Patent Publication Number: US-8532304-B2

Title: Administration of wireless local area networks

Description:
This application claims priority to provisional U.S. Application Ser. No. 60/667,661, filed Apr. 4, 2005, entitled “Easy, Flexible, and Secure Network Setup,” and provisional U.S. Application Ser. No. 60/673,806, filed Apr. 22, 2005, entitled “Secure, Easy, and Flexible Network Setup,” each of which is herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to computers and computer networks. More specifically, the invention provides systems and methods for the administration of wireless networks, such as a wireless local area network (WLAN). 
     BACKGROUND OF THE INVENTION 
     Setting up a home wireless network, such as a wireless local area network (WLAN), can be a very difficult process for most computer users, thus presenting a significant obstacle to efficient utilization of WLANs. One of the difficulties users encounter is determining how to best secure a WLAN. Wireless networks have typically been protected with a single Pre-Shared Key (PSK). However, the use of a single pre-shared secret key requires that a user re-configure the entire network if the user wants to deny future access to a device that was previously authorized for use on the WLAN. While the latest wireless LAN standard 802.11i (also known as “WPA2”) supports the use of multiple PSKs, some access points (APs) do not support the use of multiple PSKs. The availability of multiple PSKs enables selective revocation of security associations, which makes removing guests possible. 802.11i specifies from the PSK onward, but it does not specify how PSKs are created. In addition, 802.11i does not specify how to group PSKs or how to remove a PSK when it is no longer needed. 
     Other 802.11X protocols specify how PMKs (Pairwise Master Keys, which are similar to PSKs, except that a PMK is valid only for a single session) are created using a separate protocol between a device and an authentication server on the network. However, like 802.11i, 802.11X also does not specify how to group PMKs (removal is implicit at the end of the session). 
     Existing proposals for solving the network setup problem attempt to exploit proximity. For example, one known approach exploits physical proximity by using a physically secure “out-of-band” (OOB) channel  1 . 1 . The OOB channel can be based on NFC (Near Field Communication), infrared, portable USB memory stick or any other communication technology that is based on physical proximity. The OOB is used to transfer the network identifier (e.g., a SSID) and a shared key from one device to another. Because the transferred key is used directly as the PSK, no additional protocols are needed. To add a new device to the network, the only user interaction needed is to touch the new device with a “token.” The token can be a simple special-purpose device, or it can be part of another device, e.g., part of a WLAN client device that is already in the network.  FIG. 1  illustrates this approach when an “introducer” is used to admit a new device into the network  1 . 2 . Note that the introducer can be the AP itself. While this approach provides intuitive user interaction and allows delegation of access from one device to another, guest access remains cumbersome. Because the same PSK is used by all the devices, the only way to remove guest access is to remove all devices from the network, and then add allowed devices again, one by one. 
     Another known approach exploits time proximity using in-band configuration. A proposal by Broadcom for Secure Easy Setup (SES) falls into this category. In SES, network setup is performed by first putting the AP into a configuration mode, and then placing the new device into its configuration mode, e.g., by pressing a button on the respective devices. Once in configuration mode, the devices locate each other using some protocol to agree on a PSK.  FIG. 2  illustrates an example of an “in-band” solution. Pairing of the new device and the AP in the in-band approach is done utilizing WLAN pairing methods  2 . 1  and  2 . 2 . In-band solutions present a variety of problems, including the possibility of accidental pairing with an unintended device and the threat of a man-in-the-middle attack (because the initial key agreement protocol is not authenticated). In addition, guest access is cumbersome as in the OOB case, and no device-to-device delegation of access rights is possible. 
     The OOB and in-band approaches have advantages and disadvantages. The OOB approach is more intuitive and secure, but because of the extra hardware required, it is unreasonable to expect that all devices will have suitable out-of-band channels available. The in-band approach does not allow delegation of access and is less secure, but it is less expensive and is more likely to start appearing in commercial APs and client devices. Neither approach supports easy guest access management. 
     Thus, it would be an advancement in the art to provide methods and systems that allow for simpler and more efficient wireless network setup and administration that overcome the above limitations and disadvantages. 
     BRIEF SUMMARY OF THE INVENTION 
     The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to the more detailed description provided below. 
     To overcome limitations in the prior art described above, and to overcome other limitations that will be apparent upon reading and understanding the present specification, the present invention is directed to methods and systems for managing access to a wireless local area network. A wireless access point (AP) or other access controller may use a unified approach that utilizes an out-of-band channel, or other first communication channel, to communicate authentication key and network address information to a guest device, and utilizes an in-band channel, or other second communication channel, to establish communications with the guest device, and also provides support for in-band setup on all devices. The ability to use out-of-band where possible provides for an increase to security and usability, and the possibility of delegating access from one device to another. The unified approach thereby also provides easy management of guest access to the WLAN. 
     According to a first aspect of the invention, a method may manage access to a wireless access point (AP) or other access controller by a mobile terminal, where the AP uses an out-of-band communication channel and an in-band communication channel. An authentication key (AK) corresponding to the mobile terminal is established, and then sent to the mobile terminal via the out-of-band channel. The AP receives a key agreement request from the mobile terminal via the in-band channel, and establishes an access key corresponding to the mobile terminal based on the received key agreement request, when the mobile terminal is authorized to access the AP. The AP authorizes the mobile terminal to communicate through the AP upon successful completion of the previous step. The AK is used to authenticate the key agreement. 
     According to another aspect of the invention, an alternative method manages access to a wireless access point (AP) or other access controller by a mobile terminal, where the AP uses an out-of-band communication channel and an in-band communication channel. An address of the AP is sent to a master device. A guest authentication key (AK) corresponding to the mobile terminal is generated, and corresponding information is sent to the mobile terminal from the master device. The mobile terminal sends a second AK to the AP, which compares the guest AK with the second AK. The AP grants access to the mobile terminal when the second AK matches the guest AK. 
     According to another aspect of the invention, a new mobile terminal may be adapted to communication with the network. The mobile terminal may include a processor controlling overall operation of the mobile terminal, a first transceiver for sending and receiving communications over a first communication channel in-band with a wireless access point (AP) or other access controller, and a receiver for receiving communications over a second communication channel out-of-band with the wireless access point (AP). The mobile terminal may also include memory storing computer executable instructions that, when executed by the processor, cause the mobile terminal to perform a method for accessing a wireless local area network. The method may performs steps receiving a guest authentication key (AK) and an address of the wireless AP via the second communication channel, and sending the guest AK to the AP via the first communication channel to establish communications with the AP. 
     Those of skill in the art will appreciate that the above is merely an introduction to the subject matter described in more detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention and certain advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
         FIG. 1  illustrates a prior art out-of-band method. 
         FIG. 2  illustrates a prior art in-band method. 
         FIG. 3  illustrates a network architecture that may be used according to one or more illustrative aspects of the invention. 
         FIG. 4  illustrates a unified out-of-band/in-band method according to one or more illustrative aspects of the invention. 
         FIG. 5  illustrates a network architecture that may be used according to one or more illustrative aspects of the invention. 
         FIG. 6  illustrates a method according to an SES protocol. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description of the various illustrative embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various example embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. 
     One or more aspects of the invention may be used in the following illustrative scenario. With reference to  FIG. 3 , in one embodiment of the invention, a user purchases a new high speed wireless LAN access point  301  (or other access controller) and brings the device to his or her home. The user wishes to easily connect other wireless devices  303 ,  305 ,  307 ,  309  or  311  in the home to the new access point  301  so that these devices also can use the wireless network  302 . Wireless devices are generically referred to herein as mobile terminals, and may include, but are not limited to, any device with wireless communications capabilities, such as mobile phones, smart phones, home appliances, laptop computers, desktop computers, personal digital assistants, audio/video devices, televisions, set-top boxes, personal video recorders, personal digital recorders, digital camera, digital camcorder, personal memory device, home automation and/or control devices, sensors, vehicles, and the like or any combination of them. 
     After plugging in the access point  301 , the user connects his or her WLAN enabled mobile phone  309  to the new access point  301  by simply pressing a button on both devices (not shown). The AP  301  may then be placed on a shelf or other appropriate location, e.g., where it is out of reach of children or other sources of damage or harm. To connect one of the other wireless home devices to the network  302 , such as the home stereo  307 , the user can either “touch” those devices with the mobile phone  309  or (for at least some devices) press a configuration button on both the device  307  and the AP  301  to get them to join the network  302 . Later, if the user&#39;s neighbor comes over, the user may like to show off the advanced network  302  she has built and allow the neighbor to use her own phone  311  to stream some music to the home stereo  307 . This may be accomplished, e.g., by “touching” the neighbor&#39;s phone  311  with the user&#39;s phone  309 . When the neighbor has seen enough and returns to her house, the user presses a button (not shown) on the access point  301  to end the temporary visitor permission that was granted to the neighbor, so the neighbor can no longer control the devices in the user&#39;s home. Alternatively, the user may use her phone  309  to end the temporary visitor permission. 
     The above scenario is illustrative for purposes of describing aspects of the invention and is not limiting in any way. As used herein, “touching” refers to a proximity based interaction between two devices wherein setup and/or security information is transferred or granted from one device to the other. In one example, “touching” refers to moving the devices physically close to each other so that the OOB channel (NFC, short range wireless communication, infrared, Bluetooth, UWB, WiFi, RFID, USB memory stick, etc.) can be established and needed data exchanged over the OOB channel. According to an aspect of the invention, a unified approach may be used that utilizes aspects of both the OOB and in-band approaches, thereby allowing support for the in-band approach on all devices, but also the ability to use out-of-band where possible to increase security and usability, and the possibility of delegating access from one device to another. The unified approach thereby also provides easy management of guest access to the WLAN. 
       FIG. 4  illustrates an illustrative embodiment of the invention and one possible way to achieve this unification. In step  401 , Access Point  410  and Introducer Device  412  create and share an original authentication key (OAK). AP  410  and device  412  may optionally be portions of the same device. In step  403 , introducer device  412  provides to a new device  414  via an out of band channel, the AK (where AK=f(OAK, AK-ID), as further described herein) and applicable network parameters (e.g., address of the AP, SSID). Using the AK, in step  405  the new device  414  and the access point  410  use a key agreement protocol to create a key for the new device. Finally, in step  407 , the new device  414  and the AP  410  perform link layer key agreement procedures, e.g., using 802.11i. 
     As illustrated in  FIG. 4 , the PSK may be derived from an in-band key agreement protocol. However, if an out-of-band channel is available, the OOB channel can be used to transfer the authentication key (AK) and the address of the AP  410  to the new device  414 , which triggers the in-band key agreement (i.e., the user does not have to press any buttons). The “out-of-band” channel is not limited to NFC, but it can be any means of passing the AK (and the network parameters, where feasible) to the New Device. The out-of-band channel may consist of a Personal Identification Number (PIN) typed by the user. 
     The AP  410  may have two types of “receiving modes.” In the first, “authenticated,” receiving mode, the AP  410  accepts requests for authenticated key agreements. The AK may be used to authenticate the key agreement, by default. By pressing a button on the AP  410 , the AP  410  can be put into a second, “unauthenticated,” receiving mode for a short time. Behavior in this mode may be similar as in the Broadcom approach, described above. The authentication of key agreement prevents accidental pairing and the possibility of “man-in-the-middle” type attacks. Also, there can be multiple authentication keys (e.g., owner AK, family AK, guest AK, etc.). For example, an AP may have three “tokens” each containing a different authentication key. The AP  410  may categorize security associations based on how they were authenticated. In this case, a “remove all guests” operation (e.g., a long button press) makes the AP  410  remove all security associations made using the guest authentication key or no authentication key. Any security associations made using other authentication keys, however, might not be removed by this operation. This allows effective and intuitive guest access management. 
     Each device may have a dedicated PSK, thereby enabling selective revocation of security associations. The PSK is long-lived and is derived from the run of the protocol and the value of the AK used. In this example, PSKs can be labeled and stored at the AP with the name of the owner AK used, thus allowing for knowledge of which family member issued access to which guest. 
     Delegation may be accomplished with user interaction similar to the above OOB solution. Multiple forms of “AP addresses” can be included in “network parameters.” For example, if the AP&#39;s DNS name is included, the AP can be used for remote access to the home. 
     The AP need not have an out-of-band interface, because the initial AK keys and network parameters can be delivered in the form of passive tokens. However, if the AP has an out-of-band interface, the AP can use that interface to emit the initial AK keys (owner AK) and network parameters in some limited fashion (e.g., once after purchase or full reset). The AP can use the out-of-band interface to receive initial AK keys and network parameters from the outside (e.g., once after purchase or full reset). The following Table 1 summarizes different possibilities for generation and delivery of AKs and network parameters that may be used in accordance with examples of this invention. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Authentication Key Generation and Delivery 
               
            
           
           
               
               
               
            
               
                 PARAMETER 
                 DELIVERY 
                 OUT-OF-BAND 
               
               
                 GENERATION 
                 MECHANISM 
                 CHANNEL ON AP 
               
               
                   
               
               
                 AP generates AKs and 
                 Delivered separately 
                 Not needed 
               
               
                 network parameters 
                 (e.g., passive NFC 
               
               
                   
                 tokens, PIN codes 
               
               
                   
                 printed on package). 
               
               
                   
                 Emitted via out-of-band 
                 Needed 
               
               
                   
                 channel for a limited 
               
               
                   
                 time after full reset or 
               
               
                   
                 purchase. 
               
               
                   
                 Emitted via in-band 
                 Not needed 
               
               
                   
                 channel for a limited 
               
               
                   
                 time after full reset or 
               
               
                   
                 purchase. (Less secure, 
               
               
                   
                 but could be used to 
               
               
                   
                 avoid extra hardware 
               
               
                   
                 costs.) 
               
               
                 AP receives AKs and 
                 Received via out-of- 
                 Needed 
               
               
                 network parameters from 
                 band channel for a 
               
               
                 an external device (e.g., 
                 limited time after full 
               
               
                 phone) 
                 reset or purchase. 
               
               
                   
                 Received via in-band 
                 Not needed 
               
               
                   
                 channel for a limited 
               
               
                   
                 time after full reset or 
               
               
                   
                 purchase. (Less secure, 
               
               
                   
                 but could be used to 
               
               
                   
                 avoid extra hardware 
               
               
                   
                 costs.) 
               
               
                   
               
            
           
         
       
     
     As mentioned above, the out-of-band channel is not limited to NFC. Additional examples of OOB channels include: SMS (Short Message Service), MMS (multimedia messaging service), or similar telecommunications messaging services. Using SMS, a user may pick a contact from an address book, select what type of access to grant, and then send an SMS to the contact with the AP address and AK. The device receiving the SMS may then perform steps  405  and  407  shown in  FIG. 4 . This combined approach preserves advantages of both approaches, and it enables easy guest access management. 
     Revocation: In the simplest case, there is only one AK, and that AK may be used for delegating owner access. Guests can be admitted using an unauthenticated pairing, as in the basic Broadcom approach described above. The difference is that when an owner wants to remove guest access, the entire network need not be recreated. Rather, just the PSKs that were created without any authentication are removed. 
     When guest access is granted using a guest AK, then when this guest access is to be revoked, the AP removes or marks invalid the PSK that was used by the guest during his or her access period. As mentioned above, this action may be initiated or achieved by pressing a button on the access point or other access controller for a predetermined amount of time, which would revoke all guest access to the network. More fine-grained approaches also are possible without departing from this invention, but from an end-user usability perspective, such a one-button approach has certain advantages and appeal. Alternatively, removing or marking the PSK as invalid may be initiated or achieved by using the user/introducer device  412 , e.g., by transmitting a request for revocation to the AP or by browsing a table of authenticated users/user devices. 
     Even after revocation, guests will still hold the valid AK, and thus the possibility to obtain a new PSK using an authenticated SES request. In order to prevent this, the AK used by guests is preferably changed as part of the reset guest access procedure. Thus, along with removing the guest PSKS, the AP preferably determines a new AK for accepting authenticated SES requests. In addition, after this type of AK reset, the existing owner devices are made capable of once again granting access to guests. 
     In general, the AK is determined by AK=f(OAK, AK-ID), wherein AK-ID may be any parameter or subfunction of multiple parameters. Three ways of allowing owner devices to grant access to guests include, e.g., timestamp, sequence number, and download procedures, as discussed further below. AK-ID may represent any single parameter or any combination of parameters based on some predefined function. Other parameters that may be incorporated into the calculation of AK-ID include, e.g., category type, MAC address and user device name or ID. Those of skill in the art will appreciate that other parameters may also or alternatively be used in any combination. AK-ID may be thought of as a data structure or computation that encodes various information in some predetermined manner. 
     An AK can therefore be derived from an OAK shared between the introducing device and the AP, and one or more other variables storing additional information unique to the new device, and the address of the AP as provided by the introducing device to the new device. The one or more other variables may be transferred by the new device as part of the key agreement protocol such that the AP can derive the same AK. The AK may then be used to authenticate the key agreement protocol, as the AK is not itself transferred. Other illustrative approaches are described below. 
     Timestamp: in this approach, the guest AK used is a function of time. Each group (e.g., family, guests, etc.) has an “original AK” (OAK). The OAK is not given out during delegation. Instead, a transient AK may be derived from the OAK, for example, AK=f(OAK, time), where OAK is as mentioned above and time could be any time based value, e.g., milliseconds since 1.1.1970 (standard Unix). Both the AP and the delegating owner devices/master devices can calculate the same AK using this function, and the guest device receives the AK and presents it to the AP along with the AK identifier which includes “time.” The access point might accept authenticated SES requests only when an AK is used that it recognizes. Derived AKs will thus have limited lifetimes, e.g., one day. This implies that the guests only have one day in which to issue the authenticated SES requests. After that the access point will no longer accept that AK. A potential disadvantage with this approach is that differences in clock synchronization between the AP and the delegating devices (which might be such that the device time is set by the user) may cause inconsistencies. 
     Sequence number: This approach involves using sequence numbers rather than timestamps in order to avoid the clock synchronization problems mentioned above. OAK is as before, and AK=f(OAK, sequence number). The AP maintains a sliding window of acceptable sequence numbers. The AP updates the window whenever it receives a new sequence number. Because sequence numbers have a short life time, old unused sequence numbers will automatically expire. The result is that an AK can only be used for a short period of time. 
     Download: in this approach the AP generates a new guest AK when the guest access is to be reset and the individual owner devices then obtain the new guest AK from the AP using either an in-band or out-of-band method. In such a scenario, the owner devices have knowledge of the owner AK in order to allow them to unpackage the new guest AK. This method has the disadvantage that it requires action on the part of the end users (or devices) in order to obtain the new AK. 
     The invention may be practiced in any suitable network environment, and it is not limited to any specific network architecture.  FIG. 5  presents another sample network operating environment in which one or more illustrative aspects of the invention may be practiced. Access point  501  incorporates a WLAN access point as well as access to WLAN Server(s) and other networks such as the internet  503 . First Network  505  may include a WLAN network or NFC, such as RFID. Master device  507  may include a mobile communication device or remote control device having access to first and second networks  505  and  509 . Second network  509  may include an out-of-band channel such as NFC or RFID. Second network  509  may alternatively include WLAN, short range radio (e.g., Bluetooth), wireless telecom (SMS, MMS), IrDA, and the like. New Device  511  may include a mobile communication device, remote control device, peripheral devices, consumer electronic devices, or other device having access to second and third networks  509 ,  513 . Third network  513  may include an in-band channel such as the WLAN network or an out-of-band channel as NFC or RFID. 
     In the architecture of  FIG. 5 , where one of the devices has a display, e.g., a mobile phone, when the user “touches” the home appliance (e.g., a stereo), the mobile telephone may display a picture of the appliance transmitted from the appliance on the phone display. The user, by pushing a button, can change the network parameters for only the appliance shown in the display, thus giving users a better understanding of which appliances to pair. In the WLAN case, the pairing is between a device and the access point (and not between devices), but the idea need not be limited to the WLAN case. In this case, an image of the device may be displayed on a display of the AP, or alternatively, an image of the AP may be displayed on a display of the device. The picture may be transmitted in step  403  or before step  403 . The picture may be delivered via NFC or any other communication network. This function requires significant memory space, and it could turn the “touch” into a “hold” meaning that the touching takes a longer time. Alternative to displaying a picture, the mobile phone may display a device name, similar to Bluetooth devices, preferably with more description, e.g., “Philips TV set,” “France Telecom WLAN access point,” “Sony HiFi stereo,” “Nokia 6600,” “Sam&#39;s PDA,” etc. 
     Some devices, however, may have the same pseudo-unique name, thus the connection may be to/from another device than was intended. Typically the mistake will be detected immediately, but only after at least one transmission has been taken place, and the data was transmitted to wrong device and the intended receiver did not receive anything. When a wireless connection between two cellular phones is desired, the proof of other party&#39;s identity may be obtained from the cellular network. One cell phone or mobile terminal may call the other (without the other end answering the call—meaning it is free of charge) to verify the device. That is, to call the other device the caller needs to know the number of the called party. In addition, the called party is able to verify the moment when it is being called (e.g., based on caller ID). Thus the proof of the identity of the devices is not obviously visible to external parties. 
     In one embodiment of the invention, proving the identity with a (unanswered) call may be performed as follows: the device to be authenticated (device A) sends its phone number over a wireless connection (such as Bluetooth or WLAN) to the device that wishes to authenticate itself (device B). An authentication application in device B waits for some predetermined or randomly chosen time and dials device A via a wireless telecom network. When device A detects the call, it immediately informs device B about the call via a wireless connection (such as Bluetooth, WLAN). An authentication application in device B may now decide if the response from A came fast enough to the call it made (during some predetermined period of time), thereby causing B to approve A&#39;s identity (i.e., the phone number it sent). Alternatively or additionally, the identity of device A (phone number and name from address book of device B, or phone number is just transmitted) may be displayed to the user making the connection on a display of device B and be asked the what permission should be granted for the connection. This technique works even if the network does not transmit the phone number of device A (e.g., if the phone number is secret or the user is roaming in such a network that the number is not transmitted). Mutual authentication may be based on the phone number of device A (if the network provides it) or on another call from the opposite direction. This method may be useful, e.g., in step  403  in  FIG. 4 . 
     An alternative embodiment of the invention, proving the identity with a (unanswered) call may be performed as follows: the device to be authenticated (device A) sends its phone number over a wireless telecommunication connection to the device that wishes to authenticate itself (device B), i.e., device A calls device B. An authentication application in device B stores the phone number of device A in an access database and waits for some predetermined or randomly chosen time and dials device A via a wireless telecom network. When device A detects the call, it immediately informs device B about the call via a wireless connection (such as Bluetooth or WLAN) including the phone number of device B and its own phone number. A&#39;s phone number may optionally be used to computer the key used to protect the wireless connection. An authentication application in device B may check now if the phone number of device A is in the access database, if the response from A came fast enough to the call it made (during some predetermined period of time), thereby causing B to approve A&#39;s identity (i.e., the phone number it sent). This method is useful, e.g., in step  403  in  FIG. 4 . 
     Further, in one embodiment of the invention, when device A informs device B about the call via a Bluetooth connection this information may now include the phone number of the device B, the phone number of device A and also Bluetooth identification information. A&#39;s phone number may optionally be used to computer the key used to protect the wireless connection. An authentication application in device B may check if the phone number and the Bluetooth identification information of device A are in the access database, if the response from device A came fast enough to the call it made (during some predetermined period of time), thereby causing device B to approve device A&#39;s identity (i.e., the phone number it sent). Authentication may also be done by checking a pair A (phone number, Bluetooth identification information) in the access database. This method may be useful, e.g., in step  403  in  FIG. 4 . 
     The immediately above described method may be used, e.g., in the following example situations: 
     1) A WLAN access point device (device B) and a new device (device A) have wireless telecom capabilities. This wireless telecom access is used to share information needed for establishing WLAN access between the devices, like in step  403  in  FIG. 4 . In this case the devices may initialize WLAN access set-up automatically after sharing needed information. Alternatively, the set-up of WLAN access may be manually initiated by the user. 
     2) Mr. Marty Manager sits in a meeting with his customers and realizes that he does not have the latest presentation of his product stored on his smartphone. He sends a SMS message to his secretary and asks her to send it via ad-hoc WLAN to his phone. His secretary launches an ad-hoc application on her the phone, which initiates the ad-hoc connection by sending her phone number to Marty&#39;s phone, thus initiating the connection. Marty accepts the connection from his secretary (it is shown based on the number the call was made to—or was intended to be made to, depending on the security level settings). When the connection is up, the file may be sent to Marty&#39;s smartphone. 
     3) When a device A wishes to make a connection to device B, it creates a wireless connection to device B and the devices exchange their telephone numbers over the connection. The UI on the phones/devices show the user name of the calling device (if it is on the phone&#39;s phonebook) or minimally, the phone number. The UI then asks the user if the connection may be established and authenticated. During the authentication phase the devices make a phone call to the other device, thus proving with the call that the device is who it claims to be. 
     The above method can be used between devices that are not physically visible to each other, it is enough that they are within the reach of wireless connectivity. The connection establishing process is simple to the user, especially if the responder&#39;s phone number can be browsed from the phonebook (from the user&#39;s point of view making the connection is as easy as making a call). 
     According to an aspect of the invention, network access may be based on the AK and the MAC address of a device. To allow network access to the new device, a delegating device may give the AK to the new device out of band, but the delegating device does not communicate with the AP, nor is there a special key agreement protocol between the new device and the AP. When the new device contacts the AP, the AP and the new device independently derive a new PSK from the AK and the MAC address of the device. For instance, PSK=f(AK, MAC address), where f is a suitable key derivation function. To revoke network access from the device, the owner may use the AP&#39;s management interface to mark the target device as “revoked.” Thereafter, the PSK of that device is removed and the AP may add the MAC address of the device to a list of revoked devices. A device whose MAC address is on that list will not be able to establish a PSK with the AP, i.e., it will not be able to do Step (1) above, unless access has been re-granted to the device. 
     One advantage of this approach is that the new device and the AP can derive the PSK independently, without new key agreement protocol messages. Knowledge of AK and the device&#39;s MAC address is enough. A disadvantage of this approach, however, is that the AP must keep track of revoked MAC addresses. Also, this approach is less secure than deriving the PSK from the AK using a key agreement protocol, because MAC addresses can be forged. Finally, allowing a previously revoked device back into the network requires the delegator to interact with the AP to remove its MAC address from the list of revoked devices, thereby requiring knowledge of an additional protocol. 
     According to another aspect of the invention an authenticated devices database may be used (see table 2). The AP may contain an authenticated devices database, e.g., a table, storing (1) the MAC address of each device that is part of the WLAN network and (2) a key, PSK, that the AP shares with the device: {MAC address, PSK}. When a device contacts the AP, the AP searches the MAC address of the contacting device from that table and uses the associated PSK in communicating with that device if the MAC address is found. If the MAC address is not found, the AP may, e.g., refuse to communicate with the device, send a predetermined message to the device, or use some other procedure defined for unauthenticated devices. The authenticated devices database may further include a device group (DG) record: {MAC address, PSK, DG}. The DG field may include, for example, at least a type and AK: e.g., DG={Type, AK}. Type may identify a device, e.g., as “unauthenticated,” in which case the AK field would be empty. As another example, the Type value could be “Guest,” in which case the AK would be that reserved for guests. As a third example, the Type value could be “Home,” in which case the AK will be that reserved for the home devices, such as consumer electronics devices or domestic appliances. Other Type values may include “Sensor” describing different sensors connected to the AP. The specific number of different types is not limited. The DG record of a device is initialized based on the value of the AK that the device knows, e.g., when that device joins the network. Additionally, the database may have a column describing who has given the access rights. Additionally, the device group may include a column for Original AK (OAK). Table 2 shows an example of information that may be included in an authenticated devices database. Other Type values may alternatively be used depending on system needs, e.g., an expiration date associated with a database entry to ensure automatic cancellation of user rights (otherwise revocation may occur when the user is removed from the database or when the expiration time is cancelled or changed). An example of an authenticated devices database is shown below in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Authenticated devices database 
               
            
           
           
               
               
               
            
               
                   
                 Device group (DG) 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Given by (Authenticator) 
                 Type 
                 AK 
                 OAK 
                 MAC 
                 PSK 
                 Device name 
               
               
                   
               
               
                 Master device 
                 Unauthenticated 
                 — 
                 — 
                 MAC1 
                 PSK1 
                 Stereo 1 
               
               
                 Master device 
                 Sensor 
                 AK2 
                 OAK3 
                 MAC2 
                 PSK2 
                 Temperature, bed room 1 
               
               
                 Master device 
                 Home 
                 AK9 
                 OAK1 
                 MAC9 
                 PSK9 
                 TV 1 
               
               
                 Mother 
                 Guest 
                 AK3 
                 OAK2 
                 MAC3 
                 PSK3 
                 Bob&#39;s phone 
               
               
                 Jack 
                 Guest 
                 AK4 
                 OAK2 
                 MAC4 
                 PSK4 
                 Pete&#39;s game device 
               
               
                 Jack 
                 Guest 
                 AK5 
                 OAK2 
                 MAC5 
                 PSK5 
                 Pate&#39;s music player 
               
               
                 Jane 
                 Unauthenticated 
                 — 
                 — 
                 MAC6 
                 PSK6 
                 NN 
               
               
                 Dad 
                 Sensor 
                 AK7 
                 OAK3 
                 MAC7 
                 PSK7 
                 Humidity bed room 1 
               
               
                 Dad 
                 Guest 
                 AK8 
                 OAK2 
                 MAC8 
                 PSK8 
                 Mary&#39;s camera 
               
               
                   
               
            
           
         
       
     
     As described above, when a device contacts the AP, the AP will search the MAC address of the contacting device from the authenticated devices database and use the associated PSK in communicating with that device if the MAC address is found. The existence of the DG record allows the AP to manage different groups of devices. For instance, without the DG field, the revocation of network access of a guest device requires the owner to know the MAC address or the PSK of that device. If he does not know those, then he must find them out (e.g., by examining the MAC addresses of all his home devices), or he must change the PSK values of all his devices, i.e., he must scan or rekey the whole network to revoke the guest device. 
     In contrast, consider the same operation when the DG record is present in the AP table. When the owner instructs the AP to revoke access to all guest devices, the AP point simply removes all records whose DG “Type” field equals “Guest.” Additionally, information on who has given the access rights may be used to make intelligent decisions. In an additional example, a master device may wirelessly access and manage the authenticated devices database. Alternatively, the authenticated devices database may be accessed by a personal computer in a WLAN home network. A revocation of a user may happen by removing the user from the list or canceling or changing the user device&#39;s expiry date/time. Alternatively, the table may also include expiry dates for user devices. This ensures automatic cancellation of user rights. Alternatively, the user can use the “device name” field to identify the devices whose access should be revoked. 
     According to an aspect of the invention, the information transferred using the out of band channel may include a derived PSK, a random passphrase, or one or more&lt;AK type, AK version, AK value&gt;pairs. “AK type” may be a fixed size integer, optionally with some reserved values (e.g., 0=visitor, 1=owner). AK version is a number and its contents depend on the scheme used for revocation. If sequence numbers are used as the basis of revocation, AK version may contain&lt;ownerID+sequenceNumberOwnerUsedWhenIssuingAK&gt;. If a time based approach is used, the AK version may contain&lt;ownerID|timestamp of when the AK was issued&gt;. If revocation of guests leads to a new guest AK being created at the AP and owners needing to download this new AK, there is no information needed in this field. 
     As discussed above, Broadcom has proposed SES. The Broadcom proposal may be modified according to one or more aspects of the invention, where the key agreement protocol preferably supports optional authentication. Authentication preferably uses an AK, and the protocol messages preferably are changed to identify the AK type. (If the latter is not possible, only two groups can be supported: authenticated=owner, unauthenticated=guest.) When the resulting PSK is stored, the AK type is also stored. Two types of reset may be used, one to remove all guest security associations (e.g., long button press) and a second to completely reset the system. Also, the the AP may be permanently in a mode where it can accept authenticated requests for PSKS, i.e., there is no requirement for button presses in order to reach this mode. 
     The SecureEasySetup (SES) as described above and, for example, at www.broadcom.com/press/release.php?id=659800, is a simple protocol for configuring secure WLAN connections proposed by Broadcom. The SES protocol assumes that both the client device and the access point (AP) have a button (the button can be a software or harware button or switch, e.g., on/off switch). In order to add a new client device to the WLAN network, the user first presses a button on the AP and then on the client device. The result of these two button presses is that the client receives a WPA (“WiFi Protected Access”) key and an SSID (“Service Set Identifier”) from the AP. Aspects of the present invention further improve on the systems and methods described above. For example, as will be described below, aspects of the present invention make network access more secure and user accessible in situations outside of an individual user&#39;s home. As even more specific examples, suitable systems and methods may be provided to allow visitors, for example, in hotels, restaurants, and the like, to securely, temporarily, and easily access the network system. 
     When enabling visitor access to networks, hotels, restaurants, and other public access places may not wish to remove all visitor accounts at any given time (rather, network guests or visitors may enter and leave the network at many different times). Accordingly, in accordance with at least some examples of the invention, as described in more detail below, expiration information may be added to an authentication key ID and/or expiration information may be provided via calculation of an authentication key. In some examples, if the expiration information=0, this may be used to indicate that the AK does not expire automatically. 
     Before clients can be added into a WLAN network, the AP needs to generate a WPA key and an SSID. A WPA key is the specification by WiFi Alliance based on a version of 802.11i. It is intended to be a stopgap measure until 802.11i is ready. WPA-2 is intended to be 802.11i. 802.11i is an official IEEE standard for security of Wireless LANs. In systems and methods in accordance with at least some examples of this invention, the WPA key is a pre-shared key between the WLAN client and an access point (also called a “PSK” herein). An SSID is a unique identifier for a WLAN network. Access points (APs) broadcast the SSID. 
     In at least some examples of this invention, a client may be added to a WLAN network by pressing a button provided on the AP for an extended time period (e.g., five seconds). While the AP generates the WPA key and the SSID, it will flash LED lights or give some other indication to the user. If the AP had any existing pairings, they will be removed during this process. Once a new network is generated, users can add new devices to the network by pressing a single button on the AP and the client device. 
       FIG. 6  illustrates the protocol of adding new clients into a network using the SES protocol. In step  601 , a button press on the AP  610  causes the AP to go into reception mode for some period of time, e.g., two minutes. That is, the AP waits in a state for that time where it is available to establish secure tunnel communication with a client device. In step  602 , a button press on client device  611  initiates a search by the client to locate an AP, e.g., AP  610 , which is in reception mode. After the client  611  has found AP  610 , the client  611  establishes a secure tunnel with AP  610  in step  603 . If the AP had already created a secure tunnel with another client, it will not start to secure a tunnel establishment, but instead it replies with a warning or error message. In step  604  the client  611  receives a protocol message for continuing secure tunnel establishment. The protocol message may include the WPA key and SSID. 
     The SES protocol of  FIG. 6  is user-friendly and somewhat secure. However, it still has a few drawbacks, including that client pairing with an unintended AP is possible, AP pairing with an unintended client is possible, man-in-the-middle attacks are possible, and all the pairings are permanent. It is not possible to give temporary access, for example, to visitors. Some of these vulnerabilities assume that there is another, possibly malicious AP or client present and in reception mode (these are denoted as “AP_OTHER” and “CLIENT_OTHER” in the description below). The AP that the user wants to pair with her client is designated as “AP_OK” and her client is designated as “CLIENT_OK” in the description below. 
     Thus, various improvements may be made to the SES protocol in accordance with one or more aspects of the invention. Client pairing with an unintended AP can be prevented in various ways. First, if the client finds more than one AP, the client can abort the pairing procedure and warn the user. Second, the access points can be shipped with predefined names (such as “Tiger” and “Lion”) that are drawn from a relatively large pool of names, and these names may be printed on top of the AP. If the client finds more than one AP, the user may then be asked to select the correct AP from a list of names. This feature can help reduce accidents. If there is more than one AP with the same name, then the client may be adapted to abort the pairing procedure. 
     A client also can pair with an unintended AP if the user presses the button on the client device after the predetermined amount of time (e.g., two minutes) from the button pressing on the AP_OK device such that the AP_OK device is no longer in reception mode. This situation could be prevented, for example, if the AP gives some indication (such as flashing light) when it is in reception mode and a different kind of indication (such as constant light for five seconds) when the pairing has been successfully established. In this way, the user could verify after pressing the button on client that the indication on AP has changed from the reception mode to the successfully paired mode. Also, the client user can see, prior to pressing the client button, whether the AP is in receiving mode. If a successful pairing does not happen, but rather the client has paired with AP_OTHER, then the incorrect pairing may be removed from the client manually. 
     An AP pairing with an unintended client can be prevented as well. For example, an AP can pair with a CLIENT_OTHER if the user of CLIENT_OTHER presses the button on his/her client device faster than the user of CLIENT_OK device presses his/her button. In this case, a warning message may be sent to CLIENT_OK. This situation may be detected and handled in a variety of different ways. For example, the situation may be detected if there is a pairing protocol between the CLIENT and the AP and the AP continues to listen to client requests for some time even after a first client successfully completes a pairing, e.g., until the AP pairing time interval (e.g., 2 minutes in this example system and method) runs out. If CLIENT_OTHER pairs first, then when CLIENT_OK tries to pair with AP_OK, AP_OK will return a warning message to CLIENT_OK indicating that pairing is no longer possible and the reason for it (e.g., that another device has already paired). On receiving the warning message, CLIENT_OK may be adapted to display a message to the user saying something like “AP refused to admit your device because another device got there before you. Hold down the cancel key on the AP for 3 seconds to kick the other device out of your AP&#39;s network,” or other appropriate message based on the system design. 
     When CLIENT_OTHER arrives before CLIENT_OK, the AP might not recognize CLIENT_OK and/or it might not recognize that a wrong user (CLIENT_OTHER) has been paired (the AP might not have any way of recognizing these situations). For this reason, the AP might not be adapted to take any action automatically, on its own, but rather, the AP sends a warning message at least to the client device attempting the later pairing. If CLIENT_OK receives the warning message, then the user of CLIENT_OK can perform the REMOVE_LAST_OPERATION described below and/or take other appropriate action. If CLIENT_OTHER receives the warning, then, by definition, its user cannot act on the warning because that user presumably will not have physical access to do the REMOVE_LAST_OPERATION function on the AP (e.g., the unauthorized client user presumably will not have physical access to the AP). 
     A REMOVE_LAST_OPERATION function associated with the AP may be performed at any desired time, for example, when the user receives a warning message at CLIENT_OK as described above. Performing this operation erases, terminates, or otherwise eliminates the unintended pairing established with CLIENT_OTHER, and optionally, again makes the AP available for pairing with CLIENT_OK. The REMOVE_LAST_OPERATION function may be activated, for example, by pressing the same SES button longer or shorter than in a normal pairing, or, if desired, another button may be provided for this operation. 
     Man-in-the-middle attacks may be prevented by allowing the user to compare the hashes of the agreed pairwise WPA key. For example, if both the client and the AP have a single LED, the devices could present the hash of the AP&#39;s public key one bit a time with the LED (1-bit could be presented with a green light and 0-bit with no light, for example), to thus ensure that the client has paired with AP_OK. If both devices have small displays, the hash could be presented one byte at a time as hexadecimal characters. If both devices have audio output, the hash could be represented as a sound sequence (using different frequencies or different amplitudes to represent 1 and 0). The AP may broadcast a list of its hash outputting capabilities, and the client is assumed to choose one from the list. 
     This comparing process is optional. If the user does nothing after the normal SES protocol, no comparison of hashes would be performed. However, if the user wants to compare hashes, she can perform a COMPARE_HASHES_OPERATION after the normal SES protocol. If users do not use the COMPARE_HASHES_OPERATION, the same level of security as in the original SES may be provided and achieved. The COMPARE_HASHES_OPERATION, however, allows a security-conscious user to achieve a higher level of security against an active man-in-the-middle. 
     Once the user has performed a COMPARE_HASHES_OPERATION, both of the devices show the first part of the hash. If the hash parts are different, a man-in-the-middle attack has occurred and the user may be prompted or otherwise know to perform the REMOVE_LAST_OPERATION on the AP. If the hash parts are identical, the user can either do nothing and this pairing will be accepted. Alternatively, the user can select NEXT_PART_OPERATION on both of the devices. As a result of this operation, both of the devices show the next part of the hash and the user can again choose either to remove this pairing, accept this pairing by doing nothing, or move on to the next hash part. Comparing hashes using audio output may be one desirable user-friendly approach because the human ear can more easily differentiate between sound sequences that are out of key or out of phase. 
     The more the user continues with this hash comparing process, the smaller the possibility of a successful man-in-the-middle attack. Comparing one bit reduces the possibility of successful attack by 50 percent. Comparing two bits reduces the possibility by 75 percent, and so on. The pairing protocol can be based, for example, on MANA (“Manual Authentication for Wireless Devices”, Gehrmann et al, Cryptobytes Spring 2004), which allows a high level of security against man-in-the-middle attacks even with relatively short check values. 
     According to an aspect of the invention, the SES protocol may be modified to provide for temporary access. The basic SES protocol only allows users to add devices permanently into the wireless network. However, it would be an improvement to also allow temporary access, e.g., for visitors, hotel guests, etc. When a visitor arrives, the user can give her temporary access to the network, for example, by performing an ADD_VISITOR_OPERATION on the AP instead of pressing the normal SES button. This action starts the normal SES protocol execution and the visitor is required to press the button on her device within the predetermined amount of time, e.g., two minutes. If the SES negotiation is successful, the AP will remember this client as a visitor. Examples of ways that temporary access may be provided are described above. 
     Temporary access may be revoked is various ways. When the user wants remove all the visitors from the network, she can perform a REMOVE_VISITORS_OPERATION on the AP. As a result of this operation, the AP will send a new WPA key to all other clients belonging to the network, and visitors will not receive this new key. Removal of less than all visitors may be accomplished as described above. 
     According to an aspect of the invention, different operations may be mapped to actual actions performed by the user. Those of skill in the art will appreciate that these are examples only, and other mappings may also or alternatively be used. Any way of mapping a user action to AP or client device functions may be used without departing from the scope of the invention. Notably, the various buttons described below (e.g., the “SES” and “Visitor” buttons) may be located directly on the AP and/or on another control device operatively coupled to the AP (e.g., by a wireless connection, a remote controller, etc.), for use, for example, in the event that the AP is located in a remote or hard to reach location. Table 3 below shows examples of possible mappings of device operations to various user actions. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Mappings from operations to actions 
               
            
           
           
               
               
               
            
               
                   
                 Operation 
                 Actions 
               
               
                   
                   
               
               
                   
                 REMOVE_LAST_OPERATION 
                 Press SES button for 
               
               
                   
                   
                 three seconds 
               
               
                   
                   
                 after pairing 
               
               
                   
                 COMPARE_HASHES_OPERATION 
                 Press SES button 
               
               
                   
                   
                 shortly after pairing 
               
               
                   
                 NEXT_PART_OPERATION 
                 Press SES button 
               
               
                   
                   
                 shortly when current 
               
               
                   
                   
                 hash part is being 
               
               
                   
                   
                 shown 
               
               
                   
                 ADD_VISITOR_OPERATION 
                 Press another button 
               
               
                   
                   
                 (labeled as Visitor 
               
               
                   
                   
                 Button) shortly 
               
               
                   
                 REMOVE_VISITORS_OPERATION 
                 Press another button 
               
               
                   
                   
                 (labeled as Visitor 
               
               
                   
                   
                 Button) for three 
               
               
                   
                   
                 seconds 
               
               
                   
                   
               
            
           
         
       
     
     The basic SES protocol is attractive because it is user-friendly and relatively secure. However, it still has drawbacks. Aspects of this invention provide various extensions to the basic SES protocol that make the protocol more secure and useful, without sacrificing the usability advantage of SES. It should be noted that these extensions do not complicate the normal SES protocol from the point of view of the user. The user can eliminate accidental unintended pairings with the simple REMOVE_LAST_OPERATION, but she is not forced to do so. 
     Preventing active man-in-the-middle attacks is considerably more difficult and in many scenarios active man-in-the-middle attacks are not realistic. In security critical situations an advanced user could, however, use the hash comparing method described above to improve the security of the normal SES protocol. 
     The ADD_VISITOR_OPERATION and REMOVE_VISITORS_OPERATION provide useful extensions to the SES protocol. Without these the user cannot add visitor devices and/or she has re-configure the entire network once the user leaves the network. 
     One or more aspects of the invention may be embodied in computer-executable instructions, such as in one or more program modules, executed by one or mote computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. The computer executable instructions may be stored on a computer readable medium such as a hard disk, optical disk, removable storage media, solid state memory, RAM, etc. As will be appreciated by one of skill in the art, the functionality of the program modules may be combined or distributed as desired in various embodiments. In addition, the functionality may be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA), and the like. 
     The present invention includes any novel feature or combination of features disclosed herein either explicitly or any generalization thereof. While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims.