PAIRING METHOD OF ELECTRONIC END DEVICES, CORRESPONDING END DEVICES AND CORRESPONDING PROGRAM

Description

1. Domain

[0001] The invention relates to the field of authentication. More particularly, the invention relates to the hardware authentication of devices with each other. 2. State of the art

[0002] It is well known that many protocols exist that allow two devices to authenticate each other before transmitting or exchanging confidential information. This is the case, for example, when a wireless communication terminal wants to authenticate itself on a user's local network, such as a Wi-Fi network. To do this, before any data exchange, the terminal must authenticate itself on the communication network. This authentication generally involves entering a key, password, or passphrase. One of the problems with this type of pairing is that the terminals must necessarily have the means to enter these keys, passwords, or passphrases.

[0003] Other areas require authentication between wireless devices. This is the case, for example, with devices that communicate using Bluetooth® technology. Bluetooth is a wireless technology for creating personal wireless networks operating in the 2.4 GHz frequency band without requiring authorization, with a maximum range of about ten meters. These networks are generally composed of mobile devices such as cell phones, personal digital assistants (PDAs), and laptops. By default, Bluetooth communication is not authenticated, and any device can exchange data with any other device.

[0004] A Bluetooth device (for example, a mobile phone) may choose to request authentication to provide a particular service. Bluetooth authentication is usually performed with PIN codes.Again, this type of authentication requires entering a key or PIN, usually on both devices wishing to communicate. By default, the user must enter the same PIN on both devices. Once the user has entered the PIN, both devices generate a key to connection (link key). This link key can then be saved either on the devices themselves or on an external storage device. During the next exchange, both devices will use the previously generated link key. This procedure is called coupling. French patent application No. 2 985 148 (National registration No. 11 62408) discloses an example of a method for pairing electronic devices. When the pairing key is lost by one of the devices, the pairing operation must be repeated so that a new key can be generated.

[0005] When the data to be exchanged between the two Bluetooth terminals is sensitive data (such as banking data, for example), the exchanges following the pairing phase are encrypted, for example using the E0 algorithm. E0 is the stream cipher algorithm used to protect the confidentiality of data exchanged in Bluetooth.

[0006] The problem however is the same as for the WEP key or the WPA key: Prior to any encrypted exchange, the user must enter on the terminal the PIN code, the length of which varies from 4 to 16 characters, knowing that for the most secure applications, the 16-character PIN code is preferred.

[0007] However, such entry proves impossible when at least one of the two devices lacks a keyboard. The Bluetooth protocol suite, in particular, cannot establish a secure connection between two devices when at least one of them does not have a way to enter a PIN. Even when both devices have input devices, there are additional problems with entering them. Whether using Wi-Fi or Bluetooth, entering a PIN or key that is too long leads to at least two problems: On the one hand, there is a significant risk of error during data entry. Indeed, it is almost certain that the entry will contain at least one mistake. This is particularly true when the entry is made using masked characters (the entered characters are not displayed, but instead a series of asterisks is shown); on the other hand, since the entry is manual, there is no guarantee that a malicious person will not be monitoring the entry in order to steal the PIN or key for fraudulent use.

[0008] Security solutions have been proposed, primarily for setting up a Wi-Fi connection. These solutions involve the near-simultaneous activation of the two devices to be connected. One such solution is called "Wi-Fi Protected Setup (WPS)" and is a simple and secure wireless local area network standard. However, this solution does not solve all problems, since one variant of WPS requires entering a PIN code.

[0009] In other words, it is necessary to provide a connection solution that is both simple and discreet in order to avoid input errors and to ensure the confidentiality of the data required for connection or pairing. 3. Summary

[0010] The invention does not have these drawbacks of the prior art. The invention relates to a method of pairing a first terminal, called the communication terminal wishing to transmit and receive data, with a second terminal, called the acceptor terminal.

[0011] According to the present technique, said method comprises, at the level of the accepting terminal: a first insecure pairing phase, of said transactional terminal with said communication terminal, delivering at least one pairing parameter to said communication terminal, via a first bidirectional wireless communication channel of radio type; a second secure pairing phase, of said transactional terminal with said communication terminal, said second pairing phase implementing a second unidirectional communication channel, used by said transactional terminal to transmit a security data of said first communication channel to said communication terminal, according to said at least one pairing parameter of said communication terminal.

[0012] Thus, unlike traditional pairing methods, which primarily use a single bidirectional communication channel such as radio, this technique enables secure pairing in two stages: the first stage performs a standard, insecure pairing to obtain an identifier for the communicating terminal, while the second stage performs a secure, complementary pairing, taking into account the identifier obtained during the initial insecure pairing, using a unidirectional communication channel. It is the combination of these two successive pairing stages that achieves the desired result: securing the connection (e.g., Bluetooth) established between the first and second terminals, starting from an initial insecure connection, without any human intervention.

[0013] According to the present technique, the second pairing phase includes, at the accepting terminal level: a step of generating the security data for said first communication channel; a step of transmitting, via the second unidirectional communication channel, said security data for said first communication channel in the form of a representation; a step of generating a challenge using said security data for said first communication channel; a step of transmitting, via the first communication channel, to said communication terminal, said challenge; a step of receiving, via the first communication channel, a response to said challenge from the communication terminal.

[0014] According to the present technique, the second pairing phase includes, at the communication terminal level: a step of receiving, via the second unidirectional communication channel, a representation of said security data from said first communication channel; a step of decoding said representation delivering said security data from said first communication channel; a step of receiving, via the first communication channel, said challenge; a step of resolving said challenge using said security data from said first communication channel, delivering a; and a step of transmitting, via the first communication channel, the response to said challenge.

[0015] Thus, in this second pairing phase, the described technique combines the information transmitted via the second communication channel with that transmitted via the first communication channel so that the transaction terminal can establish a secure connection with the communication terminal. When the transaction terminal is able to verify that the challenge has been met by the communication terminal, this means that the communication terminal possesses the cryptographic material transmitted via the first unidirectional communication channel; the communication between the two terminals is then secure.

[0016] According to a particular characteristic, the security data for said first communication channel is an encryption key.

[0017] More specifically, it is a symmetric encryption key.

[0018] This key can thus serve as a basis for subsequent exchange between the two terminals and / or for the construction of an even more efficient crypto system in a later phase, in order to guarantee maximum security in exchanges.

[0019] According to a particular embodiment, a representation belongs to a type of representation and in that said type of representation belongs to the group comprising: a series of activations and deactivations of at least one light-emitting diode; a sound sequence; a message transmitted wirelessly via NFC or via a wired connection.

[0020] Thus, an attacker must necessarily be in close proximity to both terminals to attempt to capture data passing through the second communication channel.

[0021] According to a particular embodiment, said communication terminal is an intelligent terminal of the smartphone type and said transactional terminal is a payment terminal slave of said communication terminal.

[0022] According to a particular embodiment, said acquisition step of said representation by said communication terminal on the second communication channel includes a step of acquiring a video sequence representative of said representation.

[0023] According to a particular embodiment, said acquisition step of said representation by said communication terminal on the second communication channel includes a step of acquiring a sound sequence representative of said representation.

[0024] This technique also relates, from another perspective, to a communication terminal wishing to transmit and receive data with an accepting terminal, comprising: means for implementing a first phase of insecure pairing with said accepting terminal, via a first two-way wireless radio communication channel; and means for implementing a second phase of insecure pairing with said accepting terminal, a second one-way communication channel, comprising: means for receiving a representation of security data from said first communication channel via the second one-way communication channel; means for decoding said acquired representation delivering said security data from said first communication channel; means for receiving, via the first communication channel, a challenge; means for resolving said challenge using said security data from said first communication channel, delivering a;means of transmitting, via the primary communication channel, the response to said challenge.

[0025] This technique also relates, from another perspective, to a transaction terminal wishing to transmit and receive data with a communication terminal, comprising: means of implementing a first phase of insecure pairing with said accepting terminal, via a first two-way radio-type wireless communication channel; and means of implementing a second phase of insecure pairing with said accepting terminal, a second one-way communication channel, comprising: means of generating security data for said first communication channel enabling pairing of said transaction terminal and said communication terminal; means of transmitting, via a second one-way communication channel, said security data for said first communication channel.

[0026] The invention also relates to an information carrier readable by a data processor, and comprising instructions of a program as mentioned above.

[0027] The information medium can be any entity or device capable of storing the program. For example, the medium can include a storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a floppy disk or a hard disk drive.

[0028] On the other hand, the information medium can be a transmissible medium such as an electrical or optical signal, which can be transmitted via an electrical or optical cable, by radio, or by other means. The program according to the invention can, in particular, be uploaded to a network such as the Internet.

[0029] Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the process in question.

[0030] According to one embodiment, the invention is implemented using software and / or hardware components. In this context, the term "module" in this document may refer to a software component, a hardware component, or a set of hardware and software components.

[0031] A software component corresponds to one or more computer programs, one or more subroutines of a program, or more generally to any element of a program or software capable of implementing a function or set of functions, as described below for the module in question. Such a software component is executed by a data processor of a physical entity (terminal, server, etc.) and is capable of accessing the hardware resources of that physical entity (memory, storage media, communication buses, input / output cards, user interfaces, etc.).

[0032] Similarly, a hardware component corresponds to any element of a hardware assembly capable of implementing a function or set of functions, as described below for the module in question. This could be a programmable hardware component or one with an integrated processor for software execution, for example, an integrated circuit, a smart card, a memory card, an electronic board for running firmware, etc. 4. Figures

[0033] Other features and advantages will become clearer upon reading the following description of a preferred embodiment, given by way of simple illustration and not limitation, and the accompanying drawings, among which: there figure 1 describes the general principle of secure pairing as proposed herein; the figure 2 describes the steps of the second pairing phase; the figure 3is a simplified representation of a transactional terminal according to the present technique; the figure 4 is a simplified representation of the communication terminal according to the present technique. 5. Description of an embodiment

[0034] As previously explained, the present technique offers a new method of secure pairing (using an encryption key) for pairing two devices. The invention applies particularly to Bluetooth pairing technology, but it can also be applied to other protocols that include the possibility of using two successive pairing phases, one insecure and the other secure. The principle is that the second phase takes place between two terminals that have already been paired once and, for the second time, have a trusted connection: either through the necessary immediate proximity (short-propagation audio / visual message, NFC message) or direct wired connection, or even through a trusted third party between the two terminals (such as a server that already shares a secret with each of the devices).

[0035] In a particular embodiment, which will be described later, the solution implements two Bluetooth terminals: one that initiates the pairing process and the other that accepts it. More specifically, the pairing process takes place between a smart communication terminal, also known as a "smartphone," and a subordinate payment terminal. A subordinate payment terminal (transaction terminal) is defined as a payment terminal whose operation is contingent upon pairing with a communication terminal: the slave payment terminal requires, at least in part, resources provided by the communication terminal to be able to perform payment transactions.Such payment terminals (coupled with communication terminals) are used, for example, by mobile professionals (taxi drivers, professionals, street vendors), who need a compact payment terminal that requires little maintenance, delegating part of the transaction to the communication terminal or using its resources (e.g., network communication resources, wifi, 3g, 4g, etc.) to carry out the transaction.

[0036] Subsequently, reference is made respectively to a communication terminal and a transactional terminal to designate these two terminals respectively, it being understood that the proposed technique can be used in situations other than that previously described, and more particularly in any situation where secure pairing must be carried out.

[0037] The process is described in relation to the figure 1In this context, the Com-Term communication terminal has a unidirectional electronic receiver (such as a microphone, a device for reading and decoding images like the cameras on smartphones, or other similar electronic devices), and the P-Term transaction terminal has a unidirectional electronic transmitter to transmit a key (the transaction terminal typically has a visual indicator such as an LED or an audible indicator such as a buzzer or speaker). Other unidirectional transmission technologies (i.e., those not allowing reception on the same channel) can also be considered. These technologies are used to establish the second unidirectional communication channel, which is considered a reliable channel due to its short distance.

[0038] The term "representation" used here refers to any type of visual or auditory rendering of numeric or alphanumeric data (e.g., emission of light signals, sound pulses, etc.). According to this technique, the representation comprises a set of data that can be rendered by the transaction terminal and acquired by the communication terminal. According to this technique, the representation is not interpretable by a human (it is not directly readable and understandable or audible and understandable). In one specific embodiment, the representation takes the form of a sequence of activations and deactivations of one or more light-emitting diodes (LEDs). In this embodiment, the communication terminal acquires the sequence of activations and deactivations of the LED(s).From this sequence of acquired activations and deactivations, it recreates the representation and decodes it to obtain the security data for the first communication channel. In this embodiment, the security data for the first communication channel is an encryption key. It is also possible for this security data for the first communication channel to be of a different nature than an encryption key (such as a certificate or signature of identification data, or a transaction terminal identifier): the principle being that the security data for the first communication channel can enable subsequent secure exchanges between the two terminals, thus reinforcing the initial pairing phase on the first communication channel. In any case, in this embodiment, there is therefore a double encoding of the encryption key. This is advantageous from several points of view.On the one hand, the fact that the representation can be deduced from the sequence of activations and deactivations of the LED(s) prevents a fraudster from perceiving that this displayed blinking contains data. On the other hand, obtaining the key requires implementing a method to discover (decode) the representation, which effectively constitutes double encryption and increases security.

[0039] In the case of a sound sequence, the advantages are similar. Firstly, because the sequence is generated by the transaction terminal, a fraudster therefore does not know when it will be generated. Secondly, as with LED flashing, because the sound sequence again represents an encoding of the encryption key, decoding is necessary to obtain the encryption key. Thirdly, the sound sequence can be emitted on frequencies imperceptible to a fraudster, making it impossible for them to know when the code is transmitted. Depending on the embodiment, the sound sequence could, for example, be a DTMF sequence. Thus, within the framework of this technique, several types of representations can be used during the second pairing phase.As will be shown later, the different types of representations can be used jointly or successively, depending on the situation.

[0040] According to this technique, the first pairing phase (A00) is generally performed in two steps, in an insecure mode, which is not detailed further herein. Following this first insecure pairing phase, certain data is acquired by both the transaction terminal and the communication terminal: this includes, for example, identification data (such as Bluetooth MAC addresses). This first phase allows the two terminals to recognize each other and tag the pairing as insecure. Subsequently, or more or less immediately after this first phase, the second pairing phase (B00) is implemented. In one particular embodiment, the first pairing phase is a "Simple Works" type phase.

[0041] According to the present technique, the second phase (B00) of pairing is carried out in two stages: The P-Term transaction terminal reproduces (by flashing LEDs or emitting sounds) the REPRS representations of the encryption key; in addition, other parameters can also be reproduced (address of the transaction terminal for example, this aspect is detailed later) the Com-Term communication terminal acquires (by video reading or audio recognition) the encryption key with the help of the representation reader.

[0042] Therefore, no input is required, either on the communication terminal side or the accepting terminal side, which simplifies and speeds up the process (providing an additional security measure). At least one pairing parameter for the communication terminal is used by the transaction terminal during the second phase: this could be the MAC address of the communication terminal, a public key of the communication terminal, or an identifier of the communication terminal.This pairing parameter for the communication terminal can be used in various ways (cumulative or not) by the transaction terminal: for example, to generate the encryption key, or to encrypt the message transmitted to the communication terminal via the second channel, or to update a pairing list (internal to the transaction terminal) within the transaction terminal's memory. This list allows the transaction terminal to identify the communication terminals with which it has a pairing, whether secure or not. Therefore, this pairing parameter for the communication terminal can be stored solely in the transaction terminal's memory for future use.

[0043] A pairing validation mechanism based on a challenge / response exchange with authentication is then initiated, and the two terminals are then connected: The P-Term transaction terminal constructs a challenge from the encryption key that has just been transmitted through the unidirectional communication channel (LED, Buzzer) and transmits this challenge through the first communication channel (Bluetooth); the Com-Term communication terminal receives this challenge through the first communication channel and then performs the operations necessary to construct its own challenge (possibly using the information contained in the first decrypted challenge) and transmits it to the P-Term transaction terminal.

[0044] When these challenge / response exchanges proceed as expected from both the transaction terminal and the communication terminal, the pairing is considered secure.

[0045] According to this technique, it is important to perform an initial insecure pairing phase before the second secure pairing phase. This initial pairing phase allows the two terminals to exchange data, including identifying information (such as the terminals' MAC addresses), to perform a preliminary recognition (a kind of insecure handshake). The significant advantage of this method is that, since the terminals have already paired, it is possible to continue the communication using the resources previously reserved during this initial pairing. In a way, the existing pairing is leveraged to secure it by using a second communication channel, inaccessible to an attacker.Optionally, the transmission of the encryption key (or other security data) can itself be encrypted using a public key of the communication terminal. This public key is then transmitted via the first unsecured channel during the initial pairing phase. This public key is then included in the pairing parameters of the communication terminal, along with, for example, the terminal's MAC address or a terminal identifier (IMEI, IMSI, or other identifier). This strengthens the security of the proposed solution and also allows for the transmission of encrypted data rather than a direct code.

[0046] More specifically, the second pairing phase (B00) in relation to the figure 2 As explained, this second phase includes steps implemented by the communication terminal (Com-Term) and by the slave terminal (P-Term). a generation step (B01) of the encryption key (CK); a transmission step (B02), via the second unidirectional communication channel (CC#2), of said encryption key (CK) in the form of a representation (REPRS); a generation step (B03) of a challenge (Chall) using said encryption key (CK); a transmission step (B04), via the first communication channel, to said communication terminal, of said challenge (Chall); a reception step (B05), via the second unidirectional communication channel, of a representation (REPRS) of said encryption key (CK); a decoding step (B06) of said representation (REPRS) delivering said encryption key (CK); a reception step (B07), via the first communication channel, of said challenge (Chall); a resolution step (B08) of said challenge (Chall) using said encryption key (CK), delivering a (Resp);and a transmission step (B09), via the first communication channel, of the response (Resp) to the challenge (Chall). a reception step (B10), via the first communication channel, of a response (Resp) to the challenge (Chall) from the communication terminal. ;

[0047] If this second pairing phase fails (in other words, the communicating terminal does not have the necessary data to meet the challenge), the identifier of that terminal is "revoked" (marked as "insecure") and the transaction terminal (payment terminal) will not use it to exchange data (for example, to carry out payment transactions). Advantageously, prior to this second phase, the second terminal, which is about to begin the secure transmission phase, limits the radio transmission power of the first transmission channel (for example, for Bluetooth, it switches to class three and the power is limited to one meter): the advantage is that it prevents a potential attacker from capturing exchanged data while at a long distance from the two terminals.

[0048] The encryption key is randomly generated on the transaction terminal and consists of the maximum number of characters possible, ensuring a high level of security for the link between the two terminals. In the case of an application using Bluetooth technology, for example, the encryption key comprises between 64 and 256 bits, and more specifically 128 bits. In this embodiment, the encryption key is a symmetric key, usable by both the transaction terminal and the communication terminal to encrypt exchanges. This symmetric encryption key can then be used to construct, between the two terminals, a cryptosystem based on asymmetric keys.

[0049] Furthermore, the encryption key is generated asynchronously, either before or after the pairing decision between the communication terminal (Com-Term) and the transaction terminal (P-Term), and is therefore not stored in non-volatile memory within the transaction terminal (P-Term). The decision is made during the initial pairing phase. The encryption key is random and volatile.

[0050] When two terminals are already paired, a new pairing can also be established with a new random encryption key, which allows the encryption keys to be changed periodically and thus further increases the security of this link.

[0051] The invention has been described in a particular embodiment. It is understood that the invention is by no means limited to this embodiment. The invention also relates to the terminals used to enable pairing as previously described. More specifically, the invention relates to an acceptor terminal, such as a payment terminal. According to the present technique, the transaction terminal comprises: insecure pairing means (for example, in the form of a standard pairing protocol implemented in a software module), means for generating an encryption key in response to an initial insecure pairing phase, and means for returning the encryption key in the form of a representation.

[0052] All of these mechanisms are controlled by a specifically adapted computer program, based on an initial pairing protocol, to generate an encryption key, transform it into a representation, and then reproduce that representation. The computer program also includes a phase that suspends the pairing process until the pairing procedure has been completed at the communication terminal.

[0053] The invention also relates to a communication terminal, such as a smartphone. According to the present technique, the communication terminal comprises: means for obtaining a representation of an encryption key in response to an initial, insecure pairing phase, and means for decoding the acquired representation that yields an encryption key. These means for obtaining the key may, as previously indicated, consist of an optical sensor, a camera, or a microphone.

[0054] All of these mechanisms are controlled by a specifically adapted computer program, based on an initial pairing protocol, to obtain one or more representations, decode them into an encryption key, and implement the subsequent pairing (challenges / responses). The computer program also includes a phase that suspends the pairing process until the pairing procedure has been completed at the receiving terminal.

[0055] We present, in relation to the figure 3 , an embodiment of a transactional terminal according to the present technique.

[0056] Such a transaction terminal includes a memory 31 consisting of a buffer memory, a processing unit 32, equipped for example with a microprocessor P, and controlled by the computer program 33, implementing the modification process according to the present technique.

[0057] At initialization, the code instructions of computer program 33 are, for example, loaded into RAM before being executed by the processor of processing unit 32. Processing unit 32 receives at least one input, I, such as a pairing decision. The microprocessor of processing unit 32 implements the steps of the pairing process described above, according to the instructions of computer program 33, to deliver processed information T, such as the representation(s) necessary for pairing the terminal. For this purpose, the terminal includes, in addition to buffer memory 31, the previously described means. These means are controlled by the microprocessor of processing unit 32.

[0058] We present, in relation to the figure 4 , an embodiment of a communication terminal according to the present technique.

[0059] Such a device includes a memory 41 consisting of a buffer memory, a processing unit 42, equipped for example with a microprocessor P, and controlled by the computer program 43, implementing the pairing process according to the present technique.

[0060] At initialization, the code instructions of computer program 43 are, for example, loaded into RAM before being executed by the processor of processing unit 42. Processing unit 42 receives at least one input information I, such as a representation from an accepting terminal. The microprocessor of processing unit 42 implements the steps of the modification process described previously, according to the instructions of computer program 43, to deliver processed information T, such as the encryption key. For this purpose, the device includes, in addition to the buffer memory 41, the means described previously. These means are controlled by the microprocessor of processing unit 42.

[0061] As has been perfectly understood, the pairing process as previously described actually comprises a first sub-pairing process which is implemented on the communication terminal and a second sub-pairing process which is implemented on the accepting terminal.

Claims

1. A method for pairing a first terminal, referred to as a communication terminal (Com-Term), seeking to transmit and receive data with a second terminal, referred to as a transactional terminal (P-Term), wherein said method includes: - an unsecured first pairing phase (A00) for pairing said transactional terminal with said communication terminal, delivering at least one pairing parameter for pairing to said communication terminal (Com-Term) via a bidirectional wireless radio first communication channel (CC#1); - a second pairing phase (B00) for pairing said transactional terminal (P-Term) with said communication terminal (Com-Term), wherein said second pairing phase includes: ∘ limitation of the radio transmission power of the first transmission channel by said transactional terminal; ∘ implementation of a unidirectional second communication channel (CC#2), which is used by said transactional terminal to transmit security data for securing said first communication channel (CK) to said communication terminal (Com-Term), as a function of said at least one pairing parameter for pairing to said communication terminal, wherein said security data is transmitted in the form of a representation in the form of a visual or audio sequence; ∘ transmission, by said transactional terminal to said communication terminal, via the first communication channel with a limited radio transmission power, of a challenge (Chall) generated as a function of said security data.

2. A pairing method according to claim 1, characterised in that said second pairing phase (B00) includes, at said transactional terminal (P-Term): - a step of generating (B01) the security data for securing said first communication channel (CK); - a step of transmitting (B02), via the unidirectional second communication channel (CC#2), said security data for securing said first communication channel (CK) in the form of a representation (REPRS); - a step of generating (B03) said challenge (Chall) using said security data for securing said first communication channel (CK); - a step of transmitting (B04), via the first communication channel, said challenge (Chall) to said communication terminal; - a step of receiving (B10), via the first communication channel, a response (Resp) to said challenge (Chall) from the communication terminal.

3. A pairing method according to claim 1, characterised in that said second pairing phase (B00) includes, at said communication terminal (Com-term): - a step of receiving (B05), via the unidirectional second communication channel, a representation (REPRS) of said security data for securing said first communication channel (CK); - a step of decoding (B06) said representation (REPRS), delivering said security data for securing said first communication channel (CK), - a step of receiving (B07), via the first communication channel, said challenge (Chall); - a step of solving (B08) said challenge (Chall) using said security data for securing said first communication channel (CK), delivering a response (Resp); and - a step of transmitting (B09), via the first communication channel, the response (Resp) to said challenge (Chall).

4. A pairing method according to claim 1, characterised in that the security data for securing said first communication channel (CK) is an encryption key.

5. A pairing method according to claim 4, characterised in that said encryption key (CK) is a symmetric encryption key.

6. A pairing method according to claim 1, characterised in that a representation belongs to a representation type and in that said representation type belongs to the group including: - a succession of activations and deactivations of at least one light-emitting diode; - an audio sequence.

7. A pairing method according to claims 1 to 6, characterised in that said communication terminal is a smartphone-type intelligent terminal and in that said transactional terminal is a slave payment terminal of said communication terminal.

8. A method according to claim 7, characterised in that said step of acquiring said representation by said communication terminal includes a step of acquiring a video sequence representative of said representation.

9. An initiator communication terminal seeking to transmit and receive data with an acceptor terminal, including - means for implementing a first unsecured pairing phase for pairing with said acceptor terminal, via a bidirectional wireless radio first communication channel (CC#1); and - means for implementing a second unsecured pairing phase for pairing with said acceptor terminal, via a unidirectional second communication channel (CC#2), including: ∘ means for receiving a representation (RepRs) of security data for securing said first communication channel (Ck) via the unidirectional second communication channel (CC#2) in the form of a representation in the form of a visual or audio sequence; ∘ means for decoding said acquired representation, delivering said security data for securing said first communication channel; ∘ means for receiving a challenge (Chall) via the first communication channel (CC#1) with a limited radio power, ∘ means for solving said challenge (Chall) using said security data for securing said first communication channel (CK), which delivering a response (Resp); ∘ means for transmitting, via the first communication channel (CC#1), the response (Resp) to said challenge (Chall).

10. An acceptor terminal seeking to transmit and receive data with a communication terminal, including: - means for implementing a first unsecured pairing phase for pairing with said acceptor terminal, via a bidirectional wireless radio first communication channel (CC#1); and - means for implementing a second unsecured pairing phase for pairing with said acceptor terminal, via a unidirectional second communication channel (CC#2), including: - means for limiting the radio transmission power of the first transmission channel; - means for generating security data for securing said first communication channel enabling the pairing of said transactional terminal and said communication terminal; - means for transmitting, via a unidirectional second communication channel, said security data for securing said first communication channel to the communication terminal, wherein said security data is transmitted in the form of a representation in the form of a visual or audio sequence; - means for transmitting to said communication terminal, via the first communication channel with a limited radio transmission power, a challenge generated as a function of said security data.

11. A computer program product downloadable from a communications network and / or stored on a computer-readable medium and / or executable by a microprocessor, characterised in that it includes program code instructions for executing a pairing method according to claims 1 to 8 when it is executed by a processor.