Devices and methods for secure communication in a wireless network

Abstract

A transmitter station (110; 120) for a wireless communication network (100), in particular a Wi-Fi network (100) is disclosed. The transmitter station (110; 120) is configured to broadcast successively a plurality of beacon frames (140) to one or more receiver stations (120; 110) of the wireless communication network (100), wherein each beacon frame (140) comprises information for synchronizing a timer. Moreover, the transmitter station (110; 120) is configured to send a data frame (150) to the one or more receiver stations (120; 110), wherein the data frame (150) comprises an encrypted timer value associated with the data frame (140). The transmitter station (110; 120) and the one or more receiver stations (120; 110) may detect a man-in-the-middle attack and, in response, perform suitable counter measures.

Description

[0001] DEVICES AND METHODS FOR SECURE COMMUNICATION IN A WIRELESS NETWORK

[0002] TECHNICAL FIELD

[0003] The present invention relates to wireless communications. More specifically, the present invention relates to devices and methods for secure communication in a wireless network, in particular a Wi-Fi network.

[0004] BACKGROUND

[0005] IEEE 802.11 -based WLANs (also referred to as Wi-Fi networks) have become popular at an unprecedented rate. Security of Wi-Fi networks is important, because in unsecure Wi-Fi networks adversaries may collect personal information and steal identities of users, compromise financial and other sensitive business data, eavesdrop on communications, and more. For instance, man-in-the-middle (MitM) attacks are a common form of security attack towards Wi-Fi networks that allow attackers to catch and manipulate communication between, for instance, an access point, AP, and a non-AP station of a Wi-Fi network. A multichannel, MC, MitM attack is an advanced MitM attack using two different channels allowing the attacker to forward frames between both channels so that the attacker legitimately may manipulate, e.g., block, delay, modify, inject, and / or replay, encrypted frames between an AP and non-AP stations. Detecting an MitM and in particular an MC-MitM attack is challenging because the attacker acquires the MitM position between an already connected non-AP station and an AP in a Wi-Fi network without disconnecting the non-AP station from the Wi-Fi network.

[0006] SUMMARY

[0007] It is an objective to provide improved devices and methods for secure communication in a wireless network, in particular an IEEE 802.11 based Wi-Fi network, in particular allowing to detect an MitM and in particular an MC-MitM attack in real time.

[0008] The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. According to a first aspect a transmitter station for a wireless communication network is provided. The transmitter station is configured to broadcast successively a plurality of beacon frames to one or more receiver stations of the wireless communication network, wherein each beacon frame comprises information for synchronizing a timer. The transmitter station is further configured to send a data frame to the one or more receiver stations, wherein the data frame comprises an encrypted timer value associated with the data frame, for instance, a timestamp created during the generation or the transmission of the data frame.

[0009] In a further possible implementation form, the data frame comprises a header and an encrypted payload, wherein the encrypted payload comprises the encrypted timer value.

[0010] In a further possible implementation form, the timer is a timing synchronization function, TSF, timer.

[0011] In a further possible implementation form, the transmitter station is further configured to receive from the one or more of the plurality of receiver stations an indication that the data frame has been potentially relayed and / or tampered with by an attacker.

[0012] In a further possible implementation form, the transmitter station is a multi-link transmitter station configured to communicate via a plurality of links with the one or more receiver stations of the wireless communication network.

[0013] In a further possible implementation form, the wireless communication network is a Wi-Fi network.

[0014] In a further possible implementation form, the transmitter station is an access point, AP, or a non-AP station.

[0015] According to a second aspect a method for operating a transmitter station in a wireless communication network is provided. The method comprises the steps of broadcasting successively a plurality of beacon frames to one or more receiver stations of the wireless communication network, wherein each beacon frame comprises information for synchronizing a timer; and sending a data frame to the one or more receiver stations, wherein the data frame comprises an encrypted timer value associated with the data frame. The method according to the second aspect of the present disclosure can be performed by the transmitter station according to the first aspect of the present disclosure. Thus, further features of the method according to the second aspect of the present disclosure result directly from the functionality of the transmitter station according to the first aspect of the present disclosure as well as its different implementation forms described above and below.

[0016] According to a third aspect a receiver station for a wireless communication network is provided. The receiver station is configured to receive successively a plurality of beacon frames from a transmitter station of the wireless communication network and to synchronize a timer based on information included in each beacon frame for obtaining a synchronized timer. Moreover, the receiver station is configured to receive a data frame from the transmitter station, wherein the data frame comprises an encrypted timer value, e.g. an encrypted timestamp, associated with the data frame, for instance, a timestamp created during the generation or the transmission of the data frame. The receiver station is further configured to decrypt the encrypted timer value associated with the data frame for obtaining the plaintext timer value and to determine a time-of-flight duration and, thus, a potential propagation delay of the data frame based on the timer value and the synchronized timer.

[0017] In a further possible implementation form, the data frame comprises a header and an encrypted payload, wherein the encrypted payload comprises the encrypted timer value.

[0018] In a further possible implementation form, the timer is the timing synchronization function, TSF, timer.

[0019] In a further possible implementation form, the receiver station is configured to further process the data frame, if the time-of-flight duration of the data frame is smaller than a threshold value.

[0020] In a further possible implementation form, the receiver station is configured to discard the data frame, if the time-of-flight duration of the data frame is equal to or larger than a threshold value.

[0021] In a further possible implementation form, the receiver station is further configured to inform the transmitter station that the data frame has been potentially relayed and / or tampered with by an attacker, if the time-of-flight duration of the data frame is equal to or larger than the threshold value. In a further possible implementation form, the wireless communication network is a Wi-Fi network.

[0022] In a further possible implementation form, the receiver station is an access point, AP, or a non-AP station.

[0023] According to a fourth aspect a method of operating a receiver station for a wireless communication network is provided. The method comprises the steps of receiving successively a plurality of beacon frames from a transmitter station of the wireless communication network; synchronizing a timer based on information included in each beacon frame for obtaining a synchronized timer; receiving a data frame from the transmitter station, wherein the data frame comprises an encrypted timer value associated with the data frame; decrypting the encrypted timer value associated with the data frame for obtaining the plaintext timer value; and determining a time-of-flight duration of the data frame based on the timer value and the synchronized timer.

[0024] The method according to the fourth aspect of the present disclosure can be performed by the receiver station according to the third aspect of the present disclosure. Thus, further features of the method according to the fourth aspect of the present disclosure result directly from the functionality of the receiver station according to the third aspect of the present disclosure as well as its different implementation forms described above and below.

[0025] According to a fifth aspect a computer program product is provided, comprising program code which causes a computer or a processor to perform the method according to the second aspect or the method according to the fourth aspect, when the program code is executed by the computer or the processor.

[0026] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

[0028] Fig. l is a schematic diagram showing a Wi-Fi network, including a transmitter station according to an embodiment in the form of an access point, AP, and a receiver station according to an embodiment in the form of a non-AP station as well as a man-in-the-middle, MitM, device trying to perform a MitM attack;

[0029] Figs. 2a and 2b show the communication of between a transmitter station according to an embodiment in the form of an AP and a receiver station according to an embodiment in the form of a non-AP station directly (figure 2a) and via a man-in-the-middle, MitM, device between the AP and the non-AP station (figure 2b);

[0030] Fig. 3 is a schematic diagram illustrating a data frame transmitted by a transmitter station according to an embodiment to a receiver station according to an embodiment;

[0031] Fig. 4 is a schematic diagram illustrating the processing flow and the resulting delay in a man- in-the-middle device for handling a frame transmitted by a transmitter station according to an embodiment to a receiver station according to an embodiment;

[0032] Fig. 5 is a table illustrating a data packet delay analysis while relayed by a man-in-the-middle, MitM, device;

[0033] Fig. 6 is a flow diagram illustrating the handling of a data packet by a receiver station according to an embodiment received from a transmitter station according to an embodiment;

[0034] Fig. 7 is a schematic diagram illustrating the processing flow implemented by a transmitter station according to an embodiment for generating a data packet;

[0035] Fig. 8 shows a flow diagram illustrating steps of a method of operating a transmitter station according to an embodiment; and

[0036] Fig. 9 shows a flow diagram illustrating steps of a method of operating a receiver station according to an embodiment. In the following, identical reference signs refer to identical or at least functionally equivalent features.

[0037] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

[0039] For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically noted otherwise.

[0040] Figure 1 shows an exemplary wireless communication network 100, in particular a Wi-Fi network 100 including an access point, AP, 120 and a non-AP station 110 in the form of, for instance, a smartphone 110 as an example for a plurality of non-AP stations which may be associated and communicate with the AP 120. In an embodiment, the wireless communication network 100 is a WLAN in accordance with the IEEE 802.11 framework of standards (also referred to as a Wi-Fi network 100). As illustrated in figure 1, the non-AP station 110 comprises processing circuitry 111 and a communication interface 113, in particular a wireless communication interface 113 in accordance with the IEEE 802.11 framework of standards for communicating with the AP 120. The processing circuitry 111 of the non-AP station 110 may be implemented in hardware and / or software and may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. The non-AP station 110 may further comprise a memory 115 configured to store executable program code which, when executed by the processing circuitry 111, causes the non-AP station 110 to perform the functions and methods described herein.

[0041] Likewise, the AP 120 illustrated in figure 1 comprises processing circuitry 121 and a communication interface 123, in particular a wireless communication interface 123 in accordance with the IEEE 802.11 framework of standards for communication with the non- AP station 110. The processing circuitry 121 of the AP 120 may be implemented in hardware and / or software and may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. As illustrated in figure 1, the AP 120 may further comprise a memory 125 configured to store executable program code which, when executed by the processing circuitry 121, causes the AP 120 to perform the functions and methods described herein.

[0042] The AP 120 and the non-AP station 110 exchange a plurality of beacon frames 140 and a plurality of data frames 150 (also referred to as data packets 150) via a channel 125. In an embodiment, the AP 120 may be a multi-link device, MLD, AP 120 and the non-AP station 110 may be an MLD station 110 configured to communicate via a plurality of channels, i.e. links with each other.

[0043] Figure 1 further shows a man-in-the-middle, MitM, device 130. The MitM device 130 may be operated by an adversary or attacker trying to intercept the communication between the AP 120 and the non-AP station 110 via the channels 126a, b. More specifically, the MitM device 130 may use two different channels 126a and 126b for simultaneously communicating with both the AP 120 and the non-AP station 110. The AP 120 and the non-AP station 110 may remain unaware of such an MitM attack since their original connection via the channel 125 (which may define a current security association) is not disturbed by the MitM device 130.

[0044] A malicious MitM device 130 may send, for instance, its own beacon frames to the non-AP station 110 with the MAC address of the AP 120 or alternatively forward the beacon frames from the AP 120 For a MitM attack a malicious MitM device 130 with a dual interface setup may clone the targets, i.e. the AP 120 and the non-AP station 110 on different channels, for instance, the channels 126a, b. The rogue AP implemented by the malicious MitM device 130 sends a Channel Switch Announcement (CSA) to the non-AP station 110 using a spoof beacon or action frame or jam the channel and force the non-AP station 110 to scan for a new channel. Moreover, the rogue AP implemented by the malicious MitM device 130 advertises beacons on the rogue channel, i.e. the channel 126b. The non-AP station 110 changes the channel and “connects” to the rogue AP implemented by the malicious MitM device 130. As will be appreciated, there is no new connection flow, i.e. the non-AP station 110 changes the channel and simply continues the data traffic with the AP 120 via the new channels 126a, b and the malicious MitM device 130. The malicious MitM device 130, in turn, implements a rogue non-AP station “connected” to the AP 120, i.e. replacing the non-AP station 110. The rogue non-AP station implemented by the malicious MitM device 130 may the software / firmware and set a fake association to the AP 120, such that the rogue non-AP station implemented by the malicious MitM device 130 will send ACKs when it receives unicast frames from the AP 120.

[0045] As will be described in more detail in the following, the AP 120 and the non-AP stations 110 according to embodiments disclosed herein are configured to detect such an MC-MitM attack and perform suitable countermeasures. Embodiments disclosed herein make use of a time measurement of a frame, i.e. packet transmitted from the AP 120 to the non-AP station 110. These embodiments are based on the finding that the time a frame, i.e. packet propagates from the AP 110 via a relay, such as the MitM device 130, to the non-AP station 110 is significantly higher than the time a frame, i.e. packet propagates from AP 120 directly to the non-AP station 110, as illustrated in figures 2a and 2b.

[0046] In the following embodiments of the AP 120 and the non-AP station 110 will be described for a scenario, where the AP 120 is the transmitter station, while the non-AP station 110 is the receiver station. The person skilled in the art, however, will appreciate that these embodiments may also apply to scenarios, wherein the non-AP station 110 is the transmitter station and the AP 120 is the receiver station.

[0047] As will be described in more detail below, the AP 120 is configured to broadcast successively a plurality of beacon frames 140 to one or more receiver stations, including the non-AP station 110 of the wireless communication network 100, wherein each beacon frame 140 comprises information for synchronizing a timer 122b (illustrated in figure 7) of the non-AP station 110 with a timer of the AP 120. In an embodiment, both the AP 120 and the non-AP station 110 may implement, for instance, a timing synchronization function, TSF, timer 122b. In an embodiment, the information for synchronizing the timer of the non-AP station 110 with the timer 122b of the AP 120 may include a current value of the timer 122b indicating, for instance, the time when the respective beacon frame 140 was generated or transmitted by the AP 120.

[0048] The AP 120 is further configured to send a plurality of data frames 150 to the non-AP station 110, wherein, as illustrated in figure 3, each data frame 150 comprises an encrypted timer value 150c* associated with the data frame 150. As illustrated in figure 3, the encrypted timer value 150c* may be part of an encrypted payload 150b* of the data frame 150, which may further include a non-encrypted header 150a. As already described above, the timer value 150c (illustrated in figure 7) may be a TSF timer value 150c indicating, for instance, the time when the respective data frame 150 was generated or transmitted by the AP 120. In an embodiment, the AP 120 is configured to generate the encrypted payload 150b* including the encrypted timer value 150c* based on one or more cryptographic keys negotiated during the association of the non-AP station 110 with the AP 120 or derived therefrom.

[0049] In an embodiment, the AP 120 and the non-AP station may comprise a TSF timer 122b implemented as a running counter of, for instance, 8 Bytes, incremented with a 1 microsecond resolution. In an embodiment, the AP 120 is configured to advertise its current TSF timer value on each beacon frame 140 with a period of about 100ms. As already described above, the non-AP station 110 is configured to synchronize its own TSF timer based on the TSF timer value advertised by the AP 120. In an embodiment, the non-AP station 110 may use the TSF timer as part of a power save wake up clock.

[0050] As already described above, for each beacon frame 140 received from the AP 120 the non-AP station 110 is configured to synchronize its TSF timer based on the information, e.g. the current TSF timer value of the AP 120, included in the beacon frame 140. Once the non-AP station 110 receives a data frame, such as the data frame 150 illustrated in figure 3, from AP 120, the non-AP station 110 is configured to decrypt the encrypted timer value 150c* associated with the data frame 150 for obtaining the timer value 150c and to determine a time- of- flight, TOF, duration of the data frame 150 based on the timer value 150c and its synchronized timer 122b, for instance, by taking the difference between the timer value 150c and its synchronized timer 122b.

[0051] Figure 4 is a schematic diagram illustrating the processing flow and the resulting delay in the MC-MitM device 130 for handling a frame transmitted by the AP 120 according to an embodiment to the non-AP station 110 according to an embodiment. As illustrated in figure 4, for performing an MC-MitM attack the MitM device 130 may implement two Wi-Fi cards A and B, which may be a built-in card integrated into the device and another card, such as a plug-and-play wireless card. As further illustrated, for routing and relaying a packet from the AP 120 to the non-AP station 110 the packet has to be processed by a PHY layer 131a and a MAC layer 131b of the Wi-Fi card A, a bridge 132 of the MitM device 130 and a MAC layer 133b and a PHY layer 133a of the Wi-Fi card B, which will take a significantly large amount of time.

[0052] Figure 5 is a table illustrating a data packet delay analysis, which shows that even with a maximum time drift between the AP 120 and the non-AP station 110, an MitM attack by a malicious MitM device 130 can still be easily detected by the AP 120 and the non-AP station 110, as will be described in more detail in the following. Typical drift times for the AP 120 and the non-AP station 110 in the form of, for instance a laptop 110, may be ±20ppm and ±100ppm, respectively. The drift time may be estimated in the following way:

[0053] PPM * time interval = drift time

[0054] PPM, relative part: 120PPM = 0.000 J 2

[0055] Drift Time (the total drift should be no more than half of the MitM delay analysis(24 microseconds in SDR)

[0056] 24 / 2 = 12 microseconds

[0057] 0.00012 * time interval = 0.012 milliseconds (12 microsecond) time interval = 100 milliseconds

[0058] The maximum time-of-flight (TOF) from the AP 120 to the non-AP station 110 may be estimated as: propagation delay(nanosecond) + maximum drift time (12 microsecond) == 13 microseconds

[0059] The minimum TOF (SDR) between the AP 120, the MitM device 130 and the non-AP station 110 may be estimated as: propagation delay(nanosecond) + minimum drift time (0 microsecond) + MitM delay (24 microsecond) == 25 microseconds

[0060] Thus, even with a timer drift of 12 microseconds, a relayed packet may be identified.

[0061] Figure 6 is a flow diagram illustrating the handling of a data packet 150 by the non-AP station 110 according to an embodiment. In a step 601 of figure 6 the non-AP station 110 receives a data packet 150 either directly from the AP 120 or via the MitM device 130. In step 603 the non-AP station 603 is configured to check whether the time the last beacon frame has been received is smaller than the maximum allowed time from the last beacon. Step 603 allows to make sure that the time drift from the last beacon is not in the same order of the minimum delay in the MitM device 130 (for instance, a typical beacon interval may be 100 ms, as used in this example, or larger). If this is not the case, the non-AP station 110 may ignore the MitM detection flow and pass the data packet to the network (see 604). Otherwise, the non-AP station 110 determines in step 605 of figure 6 the TOF of the packet based on the decrypted timer value in the way described above. If the TOF determined in step 6 is within acceptable ranges, the non-AP station 110 will accept and further process the packet (see steps 607 and 609 of figure 6). Otherwise, the non-AP station 110 has detected a potential MitM attack (see step 608 of figure 6) and perform suitable counter measures.

[0062] Figure 7 illustrates the processing flow at the transmitter station, for instance, the AP 120. In a first stage a Wi-Fi driver 122a of a host 121a implemented by the AP 120 holds a SW descriptor that includes pointers to both the payload 150b and the Wi-Fi header 150a, as generated by the Wi-Fi driver 122a. In a further stage the Wi-Fi driver 122a passes the Tx descriptor to the firmware (FW) 121b. When the MAC layer wins the transmission opportunity (TxOP) is prepares the packet 150 for transmission in real time. To this end, the FW 121b reads the TSF counter value, i.e. the TSF timer value 150c from the MAC HW TSF counter block 122b and arranges the TSF timer value 150c at the head of the packet payload 150b. The enhanced packet payload 150b (including the TSF timer value 150c) is injected into the MAC HW encryption block 124, which generates the encrypted packed payload including the encrypted TSF timer value 150c. To this output of the MAC HW encryption block 124 the Wi-Fi header 150a is added. The complete bitstream PPDU is passed to the PHY layer 121 d for transmission to the receiver station, for instance, the non-AP station 110.

[0063] Figure 8 shows a flow diagram illustrating steps of a method 800 for operating a Wi-Fi transmitter station, such as the non-AP station 110 or the AP 120, for communication with at least one Wi-Fi receiver station, such as the AP 120 or the non-AP station 110. The method 800 comprises a step 801 of broadcasting successively a plurality of beacon frames to one or more receiver stations, such as the non-AP station 110 of the wireless communication network 100, wherein each beacon frame 140 comprises information for synchronizing a timer of the non-AP station 110. Moreover, the method 800 comprises a step 803 of sending a data frame 150 (also referred to as data packet 150) to the one or more receiver stations, including the non-AP station 110, wherein the data frame 150 comprises an encrypted timer value 150c* associated with the data frame 150.

[0064] As the method 800 can be implemented by the AP 120 or the non-AP station 110, further features of the method 800 result directly from the functionality of the AP 120 or the non-AP station 110 as well as its different embodiments described above and below.

[0065] Figure 9 shows a flow diagram illustrating steps of a method 900 for operating a receiver station, such as the non-AP station 110, in a wireless communication network 100. The method 900 comprises a step 901 of receiving successively a plurality of beacon frames 140 from a transmitter station, such as the AP 120, of the wireless communication network 100. Moreover, the method 900 comprises a step 903 of synchronizing a timer based on information included in each beacon frame 140 for obtaining a synchronized timer. The method 900 further includes a step 905 of receiving a data frame 150 from the transmitter station, such as the AP 120, wherein the data frame 150 comprises an encrypted timer value 150c* associated with the data frame 150. Moreover, the method 900 comprises a step 907 of decrypting the encrypted timer value 150c* associated with the data frame 150 for obtaining the timer value 150c. The method 900 further comprises a step 909 of determining a time-of- flight duration of the data frame 150 based on the timer value 150c and the synchronized timer, e.g. by taking the difference between the timer value 150c and the synchronized timer of the non-AP station 110.

[0066] As the method 900 can be implemented by the AP 120 or the non-AP station 110, further features of the method 900 result directly from the functionality of the AP 120 or the non-AP station 110 as well as its different embodiments described above and below.

[0067] The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

[0068] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

[0069] The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

[0070] In addition, functional units in the embodiments of the invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

CLAIMS1. A transmitter station (110; 120) for a wireless communication network (100), wherein the transmitter station (110; 120) is configured to: broadcast successively a plurality of beacon frames (140) to one or more receiver stations (120; 110) of the wireless communication network (100), wherein each beacon frame (140) comprises information for synchronizing a timer (122b); and send a data frame (150) to the one or more receiver stations (120; 110), wherein the data frame (150) comprises an encrypted timer value (150c*) associated with the data frame (150).

2. The transmitter station (110; 120) of claim 1, wherein the data frame (150) comprises a header (150a) and an encrypted payload (150b*), wherein the encrypted payload (150b*) comprises the encrypted timer value (150c*).

3. The transmitter station (110; 120) of claim 1 or 2, wherein the timer (122b) is a timing synchronization function, TSF, timer (122b).

4. The transmitter station (110; 120) of any one of the preceding claims, wherein the transmitter station (110; 120) is further configured to receive from the one or more of the plurality of receiver stations (120; 110) an indication that the data frame (150) has been potentially relayed and / or tampered with.

5. The transmitter station (110; 120) of any one of the preceding claims, wherein the transmitter station (110; 120) is a multi-link transmitter station (110; 120) configured to communicate via a plurality of links with the one or more receiver stations (120; 110) of the wireless communication network (100).

6. The transmitter station (110; 120) of any one of the preceding claims, wherein the wireless communication network (100) is a Wi-Fi network (100).

7. The transmitter station (110; 120) of any one of the preceding claims, wherein the transmitter station (110; 120) is an access point, AP, (110) or a non-AP station (120).

8. A method (800) for operating a transmitter station (110; 120) in a wireless communication network (100), wherein the method (800) comprises: broadcasting (801) successively a plurality of beacon frames (140) to one or more receiver stations (120; 110) of the wireless communication network (100), wherein each beacon frame (140) comprises information for synchronizing a timer (122b); and sending (803) a data frame (150) to the one or more receiver stations (120; 110), wherein the data frame (150) comprises an encrypted timer value (150c*) associated with the data frame (150).

9. A receiver station (120; 110) for a wireless communication network (100), wherein the receiver station (120; 110) is configured to: receive successively a plurality of beacon frames (140) from a transmitter station (110; 120) of the wireless communication network (100); synchronize a timer (122b) based on information included in each beacon frame (140) for obtaining a synchronized timer (122b); receive a data frame (150) from the transmitter station (110; 120), wherein the data frame (150) comprises an encrypted timer value (150c*) associated with the data frame (150); decrypt the encrypted timer value (150c*) associated with the data frame (150) for obtaining the timer value (150c); and determine a time-of-flight duration of the data frame (150) based on the timer value (150c) and the synchronized timer (122b).

10. The receiver station (120; 110) of claim 9, wherein the data frame (140) comprises a header (150a) and an encrypted payload (150b*), wherein the encrypted payload (150b*) comprises the encrypted timer value (150c*).

11. The receiver station (120; 110) of claim 9 or 10, wherein the timer (122b) is the timing synchronization function, TSF, timer (122b).

12. The receiver station (120; 110) of any one of claims 9 to 11, wherein the receiver station (120; 110) is configured to further process the data frame (150), if the time-of-fhght duration of the data frame (150) is smaller than a threshold value.

13. The receiver station (120; 110) of any one of claims 9 to 12, wherein the receiver station (120; 110) is configured to discard the data frame (150), if the time-of-fhght duration of the data frame (150) is equal to or larger than a threshold value.

14. The receiver station (120; 110) of claim 13, wherein the receiver station (120; 110) is further configured to inform the transmitter station (110; 120) that the data frame (150) has been potentially relayed and / or tampered with, if the time-of-fhght duration of the data frame (150) is equal to or larger than the threshold value.

15. The receiver station (120; 110) of any one of claims 9 to 14, wherein the wireless communication network (100) is a Wi-Fi network (100).

16. The receiver station (120; 110) of any one of claims 9 to 15, wherein the receiver station is an access point, AP, (110) or a non-AP station (120).

17. A method (900) of operating a receiver station (120; 110) for a wireless communication network (100), wherein the method (900) comprises: receiving (901) successively a plurality of beacon frames (140) from a transmitter station (110; 120) of the wireless communication network (100); synchronizing (903) a timer (122b) based on information included in each beacon frame (140) for obtaining a synchronized timer (122b); receiving (905) a data frame (150) from the transmitter station (110; 120), wherein the data frame (150) comprises an encrypted timer value (150c*) associated with the data frame (150);decrypting (907) the encrypted timer value (150c*) associated with the data frame (150) for obtaining the timer value (150c); and determining (909) a time-of-fhght duration of the data frame (150) based on the timer value (150c) and the synchronized timer (122b).

18. A computer program product comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the method (800) of claim 8 or the method (900) claim 17 when the program code is executed by the computer or the processor.

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