WO2008087355A2

WO2008087355A2 - Wireless network roaming method

Info

Publication number: WO2008087355A2
Application number: PCT/FR2007/052614
Authority: WO
Inventors: Jérôme RAZNIEWSKI; Loïc HOUSSIER; Stanislas Francfort
Original assignee: France Telecom
Priority date: 2006-12-29
Filing date: 2007-12-21
Publication date: 2008-07-24
Also published as: WO2008087355A3; FR2911036A1

Abstract

The invention relates to a roaming method for a station (A') moving from a first access point (B1) to a second access point (B') in a wireless network, said method being characterised in that it comprises: a step (6A') of receiving, from the first access point (B'), data comprising a master key (PMK) encrypted by means of a secret (K) known at least to an authentication server (C), the first access point (B') and the second access point (B'), wherein said master key (PMK) results from a negotiation between the authentication server (C) and the station (A') and was received by the first access point (B') from the authentication server; and a step (7A') of sending the encrypted master key (PMK) to the second access point.

Description

Roaming process in a wireless network

The invention relates to wireless access technologies for telecommunications networks, for example IEEE 802.1 1 type networks standardized by the Institute of Electrical and Electronics Engineers (IEEE).

It more specifically concerns the security of terminals in a roaming situation in a wireless network.

The invention finds a particularly interesting application in the context of a voice over IP application (the term commonly used is the term "Voice over IP" or "VoIP") in a wireless network.

Currently, the wireless networks specified in the IEEE 802.1 1 standards are widely used in corporate networks, residential networks or access areas called hotspots (English for an area with a high concentration of users, such as railway stations, airports, trains, hotels with wireless networks connected to the Internet). A standard called 802.11 i addresses the major security issues of wireless networks. However, one issue that is not addressed in 802.1 1 i is the introduction of appropriate mechanisms to allow wireless terminals to roam (the term commonly used in wireless networks is the term English "roaming" is also more commonly referred to as "handover" in mobile telephony) without performing a complete authentication with an authentication server, for example a server "RADIUS" ("Remote Authentication Dial-ln" User Service "). When it comes to voice over IP, quality of service is essential.

However, roaming mechanisms in a wireless network proposed by the standard voice over IP, induces transfer times in the network access and reauthentication far too long. At access point level the delay goes from 800 ms to 1 s, to which must be added the time necessary to send information to the authentication server which can go up to 3 s. Such a delay is not acceptable during a telephone call. The document available at http://www.cisco.com/en/US/products/hw/wireless/ps458/prod technical refers to nceO9186a00801 c5223.html # wp39137 discloses an architecture suitable for roaming client workstations in a wireless network (called "fast secure roaming"). The architecture includes a key controller (called "WDS" for "Wireless Domain Services"), an intermediate device between a RADIUS authentication server and access points of the wireless network. When a client station attaches to a first access point of the wireless network, it authenticates conventionally with the authentication server that generates a key "PMK" (the English "Pairwise Master Key" ) that it transmits to the client station. The authentication server then transmits the PMK key to the key controller. It is then generated by the key controller and the client station, from the PMK key and public information on the identity of the first access point, a key PMK ¹ . The key PMK 'is sent by the key controller to the first access point. When the client station is roaming, away from the radio range of the first access point and within radio range of a second access point, the second access point issues a request to the key controller to obtain a key PMK ", derived from the key PMK and public information on the identity of the second access point, the client station performs the same key derivation operations in order to 'get the PMK key'.

Thus, it is not necessary for the client station, when roaming, to perform an authentication with the RADIUS server again, which reduces the time required to take into account roaming. However, the architecture thus defined is proprietary. The key derivation from the first key PMK, to obtain the successive keys PMK ', PMK "is also proprietary, which requires access points and specific client stations, and a key derivation algorithm PMK, PMK specific, not defined by the standard 802.1 1 1. Such a constraint is not conceivable for example in a hotspot-type network, in which the configuration of the client stations that access the network is not controlled. many exchanges between access points and a core network equipment, here the key controller, which, in the case of a VoIP-type application, demanding in terms of quality of service, leads to a limitation of the number of client stations and access points managed simultaneously.

The present invention overcomes all or part of the disadvantages mentioned. To this end, the invention relates to a roaming management method of at least one station in a wireless network, between a first access point and a second access point, the method being characterized in that it comprises a step of reception by the second access point from the station of a master key (PMK) encrypted by means of a secret (K) shared at least between an authentication server, said first point of access access and said second access point, said master key (PMK) originating from a negotiation between the authentication server and said station, and having been received from the authentication server by said first access point.

Advantageously, the roaming management method comprises a step of sending by the first access point to the data station comprising said encrypted master key (PMK).

The invention also relates to a method of roaming a station from a first access point to a second access point of a wireless network, the method being characterized in that it comprises:

a step of receiving the first data access point comprising a master key (PMK) encrypted by means of a secret (K) shared at least between an authentication server, said first access point and said second point; access, said master key (PMK) originating from a negotiation between the authentication server and said station and having been received from the authentication server by said first access point, and

a step of sending to the second access point of said encrypted master key (PMK). Advantageously, the method according to the invention uses a known secret of the access points and the authentication server in order to transfer securely to the radio link, via a station in progress. roaming in the wireless network, the PMK master key that has been negotiated by the authentication server and the station, and then distributed by the authentication server to the access point. The master key PMK being used by an access point and a station to derive an encryption and authentication key PTK, the station being roamed from the first access point to the second access point n ' Thus, there is no need to authenticate again with the authentication server in order to obtain a new encryption and authentication PTK key for its exchanges with the second access point. Indeed, the new encryption and authentication key PTK can be derived by the second access point and then distributed to the station. Thus, the time required to establish security when roaming the station from the first access point to the second access point is very short since it is not necessary to establish a dialogue, usually expensive in time, between the station and a network equipment, such as the authentication server. In the case of a real-time application of the Voice over IP type, the method according to the invention contributes to avoiding untimely cuts in communications during roaming situations. Thus, the method according to the invention improves the quality of service of such an application.

In addition, the method according to the invention does not modify the message exchanges between the station, the access point and the authentication server, in accordance with the 802.11 i standard. In particular, it does not modify the messages exchanged during the procedure of attaching a station to an access point, defined by the state machine 802.11. Thus, the implementation of the method according to the invention requires only a software update of the access points and stations. Access points and / or stations that do not have such an update continue to operate in accordance with 802.11 i. Thus, it is easy to implement the method according to the invention in a hotspot type network in which any type of station can access the network. In addition, the method is not limited by the number of access points in the network, nor by the number of stations in roaming situations that can be managed at the same time. Advantageously, with the roaming management method according to the invention, said data are encrypted before sending by means of a PTK authentication and encryption key, said PTK authentication and encryption key having been derived from from the PMK master key. Advantageously, the sending of the encrypted PMK master key by means of the secret K of the first access point to the station is secured by encryption by means of the PTK authentication key and encryption specific to the station.

Advantageously, the roaming method according to the invention further comprises a step of verifying a signature of a random number X received from the second access point, said random number and said signature of said random number being received from the first point. access with the encrypted PMK master key.

Advantageously, the method according to the invention makes it possible to authenticate the access points during the roaming phase and makes it possible to avoid sending to unrecognized access points, such as pirate access points. , information, even if this information is encrypted.

The invention also relates to a signal to be transmitted from an access point to a station in a wireless network, said signal comprising data comprising a PMK master key encrypted by means of a secret K shared at least between the access point and an authentication server, said PMK master key being the result of a negotiation between the authentication server and said station and having been received from the authentication server by said access point.

Advantageously, only one parameter of the signal is adapted according to the invention. Thus, the 802.11 i protocol is not modified by adding new types of signals.

The invention also relates to an access point of a wireless network, adapted for roaming management of at least one station in a wireless network, between said access point and another access point, the access point including,

means for storing a secret K shared at least between an authentication server, said access point and said other access point, the access point being characterized in that it comprises reception means, arranged to receive from the station a PMK key encrypted by means of said secret K, said PMK master key being the result of a negotiation between the authentication server and said station, and having been received from the authentication server by said access point.

Advantageously, the access point according to the invention further comprises sending means, arranged to send to the station data including the master key PMK encrypted by means of the secret K.

The invention also relates to a station of a wireless network adapted to roam from a first access point to a second access point of a wireless network, the station being characterized in that it comprises :

reception means, arranged to receive data from the first access point comprising a PMK master key encrypted by means of a secret K shared at least between an authentication server, said first access point and said second point; access, said master key PMK being the result of a negotiation between the authentication server and said station and having been received from the authentication server by said first access point, and

means of sending, arranged to send to said second access point, said encrypted master key PMK.

The invention also relates to a wireless network comprising:

at least two access points according to the invention, and

at least one station according to the invention.

The invention also relates to a computer program on a data medium and loadable in the internal memory of an access point associated with a wireless interface, the program comprising portions of code for executing the steps of the method roaming management system according to the invention when the program is executed on said access point.

The invention also relates to a partially or totally removable data storage means comprising computer program code instructions for executing the steps of the roaming management method according to the invention. The invention also relates to a computer program on a data carrier and loadable in the internal memory of a station associated with a wireless interface, the program comprising portions of code for the execution of the steps of a method of roaming according to the invention when the program is executed on said station.

The invention also relates to a partially or completely removable data storage means comprising computer program code instructions for executing the steps of a roaming method according to the invention.

Many details and advantages of the invention will be better understood on reading the description of a particular embodiment with reference to the accompanying drawings given in a non-limiting manner and in which:

FIG. 1 is a block diagram of a state machine which illustrates the operation during an 802.11 authentication of a network equipment of known station or access point type of the prior art;

FIG. 2 is a diagram that presents a standard authentication scenario according to the 802.11 i standard;

FIG. 3 presents an authentication scenario according to the invention, in accordance with the 802.11 standard and adapted to the roaming of a station.

FIGS. 4a and 4b are representations of information elements according to the invention;

FIG. 5 is an example of a functional representation of an access point according to the invention; FIG. 6 is an example of a functional representation of a station according to the invention;

FIG. 7 is an exemplary architecture of a wireless network according to the invention.

The security implemented in the 802.11 i standard induces the generation of several secret keys during exchanges between a station, an access point and a RADIUS authentication server. Among the secret keys generated, some are used to derive other secret keys and some of the secret keys generated or derived, some are used to secure traffic. Thus, during different phases of the 802.11 i protocol, a master key called "PMK" (of the English "Pairwise Master Key") is negotiated between the authentication server and the station during an authentication phase. . The PMK master key is then distributed by the authentication server to the access point during a key exchange phase. During this exchange phase which takes place in 4 steps and is usually called the "4-way handshake", during which 4 signals are exchanged, it is calculated by the station and the access point a key authentication and encryption of traffic between the access point and the station (the term commonly used to describe traffic between the access point and the station is the English term "unicast"). The authentication and encryption key is called "PTK" (of the English "Pairwise Transient Key"), it is generated from the master key PMK and it is used for the authentication and encryption of unicast traffic between the station and access point; it is specific to the station. The authentication and encryption key PTK also serves to securely transmit the access point to the station a group secret key called GTK (Group Transient Key) defined by the access point and used to authenticate frames to multiple stations. The traffic destined for several stations is a broadcast-type traffic (the term commonly used is the term "broadcast") when it is a matter of broadcasting a message to all the stations of a network, and a traffic of type Restricted broadcast (the term commonly used is the term "multicast") when it comes to broadcasting a message to a limited number of stations in a network.

The authentication and key exchange phases use an authentication transport protocol called "EAP" (Extensive Authentication Protocol) based on pre-existing authentication methods.

In a wireless network for a device, for example a client station, to exchange data with another device in a network wireless constituting access to the network, for example an access point, it is necessary to attach this first equipment, the station, to the network.

802.11 technologies provide that the attachment of a client device to an access point is performed during a known attachment procedure. The attachment procedure is a three-step process in which management frames are exchanged between the client equipment and the access point.

To implement a procedure for attaching a station to an access point, a station and an access point may operate in accordance with a tri-state state machine. The access point can of course include several state machines, each managing the attachment to a station, and decide to assign such state machine to such station when the latter seeks to establish an attachment. FIG. 1 shows the operation known in the prior art of the state machine in equipment of the station or access point type.

The equipment state machines completely detached from each other are in a state 1. In this state 1, the equipment can exchange class 1 messages or frames, for example point search frames. access ("PROBE REQUEST"), response to the search ("PROBE RESPONSE") or specific frames called beacons ("BEACON"). After a successful authentication, following an exchange of authentication request management frames ("AUTHENTICATION REQUEST") issued by a station, and positive authentication response ("AUTHENTICATION RESPONSE") issued in response by a point d access, the state machines are in a state 2, and only after a successful association, following an exchange of management frames of the type request association ("ASSOCIATION REQUEST") issued by a station , and positive association response ("ASSOCIATION RESPONSE") issued by the access point that the state machines go into a state 3.

Two devices in a state i, ranging from 1 to 3, can exchange between them messages or frames of class between 1 and i. Frames class 3 allow the transport of data in the ordinary meaning of the term, for example data corresponding to the text of an email.

To terminate an attachment between two devices, a disassociation notification ("DISASSOCIATION" in English) and / or a de-authentication notification ("DEAUTHENTICATION" in English) can be transmitted from one device to another. Both devices go from state 3 to state 2 when a dissociation notification is transmitted from one device to another. A de-authentication notification switches devices from state 2 to state 1, or from state 3 to state 1.

The message exchanges defined by the 802.1 1 i standard are presented in FIG.

In a wireless network not shown, a station A wishes to access said network via an access point B. In order to authenticate the station A and implement the security protocol 802.1 1 i, the station A and the point B access dialogue with a authentication server C type "RADIUS" ("Remote Authentication Dial-User Service"). In a known manner, in a network, the authentication server and the known access points of said server share a secret K. The exchanges of messages conforming to the 802.11 protocol i are grouped into 4 phases 10, 1 1, 12 and 13.

In a phase of attachment of the station A to the access point B, conventional messages conforming to those represented on the state machine shown in FIG. 1 are exchanged. Only the PROBE REQUEST and ASSOCIATION RESPONSE messages are represented. During the attachment phase are negotiated security policy parameters such as the list of security protocols, the list of authentications supported by station A and access point B.

In a phase 1 1 of authentication of the station A with the authentication server C, the station A and the authentication server C together define a master key "PMK" (of the English "Pairwise Master Key") which will be used to derive other keys. The authentication phase is based on a method carried by the EAP authentication protocol and negotiated during the attachment phase. Only a few messages are represented. In particular, the EAP messages represented in the "EAP messages" arrow, specific to the authentication method selected, are not detailed. The exchange of the EAP messages between the station A and the authentication server C leads to the derivation of the master key PMK shared by the station A and the authentication server C. The master key PMK is distributed by the server of authentication C to access point B at the end of authentication phase 11 in a "RADIUS Access Accept" message.

In a phase 12 key exchange EAP, usually called "4-way handshake", an authentication key and "PTK" ("Pairwise Transient Key") is derived from the key PMK master. The PTK authentication and encryption key enables the authentication and encryption of unicast data exchanged between access point B and station A, as well as the secure distribution of a "GTK" group key (from the "Groupwise Transient Key") used for encryption and integrity checking of broadcast and multicast traffic. The GTK group key is distributed from the access point B to the station A during the key exchange phase 12, in a secure manner by encryption using the authentication key and PTK encryption. The signals exchanged during the key exchange phase 12 are "EAPoL-Key" type signals. A first signal received by the station allows it to derive the encryption and authentication key PTK. A second signal allows the access point to derive the encryption and authentication PTK key. A third signal makes it possible to install the PTK key and to transmit from the access point B to the station A the GTK group key. A fourth signal verifies the installation of the encryption and authentication PTK key.

In a phase 13 of data transmission between the station A and the access point B, data is transmitted securely between the station A and the access point B, either using the key PTK encryption and authentication of unicast data, either using the encryption key GTK and broadcast or muiticast traffic integrity checks, depending on the type of traffic.

Figure 3 shows the steps of the roaming method according to the invention. A station A 'according to the invention accesses a wireless network not shown via a first access point B' according to the invention. The station A 'traveling in the wireless network roams from the first access point B' to a second access point B 'according to the invention.The wireless network comprises the authentication server C. in known manner, the authentication server C and the known access points B ¹ , B "of said server share the secret K.

In accordance with 802.11 i, the station A 'which accesses the wireless network associates with the access point B' during the attachment phase. The message exchanges are consistent with the exchanges presented in Figure 1, they are represented by dotted lines in order not to overload the figure. Then, the station A 'authenticates with the authentication server C during the authentication phase 11. At the end of authentication phase 11, the authentication server C and the station A 'have derived the master key PMK, and the authentication server C has transmitted to the access point B ¹ the master key PMK. Thus, in a step _1A s station A ¹ has the master key PMK in a memory not shown. In a step 2 _C , the authentication server C has the master key PMK in a memory not shown and in a step _B '3, the access point B ¹ has the master key PMK in a memory not shown.

During the key exchange phase 12 between the station A 'and the first access point B', in a step 4 _B 'according to the invention, the access point B' calculates and stores in its memory the master key PMK encrypted by means of the secret K shared by the access points B ', B "and the authentication server C. In an alternative embodiment of the invention not shown, the master key PMK encrypted by means of the secret K is computed and transmitted to the access point B 'by the authentication server C. During the exchange of the four signals of the key exchange phase 12, the authentication and encryption key PTK is derived , installed and verified by the station A 'and the access point B'. According to the invention, in a step 5B- the third signal of the key exchange phase 12 is modified before being sent, to transport from the access point B 'to the station A', in a data field of the frame, data comprising the mean encrypted PMK master key secret K and calculated in step 4 _B ¹ . The signal also includes the GTK group key that will be used for broadcast or multicast traffic.

In one embodiment of the invention, the data field of the third signal is the concatenation of the length of the value corresponding to the encrypted master key PMK by means of the secret K, the master key PMK encrypted by means of the secret K and the GTK group key. The data field thus defined is represented in the figure by:

Length || Encrypted_K (PMK) || GTK

Preferably, these data are transmitted in encrypted form to the attention of the station A 'using the authentication and encryption key PTK. Thus, the transmission is done in a secure way.

The signal is received by the station A "in a step _6A 'In the step _6A s the station A' decrypts by means of the authentication and encryption key PTK the received encrypted data and stores in memory the key PMK master encrypted by means of the secret K thus obtained, and the GTK group key In the data transmission phase 13, the access point B 'and the station A' exchange data, using, according to the type of the messages exchanged the GTK group key, or the PTK authentication and encryption key.

Station A ', when roaming in the wireless network, leaves the radio coverage area of the first access point B' and enters the radio coverage area of the second access point B ". connection of the station A 'with the wireless network, a roaming procedure of the station according to the invention will be described.

In the attachment phase of the station A ¹ to the second access point B ", management frames are exchanged between the station A ¹ and the second access point B": the station A 'sends a frame of access point search (PROBE REQUEST), access point B "responds by sending a search response frame (PROBE RESPONSE). Station A 'then sends an authentication request frame (AUTHENTICATION REQUEST) according to the invention which includes a field indicating that it wishes to initiate a fast roaming procedure. The second access point B "responds by sending a positive authentication response frame (AUTHENTICATION RESPONSE) according to the invention which comprises a field indicating acceptance to practice fast roaming. In step ¹ 7A, the station A 'sends an association request frame (ASSOCIATION REQUEST) according to the invention which comprises the encrypted master key PMK by means of the secret K ₁ and that it has received from the first access point B', preferably encrypted to him during the key exchange phase 12. In a step 8B ", the second access point B" receives the association request, decrypts by means of the secret K the received encrypted master key PMK and associates it at station A "in his memory. The second access point B "responds by sending a positive association response frame (ASSOCIATION RESPONSE).

In the key exchange phase 12 between the station A 'and the second access point B', which follows the previous association phase, a new authentication and encryption key PTK is derived from the master key PMK, installed and verified, and a GTK group key is transmitted securely from the second access point B "to the station A ¹ .

Thus, it was not necessary to make a complete authentication with the authentication server for the station A ^{1 to} obtain a PTK authentication and encryption key for its exchanges with the second access point B ". two access points B ¹ and B "are shown in the figure. The method is not limited to roaming from a first access point to a second access point. Homelessness may continue with other unrepresented access points.

Figures 4a and 4b show information elements according to the invention. The 802.11 standard allows the addition of parameters in the management frames. These parameters are, in the standard, optional parameters or so-called "tagged parameters" parameters. The addition of parameters makes it possible to specify functionalities according to the invention. Thus, new information elements (the term commonly used is the term "information element") are defined to be integrated into management frames exchanged during the association phase 10 according to Figure 3.

The content of a first piece of information is presented in Figure 4a. The first piece of information, called fast roaming (or "fast roaming" in English) makes it possible to specify whether the stations and the access points that exchange management frames support and want to implement the roaming process according to the 'invention. The first piece of information includes a first field identifying it ("ID Element"), a second field ("Length") that specifies the length of the first piece of information, and a third field that represents the value ("Value"). ") carried by the first piece of information. Different values can be assigned to the third field. In one embodiment of the invention, the value field may contain: 0, not to enable fast roaming, 1 to enable fast roaming, 2 to accept fast roaming, and 3 to deny fast roaming. The first piece of information is added in management frames of the "AUTHENTICATION REQUEST" type sent by the stations to indicate whether or not they wish to implement fast roaming according to the invention. The first piece of information is also added in "AUTHENTICATION RESPONSE" management frames sent in response by the access points to indicate to the stations whether or not they agree to implement fast roaming according to the invention.

The content of a second piece of information is presented in Figure 4b. This piece of information is called "Encrypted". It includes a first field that identifies it, a second field that specifies the length of the information element, and a third field that specifies the value that carries the second piece of information. The value field includes the value provided by the station at the access point which is the PMK master key encrypted by means of the K secret shared by the authentication server and access points. The second piece of information is added in "ASSOCIATION REQUEST" type management frames.

In a second embodiment of the invention not shown, and corresponding to an optimization of the invention, the access points are authenticated by the station before performing the key exchange phase 12 between the station A ¹ and the first access point B ¹ according to FIG. 3. Advantageously, the method makes it possible to avoid sending information, even encrypted, to a pirate access point and to be assured of the authenticity from the access point.

The second embodiment will be described in relation to FIG. 3. In step _4B 'according to FIG. 3, in addition to the calculation of the encrypted master key by means of the secret K shared between the authentication server C and the access points, the access point B 'chooses a random number X and calculates the signature of the random number X. It uses for this purpose a cryptographic signature algorithm, for example SHA (for "Secure Hash Algorithm").

During the key exchange phase 12 between the station A 'and the first access point B', the access point B 'sends to the station A' in the third signal of the exchange during the exchange. step 5B ', the master key encrypted by means of the secret K, the random number X, and the signature of the random number X calculated in step 4 _B '. The value of the master key PMK, the random number X and the signature of the random number are for example concatenated to be sent in the signal. The sending is preferably secured to the access point, by encryption by means of the authentication key and PTK encryption of the station A '. The station A 'decrypts Step 6 _A' data received in the frame and retains in its memory the master key PMK encrypted using the secret K, the random number and the signature of the random number. The station A 'associates these values with its current connection with the access point B'. When roaming station A 'and in accordance with FIG. 3, station A' sends to second access point B "during the next association phase 10 an authentication request frame (AUTHENTICATION REQUEST) which furthermore includes the field indicating that it wants to make fast roaming, a second field containing the random number X.

Upon reception of the authentication request frame, the second access point B "retrieves the random number X sent by the station, then calculates the signature of X that it inserts as an information element in the response frame. positive authentication (AUTENENTICATION RESPONSE), along with the second piece of information indicating that it agrees to do fast roaming.

Upon receipt of the authentication response frame, the station A 'verifies that the signature of the random number X, received in the authentication response frame is identical to that received from the first access point B' at the end of the authentication response frame. key exchange phase 12.

Then, the station A 'and the second access point B "realize a key exchange phase 12, during which the second access point B" sends to the station A' the encrypted master key by means of the secret K and preferably in a secure manner, a new random number X1 and the signature of this new random number, in order to authenticate a third access point during a future roaming between the second and the third point of access.

In a third variant of the invention not represented, it is the authentication server C which, during the authentication phase 11, sends the station the random number X and the signature of the random number X.

With reference to FIG. 5, an exemplary functional representation of an access point B ', B "according to the invention is presented .The access point B', B" comprises several modules: a memory 50 and modules 51, 52, 53 and 54 articulated around a microprocessor 55.

Said microprocessor 55 or "CPU" (of the "Central Processing Unit") is a processing unit. The memory 50 makes it possible to perform calculations, load software instructions corresponding to the steps of the roaming management method described above, and have them executed by the microprocessor 55. The memory 50 is adapted to store the shared secret K at least between the access points B ", B" and the authentication server not shown, and to store the keys generated during the authentication 802.11 i: the master key (PMK) transmitted by the authentication server, the encryption and authentication key (PTK) derived from the master key (PMK) and calculated, installed and verified during the key exchange phase with a station of the wireless network not shown. The memory 50 is also adapted to store the information received by receiving means 52 described below.

The access point B ', B "further comprises:

- A radio interface 54, arranged to communicate by radio with other equipment of a wireless network such as a station.

a controller 53 arranged to translate signals received by the radio channel into digital signals, and to translate digital signals into signals to be transmitted on the radio channel via the radio interface 54.

means 51 for sending, arranged to send data to the station comprising the master key PMK encrypted by means of the secret K.

the reception means 52, arranged to receive from the station A 'a key PMK encrypted by means of said secret K, said master key PMK being the result of a negotiation between the authentication server and said station, and having been received from the authentication server by said access point B '. Said encrypted PMK master key is received via the radio interface and the controller 53. The decryption of the encrypted master key PMK by means of the secret K, in order to initiate a key exchange phase with the current station roaming can be performed by unrepresented decrypting means.

- A communication bus 56 arranged to allow the means described above to communicate.

The modules 51, 52 which implement the previously described roaming management method are preferably software modules comprising software instructions for the processor to execute the process steps. The software modules may be stored in a second memory of the access point B ', B "not shown or transmitted by a data medium, which may be a storage medium, fixed or removable, for example a CD-ROM. ROM, a magnetic floppy disk or a disk hard, or a transmission medium such as an optical signal or radio or a telecommunications network.

With reference to FIG. 6, an example of a functional representation of a station A 'according to the invention is presented.

The station A 'comprises several modules: a memory 60 and modules 61, 62, 63 and 64 articulated around a microprocessor 65.

Said microprocessor 65 is a processing unit. The memory 60 makes it possible to perform calculations, to load software instructions corresponding to the steps of the roaming method of the station from a first access point to a second access point according to the invention described above, and to execute them. by the microprocessor 65.

The memory 60 is adapted to store the keys generated during the authentication 802.11 i: the master key (PMK) negotiated with the authentication server not represented during the authentication phase, the encryption key and authentication (PTK) derived from the master key (PMK) and calculated, installed and verified during the key exchange phase with an unrepresented access point. The memory is also adapted to store the information received by receiving means 61 described below.

Station A ¹ furthermore comprises:

a radio interface 64, arranged to communicate by radio with other equipment of a wireless network.

a controller 63 arranged to translate signals received by the radio channel into digital signals, and to translate digital signals into signals to be transmitted over the radio channel via the radio interface 64.

the reception means 61, arranged to receive from the first access point B ¹ a PMK master key encrypted by means of a secret K shared at least between the authentication server, said first access point B ¹ and said second access point B ", said PMK master key being the result of a negotiation between the authentication server and said station and having been received from the authentication server by said first access point B '. means 61 receive the master key encrypted securely to the attention of station. The decryption of this secure sending by means of the authentication key and PTK encryption of the station can be performed by unrepresented decryption means. means 62 for sending, arranged to send to said second access point B ", said encrypted master key PMK.The master key encrypted with the secret K corresponds to the value received by the reception means 61, decrypted.

- A communication bus 66 arranged to allow the means described above to communicate. The modules 61, 62 which implement the roaming method of the previously described station are preferably software modules comprising software instructions for the processor to execute the steps of the method. The software modules can be stored in a second memory of the station A 'not shown or transmitted by a data medium. This may be a storage medium, fixed or removable, for example a CD-ROM, a magnetic diskette or a hard disk, or a transmission medium such as an optical signal or radio or a telecommunications network.

Figure 7 is an exemplary architecture of a wireless network 70 according to the invention.

The wireless network 70 comprises at least two access points B ', B "according to the invention connected to a network 71 of the Internet or intranet type via a wired link.The wireless network also comprises at least one station A' according to the invention. The radio coverage areas of the access points B ', B "are respectively represented by dashed circles 72, 73. The station A' which moves in the wireless network 70, illustrated by the arrow , passes from the radio coverage area 72 of the access point B 'to the radio coverage area 73 of the access point B "and implements the roaming method according to the invention. ", B" implement the roaming management method according to the invention. In a variant of the wireless network architecture according to the invention, not shown, a so-called community wireless network is considered in which the network architecture comprises high-speed home terminal equipment provided by one or more providers. Internet access. These home terminal equipments act as access points according to the invention. They are located for example in apartments of a building which constitutes the wireless network according to the invention. The invention makes it possible to offer users of the wireless network real-time services such as a good quality VoIP service in an easy manner, by updating the software of the equipment, despite heterogeneous Internet access providers.

Claims

A method of roaming management of at least one station (A ¹ ) in a wireless network between a first access point (B ') and a second access point (B "), the method being characterized in that it comprises a step of receiving (8 _B ) by the second access point (B ") from the station (A ') of a master key (PMK) associated with the station and encrypted at the means of a secret (K) shared at least between an authentication server (C), said first access point (B ") and said second access point (B"), said master key (PMK) being supplied to said first access point (B ') by the authentication server (C).

2. Management method according to claim 1, comprising a step of sending (5B) by the first access point (B ') to the data station (A') comprising said encrypted master key (PMK).

The management method according to claim 2, wherein said data is encrypted before sending by means of an authentication and encryption key (PTK), said authentication and encryption key (PTK) having been derived from the master key (PMK).

4. A method of roaming a station (A ') from a first access point (B') to a second access point (B ") of a wireless network, the method being characterized in that that he understands:

a step (6 _A ) for receiving the first access point (B ') of data comprising a master key (PMK) associated with the station and encrypted by means of a secret (K) shared at least between a data server; authentication (C) ₁ said first access point (B ¹ ) and said second access point (B "), said master key (PMK) being provided to said first access point (B ') by the server authentication (C), and - a step (7 _A ) of sending to the second access point of said master key

(PMK) encrypted.

The roaming method according to claim 3, further comprising a step of verifying a signature of a random number (X) received from the second access point (B "), said random number and said signature of said number randomly being received from the first access point (B ') with the encrypted master key (PMK).

A signal (EAPoL-Key3) for transmission from an access point (B ') to a station (A') in a wireless network, said signal comprising data comprising a master key (PMK) associated with the station and encrypted by means of a secret (K) shared at least between the access point (B ') and an authentication server (C), said master key (PMK) being supplied to said access point ( B ') by the authentication server (C).

7. Access point (B ') of a wireless network adapted for roaming management of at least one station (A') in a wireless network between said access point (B ') and another access point (B "), the access point comprising,

storage means (50) for a secret (K) shared at least between an authentication server (C), said access point (B ') and said other access point

(B "), - deciphering means arranged to decrypt a key (PMK) associated with the station and encrypted by means of said secret (K), the access point being characterized in that it comprises means (52) receiver, arranged to receive from the station (A ') said key (PMK) associated with the station and encrypted by means of said secret (K).

8. Access point according to claim 7, further comprising means (51) for sending, arranged to send to the station (A ') data comprising the master key (PMK) encrypted by means of the secret (K) .

9. A station (A ') of a wireless network adapted to roam from a first access point (B') to a second access point (B ") of a wireless network, the station (A ¹ ) being characterized in that it comprises:

means (61) for receiving, arranged to receive data from the first access point (B ') comprising a master key (PMK) associated with the station and encrypted by means of a secret (K) shared at least between an authentication server (C), said first access point (B ¹ ) and said second access point (B "), said master key (PMK) being supplied to said access point (B ¹ ) by the authentication server (C), and sending means (62) arranged to send said second access point (B ") said encrypted master key (PMK).

10. Wireless network (70) comprising:

at least two access points according to claim 7 or claim 8, and

at least one station according to claim 9.

11. Computer program on a data carrier and loadable in the internal memory of an access point associated with a wireless interface, the program comprising portions of code for executing the steps of the management method according to the one of claims 1 to 3 when the program is executed on said access point.

12. Partially or fully removable data storage means comprising computer program code instructions for executing the steps of the management method according to one of claims 1 to 3.

13. Computer program on a data medium and loadable in the internal memory of a station associated with a wireless interface, the program comprising portions of code for executing the steps of a roaming method according to claim 4 or claim 5 when the program is run on said station.

A partially or fully removable data storage medium, comprising computer program code instructions for performing the steps of a roaming method according to claim 4 or claim 5.