Channel-based secret key sharing

Abstract

Some embodiments in the present disclosure relate to generating a shared secret key for frequency division duplex communication. A first bit sequence is transmitted from a first wireless device over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key. From the second wireless device, the first wireless device receives a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band. The channel-affected second bit sequence is based on the public key. The channel-affected second bit sequence is transmitted over the first frequency band to the second wireless device. From the second wireless device, the first wireless device receives a channel-affected transmission of the first bit sequence over the second frequency band. The first wireless device obtains the shared secret key based on the channel-affected transmission of the first bit sequence

Description

[0001] Channel-based Secret Key Sharing

[0002] The present disclosure relates to encrypting of bit sequences. In particular, the present disclosure provides methods and apparatuses for generating a shared secret key for encryption of said bit sequences.

[0003] BACKGROUND

[0004] Wireless communication has been advancing over several decades now. Exemplary notable standards organizations include the 3rd Generation Partnership Project (3GPP) and IEEE 802.11 , commonly referred to as Wi-Fi.

[0005] Wireless communication systems may be vulnerable to eavesdropping attacks due to their broadcast feature. For wireless transmissions, eavesdropping of transmitted information may be avoided by encrypting said information. An encryption process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor.

[0006] SUMMARY

[0007] The present invention relates to methods and apparatuses for generating a shared secret key.

[0008] The invention is defined by the scope of independent claims. Some of the advantageous embodiments are provided in the dependent claims.

[0009] According to an embodiment, a method is provided for generating a shared secret key for frequency division duplex (FDD) communication for a first wireless device, the method comprising: transmitting a first bit sequence over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key, and the public key is a predetermined bit sequence; receiving, from the second wireless device, a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band, and the channel- affected second bit sequence is based on the public key; transmitting the channel-affected second bit sequence over the first frequency band to the second wireless device; receiving, from the second wireless device, a channel-affected transmission of the first bit sequence over the second frequency band; and obtaining the shared secret key based on the channel- affected transmission of the first bit sequence.

[0010] According to an embodiment, a method is provided for generating a shared secret key for frequency division duplex (FDD) communication for a second wireless device, comprising: transmitting a second bit sequence over a second frequency band of a wireless channel to a first wireless device, wherein the second bit sequence is based on a public key, and the public key is a predetermined bit sequence; receiving, from the first wireless device, a channel- affected first bit sequence over a first frequency band of the wireless channel, wherein the first frequency band is different from the second frequency band, and the channel-affected first bit sequence is based on the public key; transmitting the channel-affected first bit sequence over the second frequency band to the first wireless device; receiving, from the first wireless device, a channel-affected transmission of the second bit sequence over the first frequency band; and obtaining the shared secret key based on the channel-affected transmission of the second bit sequence.

[0011] According to an embodiment, a wireless device is provided for generating a shared secret key for frequency division duplex (FDD) communication for said wireless device, the wireless device being a first wireless device, comprising: processing circuitry configured to transmit a first bit sequence over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key, and the public key is a predetermined bit sequence; receive, from the second wireless device, a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band, and the channel-affected second bit sequence is based on the public key; transmit the channel-affected second bit sequence over the first frequency band to the second wireless device; receive, from the second wireless device, a channel-affected transmission of the first bit sequence over the second frequency band; obtain the shared secret key based on the channel-affected transmission of the first bit sequence.

[0012] According to an embodiment, a wireless device is provided for generating a shared secret key for frequency division duplex (FDD) communication for said wireless device, the wireless device being a second wireless device, comprising: processing circuitry configured to transmit a second bit sequence over a second frequency band of a wireless channel to a first wireless device, wherein the second bit sequence is based on a public key, and the public key is a predetermined bit sequence; receive, from the first wireless device, a channel-affected first bit sequence over a first frequency band of the wireless channel, wherein the first frequency band is different from the second frequency band, and the channel-affected first bit sequence is based on the public key; transmit the channel-affected first bit sequence over the second frequency band to the first wireless device; receive, from the first wireless device, a channel- affected transmission of the second bit sequence over the first frequency band; obtain the shared secret key based on the channel-affected transmission of the second bit sequence.

[0013] These and other features and characteristics of the presently disclosed subject matter, as well as the methods of operation and functions of the related elements of structures and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the disclosed subject matter. As used in the specification and the claims, the singular form of “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0014] BRIEF DESCRIPTION OF DRAWINGS

[0015] An understanding of the nature and advantages of various embodiments may be realized by reference to the following figures.

[0016] Fig. 1 is a block diagram illustrating a basic communication system;

[0017] Fig. 2 illustrates exemplarily communication in a Frequency Division Duplex (FDD) system;

[0018] Fig. 3 is a schematic drawing illustrating the obtaining of a shared secret key for a first and a second wireless device,

[0019] Fig. 4 is a schematic drawing illustrating the obtaining of a shared secret key for a first and a second wireless device according to a first exemplary implementation,

[0020] Fig. 5 is a schematic drawing illustrating the obtaining of a shared secret key for a first and a second wireless device according to a second exemplary implementation,

[0021] Fig. 6 is a schematic drawing illustrating the obtaining of a shared secret key for a first and a second wireless device according to a third exemplary implementation,

[0022] Fig. 7 is an exemplary flowchart for the obtaining of a shared secret key; Fig. 8 is an exemplary flowchart for the transmitting of an encrypted bit sequence;

[0023] Fig. 9 is an exemplary flowchart for the receiving of an encrypted bit sequence;

[0024] Fig. 10 is a block diagram illustrating an exemplary apparatus for obtaining a shard secret key;

[0025] Fig. 11 is a block diagram illustrating an exemplary memory for an apparatus obtaining a shard secret key.

[0026] DETAILED DESCRIPTION

[0027] For purposes of the description hereinafter, the terms “end,” “upper,” “lower,” “right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” “lateral,” “longitudinal,” and derivatives thereof shall relate to the disclosed subject matter as it is oriented in the drawing figures. However, it is to be understood that the disclosed subject matter may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments or aspects of the disclosed subject matter. Hence, specific dimensions and other physical characteristics related to the embodiments or aspects disclosed herein are not to be considered as limiting unless otherwise indicated.

[0028] No aspect, component, element, structure, act, step, function, instruction, and / or the like used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” are intended to include one or more items and may be used interchangeably with “one or more” and “at least one.” Furthermore, as used herein, the term “set” is intended to include one or more items (e.g., related items, unrelated items, a combination of related and unrelated items, and / or the like) and may be used interchangeably with “one or more” or “at least one.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based at least partially on” unless explicitly stated otherwise.

[0029] Fig. 1 illustrates an exemplary wireless system WiS in which Tx represents a transmitter and Rx represents a receiver of the wireless signal. The transmitter Tx is capable of transmitting a signal to the receiver Rx or to a group of receivers or to broadcast a signal over an interface Itf. The interface may be any wireless interface. The interface may be specified by means of resources, which can be used for the transmission and reception by the transmitter Tx and the receiver Rx. Such resources may be defined in one or more (or all) of the time domain, frequency domain, code domain, and space domain. There may be separate devices including the functionality of the Rx and Tx, respectively. The transmitter Tx and receiver Rx may be implemented in any device such as a base station (eNB, AP) or terminal (UE, STA), or in any other entity of the wireless system WiS. A device such as a base station, access point, or terminal may implement both Rx and Tx. It is noted that in general, the “transmitter” and “receiver” may be also both integrated into the same device. In other words, the devices Tx and Rx in Fig. 1 may respectively also include the functionality of the Rx and Tx, respectively.

[0030] The present disclosure is not limited to any particular transmitter Tx, receiver Rx and / or interface Itf implementation. However, it may be applied readily to some existing communication systems as well as to the extensions of such systems, or to new communication systems. Exemplary existing communication systems may be, for instance the 5G New Radio (NR) in its current or future releases, and / or the IEEE 802.11 based systems such as the recently studied IEEE 802.11 be or the like. The wireless signal is not necessarily a communication signal in the sense that it does not necessarily carry out human or machine communication. It may be, in particular, a sensing signal such as a radar signal or sounding a signal or any other kind of wireless signal from a wireless device such as, for example, some signal reporting (sensing) results to another device(s).

[0031] The present disclosure is also applicable to other communication technologies such as 3G, communication technologies under long-term evolution (LTE) / LTE Unlicensed (LTE-U) or future communication technologies such as 6G standards or other future standards.

[0032] In general, the described implementations may be implemented in any device, system or network that is capable of transmitting and receiving RF signals according to any of the wireless communication standards, including any of the IEEE 802.11 standards, the Bluetooth standard, code division multiple access (CDMA), wideband CDMA (W-CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), Terrestrial Trunked Radio (TETRA), Global System for Mobile communications (GSM), General Packet Radio Service (GPRS), Enhanced Data GSM Environment (EDGE), Evolution Data Optimized (EV- DO), 1xEV-DO, EV-DO Rev A, EV-DO Rev B, High Speed Packet Access (HSPA), High Speed Downlink Packet Access (HSDPA), High Speed Uplink PacketAccess (HSUPA), Evolved High Speed Packet Access (HSPA+), Long Term Evolution (LTE), or other known signals that are used to communicate within a wireless, cellular or loT network, such as a system utilizing 3G, 4G, or 5G, or further implementations thereof, technology. OFDM transmission

[0033] Orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G / 5G mobile communications.

[0034] Rather than transmit a high-rate stream of data with a single subcarrier, OFDM makes use of a large number of closely spaced orthogonal subcarriers that are transmitted in parallel. Each subcarrier is modulated with a conventional digital modulation scheme (such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 16QAM (Quadrature Modulation), etc.) at low symbol rate.

[0035] For example, an obtained bit sequence may be modulated by a BPSK modulation, i.e. bit 0 may be represented as -1 and bit 1 represented as +1 . Such a representation may be assigned to multiple OFDM symbols, where data subcarriers from -26 to -1 and +1 to +26 are used. A cyclic prefix may be added. Each OFDM symbol is convolved with a 1O-tap Rayleigh fading channel. By concatenation of multiple symbols a long transmit sequence is formed.

[0036] A received vector is then grouped into multiple symbols. The cyclic prefix is removed. The time domain received symbol is converted into the frequency domain. The received symbols are demodulated and converted into bits.

[0037] Based on an estimation of the transmission channel, the received signal may be equalized to remove channel effects.

[0038] TDD and FDD communication

[0039] Time Division Duplex or Duplexing (TDD) is a communication technique where uplink and downlink communications are sent on the same frequency band at different time slots. Uplink and downlink communication are separated by guard times (period) to avoid overlaps.

[0040] Frequency Division Duplex or Duplexing (FDD) is a duplexing technique that employs separate frequency bands for uplink and downlink communication. For example, 2G, 3G and 4G networks like GSM, UMTS and LTE have adopted it as their primary duplex scheme. In FDD communication, the available frequency spectrum is split into two parts. One part of the frequency spectrum is reserved for communicating from the mobile phone to the radio network (uplink). In contrast, the other part of the spectrum is used for communicating from the mobile radio network to the phone (downlink). In FDD communication, some part of the overall frequency spectrum may be used as a guard band so that the uplink and downlink frequency bands have a clear separation to avoid any potential interference. FDD offers a continuous flow of data in both uplink and downlink directions.

[0041] For example, the primary frequency band for the original GSM networks is from 890 MHz to 960 MHz. In this band, the first part from 890 MHz to 915 MHz is reserved for uplink communication, and the second part from 935 MHz to 960 MHz is dedicated to downlink communication. A 20 MHz band (from 915 MHz to 935 MHz) is used as a guard band between these two bands.

[0042] Fig. 2 exemplarily illustrates a FDD communication, in which a first wireless device 210 transmits over a first frequency band 230 to a second wireless device 220. In addition, the second wireless device 220 transmits over a second frequency band 240 to the first wireless device 210.

[0043] Encryption

[0044] In order to secure communication systems, encryption methods are applied to the information to be transmitted. For example, symmetric cipher and secret keys effectively secure confidential data exchange from being intercepted.

[0045] Such symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both the encryption of plaintext and the decryption of ciphertext. The keys may be identical, or there may be a simple transformation to go between the two keys. The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link.

[0046] A shared secret is a piece of data, known only to the parties involved, in a secure communication, such as a key of a symmetric cryptosystem. The shared secret may be a password, a passphrase, a big number, or an array of randomly chosen bytes.

[0047] The shared secret may be shared beforehand between the communicating parties, in which case it is also be called a pre-shared key, or it may created at the start of the communication session by using a key-agreement protocol. For example, Alice wants to secretly transmit the plain text message m to Bob using the encryption cipher Ek, where k is a cryptographic key. Alice first transforms the plaintext into ciphertext c, in order to securely send the message to Bob, as follows: c = Ek(j ).

[0048] In a symmetric-key system, Bob knows Alice's encryption key. Once the message is encrypted, Alice may safely transmit it to Bob. In order to read Alice's message, Bob decrypts the ciphertext using E)”1which is known as the decryption cipher Dk.

[0049] Generation of a shared secret key

[0050] Security and power consumption are some of the concerns in many wireless networks as part of the fast progress in various applications over these networks. Several security algorithms may be implemented in different network layers, which, however may lead to hardware complexity issues. Said issues may be related to the battery consumption of remotely connected devices as well as the power consumption of fixed nodes, which prompt environmental consideration through the network design and operation to minimize energy consumption.

[0051] For example, physical (PHY) layer-based algorithms may be used for establishing security. In the PHY layer security, wireless channel characteristics are used for establishing shared secret keys based on the features of the wireless channel.

[0052] The characteristics of a wireless channel may be used as a (common) random resource for users to generate a secret key.

[0053] For example in TDD, the random and reciprocity features of fading channel may be used in a shared secret key generation.

[0054] In the FDD communication, uplink and downlink frequency bands are non-overlapping. An exemplary illustration for the generation of a shared secret key is given in Fig. 3. A first wireless device 310, herein also referred to as Alice, and / or a second wireless device 311 , herein also referred to as Bob, generate a shared secret key based on a known bit sequence b. Such known bit sequence may be called public key. An obtaining of a shared secret key is exemparily illustrated in the flowchart in Fig. 7. In order to generate a shared secret key for FDD communication for a first wireless device 310, a first bit sequence 320 is transmitted S710 in a first frequency band 350 of a wireless channel to a second wireless device 311. The first bit sequence 320 is based on a public key. The first bit sequence 320 may be different from the public key. The public key is a predetermined bit sequence. Such public key may be predetermined based on a (e.g. received) configuration of the wireless device, a standard, or the like. For example, such a public key bit sequence may have a length of 2048 bits. The public key is a bit sequence that is publicly known by a plurality of wireless devices, the plurality of wireless devices includes the first wireless device and the second wireless device.

[0055] For example, training bits such as pilots in OFDM may be used as a public key. When using training bits for shared secret key generation, there may be no need to send new (additional) bits for the secret key generation.

[0056] For example, the first bit sequence 320 may be the public key bit sequence or may be obtained by the first wireless device 310 from the public key bit sequence. Such an obtaining may be based on a (predetermined) bit-operation, a configuration of the first wireless device, a standard, or the like.

[0057] The first wireless device 310 receives S720 from the second wireless device 311 , a channel- affected second bit sequence 330 in a second frequency band 360 of the wireless channel. The second frequency band 360 is different from the first frequency band 350. In other words, the first frequency band 350 and the second frequency band are non-overlapping 360. The channel-affected second bit sequence 330 is based on the public key.

[0058] For example, the channel-affected second bit sequence 330 is obtained by transmitting a second bit sequence 321 from the second wireless device 311 to the first wireless device 310. The second bit sequence 321 may be based on the public key. The second bit sequence 321 may be different from the public key.

[0059] For example, the second bit sequence 321 may be the public key bit sequence or may be obtained by the second wireless device 311 from the public key bit sequence. Such an obtaining may be based on a (predetermined) bit-operation, a configuration of the wireless device, a standard, or the like.

[0060] In other words, in the receiving of the channel-affected second bit-sequence 330, the second bit sequence 321 is affected by the transmission over the second frequency band 360 of the wireless channel. Such a receiving of the channel-affected second bit-sequence may be a reception in an OFDM transmission scheme, which may not include channel equalization. The effects of the channel are still included in the received bit sequence. Such a transmission scheme is exemplarily described in section OFDM transmission.

[0061] Moreover, the channel-affected second bit sequence 330 is transmitted S730 over the first frequency band 351 to the second wireless device 311. In other words, the received channel- affected second bit sequence 330 is re-transmitted to the second wireless device 311 .

[0062] Furthermore, a channel-affected transmission of the first bit sequence 340 is received S740 from the second wireless device 311 over the second frequency band 361. The channel- affected transmission of the first bit sequence 340 is based on the first bit sequence 320 and is affected by the transmission over the second frequency band 361 of the wireless channel.

[0063] A shared secret key is obtained S750 based on the channel-affected transmission of the first bit sequence 340. Such a shared secret key is a bit sequence that may be used for encrypting information that is to be shared between the first communication device and the second communication device.

[0064] For example, the shared secret key may be the channel-affected transmission of the first bit sequence 340. For example, the shared secret key may be or may be obtained by the first wireless device 310 from the channel-affected transmission 340 of the first bit sequence. Such an obtaining may be based on a (predetermined) bit-operation, a configuration of the first wireless device 310, a standard, or the like.

[0065] In order to generate a shared secret key for FDD communication for the second wireless device 310, a second bit sequence 321 is transmitted in a second frequency band 360 of a wireless channel to the first wireless device 310. Similarly as for the first bit sequence, the second bit sequence 321 is based on a public key. The second bit sequence 321 may be different from the public key. As mentioned above, the public key is a predetermined (publicly known) bit sequence.

[0066] For example, the second bit sequence 321 may be the public key bit sequence or may be obtained by the second wireless device 311 from the public key bit sequence. Such an obtaining may be based on a (predetermined) bit-operation, a configuration of the first wireless device, a standard, or the like.

[0067] The second wireless device 311 receives from the first wireless device 310, a channel-affected first bit sequence 331 over the first frequency band 350 of the wireless channel. As mentioned above, the first frequency band 350 and the second frequency band are non-overlapping 360.

[0068] The channel-affected first bit sequence 331 is based on the public key.

[0069] For example, the channel-affected first bit sequence 331 is obtained by transmitting the first bit sequence 320 from the first wireless device 310 to second wireless device 311 . The first bit sequence 320 may be based on the public key. The first bit sequence 321 may be different from the public key.

[0070] For example, the first bit sequence 320 may be the public key bit sequence or may be obtained by the first wireless device 310 from the public key bit sequence. Such an obtaining may be based on a (predetermined) bit-operation, a configuration of the wireless device, a standard, or the like.

[0071] In other words, in the receiving of the channel-affected first bit-sequence 331 , the first bit sequence 320 is affected by the transmission over the first frequency band 350 of the wireless channel.

[0072] Such a receiving of the channel-affected first bit-sequence may be a reception in an OFDM transmission scheme, which may not include channel equalization. The effects of the channel are still included in the received bit sequence.

[0073] Moreover, the channel-affected first bit sequence 331 is transmitted over the second frequency band 361 to the first wireless device 310. In other words, the received channel-affected second bit sequence 331 is re-transmitted to the first wireless device 310.

[0074] Furthermore, a channel-affected transmission of the second bit sequence 341 is received from the first wireless device 310 over the first frequency band 390. The channel-affected transmission of the second bit sequence 341 is based on the second bit sequence 321 and is affected by the transmission over the first frequency band 351 of the wireless channel.

[0075] A shared secret key is obtained based on the channel-affected transmission of the second bit sequence 341. Such a shared secret key is a bit sequence that may be used for encrypting information that is to be shared between the first communication device and the second communication device.

[0076] For example, the shared secret key may be the channel-affected transmission of the second bit sequence 341 . For example, the shared secret key may be obtained by the second wireless device 311 from the channel-affected transmission of the second bit sequence 341. Such an obtaining may be based on a (predetermined) bit-operation, a configuration of the second wireless device 311 , a standard, or the like. In the exemplarily illustration of Fig. 3, Alice transmits the bit sequence b in a first frequency band of a wireless channel to Bob. Bob receives channel-affected bits h b. Bob may transmit the channel-affected bits h b in a second frequency band of the wireless channel to Alice. Alice may receive channel-affected bits h2h1b. In addition, Bob transmits the (known) bit sequence b over the second frequency band of the wireless channel to Alice. Alice receives channel- affected bits h2b. Alice may transmit the channel-affected bits h2b over the first frequency band of the wireless channel to Bob. Bob may receive channel-affected bits h h2b. However, the present invention is not limited to the first bit sequence and / or the second bit sequence being identical to the public key.

[0077] Moreover, a bit operation may be performed on a bit sequence related to the first bit sequence. Said bit operation may be performed on a bit sequence related to the second bit sequence. In other words, the bit operation on a bit sequence related to a first bit sequence is a same bit operation as the bit operation on a bit sequence related to a second bit sequence. The bit operations may be performed by the first wireless device.

[0078] A bit sequence related to the first bit sequence may be, for example, the first bit sequence 320, the channel-affected transmission of the first bit-sequence or any other bit sequence that is based on the first bit sequence. A bit sequence related to the second bit sequence may be, for example, the second bit sequence 320, the channel-affected second bit-sequence or any other bit sequence that is based on the second bit sequence.

[0079] The bit operation may be based on a private key of the first wireless device. The private key is a bit sequence that is known only by the first wireless device. For example, such a private key may be randomly generated.

[0080] For example, such a bit operation may be a bit shifting, a permutation of bits, or the like, or any other mathematical operation may be performed. For example, the direction of a bit shifting operation may be chosen randomly. For example, the number of bits to be shifted in such a bit shift operation may be chosen randomly.

[0081] In an exemplary implementation, the bit operation may be a bit shifting of a predetermined number of bits in a predetermined direction. In said exemplary implementation, the predetermined number of bits and the predetermined direction may be determined based on the private key sequence of the first wireless device. For example, as mentioned above, such a determination may correspond to a random generation of a number of bits and / or a direction of the bit shifting. For example, for each generation of a shared secret key, a respective different private key may be used by the first wireless device and / or the second wireless device. In other words, a same bit operation is performed on a bit sequence related to the first bit sequence as well as on a bit sequence related to a second bit sequence.

[0082] Similarly as for the first wireless device 310, such a bit operation may be performed by the second wireless device 311. In particular, a bit operation may be performed by the second wireless device 311 on a bit sequence related to the second bit sequence. In addition, said bit operation may be performed by the second wireless device 311 on a bit sequence related to the first bit sequence.

[0083] Such bit-operations are exemplarily shown in Fig. 4 as well as in Fig. 5. In Fig. 4, Alice (first wireless device 310) and Bob (second wireless device 311) obtain the same bit sequence 420, which is publicly known by other users. This bit sequence is the so-called public key. Alice sends the known bits to Bob over h (the first frequency band 350), and Bob obtains an h affected bit sequence 431 , while Bob sends the known bits 421 to Alice over h2(the second frequency band 360). Alice obtains an h2affected bit sequence 430 when receiving the transmission of the known bits 421 from Bob. Here, the classical OFDM transmission may be used without performing a channel equalization over the transmission. Such a transmission scheme is exemplarily described in section OFDM transmission. Since the public keys are known by everybody, the channel estimation may be simplified in the exemplary implementation according to Fig. 4.

[0084] Alice and Bob may demodulate the respective received channel affected bits. Moreover, Alice and Bob perform bit shifting 470 or 481 , respectively, to the received bits based on their respective private keys. In the example of Fig. 4, the private keys may indicate how many steps the bits are to be shifted in which direction. For example, Alice private key is indicates a shift of 2 and a direction right to left. In this example, Alice shifts the last two bits to the beginning of the bit sequence. I n this example, Bob shifts the first three bits to the end of the bit sequence.

[0085] Furthermore, Alice transmits h2affected bits to Bob over hi 351 , and Bob obtains h h2affected bit sequence 441 , while Bob sends h affected bits to Alice over h2361 , and Alice obtains h2h affected bit sequence 440. Here, the classical OFDM transmission may be used without performing a channel equalization over the transmission. For example, the channel between Alice and Bob may be assumed to be correlated for known bits and h2affected bits transmission. Also, this may be the case for known bits and h affected bits transmission.

[0086] Alice performs bit shifting 471 to received bits 440 and Bob performs bit shifting 481 to received bits 441 , based on their respective private keys, thereby obtaining a shared secret key 442 and 444, respectively. In other words, in Fig. 4, the first wireless device 310 (Alice) performs a bit-operation 470 on a bit sequence related to the second bit sequence, which is the channel-affected second bit sequence 430 in Fig. 4. The bit operation of the first wireless device 310 in Fig. 4 corresponds to shifting two bits in a direction from right to left. A same bit operation 471 is performed on a bit sequence related to the first bit sequence 440, which is the received channel-affected transmission of the first bit sequence in Fig. 4.

[0087] Similarly, the second wireless device 311 (Bob) performs a bit-operation 480 on a bit sequence related to the first bit sequence, which is the channel-affected first bit sequence 431 in Fig. 4. The bit operation of the second wireless device 311 in Fig. 4 corresponds to shifting three bits in a direction from left to right. A same bit operation 481 is performed on a bit sequence related to the second bit sequence, which is the received channel-affected transmission of the second bit sequence 441 in the example of Fig. 4.

[0088] So, in the exemplary implementation of Fig. 4, the first wireless device 310 as well as the second wireless device 311 may perform a bit operation on a bit sequence related to the first bit sequence based on their respective private keys. Moreover, the first wireless device 310 as well as the second wireless device 311 may perform the respective same bit operation on a bit sequence related to the second bit sequence.

[0089] As already exemplarily mentioned above for Fig. 4, such a bit operation on a bit sequence related to a second bit sequence 470 may be performed on the channel-affected second bit sequence 440 before said transmitting of the channel-affected second bit sequence to the second wireless device 311. In other words, a bit-operation may be performed on the channel- affected bit sequence 430 that is received from the second wireless device 311 . Said channel affected bit sequence 430 is based on the second bit sequence 421 that is transmitted by the second wireless device 311 and is affected by the wireless channel due to the transmission over the second frequency band 360.

[0090] Similarly as described above for the first wireless device 310, in the second wireless device 311 , a bit operation on a bit sequence related to the first bit sequence 480 may be performed on the channel-affected first bit sequence 431 before transmitting the channel-affected first bit sequence to the first wireless device 310.

[0091] Moreover, in a first exemplary implementation for the first wireless device, as exemplarily depicted in Fig. 4, the bit operation on a bit sequence related to a first bit sequence 471 may be performed on the channel-affected transmission of the first bit sequence 440 before said obtaining of the shared secret key. In the example of Fig. 4, the bit operation on a bit sequence related to a first bit sequence 471 is a same bit operation as the bit operation on a bit sequence related to a second bit sequence 470, as already mentioned above.

[0092] Further, as shown in Fig. 4, the channel-affected transmission of the first bit sequence 440, which is received by the first wireless device 310, may be further based on a bit operation 480 that is based on a private key bit sequence of the second wireless device 311.

[0093] Similarly as described above for the first wireless device 310, in the second wireless device 311 , the bit operation on a bit sequence related to a second bit sequence 481 may be performed on the channel-affected transmission of the second bit sequence 441 before said obtaining of the shared secret key.

[0094] Similarly as described above for the first wireless device 310, in the second wireless device 311 , the channel-affected transmission of the second bit sequence 441 , which is received by the second wireless device 311 , may be further based on a bit operation 470 that is based on a private key bit sequence of the first wireless device 310.

[0095] In other words, in the example in Fig. 4, the first wireless device 310 may perform a bit operation on a bit sequence related to a first bit sequence 471. The so obtained bit sequence is transmitted from the first wireless device 310 to the second wireless device 311. Similarly, the second wireless device 311 may perform a bit operation on a bit sequence related to a first bit sequence 480. The so obtained bit sequence is transmitted from the second wireless device 311 to the first wireless device 310.

[0096] The example in Fig. 5 is similar to Fig. 4. In particular, Alice transmits a first bit sequence 520 to Bob over h (the first frequency band 350), and Bob obtains an h affected bit sequence 523, while Bob transmits a second bit sequence 521 to Alice over h2(the second frequency band 360). Alice obtains an h2affected bit sequence 522 when receiving the transmission from Bob. Analogous as in Fig. 4, Alice and Bob perform bit shifting 571 or 581 , respectively, to the received bits based on their respective private keys. Furthermore, Alice transmits h2affected bits 530 to Bob over h 351 , and Bob obtains h h2affected bit sequence 541 , while Bob transmits h affected bits 531 to Alice over h2361 , and Alice obtains an h2h affected bit sequence 540. Alice as well as Bob may obtain a shared secret key based on bit sequences 540 or 541 , respectively.

[0097] In the following, the differences with respect to the exemplary implementation in Fig. 4 will be explained in detail. In Fig. 5, the bit operation on a bit sequence related to the first bit sequence is performed by the first wireless device before transmitting the first bit sequence to the second wireless device. Similarly, the bit operation on the bit sequence related to the second bit sequence is performed by the second wireless device before transmitting the second bit sequence to the first wireless device.

[0098] In a second exemplary implementation, as exemplarily depicted in Fig. 5, the bit operation on a bit sequence related to the first bit sequence 570 may be performed on a bit sequence that is based on the public key, thereby the first bit-sequence 520 is obtained.

[0099] In other words, the bit operation 570 may be performed by the first wireless 310 device before transmitting the first bit sequence to the second wireless device 311.

[0100] In the exemplary implementation according to Fig. 5, it may be more difficult for an eavesdropper to estimate the channel. Due to performing a bit operation on the known bits before transmitting, since an eavesdropper may not know the bits that are sent. On the other hand, the legitimate user may not be affected, because it does not require estimating the channel. The disadvantage of this algorithm is that shifted bits will be publicly known when the second time Alice and Bob send their bits to each other. Therefore, the exemplary implementation according to Fig. 5 uses the bit operation to increase the difficulty in estimating the channel for eavesdroppers.

[0101] Moreover, as shown in Fig. 5, the channel-affected second bit sequence 522 may be further based on a bit operation 580 that is based on a private key bit sequence of the second wireless device 311.

[0102] Similarly as described above for the first wireless device 310, the bit operation on a bit sequence related to the second bit sequence 580 is performed on a bit sequence that is based on the public key, thereby the second bit-sequence 521 is obtained.

[0103] Similarly as described above for the first wireless device 310, the channel-affected first bit sequence 523, which is received by the second wireless device, may be further based on a bit operation 570 that is based on a private key bit sequence of the second wireless device 311 . Said bit operation 570 may be performed by the first wireless device 310 before transmitting the first bit sequence 520 to the second wireless device 310.

[0104] A third exemplary implementation is exemplarily depicted in Fig. 6. The example in Fig. 6 is similar to Fig. 4. In particular, Alice (first wireless device 310) and Bob (second wireless device 311) obtain the same bit sequence 620 and 621 , which is publicly known by other users. Alice sends the known bits to Bob over h (the first frequency band 350), and Bob obtains an h affected bit sequence, while Bob sends the known bits 621 to Alice over h2(the second frequency band 360). Alice obtains an h2affected bit sequence when receiving the transmission of the known bits 421 from Bob. Analogous as in Fig. 4, Alice and Bob perform bit shifting 670 or 680, respectively, to the received bits based on their respective private keys. Furthermore, Alice transmits h2affected bits to Bob over hi 351 , and Bob obtains h h2affected bit sequence, while Bob sends h affected bits to Alice over h2361 , and Alice obtains h2h affected bit sequence. Alice performs bit shifting 671 to received bits 640 and Bob performs bit shifting 681 to received bits 641 , based on their respective private keys, thereby obtaining a shared secret key 642 and 644, respectively.

[0105] In the following, the differences with respect to the exemplary implementation in Fig. 4 will be explained in detail. The transmitting of the channel-affected second bit sequence 630 may include adding noise 690 to said channel-affected second bit sequence 630 before said transmitting of the channel-affected second bit sequence to the second wireless device 311. Such noise 690 may be for example, artificial noise, linear impairments, null-space noise, or the like.

[0106] Moreover, as shown in Fig. 6, the channel-affected transmission of the first bit sequence 640 may be further based on noise 691 added to a channel affected first bit sequence before transmitting the channel-affected first bit sequence 631 to the first wireless device 310.

[0107] For the second wireless device 311 , the transmitting of the channel-affected first bit sequence 631 may include adding noise 691 to said channel-affected first bit sequence 631 before said transmitting of the channel-affected first bit sequence to the first wireless device 310.

[0108] Moreover, as shown in Fig. 6, for the second wireless device, the channel-affected transmission of the second bit sequence 641 may be further based on noise 690 added to a channel affected second bit sequence before transmitting the channel-affected second bit sequence 630 from the first wireless device to the second wireless device 310.

[0109] In other words, the first wireless device 310 may add artificial noise 690 to a bit sequence related to the second bit sequence before transmitting said obtained bit sequence 630 to the second wireless device 311. In addition or alternatively, the second wireless device 311 may add artificial noise 691 to a bit sequence related to the first bit sequence before transmitting said obtained bit sequence 631 to the first wireless device 310.

[0110] For example, the adding of noise according to the third exemplary implementation may be performed in addition to the first exemplary implementation as well as in addition to the second exemplary implementation.

[0111] In addition or alternatively to any of the first, the second and / or the third exemplary implementation, noise may be added to a bit sequence related to the first bit sequence in order to obtain the first bit sequence 420, 520, 620 in any of the first, the second and the third exemplary implementation before the transmitting of said first bit sequence 420, 520, 620 to the second wireless device 311. Analogously, noise may be added to a bit sequence related to the second bit sequence in order to obtain the second bit sequence 421 , 521 , 621 in any of the first, the second and the third exemplary implementation before the transmitting of said second bit sequence 421 , 521 , 621 to the first wireless device 310.

[0112] Analogously as in the third exemplary implementation, such noise may be for example, artificial noise, linear impairments, null-space noise, or the like.

[0113] In particular, in Fig. 6, Alice has an exemplary bit sequence 1 0 1 1 0 0 1 1 0 1 , and before sending it to Bob, a bit shifting-based on her secret key (e.g., two bits, right to left) may be performed. At this time, an eavesdropper may capture the signal in the air and also obtain 1 0 1 0 0 1 1 0 1 for trying to estimate the secret key. For this purpose, several methods, such as brute forcing, may be used, wherein every possibility may be tested in order to obtain Alice’s private key. To increase security, artificial noise can be added after the bit shifting. Then, the noise-added bits can be sent. Here, even if the eavesdropper tries to estimate secret keys, not only the changed bits will be wrongly demodulated for the eavesdropper, but also the remaining bits may be wrong since the eavesdropper may not learn the key. On the other hand, in the case of Bob, only noise-affected bits may be wrongly demodulated.

[0114] Adding noise may further increase security, as for an eavesdropper trying to estimate transmitted bits, the changed bits will be wrongly demodulated. This increases the difficulty in estimating a shared bit sequence and / or the difficulty in estimating the bit operation based on the private key.

[0115] Based on the environment and application, artificial noise may be increased or decreased adaptively. When the artificial noise is high, it may result in a decreased bit error rate (BER) performance, but it may be more secure. On the other hand, when the artificial noise is low, it may result in an increased BER performance, but security may be reduced.

[0116] Encryption using a shared secret key

[0117] A shared secret key, which is obtained as described above in section Generation of a shared secret key, may be used in encrypting a bit sequence for transmission.

[0118] An encryption is exemplarily depicted in the flowchart in Fig. 8. Such encrypting of a bit sequence for a first wireless device may comprise obtaining S810 a shared secret key as described above in section Generation of a shared secret ey for said first wireless device and a second wireless device.

[0119] An encrypted bit sequence may be obtained S820 based on the bit sequence and the bits of the shared secret key. For example, the bits of the bit sequence may be summed with the bits of the shared secret key. However, the present invention is not limited to summing the bits. In general, any other suitable bit operation that is based on the shared secret key may be applied to the bits of the bit sequence.

[0120] The encrypted bit sequence may be transmitted S830 to the second wireless device.

[0121] The first wireless device may decrypt an encrypted bit sequence received from the second wireless device. Such a decrypting is exemplarily depicted in the flowchart in Fig. 9. In particular, the first wireless device may obtain S910 a shared secret key as described above in section Generation of a shared secret key. Moreover, the first wireless device may receive S920 an encrypted bit sequence from the second wireless device, wherein the encrypted bit sequence is based on the bits of the shared secret key. A decrypted bit sequence may be obtained S930 based on the received encrypted bit sequence and the bits of the shared secret key.

[0122] The second wireless device may also obtain the shared secret key as described above in section Generation of a shared secret key. Moreover, the second wireless device may encrypt and / or decrypt a bit sequence analogously as explained above for the first wireless device.

[0123] For example, by using the shared secret key 0 1 0 0 1 1 0 1 1 of the example in Fig. 4, Alice may wish to transmit the following bits to Bob: 0 1 0 1 1 1 0 0 0.

[0124] Therefore, instead of sending 0 1 0 1 1 1 0 0 0 to Bob, Alice, for example, sums secret key bits with 0 1 0 1 1 1 0 0 0 and so obtains 0 0 0 1 0 0 0 1 1. Then Alice may sends this encrypted bit sequence to Bob. Since Bob also has the secret key, Bob may obtain the data by again summing secret bits with the received bits.

[0125] Implementations in software and hardware

[0126] It is noted that although embodiments and examples of the present disclosure were provided in terms of a method above, the corresponding devices providing the functionality described by the methods are also provided. Moreover, it is noted that any of the steps described above may be included as code instructions in a program, which may be executed by one or more processors. For example, a device is provided for transmitting and or receiving signals. The device may comprise a processing circuitry, which is configured to perform steps according to any of the above-mentioned methods. The device may further comprise a transceiver for performing wireless reception and / or transmission. Alternatively to the transceiver, the processing circuitry may control an external transceiver to perform wireless reception and / or transmission. The processing circuity may receive signals from a transceiver and / or may transmit signals to a transceiver. In other words, the processing circuitry may instruct the transceiver to receive and / or transmit signals.

[0127] Fig. 10 shows an exemplary device 1000, which may implement some embodiments of the present disclosure. Such a device may include memory 1010, processing circuitry 1020, a wireless transceiver 1040, and possibly a user interface 1030. The device may be, for instance a (part of) a base station or a terminal / STA, or any other device, which receives wireless signals.

[0128] The memory 1010 may store the program, which may be executed by the processing circuitry 1020 to perform steps of any of the above-mentioned methods. The processing circuitry may comprise one or more processors and / or other dedicated or programmable hardware. The wireless transceiver 1040 may be configured to receive and / or transmit wireless signals. The transceiver 1040 may include also baseband processing which may detect, decode and interpret the data according to some standard or predefined convention. The device 1000 may further include a user interface 1030 for displaying messages or status of the device, or the like and / or for receiving a user’s input. A bus 1001 interconnects the memory, the processing circuitry, the wireless transceiver, and the user interface.

[0129] Fig. 11 shows an example of the memory 1010 in a wireless device 1000 for obtaining a shared secret key, including a module 1110 for performing a bit operation based on a private key, and module 1120 for obtaining a shared secret key, and a module 1130 for controlling the transceiver 1540 to receive and / or transmit bit sequences. These modules 1110-1130 may be fetched from the memory and executed by the processing circuitry 1020.

[0130] Fig. 11 provides an exemplary implementation. A memory 1010 may include a subset of the described modules or additional modules to provide instructions to perform any of the methods described in the sections above.

[0131] For example, the exemplary device 1000 may be configured to for generating a shared secret key for frequency division duplex (FDD) communication for said wireless device, the wireless device being a first wireless device. In particular, the processing circuitry 1020 of said first wireless device may be configured to transmit a first bit sequence over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key, and the public key is a predetermined bit sequence; receive, from the second wireless device, a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band, and the channel-affected second bit sequence is based on the public key; transmit the channel- affected second bit sequence over the first frequency band to the second wireless device; receive, from the second wireless device, a channel-affected transmission of the first bit sequence over the second frequency band; and obtain the shared secret key based on the channel-affected transmission of the first bit sequence.

[0132] For example, the exemplary device 1000 may be configured to for generating a shared secret key for frequency division duplex (FDD) communication for said wireless device, the wireless device being a second wireless device. In particular, the processing circuitry 1020 of said first wireless device may be configured to transmit a second bit sequence over a second frequency band of a wireless channel to a first wireless device, wherein the second bit sequence is based on a public key, and the public key is a predetermined bit sequence; receive, from the first wireless device, a channel-affected first bit sequence over a first frequency band of the wireless channel, wherein the first frequency band is different from the second frequency band, and the channel-affected first bit sequence is based on the public key; transmit the channel-affected first bit sequence over the second frequency band to the first wireless device; receive, from the first wireless device, a channel-affected transmission of the second bit sequence over the first frequency band; and obtain the shared secret key based on the channel-affected transmission of the second bit sequence.

[0133] The exemplary device 1000 may be configured to perform any of the method described above in sections Generation of a shared secret ey and Encryption using a shared secret key.

[0134] The above examples are not to limit the present disclosure. There are many modifications and configurations, which may be used in addition or alternatively, as will be briefly described below. This present disclosure can be used in any kind of device that is receiving signals over a wireless channel.

[0135] The methodologies described herein may be implemented by various means depending upon the application. For example, these methodologies may be implemented in hardware, operation system, firmware, software, or any combination of two or all of them. For a hardware implementation, any processing circuitry 620 may be used, which may include one or more processors. For example, the hardware may include one or more of application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, any electronic devices, or other electronic circuitry units or elements designed to perform the functions described above.

[0136] If implemented as program code, the functions performed by the transmitting apparatus (device) may be stored as one or more instructions or code on a non-transitory computer readable storage medium such as the memory 610 or any other type of storage. The computer- readable media includes physical computer storage media, which may be any available medium that can be accessed by the computer, or, in general by the processing circuitry 620. Such computer-readable media may comprise RAM, ROM, EEPROM, optical disk storage, magnetic disk storage, semiconductor storage, or other storage devices. Some particular and non-limiting examples include compact disc (CD), CD-ROM, laser disc, optical disc, digital versatile disc (DVD), Blu-ray (BD) disc or the like. Combinations of different storage media are also possible - in other words, distributed and heterogeneous storage may be employed.

[0137] The embodiments and exemplary implementations mentioned above show some non-limiting examples. It is understood that various modifications may be made without departing from the claimed subject matter. For example, modifications may be made to adapt the examples to new systems and scenarios without departing from the central concept described herein.

[0138] Selected embodiments and examples

[0139] Summarizing, some embodiments in the present disclosure relate to generating a shared secret key for frequency division duplex communication. A first bit sequence is transmitted from a first wireless device over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key. From the second wireless device, the first wireless device receives a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band. The channel-affected second bit sequence is based on the public key. The channel-affected second bit sequence is transmitted over the first frequency band to the second wireless device. From the second wireless device, the first wireless device receives a channel-affected transmission of the first bit sequence over the second frequency band. The first wireless device obtains the shared secret key based on the channel-affected transmission of the first bit sequence

[0140] According to an embodiment, a method is provided for generating a shared secret key for frequency division duplex (FDD) communication for a first wireless device, the method comprising: transmitting a first bit sequence over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key, and the public key is a predetermined bit sequence; receiving, from the second wireless device, a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band, and the channel- affected second bit sequence is based on the public key; transmitting the channel-affected second bit sequence over the first frequency band to the second wireless device; receiving, from the second wireless device, a channel-affected transmission of the first bit sequence over the second frequency band; and obtaining the shared secret key based on the channel- affected transmission of the first bit sequence.

[0141] For example, the method is further comprising performing a bit operation on a bit sequence related to the first bit sequence, and performing the bit operation on a bit sequence related to a second bit sequence, wherein the bit operation is based on a private key bit sequence of the first wireless device.

[0142] In an exemplary implementation, the bit operation on a bit sequence related to a second bit sequence is performed on the channel-affected second bit sequence before said transmitting of the channel-affected second bit sequence to the second wireless device.

[0143] For example, the bit operation on a bit sequence related to a first bit sequence is performed on the channel-affected transmission of the first bit sequence before said obtaining of the shared secret key.

[0144] In an exemplary implementation, the performing the bit operation on a bit sequence related to a first bit sequence is performed on a bit sequence that is based on the public key, thereby obtaining the first bit-sequence.

[0145] For example, the bit operation is a bit shifting of a predetermined number of bits in a predetermined direction, wherein the predetermined number of bits and the predetermined direction are determined based on the private key sequence of the first wireless device.

[0146] In an exemplary implementation, the transmitting of the channel-affected second bit sequence includes adding noise to said channel-affected second bit sequence before said transmitting of the channel-affected second bit sequence to the second wireless device.

[0147] For example, the channel-affected transmission of the first bit sequence is further based on a bit operation that is based on a private key bit sequence of the second wireless device.

[0148] In an exemplary implementation, the channel-affected second bit sequence is further based on a bit operation that is based on a private key bit sequence of the second wireless device. For example, the channel-affected transmission of the first bit sequence is further based on noise added to a channel-affected first bit sequence before a transmitting of the channel- affected first bit sequence to the first wireless device.

[0149] In an exemplary implementation, a method is provided for encrypting a bit sequence for a first wireless device, the method comprising obtaining a shared secret key for said first wireless device according to any of the methods for the first wireless device above and a second wireless device, obtaining an encrypted bit sequence based on the bit sequence and the bits of the shared secret key, transmitting the encrypted bit sequence to the second wireless device.

[0150] In an exemplary implementation, a method is provided for decrypting a bit sequence for a first wireless device, the method comprising: obtaining a shared secret key for said first wireless device according to any of the methods for the first wireless device above and a second wireless device, receiving an encrypted bit sequence from the second wireless device, wherein the encrypted bit sequence is based on the bits of the shared secret key, obtaining a decrypted bit sequence based on the received encrypted bit sequence and the bits of the shared secret key.

[0151] According to an embodiment, a method is provided for generating a shared secret key for frequency division duplex (FDD) communication for a second wireless device, comprising: transmitting a second bit sequence over a second frequency band of a wireless channel to a first wireless device, wherein the second bit sequence is based on a public key, and the public key is a predetermined bit sequence; receiving, from the first wireless device, a channel- affected first bit sequence over a first frequency band of the wireless channel, wherein the first frequency band is different from the second frequency band, and the channel-affected first bit sequence is based on the public key; transmitting the channel-affected first bit sequence over the second frequency band to the first wireless device; receiving, from the first wireless device, a channel-affected transmission of the second bit sequence over the first frequency band; and obtaining the shared secret key based on the channel-affected transmission of the second bit sequence.

[0152] For example, the method further comprises performing a bit operation on a bit sequence related to the second bit sequence, and performing the bit operation on a bit sequence related to a first bit sequence, wherein the bit operation is based on a private key bit sequence of the second wireless device. In an exemplary implementation, the bit operation on a bit sequence related to a first bit sequence is performed on the channel-affected first bit sequence before said transmitting of the channel-affected first bit sequence to the first wireless device.

[0153] For example, the bit operation on a bit sequence related to a second bit sequence is performed on the channel-affected transmission of the second bit sequence before said obtaining of the shared secret key.

[0154] In an exemplary implementation, the performing the bit operation on a bit sequence related to a second bit sequence is performed on a bit sequence that is based on the public key, thereby obtaining the second bit-sequence.

[0155] For example, the bit operation is a bit shifting of a predetermined number of bits in a predetermined direction, wherein the predetermined number of bits and the predetermined direction are determined based on the private key sequence of the second wireless device.

[0156] In an exemplary implementation, the transmitting of the channel-affected first bit sequence includes adding noise to said channel-affected first bit sequence before said transmitting of the channel-affected first bit sequence to the first wireless device.

[0157] For example, the channel-affected transmission of the second bit sequence is further based on a bit operation that is based on a private key bit sequence of the first wireless device.

[0158] In an exemplary implementation, the channel-affected first bit sequence is further based on a bit operation that is based on a private key bit sequence of the first wireless device.

[0159] For example, the channel-affected transmission of the second bit sequence is further based on noise added to a channel-affected second bit sequence before a transmitting of the channel- affected second bit sequence to the second wireless device.

[0160] In an exemplary implementation, a method is provided for encrypting a bit sequence for a second wireless device, the method comprising obtaining a shared secret key for said second wireless device according to any of the methods for the second wireless device above and a first wireless device, obtaining an encrypted bit sequence based on the bit sequence and the bits of the shared secret key, transmitting the encrypted bit sequence to the first wireless device.

[0161] In an exemplary implementation, a method is provided for decrypting a bit sequence for a second wireless device, the method comprising obtaining a shared secret key for said second wireless device according to any of the methods for the second wireless device above and a first wireless device, receiving an encrypted bit sequence from the first wireless device, wherein the encrypted bit sequence is based on the bits of the shared secret key, obtaining a decrypted bit sequence based on the received encrypted bit sequence and the bits of the shared secret key.

[0162] In an exemplary implementation, a computer program is provided, the computer program stored in a non-transitory, computer-readable medium, the program comprising code instructions which, when executed on one or more processors, cause the one or more processors to perform steps of any of the methods above.

[0163] According to an embodiment, a wireless device is provided for generating a shared secret key for frequency division duplex (FDD) communication for said wireless device, the wireless device being a first wireless device, comprising: processing circuitry configured to transmit a first bit sequence over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key, and the public key is a predetermined bit sequence; receive, from the second wireless device, a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band, and the channel-affected second bit sequence is based on the public key; transmit the channel-affected second bit sequence over the first frequency band to the second wireless device; receive, from the second wireless device, a channel-affected transmission of the first bit sequence over the second frequency band; obtain the shared secret key based on the channel-affected transmission of the first bit sequence.

[0164] For example, the processing circuitry is further configured to perform a bit operation on a bit sequence related to the first bit sequence, and perform the bit operation on a bit sequence related to a second bit sequence, wherein the bit operation is based on a private key bit sequence of the first wireless device.

[0165] In an exemplary implementation, the processing circuitry is further configured to perform the bit operation on a bit sequence related to a second bit sequence on the channel-affected second bit sequence before said transmitting of the channel-affected second bit sequence to the second wireless device.

[0166] For example, the processing circuitry is further configured to perform the bit operation on a bit sequence related to a first bit sequence on the channel-affected transmission of the first bit sequence before said obtaining of the shared secret key. In an exemplary implementation, the processing circuitry is further configured to perform the performing the bit operation on a bit sequence related to a first bit sequence on a bit sequence that is based on the public key, thereby obtaining the first bit-sequence.

[0167] For example, the bit operation is a bit shifting of a predetermined number of bits in a predetermined direction, wherein the predetermined number of bits and the predetermined direction are determined based on the private key sequence of the first wireless device.

[0168] In an exemplary implementation, the processing circuitry is further configured to add noise to said channel-affected second bit sequence before the transmitting of the channel-affected second bit sequence to the second wireless device.

[0169] For example, the channel-affected transmission of the first bit sequence is further based on a bit operation that is based on a private key bit sequence of the second wireless device.

[0170] In an exemplary implementation, the channel-affected second bit sequence is further based on a bit operation that is based on a private key bit sequence of the second wireless device.

[0171] For example, the channel-affected transmission of the first bit sequence is further based on noise added to a channel-affected first bit sequence before a transmitting of the channel- affected first bit sequence to the first wireless device.

[0172] According to an embodiment, a wireless device is provided for generating a shared secret key for frequency division duplex (FDD) communication for said wireless device, the wireless device being a second wireless device, comprising: processing circuitry configured to transmit a second bit sequence over a second frequency band of a wireless channel to a first wireless device, wherein the second bit sequence is based on a public key, and the public key is a predetermined bit sequence; receive, from the first wireless device, a channel-affected first bit sequence over a first frequency band of the wireless channel, wherein the first frequency band is different from the second frequency band, and the channel-affected first bit sequence is based on the public key; transmit the channel-affected first bit sequence over the second frequency band to the first wireless device; receive, from the first wireless device, a channel- affected transmission of the second bit sequence over the first frequency band; obtain the shared secret key based on the channel-affected transmission of the second bit sequence.

[0173] In an exemplary implementation, the processing circuitry is further configured to perform a bit operation on a bit sequence related to the second bit sequence, and perform the bit operation on a bit sequence related to a first bit sequence, wherein the bit operation is based on a private key bit sequence of the second wireless device. 1 For example, the processing circuitry is further configured to perform the bit operation on a bit sequence related to a first bit sequence on the channel-affected first bit sequence before said transmitting of the channel-affected first bit sequence to the first wireless device.

[0174] In an exemplary implementation, the processing circuitry is further configured to perform the bit operation on a bit sequence related to a second bit sequence on the channel-affected transmission of the second bit sequence before said obtaining of the shared secret key.

[0175] For example, the processing circuitry is further configured to perform the performing the bit operation on a bit sequence related to a second bit sequence on a bit sequence that is based on the public key, thereby obtaining the second bit-sequence.

[0176] In an exemplary implementation, the bit operation is a bit shifting of a predetermined number of bits in a predetermined direction, wherein the predetermined number of bits and the predetermined direction are determined based on the private key sequence of the second wireless device.

[0177] For example, the processing circuitry is further configured to add noise to said channel-affected first bit sequence before the transmitting of the channel-affected first bit sequence to the first wireless device.

[0178] In an exemplary implementation, the channel-affected transmission of the second bit sequence is further based on a bit operation that is based on a private key bit sequence of the first wireless device.

[0179] For example, the channel-affected first bit sequence is further based on a bit operation that is based on a private key bit sequence of the first wireless device.

[0180] In an exemplary implementation, the channel-affected transmission of the second bit sequence is further based on noise added to a channel-affected second bit sequence before a transmitting of the channel-affected second bit sequence to the second wireless device.

[0181] According to some embodiments, the processing circuitry and / or the transceiver is embedded in an integrated circuit, IC.

[0182] Any of the apparatuses of the present disclosure may be embodied on an integrated chip.

[0183] Any of the above-mentioned embodiments and exemplary implementations may be combined. Although the disclosed subject matter has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the disclosed subject matter is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the presently disclosed subject matter contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.

Claims

CLAIMS1. A method for generating a shared secret key for frequency division duplex (FDD) communication for a first wireless device, comprising: transmitting a first bit sequence over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key, and the public key is a predetermined bit sequence; receiving, from the second wireless device, a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band, and the channel-affected second bit sequence is based on the public key; transmitting the channel-affected second bit sequence over the first frequency band to the second wireless device; receiving, from the second wireless device, a channel-affected transmission of the first bit sequence over the second frequency band; obtaining the shared secret key based on the channel-affected transmission of the first bit sequence.

2. The method according to claim 1 , further comprising performing a bit operation on a bit sequence related to the first bit sequence, and performing the bit operation on a bit sequence related to a second bit sequence, wherein the bit operation is based on a private key bit sequence of the first wireless device.

3. The method according to claim 2, wherein the bit operation on a bit sequence related to a second bit sequence is performed on the channel-affected second bit sequence before said transmitting of the channel-affected second bit sequence to the second wireless device.

4. The method according to any of claims 2 or 3, wherein the bit operation on a bit sequence related to a first bit sequence is performed on the channel-affected transmission of the first bit sequence before said obtaining of the shared secret key.

5. The method according to any of claims 2 or 3, wherein the performing the bit operation on a bit sequence related to a first bit sequence is performed on a bit sequence that is based on the public key, thereby obtaining the first bit-sequence.

6. The method according to any of claims 2 to 5, wherein the bit operation is a bit shifting of a predetermined number of bits in a predetermined direction, wherein the predetermined number of bits and the predetermined direction are determined based on the private key sequence of the first wireless device.

7. The method according to any of claims 1 to 6, wherein the transmitting of the channel- affected second bit sequence includes adding noise to said channel-affected second bit sequence before said transmitting of the channel-affected second bit sequence to the second wireless device.

8. The method according to any of claims 1 to 7, wherein the channel-affected transmission of the first bit sequence is further based on a bit operation that is based on a private key bit sequence of the second wireless device.

9. The method according to claim 8, wherein the channel-affected second bit sequence is further based on a bit operation that is based on a private key bit sequence of the second wireless device.

10. The method according to any of claims 1 to 9, wherein the channel-affected transmission of the first bit sequence is further based on noise added to a channel- affected first bit sequence before a transmitting of the channel-affected first bit sequence to the first wireless device.

11. A method for encrypting a bit sequence for a first wireless device, the method comprising obtaining a shared secret key according to any of the claims 1 to 10 for said first wireless device and a second wireless device, obtaining an encrypted bit sequence based on the bit sequence and the bits of the shared secret key, transmitting the encrypted bit sequence to the second wireless device.

12. A method for decrypting a bit sequence for a first wireless device, the method comprising obtaining a shared secret key according to any of the claims 1 to 10 for said first wireless device and a second wireless device, receiving an encrypted bit sequence from the second wireless device, wherein the encrypted bit sequence is based on the bits of the shared secret key, obtaining a decrypted bit sequence based on the received encrypted bit sequence and the bits of the shared secret key.

13. A method for generating a shared secret key for frequency division duplex (FDD) communication for a second wireless device, comprising: transmitting a second bit sequence over a second frequency band of a wireless channel to a first wireless device, wherein the second bit sequence is based on a public key, and the public key is a predetermined bit sequence; receiving, from the first wireless device, a channel-affected first bit sequence over a first frequency band of the wireless channel, wherein the first frequency band is different from the second frequency band, and the channel-affected first bit sequence is based on the public key;transmitting the channel-affected first bit sequence over the second frequency band to the first wireless device; receiving, from the first wireless device, a channel-affected transmission of the second bit sequence over the first frequency band; obtaining the shared secret key based on the channel-affected transmission of the second bit sequence.

14. The method according to claim 13, further comprising performing a bit operation on a bit sequence related to the second bit sequence, and performing the bit operation on a bit sequence related to a first bit sequence, wherein the bit operation is based on a private key bit sequence of the second wireless device.

15. The method according to claim 14, wherein the bit operation on a bit sequence related to a first bit sequence is performed on the channel-affected first bit sequence before said transmitting of the channel-affected first bit sequence to the first wireless device.

16. The method according to any of claims 14 or 15, wherein the bit operation on a bit sequence related to a second bit sequence is performed on the channel-affected transmission of the second bit sequence before said obtaining of the shared secret key.

17. The method according to any of claims 14 or 15, wherein the performing the bit operation on a bit sequence related to a second bit sequence is performed on a bit sequence that is based on the public key, thereby obtaining the second bit-sequence.

18. The method according to any of claims 14 to 17, wherein the bit operation is a bit shifting of a predetermined number of bits in a predetermined direction, wherein thepredetermined number of bits and the predetermined direction are determined based on the private key sequence of the second wireless device.

19. The method according to any of claims 13 to 18, wherein the transmitting of the channel-affected first bit sequence includes adding noise to said channel-affected first bit sequence before said transmitting of the channel-affected first bit sequence to the first wireless device.

20. The method according to any of claims 13 to 19, wherein the channel-affected transmission of the second bit sequence is further based on a bit operation that is based on a private key bit sequence of the first wireless device.

21. The method according to claim 21 , wherein the channel-affected first bit sequence is further based on a bit operation that is based on a private key bit sequence of the first wireless device.

22. The method according to any of claims 13 to 21 , wherein the channel-affected transmission of the second bit sequence is further based on noise added to a channel- affected second bit sequence before a transmitting of the channel-affected second bit sequence to the second wireless device.

23. A method for encrypting a bit sequence for a second wireless device, the method comprising obtaining a shared secret key according to any of the claims 13 to 22 for said second wireless device and a first wireless device, obtaining an encrypted bit sequence based on the bit sequence and the bits of the shared secret key, transmitting the encrypted bit sequence to the first wireless device.

24. A method for decrypting a bit sequence for a second wireless device, the method comprising obtaining a shared secret key according to any of the claims 13 to 22 for said second wireless device and a first wireless device, receiving an encrypted bit sequence from the first wireless device, wherein the encrypted bit sequence is based on the bits of the shared secret key, obtaining a decrypted bit sequence based on the received encrypted bit sequence and the bits of the shared secret key.

25. A computer program stored in a non-transitory, computer-readable medium, the program comprising code instructions which, when executed on one or more processors, cause the one or more processors to perform steps of the method according to any of claims 1 to 24.

26. A wireless device for generating a shared secret key for frequency division duplex (FDD) communication for said wireless device, the wireless device being a first wireless device, comprising: processing circuitry configured to transmit a first bit sequence over a first frequency band of a wireless channel to a second wireless device, wherein the first bit sequence is based on a public key, and the public key is a predetermined bit sequence; receive, from the second wireless device, a channel-affected second bit sequence over a second frequency band of the wireless channel, wherein the second frequency band is different from the first frequency band, and the channel-affected second bit sequence is based on the public key; transmit the channel-affected second bit sequence over the first frequency band to the second wireless device;receive, from the second wireless device, a channel-affected transmission of the first bit sequence over the second frequency band; obtain the shared secret key based on the channel-affected transmission of the first bit sequence.

27. The wireless device according to claim 26, wherein the processing circuitry is further configured to perform a bit operation on a bit sequence related to the first bit sequence, and perform the bit operation on a bit sequence related to a second bit sequence, wherein the bit operation is based on a private key bit sequence of the first wireless device.

28. The wireless device according to claim 27, wherein the processing circuitry is further configured to perform the bit operation on a bit sequence related to a second bit sequence on the channel-affected second bit sequence before said transmitting of the channel-affected second bit sequence to the second wireless device.

29. The wireless device according to any of claims 27 or 28, wherein the processing circuitry is further configured to perform the bit operation on a bit sequence related to a first bit sequence on the channel-affected transmission of the first bit sequence before said obtaining of the shared secret key.

30. The wireless device according to any of claims 27 or 28, wherein the processing circuitry is further configured to perform the performing the bit operation on a bit sequence related to a first bit sequence on a bit sequence that is based on the public key, thereby obtaining the first bit-sequence.31 . The wireless device according to any of claims 27 to 30, wherein the bit operation is a bit shifting of a predetermined number of bits in a predetermined direction, wherein the predetermined number of bits and the predetermined direction are determined based on the private key sequence of the first wireless device.

32. The wireless device according to any of claims 26 to 31 , wherein the processing circuitry is further configured to add noise to said channel-affected second bit sequence before the transmitting of the channel-affected second bit sequence to the second wireless device.

33. The wireless device according to any of claims 26 to 32, wherein the channel-affected transmission of the first bit sequence is further based on a bit operation that is based on a private key bit sequence of the second wireless device.

34. The wireless device according to claim 33, wherein the channel-affected second bit sequence is further based on a bit operation that is based on a private key bit sequence of the second wireless device.

35. The wireless device according to any of claims 26 to 34, wherein the channel-affected transmission of the first bit sequence is further based on noise added to a channel- affected first bit sequence before a transmitting of the channel-affected first bit sequence to the first wireless device.

36. A wireless device for generating a shared secret key for frequency division duplex (FDD) communication for said wireless device, the wireless device being a second wireless device, comprising: processing circuitry configured to transmit a second bit sequence over a second frequency band of a wireless channel to a first wireless device, wherein the second bit sequence is based on a public key, and the public key is a predetermined bit sequence;receive, from the first wireless device, a channel-affected first bit sequence over a first frequency band of the wireless channel, wherein the first frequency band is different from the second frequency band, and the channel-affected first bit sequence is based on the public key; transmit the channel-affected first bit sequence over the second frequency band to the first wireless device; receive, from the first wireless device, a channel-affected transmission of the second bit sequence over the first frequency band; obtain the shared secret key based on the channel-affected transmission of the second bit sequence.

37. The wireless device according to claim 36, wherein the processing circuitry is further configured to perform a bit operation on a bit sequence related to the second bit sequence, and perform the bit operation on a bit sequence related to a first bit sequence, wherein the bit operation is based on a private key bit sequence of the second wireless device.

38. The wireless device according to claim 37, wherein the processing circuitry is further configured to perform the bit operation on a bit sequence related to a first bit sequence on the channel-affected first bit sequence before said transmitting of the channel- affected first bit sequence to the first wireless device.

39. The wireless device according to any of claims 37 or 38, wherein the processing circuitry is further configured to perform the bit operation on a bit sequence related to a second bit sequence on the channel-affected transmission of the second bit sequence before said obtaining of the shared secret key.

40. The wireless device according to any of claims 37 or 38, wherein the processing circuitry is further configured to perform the performing the bit operation on a bit sequence related to a second bit sequence on a bit sequence that is based on the public key, thereby obtaining the second bit-sequence.41 . The wireless device according to any of claims 37 to 40, wherein the bit operation is a bit shifting of a predetermined number of bits in a predetermined direction, wherein the predetermined number of bits and the predetermined direction are determined based on the private key sequence of the second wireless device.

42. The wireless device according to any of claims 36 to 41 , wherein the processing circuitry is further configured to add noise to said channel-affected first bit sequence before the transmitting of the channel-affected first bit sequence to the first wireless device.

43. The wireless device according to any of claims 36 to 42, wherein the channel-affected transmission of the second bit sequence is further based on a bit operation that is based on a private key bit sequence of the first wireless device.

44. The wireless device according to claim 43, wherein the channel-affected first bit sequence is further based on a bit operation that is based on a private key bit sequence of the first wireless device.

45. The wireless device according to any of claims 36 to 44, wherein the channel-affected transmission of the second bit sequence is further based on noise added to a channel- affected second bit sequence before a transmitting of the channel-affected second bit sequence to the second wireless device.

Images