by using routines available under “Perfect Forward Secrecy”, step  67 . 
   Now, with reference to the flowchart of  FIG. 4 , a simplified illustrative run of the process set up in  FIG. 3  will be described. The simplification is made so as to illustrate an understandable process. In considering this example, it should be understood that in many processes the criteria for eavesdropping on the wireless transmissions for the intruder may be more complex. However, the complexity of such a determination is not the present invention. The invention involves the eavesdropping on the mobile intruder&#39;s wireless communications so as to determine whether he is addressing wireless LAN client computers. In a wireless LAN operating under 802.11B protocols, step  71 , with secret key encryption at the Hub server, step  72 , a conventional radio frequency eavesdropping device is set up to monitor for wireless transmissions in the order of 902 MHz at a range just about 300 feet beyond the LAN area border, step  73 . Thus, a determination is made as to whether such a 902 MHz wireless transmission has been detected, step  74 . If Yes, a further determination is made as to whether the intercepted transmission had a final address to one of the clients in the wireless LAN, step  75 . If Yes, then the secret encryption key is changed using the appropriate “Perfect Forward Security” routine described above, step  76 . Then, or if the determination in either step  74  or step  75  is No, the wireless transmissions in the LAN are continued uninterrupted, step  77 , and no further changes need be made, step  78 , the process is returned to step  74  where the eavesdropping for a further intruder transmission is continued. 
   One skilled in the art should appreciate that the processes controlling the present invention are capable of being distributed in the form of computer readable media of a variety of forms. 
   Although certain preferred embodiments have been shown and described, it will be understood that many changes and modifications may be made therein without departing from the scope and intent of the appended claims.