Method for establishing a quantum channel via satellite, satellite for establishing a quantum channel, and method for sending a request to establish a quantum channel

Abstract

One object of the invention is a method for distributing a secret key via a quantum channel using a satellite (and an associated architecture) in which the distribution planning is performed in real time by the satellite itself and by the ground quantum communication stations, without the intervention of a mission control center external to the stations. The satellite is autonomous and manages its own resources. In this architecture, the satellite autonomously and independently acquires the information necessary for mission planning from the ground mission control center. [Fig. 3B]

Description

Title of the invention: Method for establishing a quantum channel by satellite, satellite for establishing a quantum channel, and method for sending a request for establishing a quantum channel. Technical field

[0001] The present invention relates to the field of information technology security and more particularly to the field of satellite-based quantum key distribution. This field is called Satellite-Based Quantum Key Distribution (QKD). This field is a subfield of the field of quantum communication satellites. Previous technique

[0002] Quantum satellite communication relies on the transmission of qubits between a satellite, generally the transmitter, and one or two ground-based quantum communication stations, generally the receivers. A qubit is the quantum information carried by a photon. This information is, for example, the polarization state of the photon.

[0003] Quantum communication consists of establishing a quantum communication channel or quantum channel between a transmitter (the satellite) and a receiver (a ground station). The quantum channel consists of a free-space optical link transmitting a sequence of polarized photons (qubits). The quantum channel may also contain auxiliary optical links: a synchronization and clock link to ensure the synchronization of the transmitter and receiver and to temporally identify each polarized photon, and a polarization reference optical link to align the polarization reference frames (axes) of the transmitter and receiver. Figure 1C schematically illustrates a quantum communication channel between a satellite and a ground station; the link (IW>) is the free-space optical link transmitting the qubits.

[0004] Quantum key distribution (QKD) is a cryptographic protocol designed to establish a shared secret between two participants (Alice and Bob) that generates a common cryptographic key. This key is then used by the participants to encrypt their communications using a symmetric encryption algorithm. Satellite-based quantum key distribution uses one or more quantum channels to transmit random qubit sequences between the satellite and ground stations.

[0005] There are two quantum key distribution protocols: the preparation and measurement (P&M) protocol and the quantum entanglement (EB) protocol.

[0006] In the Preparation and Measurement (P&M) protocol, the transmitter (Alice or the satellite) prepares a photon by fixing its polarization state and transmits it. The receiver (Bob or the ground station) measures the photon's state. The transmitter (Alice or the satellite) transmits a random sequence of qubits to the receiver (Bob or the ground station). Due to the protocol, optical link degradation, noise, and the possible presence of an eavesdropper, the sequence detected by Bob is incomplete, lacking, and contains errors. A reconciliation process allows Alice and Bob to agree on a common sequence that will be used to generate the secret key. Figure 1A schematically illustrates the implementation of the Preparation and Measurement protocol between the satellite (Alice) and a quantum communication ground station (Bob) connected by a quantum channel (QC).The exchange of secret keys between the satellite and the ground station requires a single quantum channel. The communication link for reconciliation between the satellite and the ground station is not shown.

[0007] In the quantum entanglement (BE) protocol, a third-party transmitter (the satellite) emits pairs of entangled and polarized photons to two ground stations (Alice and Bob), one photon from each pair to each station. The entanglement property results in Alice and Bob measuring the same polarization state on each photon received from a pair of emitted photons. The random measurement of the entangled photon pairs by Alice and Bob generates a common random sequence. Degradations in the two optical links between the satellite and the two stations, noise, and the possible presence of an eavesdropper alter the random sequence shared by Alice and Bob. A reconciliation process defines a common sequence and generates the secret key. Figure 1B schematically illustrates the implementation of the entanglement protocol between the quantum communication ground station SCQ1 (Alice) and the ground station SCQ2 (Bob).The satellite is the third-party transmitter of the entangled photon pairs, which it transmits to the ground stations SCQ1 (Alice) and SCQ2 (Bob) via two quantum channels (CQ1 & CQ2). The exchange of secret keys between the two stations requires two quantum channels established with the satellite. The communication link for reconciliation between the two ground stations is not shown. For example, this reconciliation link could be a terrestrial link between the two stations or a satellite link via the satellite.

[0008] A satellite secret key distribution system is a quantum communication infrastructure comprising one or more satellites in orbit around the Earth (LEO, MEO, GEO), a set of ground-based quantum communication stations distributed around the globe capable of establishing quantum channels with the one or more satellites exchange random sequences of qubits in the form of polarized photons, and a mission control segment. The control segment includes a mission control center, a satellite control center, and a network of telemetry / command / transmission (TM / TC) stations. This system thus provides a secret key distribution service, according to a preparation and measurement protocol and / or an entanglement protocol.

[0009] The problem is to define the mission planning for each satellite, that is, to define under what conditions a satellite within line of sight of several quantum communication ground stations must choose one or two ground stations with which it will establish a quantum channel. At any given time, there are several quantum communication ground stations within optical line of sight of each satellite. A satellite is equipped with one or more optical terminals capable of establishing a quantum channel with one or more quantum communication ground stations. A quantum channel is a point-to-point optical link in free space; thus, an optical terminal on a satellite can only establish a single quantum channel with a single ground station.

[0010] Furthermore, quantum optical links are blocked by clouds. Therefore, a ground-based quantum communication station located under cloud cover cannot establish a quantum channel with a satellite. Depending on the techniques used to operate the quantum channel, other conditions must be taken into account: the level of atmospheric turbulence above the station, nighttime operation only, the presence of aerosols, etc.

[0011] Figure 2 schematically illustrates the architecture of a prior art satellite-based secret key distribution system. This system comprises the space segment consisting of the satellites, the user segment comprising all the quantum communication ground stations, and the control segment. The control segment is responsible for the management and control of the system and its mission. It includes a mission control center, a satellite control center, and a network of telemetry and remote control (TM / TC) stations with associated links.

[0012] The mission control center develops the satellite mission, that is, the planning for the use of the satellite's resources. A resource is a quantum channel that will be established for a certain time with a ground station. The quantum channel enables the provision of the key distribution service.

[0013] This planning of the allocation of quantum channels to ground stations is done according to: - requests (date and duration) for the establishment of quantum channels with stations to provide the key distribution service, - service level agreements for stations, - the key distribution matrix, that is, for each ground station, the list of other ground stations with which said station exchanges keys, - weather conditions above each station, - the position of the satellite in the orbit allowing the calculation of the dates and durations of visibility of each station.

[0014] The satellite control center develops the satellite mission plan based on the schedule provided by the mission control center and the system and satellite-specific requirements. The TM / TC station network transmits the mission plan to each satellite via a remote control / telemetry channel.

[0015] This architecture requires the existence of several links between the different elements of the system.

[0016] A quantum channel 3 is required between each ground station for quantum communication and the satellite for the exchange of secret keys. In addition, a link 1 between the ground station and the mission control center is required to exchange information such as: the required number and duration of quantum channel 3 establishments, the deadline for establishing the quantum channel, and weather forecasts over the station. However, this link 1 is critical from a security standpoint. An attack on this link could allow the identity of one or more stations to be spoofed and a quantum channel to be established with a rogue station in order, for example, to obtain secret keys or inject false keys.Alternatively, an attack could simply cause a denial of service: if this link is lost, the station(s) concerned can no longer establish a quantum channel.

[0017] Finally, the architecture of [Fig. 2] requires the use of a TM / TC link 2 to program or reprogram the mission of the satellite(s). The performance of the key distribution system depends greatly on the transmission time to each satellite of its mission plan prepared by the mission control center planner.

[0018] For optimal planning, it must be done in near real-time to account for changes in cloud cover over the stations. Therefore, the planner must know the probabilities of clearing or cloud cover over the stations to develop the best mission plan. This mission plan must be transmitted to the satellite via the satellite control center and the TM / TC station network in a near-continuous manner.

[0019] Thus, the TM / TC link must be permanent in order to reprogram the satellites in real time to react to changes in weather conditions. However, apart from the case With satellites in GEO orbit, it is difficult and very expensive to guarantee permanent global coverage of TM / TC signals. This requires, depending on the orbital altitude (MEO, LEO), a more or less dense global network of TM / TC stations to be connected to the satellite control center.

[0020] The invention aims to overcome certain problems of the prior art. To this end, an object of the invention is a method for distributing a secret key via a quantum channel through a satellite (and an associated architecture) in which the planning of the number and duration of quantum channel establishments with ground stations is carried out in real time by the satellite itself and by the ground stations, without the intervention of a mission control center external to the ground stations. The satellite is autonomous and manages its own resources. In this architecture, the satellite autonomously and independently of the ground mission control center acquires the information necessary for mission planning.

[0021] By avoiding the multiplication of TM / TC links for programming or reprogramming the satellite mission and of links between ground stations and the mission control center, the architecture of the invention offers improved security, increased simplicity, and reduced cost compared to the prior art. Summary of the invention

[0022] To this end, an object of the invention is a method for establishing a quantum communication channel via a satellite, the satellite comprising a processing unit in which data associated with a plurality of quantum communication stations are stored, including a position of said ground quantum communication stations, said method comprising the following steps implemented by the processing unit: A. Determine a position for the satellite and then determine a quantum channel establishment zone for the satellite based on said satellite position. B. From the aforementioned position of the aforementioned quantum communication ground stations, determine a subset of quantum communication ground stations consisting of at least one of the quantum communication ground stations located within the aforementioned quantum channel establishment zone C. Identify at least one of the terrestrial quantum communication stations, known as the visible station: - included in said subset, - having issued a request to establish a quantum channel, and - which is within optical line of sight of the satellite, D. Using the aforementioned data, select at least one visible station, called the selected station, with which to establish a quantum channel, then E. Establish a quantum channel between said satellite and the selected station(s).

[0023] According to one embodiment, when there is a number of visible station(s) greater than a number N > 1 of quantum channels available on the satellite, step D includes a substep of prioritizing said requests to establish a quantum channel based on information contained in said data, said information being chosen from the following list: a chronological collection of previously established quantum channel establishments with the stations, a prior agreement to establish a quantum channel with the stations and instructions issued by the mission control center, said selection of the selected station(s) consisting of choosing the N visible station(s) that issued a request to establish a quantum channel with a priority ranked among the first N.Preferably, said information includes an optical visibility duration of the visible stations calculated by the processing unit from said position of said stations, said position of the satellite and a prediction of a satellite trajectory.

[0024] According to one embodiment, step C comprises: - detect a laser signal, known as an optical visibility signal, emitted by at least one quantum communication ground station included in said subset, then - identify this or these quantum communication ground station(s) as visible station(s).

[0025] According to one embodiment, prior to step C, one of the quantum communication ground stations transmits a request to establish a quantum channel to a mission control center and then said mission control center transmits said request to the satellite, and wherein said data includes said request, step C comprising the identification of this quantum communication ground station as a visible station when it is within optical line of sight of the satellite.

[0026] According to one embodiment, the method includes a subsequent step F consisting of transmitting to a mission control center, via a satellite remote control-telemetry channel, a signal representative of the number and durations of establishment of a quantum channel and representative of the quantum communication ground station with which each quantum channel was established.

[0027] According to one embodiment, step A is repeated until said subset of quantum communication ground stations is determined in step B, and wherein steps A and B are repeated until the station(s) visible are identified in step C, and in which, steps A, B and C are repeated until the selected station(s) are selected in step D.

[0028] According to one embodiment, step E consists of exchanging, via quantum channel through said satellite, at least one secret key with the selected station(s).

[0029] Alternatively, according to another embodiment, step E consists of establishing, via said satellite, at least one secret key shared by at least two selected stations.

[0030] Another object of the invention is a method for issuing a request to establish a quantum channel implemented by a processing module of a quantum communication ground station comprising a quantum terminal capable of establishing a quantum channel with the satellite, said method comprising the following steps: I. Identify a need to establish a quantum channel from parameters stored in said processing module, said parameters including a prior agreement to establish a quantum channel with said quantum communication ground station, a chronological record of the number and durations of quantum channel establishments previously established with the station, and a number and durations of quantum channel establishments attributed to said station, II. If a need is identified, identify a satellite in a position suitable for establishing a quantum channel with said quantum communication ground station, and then determine a trajectory prediction for said satellite from said position. III. Based on meteorological data and the aforementioned trajectory prediction, determine a time window of optical visibility during which the establishment of a quantum channel between said satellite and said station is possible. IV. Issue a request to establish a quantum channel transmitted directly or indirectly to said satellite.

[0031] According to one embodiment of the method for emitting a request to establish a quantum channel, the request to establish a quantum channel is transmitted directly to said satellite, said request then being a laser signal called an optical visibility signal emitted by said station.

[0032] According to one embodiment of the quantum channel establishment request emission method, the meteorological data includes local meteorological readings at the quantum communication ground station and local weather forecasts at the quantum communication ground station for a duration of between 1 minute and 15 minutes.

[0033] Another object of the invention is a satellite capable of establishing a quantum channel, said satellite comprising: - at least one suitable satellite quantum terminal for establishing an optical channel with a ground-based quantum communication station, - an orbit determinant and propagator suitable for determining the position of the satellite, - a processing unit in which data associated with a plurality of quantum communication ground stations are stored, said data including a position of said stations, said processing unit being connected to the orbit determinator and propagator and adapted to implement the following steps: A. Determine a quantum channel establishment zone of the satellite from said satellite position determined by the orbit determinator and propagator B. From the said position of said stations, determine a subset of terrestrial quantum communication stations formed by at least one of the terrestrial quantum communication stations included in said quantum channel establishment zone of the satellite C. Identify at least one terrestrial quantum communication station, known as a visible station: D. included in said subset, E. having issued a request to establish a quantum channel, and F., which is within optical line of sight of the satellite, G. establish a quantum channel between said satellite and the selected station(s) by means of a satellite quantum terminal.

[0034] According to one embodiment, the satellite includes an optical detection device connected to the processing unit, and adapted so that step C includes the following substeps: - detect, by said optical detection device, a laser signal called an optical visibility signal emitted by at least one quantum communication ground station included in said subset, then - identify this or these quantum communication ground station(s) as visible station(s).

[0035] Another object of the invention is a communication station comprising: - a quantum terminal capable of establishing a quantum channel with the satellite, - an orbit propagation module adapted to determine the positions and trajectories of the satellite(s) from orbitography data of the satellite(s), - a processing module adapted to receive or determine local meteorological data and adapted to implement the following steps: I. Identify a need for quantum channel establishment based on parameters stored in said processing module, said parameters including a prior agreement to establish a quantum channel with said station and a chronological record of the number and durations of quantum channel establishments with said station, II. If a need is identified, identify a satellite in a position where it is capable of establishing a quantum channel with said station, and then determine a forecast of a trajectory for said satellite from said position. III. Based on the aforementioned meteorological data and the aforementioned trajectory prediction, determine a time window of optical visibility for the said satellite during which the establishment of a quantum channel between the said satellite and the said communication station is possible. IV. Issue a request to establish a quantum channel transmitted directly or indirectly to said satellite.

[0036] According to one embodiment, the quantum channel establishment request is transmitted directly to said satellite, said request then being a laser signal called optical visibility signal emitted from said quantum terminal. Brief description of the drawings

[0037] Other features, details and advantages of the invention will become apparent from the description given with reference to the accompanying drawings provided by way of example, which represent, respectively:

[0038] [Fig.1A] a schematic view of a device for implementing an optical quantum channel between a satellite and a ground station for quantum communication for quantum key distribution or exchange (QKD) according to the prior art and implementing a Prepare and Measure type protocol,

[0039] [Fig.1B], a schematic view of a device for implementing two optical quantum channels between a satellite and two ground stations of quantum communication for quantum key distribution or exchange by satellite (QKD) according to the prior art and implementing an entanglement protocol.

[0040] [Fig. 1C], a schematic view of the implementation of an optical quantum channel between a satellite and a quantum communication ground station

[0041] [Fig.2], a schematic view of a key generation architecture per node of confidence in prior art,

[0042] [Fig. 3A], a schematic view of a method for distributing secure secret keys according to the invention,

[0043] [Fig. 3B], a schematic view of a secret key distribution system according to the invention,

[0044] [Fig.3C], a schematic view of a secret key distribution system according to a method of embodiment of the invention

[0045] [Fig. 3D], a schematic view of a secret key distribution system according to a method of embodiment of the invention

[0046] [Fig.4], a schematic view of a key distribution method according to a preferred embodiment of the method of the invention

[0047] [Fig. 5], a schematic view of a method for issuing a request to establish a quantum channel according to the invention

[0048] In the figures, unless otherwise indicated, the elements are not to scale and identical references designate identical elements. Description of the implementation methods

[0049] Figure 3A schematically illustrates a method of distributing a secret key by quantum channel via a Sat satellite according to an embodiment of the invention.

[0050] Fig. 3B schematically illustrates a communication system 1 according to the invention which includes the Sat satellite and terrestrial quantum communication stations SCQ1-SCQ5.

[0051] It is important to note that the method of the invention applies to the establishment of a quantum channel for the distribution of secret keys by any protocol known to those skilled in the art. For example, according to one embodiment, the invention is implemented with a Preparation and Measure (P&M) quantum channel secret key exchange protocol in which the satellite directly distributes a secret key to a single quantum communication ground station. Alternatively, according to another embodiment, the invention is implemented with an Entagment Based (EB) quantum channel secret key establishment protocol. In this embodiment, the satellite sends pairs of entangled photons (one to each station) to two quantum communication ground stations via a respective quantum channel.Thus, these two stations share the same secret key.

[0052] In the remainder of this description, unless explicitly stated otherwise, the method of the invention implemented with a quantum channel secret key exchange protocol of the prepare-and-measure (P&M) type will be described in order to simplify the description of the invention. However, those skilled in the art will understand that the method of the invention (and the satellite adapted to implement this method) can be generalized to any channel distribution protocol known to those skilled in the art.

[0053] Thus, the SCQ1-SCQ5 quantum communication ground stations are all capable of establishing a quantum channel with the Sat satellite via their TQ quantum terminal. The quantum channel allows the exchange of qubits in order, for example, to exchange secret keys. Alternatively, the TQ quantum terminal allows the establishment, via the Sat satellite, of at least one secret key shared by two quantum communication ground stations, in the form of an entangled photon pair. The TQ quantum terminal includes the elements necessary for establishing a quantum channel to exchange secret keys according to a given protocol, such as the BB84 protocol (Bennett and Brassard 1984).The TQ terminal includes a telescope, a system for pointing and tracking the telescope towards the satellite's telescope, a device for transmitting and receiving optical signals for quantum communications, and a protocol control device for exchanging secret keys.

[0054] By way of non-limiting example, [Fig. 3B] illustrates an embodiment in which system 1 comprises five SCQ1-SCQ5 quantum communication ground stations. Alternatively, according to another embodiment, system 1 comprises a number of communication stations other than five.

[0055] The Sat satellite includes at least one TQS satellite quantum terminal comprising the elements necessary for establishing a quantum channel with a quantum communication ground station. Furthermore, it includes a processing unit (PU) adapted to implement the method of [Fig. 3A]. This processing unit (PU) stores data associated with the SCQ1-SCQ5 quantum communication ground stations, including, in particular, the geographical position of said SCQ1-SCQ5 stations, a chronological record of the number and duration of quantum channel establishments with said SCQ1-SCQ5 stations allowing estimation of the volume of secret keys previously received by the stations, the stations' prior service level agreements, and possibly specific instructions related to the stations.By "prior station service level agreement", we mean here an agreement which commits the system 1 operator to establish quantum channels between the satellite(s) and the station at a predetermined frequency and duration in order to distribute secret keys at a predetermined frequency and / or volume.

[0056] Furthermore, it includes an orbit determinator and propagator (DPO) adapted to determine the position of the Sat satellite(s) in real time within a predetermined reference frame and to predict the future positions of the satellite(s). For example, the DPO orbit determinator and propagator may include a GNSS receiver (for Geolocation and Navigation by a Satellite System) to measure the satellite's position and a software orbit propagator. The orbit propagator is an algorithm that allows the future position and speed of the satellite to be predicted from a measured initial position.

[0057] In a first step A of the method in [Fig. 3A], the processing unit UT determines the instantaneous position at T0 of the satellite Sat using the orbit determinator and propagator DPO. After determining this position, the processing unit UT calculates a quantum channel establishment zone (ZECQ) from the position of the satellite Sat. The ZECQ quantum channel establishment zone is a geographical area on the ground (shown in [Fig. 3B]) within which it is possible to establish a quantum channel between the satellite Sat and a ground-based quantum communication station located within this zone, weather conditions permitting. It is therefore the theoretical geographical area where it is possible to establish a quantum channel between the satellite and a ground-based quantum communication station located within said geographical area. The establishment of the quantum channel allows for the exchange of secret keys.

[0058] In a step B, the processing unit UT determines, from the stored positions of the SCQ1-SCQ5 quantum communication ground stations, a subset of SCQ1-SCQ4 stations consisting of at least one of the stations within the establishment zone of a ZECQ quantum channel. In the example of [Fig. 3B], the SCQ5 quantum communication ground station is therefore not in the subset because it is too far from the Sat satellite and thus outside the establishment zone of a ZECQ quantum channel.

[0059] After this step B, the method includes a step C which consists of identifying the quantum communication ground station(s) of the subset—called visible stations—that are within optical line of sight of the satellite and that have issued a quantum channel establishment RCQ request. Each RCQ quantum channel establishment request is a signal previously emitted by a respective quantum communication ground station that is transmitted directly or indirectly to the Sat satellite.

[0060] In the example of [Fig. 3B], only the terrestrial quantum communication stations SCQ1 and SCQ2 are visible stations because stations SCQ3 and SCQ4 have local weather conditions at time T0 that prevent them from establishing optical contact with the Sat satellite. It is therefore impossible to establish a quantum channel with these stations at time T0, even though they are within the quantum channel establishment zone (ZECQ).

[0061] Preferably, as illustrated in [Fig. 3C], the Sat satellite comprises an optical detection device DOD connected to the processing unit UT. In this In this embodiment, step C comprises a first substep consisting of detecting, by the optical detection device DOD, a laser signal carrying the quantum channel establishment request signal RCQ, referred to as the optical visibility laser signal SVOi, SVO2, emitted by stations SCQ1 and SCQ2. In the embodiment of [Fig. 3C], the emission of the optical visibility laser signal constitutes the quantum channel establishment request RCQ. In a second substep, the processing unit UT identifies stations SCQ1 and SCQ2 as visible stations based on the optical visibility laser signals SVOi, SVO2.

[0062] According to a first embodiment, the optical detection device DOD is capable of detecting and measuring the angle of arrival of the optical visibility laser signals SVOi emitted by the SCQi stations. From the angle of arrival measurements, the geographical positions of the stations in the quantum channel establishment zone ZECQ, said geographical positions being stored in the processing unit UT, and the current position of the satellite provided by the orbit determinator and propagator DPO, the processing unit UT determines the identity of the visible stations.

[0063] According to a second embodiment, the optical detection device (DOD) is capable of detecting and analyzing the signature of the SVOi optical visibility laser signals emitted by the SCQi stations. The signature of an SVOi optical visibility laser signal is a characteristic of the optical signal specific to the emitting station. For example, the SVOi optical visibility laser signal is modulated with on-off keying (OOK) by a binary word identifying the station emitting the laser signal. Other digital information intended for the processing unit (UT) can also modulate the SVO optical visibility laser signal. From the geographic positions of the stations within the quantum channel establishment zone (ZECQ) stored in the processing unit (UT) and the station identifier words demodulated by the optical detection device (DOD), the processing unit (UT) determines the identity of the visible stations.

[0064] Obviously, other embodiments of step C are possible.

[0065] Preferably, in the embodiment of [Fig. 3C], each optical visibility laser signal (OVL) is emitted by the pointing and tracking system of the telescope of the quantum terminal (QT) of the respective quantum communication ground station. Indeed, the pointing and tracking system establishes and maintains optical contact through the emission of laser beacons. Optical contact is necessary for establishing the quantum channel between the quantum communication ground station (QC) and the satellite. Sharing the elements of the QT thus simplifies the architecture of system 1.

[0066] Alternatively, according to another embodiment compatible with the embodiment of [Fig. 3C], one of the quantum communication ground stations A quantum channel establishment request is transmitted indirectly via the mission control center prior to step C. The quantum channel establishment request received by the mission control center is then transmitted to the satellite by the satellite control center through the TM / TC station network. In this embodiment, the data stored in the processing unit (PU) includes this request and information about the issuing station. Step C then involves identifying this communication station as visible when it is within line of sight of the satellite. In one embodiment, the request is transmitted from the mission control center to the satellite via a satellite telemetry-command channel. This simplifies the architecture of system 1 by sharing pre-existing channels.

[0067] After identifying the visible stations, the method includes a step D which consists of choosing from among the visible stations - that is to say the stations which are those with which it is possible to establish a quantum channel at T0 and which have required the establishment of the quantum channel - the station or stations with which a quantum channel will actually be established.

[0068] When there are more visible stations than N > 1 quantum channels that the Sat satellite is capable of establishing, step D includes a substep for prioritizing the quantum channel establishment requests (QCs) based on information contained in the data. This information is chosen from the following list: a chronological record of the number and duration of quantum channel establishments with visible stations, prior service level agreements with the visible stations, and specific instructions related to the visible stations transmitted by the mission control center via the TM / TC station network. Thus, selecting the visible station(s) with which a quantum channel will be established consists of choosing the N visible station(s) that have issued a quantum channel establishment (QC) request with a priority ranked among the top Ai.

[0069] For example, the processing unit UT compares the number and durations of quantum channel establishments in the time log with the frequency and duration of quantum channel establishments predetermined in the prior service level agreement. Thus, a station exhibiting a deficit in the number and duration of quantum channel establishments greater than that of another station will be classified with a higher priority.

[0070] A specific instruction transmitted to the satellite's processing unit (PU) by the mission control center is, for example, an order to refuse service to a given station due to the possible existence of a security breach in said station or due to a payment default by the operator of a ground communication station. quantum towards the satellite system manager 1. Step D will then consist of not selecting this station.

[0071] Preferably, the substep for prioritizing quantum channel establishment requests is also based on the optical visibility duration of visible stations. This optical visibility duration is calculated by the processing unit UT without meteorological considerations, based on the position of the ground quantum communication stations, the satellite's position at time T0, and the satellite trajectory prediction provided by the orbit determinant and propagator DPO. For example, when the processing unit UT calculates that the optical visibility duration of a visible station is insufficient to establish a quantum channel for a duration sufficient to provide a satisfactory quantum key distribution service, the processing unit UT will not select that station in step D. This case of insufficient duration can occur when the station is on the edge of the quantum channel establishment zone (ZECQ).As a non-limiting example, a visibility duration of less than 3 minutes is considered insufficient to establish a quantum channel.

[0072] In the case where there are a number of visible stations equal to a number N > 1 of quantum channels available on the satellite Sat, step D consists, for example, of selecting all the visible stations. Alternatively, it is possible not to select one or more visible stations when the processing unit calculates that the optical visibility time of these visible stations is insufficient to establish a quantum channel and exchange a satisfactory key volume. By "optical visibility time," we mean here a time window from T0 during which the station in question and the satellite can establish a quantum channel by taking into account only purely geometric parameters (station position, satellite position, and satellite trajectory prediction) stored in the processing unit UT.Similarly, it is possible not to select one or more visible stations when the processing unit compares the number and durations of quantum channel establishments from the time record with the frequency and duration of quantum channel establishments predetermined in the prior service level agreement of said stations and deduces that the station has obtained a number and durations of quantum channel establishments equal to or greater than those provided for in the prior agreement.

[0073] In summary, step D is a multi-variable optimization step which aims to best satisfy the quality of service commitment of the satellite system operator by prioritizing the establishment of quantum channels in an appropriate manner.

[0074] By way of non-limiting example, in the illustration in [Fig. 3C], only station SCQ1 is selected in step D because there is a single CQ1 quantum channel available in the Sat satellite and station SCQ1 has issued an establishment request of quantum channel (RCQ) that the processing unit has classified with a higher priority than that emitted by station SCQ2.

[0075] Alternatively, according to another embodiment illustrated in [Fig. 3D], there are two quantum channels CQ1, CQ2 available in the Sat satellite. Also, the two stations SCQ1 and SCQ2 are selected in step D.

[0076] The method of [Fig. 3A] includes a final step E consisting of exchanging, via the quantum channel CQi established between the satellite Sat and the selected station SCQ1 in step D, at least one secret key Kl. This secret key exchange step between the satellite Sat and the station SCQ1 is performed according to any method known to those skilled in the art, such as the BB84 Preparation and Measurement protocol. In the more general case of any quantum key distribution protocol, step E consists of establishing, via the satellite Sat, a quantum channel with the selected station(s). For example, in the embodiment of [Fig. 3D] where there are two quantum channels CQ1, CQ2 available in the satellite Sat, the quantum channel establishment protocol can be a protocol based on quantum entanglement.Thus, step E consists of establishing, via the Sat satellite, at least one secret key shared by the two selected stations SI, S2 in the form of a pair of entangled photons via the quantum channels CQ1, CQ2.

[0077] Step F may also consist of exchanging, via the quantum channels CQ1 and CQ2 established between the satellite and the two selected stations SCQ1 and SCQ2, at least one secret key Kl shared between the two stations SCQ1 and SCQ2. This secret key exchange step between the two stations SCQ1 and SCQ2 is carried out according to any method known to those skilled in the art, such as, for example, the BBM92 entanglement protocol (Bennett, Brassard and Mermin 1992).

[0078] Notably, in the method of [Fig. 3A] and the associated architecture, planning management is entirely offloaded to the Sat satellite and to the quantum communication ground stations via the transmission of RCQ quantum channel establishment requests. The satellite autonomously and independently acquires the information necessary for mission planning from the ground mission control center, and this independently of the quantum key distribution protocol. This represents a significant change compared to the prior art architecture illustrated in [Fig. 2], in which planning decisions were made by the mission control center.By avoiding the multiplication of TM / TC links for programming the satellite mission and the links between the quantum communication ground stations and the mission control center, the architecture of the invention offers improved security, increased simplicity and reduced cost compared to the prior art.

[0079] As illustrated in [Fig. 3A], preferably, the steps of the method are repeated in a loop until one or more stations are selected in step D. More specifically: - Step A is repeated in a loop until the subset of quantum communication ground stations is determined in step B - Steps A and B are repeated in a real-time loop until the visible station(s) are identified in step C. - Steps A, B and C are repeated in a loop until the selected station(s) are selected in step D.

[0080] After the quantum channel is established in step E, the processing unit repeats the steps of the method of the invention until one or more stations are again selected in step D.

[0081] Figure 4 schematically illustrates the steps of an embodiment of the method in Figure 3A. In this embodiment, the method includes a subsequent step F consisting of transmitting, via a TM / TC station to the mission control center, a signal representative of the number and duration of quantum channel establishments with the ground station with which the quantum channel was established. More generally, the signal is representative of the volume of data exchanged or distributed per quantum channel and of the communication station with which each channel was established.

[0082] Thus, the mission control center can update its database and adapt the specific instructions related to the stations transmitted to the satellite. Preferably, this signal is transmitted via a remote control / telemetry (TM / TC) channel of the satellite in order to minimize the number of channels usable by the satellite.

[0083] As mentioned above, the architecture of the invention allows the management of the planning to be deferred to the Sat satellite and to the SCQ1-SCQ5 quantum communication ground stations. The invention also relates to a method for issuing requests to establish a quantum channel (RCQ).

[0084] The steps of this method are illustrated in [Fig. 5] and are implemented by an MT processing module of each SCQ1-SCQ5 quantum communication ground station. The MT processing module is further adapted to receive or determine local meteorological data. This data consists of meteorological readings (i.e., physical measurements and instantaneous meteorological parameters) and weather forecasts. For this purpose, the station includes, for example, meteorological sensors and / or is connected to a meteorological service provider capable of transmitting local meteorological data to it.

[0085] The MT processing module of each quantum communication ground station is equipped with an MPO orbit propagation module capable of determining the positions or ephemerides of the satellite(s) over the medium term (weeks or months). The MPO orbit propagation module is periodically initialized with orbitography data from the satellite(s). This orbitography data is provided by the mission control center via the link connecting the mission control center and the quantum communication ground stations. Alternatively, this orbitography data can be provided in the form of TLEs (Two-Line Elements) by a specialized service provider or by NORAD, for example.

[0086] In a first step I of the method in [Fig. 5], the MT processing module is configured to identify a requirement for the number and duration of quantum channel establishments. This identification is performed using parameters stored in the processing module, which include, for example: a prior agreement on the frequency and duration of quantum channel establishment for the station, a stock of secret keys available in the station, and a chronological record of the number and durations of quantum channel establishments performed by the station. By "stock of available secret keys," we mean the volume of secret keys previously exchanged with the station that have not yet been used to secure a communication.

[0087] For example, when the MT processing module identifies that the secret key stock is low or zero, the processing module then identifies a need for quantum channel establishment.

[0088] According to another example, the identification of a need for quantum channel establishment is carried out only when the stock of secret keys is low or zero and the prior agreement on frequency and duration of quantum channel establishment provides for a number and durations of quantum channel establishment that have not been carried out to date.

[0089] Alternatively, when the MT processing module identifies that the secret key stock is low or zero but the prior agreement on frequency and duration of quantum channel establishment does not provide for subsequent quantum channel establishment, the MT processing module does not identify a need for quantum channel establishment.

[0090] Preferably, this identification is also based on local long-term weather forecast data (for example, over a week). For example, when local long-term weather forecasts predict significant and prolonged cloud cover, the MT processing module does not identify a need to establish a quantum channel. Indeed, in this case, the probability of successfully establishing a quantum channel is low.

[0091] If a need is identified in step I, in a second step II, the MT module is configured to identify a Sat satellite in a position suitable for establishing a quantum channel with the station. To do this, the MT module uses the satellite position predictions (ephemerides) provided by the MPO orbit propagation module and the station's geographic position to calculate the dates of future satellite visibility periods, i.e., the dates on which the station will enter the zone for establishing a ZECQ quantum channel with the satellites.

[0092] Following step II, the method includes a step III which consists of determining whether there is a time window of optical visibility during which the establishment of the quantum channel between the identified satellite and the quantum communication ground station is possible. This determination is made using meteorological data and the satellite position forecast (ephemeris) calculated in step II. In step III, the relevant meteorological data taken into account include local meteorological readings and local weather forecasts for a duration of, for example, between 1 and 15 minutes.The duration of the time window determined in Step III depends on several parameters, including the satellite's altitude, the minimum elevation of the quantum terminal telescope at the station to target the satellite, and the duration of the acquisition and mutual pointing phase of the two telescopes performed by the pointing and tracking system. For example, for a LEO satellite at an altitude of 1262 km (13 orbits per day) and a minimum elevation of 30°, the maximum time spent over a station (optical visibility time window) is 8 minutes. For a MEO satellite at an altitude of 8068 km (5 orbits per day) and a minimum elevation of 30°, the maximum duration reaches 1 hour.

[0093] Preferably, the processing module only determines the existence of such a time window when the probability of establishing a quantum channel—given the meteorological data and trajectory forecast—is very high. This probability is greater than a probability set in the prior service level agreement. This probability can be modified by the mission control center via the link connecting the station to the mission control center, depending on the network management by the system manager.

[0094] Finally, the method of [Fig.5] includes a final step IV consisting of issuing a quantum channel establishment request (QCR) transmitted directly or indirectly to the Sat satellite identified in step II.

[0095] As mentioned previously, according to one embodiment, this request is transmitted indirectly to the Sat satellite via the mission control center (with the signature of the issuing station in order to identify it). In this mode of In implementation, the request will be stored in the satellite's processing unit UT before the implementation of step C of the method in [Fig.3A].

[0096] According to another embodiment, compatible with the previous embodiment mentioned, the quantum channel establishment request (QCR) is transmitted directly to the Sat satellite, for example in the form of the optical visibility laser signal SVO emitted by the station.

[0097] Compared to the prior art architecture, the method of [Fig. 5] implemented by the quantum communication ground station according to the invention has the advantage of not requiring the acquisition of data external to the station. The station transmits its quantum channel establishment request (QCR) only if the conditions for establishing the quantum channel are met in the short term. The station transmits its request if the local clear-sky forecasts within the time window are highly probable (97% or higher, for example). The satellite allocates a resource to establish a quantum channel with a quantum communication ground station with a very high success rate (99%, for example).

[0098] The steps of the method in [Fig. 5] are preferentially repeated in a loop. More specifically, step I is repeated in a loop until a satellite is identified in step II, and steps I and II are repeated in a loop until a time window is identified in step III.

Claims

1. Demands A method for issuing a quantum channel establishment request (QCR) implemented by a processing module (PM) of a quantum communication ground station comprising a quantum terminal (QT) capable of establishing a quantum channel with a satellite and establishing a quantum communication channel (QC1-QC2) by the satellite (Sat), the satellite comprising a processing unit (PU) in which data associated with a plurality of quantum communication ground stations (QC1-QC5) are stored, including a position of said quantum communication ground stations (QC1-QC5), said method comprising the following steps I. Identify a need to establish a quantum channel from parameters stored in said processing module, said parameters including a prior agreement to establish a quantum channel with said quantum communication ground station, a chronological record of the number and durations of quantum channel establishments previously established with the station, and a number and durations of quantum channel establishments attributed to said station, II. If a need is identified, identify a satellite with a position in which it is suitable for establishing a quantum channel with said quantum communication ground station, then determine a forecast of a trajectory of said satellite from said position, III. From meteorological data and from said forecast of the trajectory, determine a time window of optical visibility during which the establishment of a quantum channel between said satellite and said station is possible, IV. Issue a quantum channel establishment request (QCR) transmitted directly or indirectly to said satellite. And the following steps implemented by the processing unit:

2. A. Determine a satellite (Sat) position and then determine a satellite quantum channel establishment zone (QECZ) from said satellite position, B. From the said position of the said quantum communication ground stations, determine a subset of quantum communication ground stations (SCQ1-SCQ4) formed by at least one of the quantum communication ground stations included in the said quantum channel establishment zone (QCEZ), C. Identify at least one of the terrestrial quantum communication stations, referred to as the visible station (SCQ1, SCQ2): - included in said subset, - having issued a quantum channel establishment request (QCR), and - which is within optical line of sight of the satellite, D. With said data, select at least one visible station, called the selected station (SCQ1), with which to establish a quantum channel, then E. Establish a quantum channel (CQi CQ2) between said satellite (Sat) and the selected station(s), the request to establish a quantum channel (QC) being transmitted to said satellite, said request being a laser signal called optical visibility signal (OVS) emitted by said station. A method according to claim 1, wherein, when there is a number of visible station(s) greater than N > 1 of available quantum channels on the satellite (Sat), step D comprises a substep of prioritizing said requests to establish a quantum channel based on information contained in said data, said information being selected from the following list: a chronological record of previously established quantum channel connections with the stations (SCQ1-SCQ5), a prior agreement to establish a quantum channel with the stations (SCQ1-SCQ5), and instructions issued by a mission control center, said selection of the selected station(s) consisting of choosing the N visible station(s). having issued a request to establish a quantum channel (QC) with a priority ranked among the first N.

3. Method according to the preceding claim, wherein said information includes an optical visibility duration of the visible stations calculated by the processing unit from said position of said stations, said position of the satellite and a prediction of a trajectory of the satellite.

4. A method according to any one of the preceding claims, comprising a later step F of transmitting to a mission control center, via a satellite remote control-telemetry channel, a signal representative of the number and durations of establishment of a quantum channel and representative of the quantum communication ground station with which each quantum channel was established.

5. A method according to any one of the preceding claims, wherein step A is repeated until said subset of quantum communication ground stations (SCQ1-SCQ4) is determined in step B, and wherein steps A and B are repeated until the visible station or stations are identified in step C, and wherein steps A, B and C are repeated until the selected station or stations are selected in step D.

6. Method according to any one of the preceding claims, wherein step E consists of exchanging, by quantum channel (CQi CQ2) via said satellite (Sat), at least one secret key (Kb K2) with the selected station(s).

7. Method according to any one of claims 1 to 5, wherein step E consists of establishing, via said satellite (Sat), at least one secret key shared by at least two selected stations.

8. A method according to any one of claims 1 to 7, wherein the meteorological data includes local meteorological readings at the quantum communication ground station and local weather forecasts at the quantum communication ground station for a duration of between 1 minute and 15 minutes.

9. A communication system (1) comprising a satellite and a ground communication station (SCQ1) capable of establishing a quantum channel (CQi CQ2), said satellite comprising: - at least one satellite quantum terminal (TQS1, TQS2) adapted to establish an optical channel with a ground-based quantum communication station, - an orbit determinant and propagator (DPO) adapted to determine a satellite (Sat) position, - a processing unit (PU) in which data associated with a plurality of quantum communication ground stations (SCQ1-SCQ5) are stored, said data including a position of said stations (SCQ1-SCQ5), said processing unit being connected to the orbit determinant and propagator (DPO) and adapted to implement the following steps: A. determine a satellite quantum channel establishment zone (QECZ) from said satellite position determined by the orbit determinator and propagator (ODP), B. from said position of said stations, determine a subset of terrestrial quantum communication stations (SCQ1-SCQ4) formed by at least one of the terrestrial quantum communication stations included in said satellite quantum channel establishment zone (ZECQ), C. Identify at least one terrestrial quantum communication station, referred to as a visible station (SCQ1, SCQ2): - included in said subset, - having issued a quantum channel establishment request (QCR), and - which is within optical line of sight of the satellite, D. From said data, select at least one visible station, called the selected station (SCQ1), with which to establish a quantum channel, then E. establish a quantum channel (CQ1) between said satellite and the selected station(s) by means of a satellite quantum terminal (TQS1, TQS2); the ground communication station (SCQ1) comprising: - a quantum terminal (QT) capable of establishing a quantum channel with the satellite,

10. - a Data Propagation Orbit (DPO) module adapted to determine satellite positions and trajectories from orbitography data of the satellite(s), - a processing module (MT) adapted to receive or determine local meteorological data and adapted to implement the following steps: I. Identify a need for quantum channel establishment based on parameters stored in said processing module, said parameters including a prior agreement to establish a quantum channel with said station and a chronological record of the number and durations of quantum channel establishments with said station, II. If a need is identified, identify a satellite in a position where it is capable of establishing a quantum channel with said station, and then determine a forecast of a trajectory for said satellite from said position. III. Based on the aforementioned meteorological data and the aforementioned trajectory prediction, determine a time window of optical visibility for the said satellite during which the establishment of a quantum channel between the said satellite and the said communication station is possible. IV. Issue a quantum channel establishment request (QCR) transmitted directly or indirectly to said satellite the satellite comprising an optical detection device (DOD) connected to the processing unit, and adapted so that step C includes the following sub-steps: - detect, by said optical detection device (ODD), a laser signal called optical visibility signal (OVS1, OVS2) emitted by at least one quantum communication ground station (QC1, QC2) included in said subset, then - identify this or these quantum communication ground station(s) as visible station(s). A communication system (1) according to the preceding claim, wherein the quantum channel establishment request (QCR) is transmitted directly to said satellite, said request being a laser signal called optical visibility signal (OVS) emitted by said quantum terminal (QT).

11. A communication system (1) according to claim 9 or claim 10, the ground station being adapted so that said quantum channel establishment request is transmitted to said satellite, said satellite then being adapted to exchange via the established quantum channel (CQ1) at least one secret key with the quantum communication ground station.

12. Communication system (1) according to claim 9 or claim 10, the ground station being adapted so that each quantum channel establishment request is transmitted to said satellite, said satellite then being adapted to generate by the quantum channels (CQi, CQ2), at least one secret key shared by the two quantum communication ground stations (SCQ1, SCQ2).

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