Method for entering a code on a touch surface of an electronic payment terminal

Abstract

The invention relates to a method for entering, on a touch surface (12), a code comprising a first number of characters, the method comprising: a) detecting contact exerted by a user on the touch surface (12); b) emitting, by the touch surface (12), a series of at least one counting vibration (26, 28, 30, 32) that can go up to a second number of vibrations; c) detecting the cessation of contact after a third number of vibrations, which is included between 1 and the second number; d) recording the third number of vibrations, which corresponds to a character of the code; e) repeating steps a) to d) until a number of characters equal to the first number is recorded, wherein, when the series of at least one counting vibration comprises two counting vibrations (26, 28, 30, 32), two consecutive counting vibrations are separated by a time interval (D1, D2, D3), the duration of which is random.

Description

METHOD FOR ENTERING A CODE ON A TOUCH SURFACE OF AN ELECTRONIC PAYMENT TERMINAL

[0001] The invention relates to a method for entering a code on a touch-sensitive surface. More specifically, the invention relates to the secure entry of a confidential identification code on a touch-sensitive surface of an electronic device such as an electronic payment terminal by a user with a visual impairment, for example a visually impaired or blind user. The invention also relates to a payment method comprising the steps of the entry method, as well as to an electronic payment terminal for implementing the entry method. The invention can also be implemented for entering an identification code on a telephone. State of the art

[0002] It is difficult for a visually impaired person to enter their PIN confidentially on an electronic payment terminal. Indeed, using a virtual keyboard on a touchscreen requires that the screen keys be detected visually. Using voice commands is not an option because a malicious person could intercept the code. There are boxes that can be added to the terminal to communicate in Braille with the payment terminal, but these systems are complex to implement because they require the installation of an additional part on the terminal, and Braille is increasingly less used (10 to 15% of the blind population).

[0003] Already known in the prior art, from document US10489567, is a method for entering a personal identification number (PIN, also called a PIN code) that does not require the installation of an additional part for use by a visually impaired user. To do this, the user communicates with the touch surface by exerting different levels of pressure on the touch surface, for a specific period of time. Each character of the code corresponds to a pressure exerted at a certain level, for a certain time. The change in pressure indicates to the terminal that a character of the code has been entered and that the entry of another character of the code begins. The user indicates that the entry of the code is complete by ceasing to exert pressure.This allows the user to enter the code without having to move their finger or stylus away from the surface, which prevents a malicious person from entering the code, for example by simply timing the time during which pressure is applied to enter a character. However, such a method is complex to implement because the user must concentrate on the time passing and the level of pressure applied, and the terminal must be equipped with a pressure sensor.

[0004] Also known from document CN107908936 is an electronic password entry system. The system includes a touch key, and after the touch key has been pressed by a finger, a micro-vibration mechanism is triggered, micro-vibrations which are returned to the finger. To enter a digit of the password, the user releases the pressure after counting the number of micro-vibrations corresponding to the digit to be entered. Such a method is simpler to implement. However, by simple timing, a malicious person could quite easily succeed in identifying the entered character.

[0005] To enhance the security of the entry process, Kamarushi et al. also describe an interface to improve PIN entry and security for the visually impaired or blind, in which a number is entered by pressing a button on the screen, which triggers vibrations. A number is entered by counting the vibrations and then releasing the pressure. To enhance security, randomized times are introduced into the vibration sequence. India Gesu describes a similar security system. However, the security level of such an entry process may be perceived as low, because an observer who manages to spy on the number of vibrations emitted by the system, for example using an accelerometer, could succeed in identifying the entered code.

[0006] The invention aims in particular to increase the security level of the input process, to a level acceptable to security organizations, in particular PCI DSS.

[0007] To this end, the subject of the invention is a method for entering a code comprising a first number of characters, preferably four characters, on a touch-sensitive surface, comprising the following steps: a) detecting contact made by a user on the touch-sensitive surface, b) emitting by the touch-sensitive surface a series of at least one counting vibration which can go up to a second number of counting vibrations, c) detecting the stopping of the contact after a third number of counting vibrations included between 1 and the second number, d) recording the third number of counting vibrations which corresponds to a character of the code, e) repeating step a) up to step d), until recording a number of characters equal to the first number, in which method, when the series of at least one counting vibration comprises at least two counting vibrations,two consecutive counting vibrations are separated by a time interval whose duration is random.

[0008] Haptic feedback is used to guide the user through the counting required to enter the code. This simplifies code entry for visually impaired users, or any other user. The user is only required to maintain pressure while counting the vibrations until the number of vibrations corresponds to the character to be entered, then release the pressure. This improves the input result, i.e., it encourages the entry of a correct code while maintaining the confidentiality of the feedback, for the user who placed their finger, and for them alone (as opposed to audio feedback).

[0009] Furthermore, the process requires a fairly simple process implementation device, which must not discriminate between different pressure levels, and which therefore requires very little learning.

[0010] Because the interval is a random time, the time taken to enter a character is unknown, and an attacker cannot identify a character simply by timing the time it is pressed. This increases the security of the process.

[0011] It is thus understood that to enter a code according to the method described above, a total number of counting vibrations is emitted which corresponds to the sum of the third numbers of counting vibrations.

[0012] It is understood that the touch surface is part of an electronic device such as an electronic payment terminal or a telephone, and that said electronic device is equipped with an operating system. To implement the method, an application of the electronic device is launched. The touch surface comprises at least one haptic actuator coupled to at least one touch key of the touch surface. The electronic device also comprises a counter of vibrations emitted by the at least one haptic actuator. During step a), the contact is detected by a sensor of a touch key of the touch surface, coupled to the haptic actuator, which triggers step b) and the start of the vibration counter. During step c), the application takes into account the number of counting vibrations for its recording during step d) in a memory of the electronic device.To improve system security, the haptic element is controlled by a secure part of the terminal ("Trust zone" or "secure element"), to ensure software integrity and thus prevent spyware from collecting haptic information. This makes it more difficult for a hacker to attack the software.

[0013] The characters in the code can be numbers or letters, or special characters such as symbols.

[0014] Contact generally corresponds to the pressure of a user's finger on the touch surface.

[0015] In a particularly advantageous embodiment, at least one decoy vibration is emitted at the end of at least one step c), while contact is no longer detected.

[0016] It is understood that this at least one decoy vibration is an additional vibration that is not taken into account for the identification of the entered character, unlike a counting vibration. It is also different from a calibration vibration as described below, which is emitted between step a) and step b). This at least one decoy vibration is not perceived by the user's finger; only the terminal knows when the contact has ceased, which corresponds to the moment when the user has removed his finger when the contact is made by pressure from a user's finger. Thus, the use of an accelerometer, stuck on the terminal, would not allow a malicious person to guess the entered code. The same is true for a malicious person, who would hear and count the vibrations. This increases the entropy of the code.

[0017] Furthermore, by adding at least one decoy vibration, the total number of vibrations emitted to enter the code is increased. This total number corresponds to the total number of counting vibrations, to which is added the total number of decoy vibrations. However, the higher the total number of vibrations, the greater the possible number of combinations to enter the code. Indeed, the possible number of combinations corresponds to the average number of vibrations emitted to encode a character multiplied by itself as many times as the first number of characters in the code. For example, if the code includes 4 characters, the number of combinations is the average number of vibrations emitted to encode a character, to the power of 4. Thus, thanks to the at least one decoy vibration, the total number of vibrations is increased, and the entropy of the code is increased.

[0018] The at least one decoy vibration is emitted by the same haptic actuator as the counting vibrations, or by another haptic actuator, coupled to a vibration sensor.

[0019] Preferably, the touch surface emits a random number of lure vibrations after contact has ceased.

[0020] The decoy vibrations may be emitted before step e), i.e. for example during the recording of a character of the code, or at least before a new contact is detected during a new step a). For example, when the code comprises 4 characters, decoy vibrations may be emitted after the entry of the first, second, third or fourth and last character of the code. The decoy vibrations may also be emitted after step c) relating to a last character of the code.

[0021] Depending on other optional features of the process, taken alone or in combination:

[0022] - For each character, a fourth average number of vibrations is emitted, which corresponds to the ratio of a total number of counting vibrations and decoy vibrations emitted during the input process, to the first number of characters included in the code,- the first number of characters included in the code is equal to 4, and- the fourth average number is at least equal to 8.5, preferably greater than or equal to 9, even more preferably greater than or equal to 10, and more preferably, it is equal to approximately 10. Under these conditions, the number of possible combinations is at least 8.5 to the power of 4, i.e. more than 5000 combinations. In a variant, the total of the number of counting vibrations and the number of decoy vibrations emitted for each character is at least equal to 8, preferably at least equal to 9, and more preferably at least equal to 10.

[0023] - For each character, the total number of counting vibrations and lure vibrations is equal to the fourth average number of vibrations, for example equal to 10.

[0024] - At least one decoy vibration is emitted only after step c) relating to a last character of the code. The emission of these decoy vibrations is therefore done at the end of the transaction, and the presence of the user during the emission of these decoy vibrations is not required. This optimizes the entry time while ensuring improved security. It is understood that the at least one decoy vibration emitted only after step c) relating to a last character of the code is at least one decoy vibration as defined in claim 1.

[0025] - At least one decoy vibration is emitted before at least one step e). It is understood that the at least one decoy vibration emitted before step e) is at least one decoy vibration as defined above.

[0026] - A total number of counting vibrations and decoy vibrations for entering a character before step e) is at most 12, preferably at most 10. Thus, the code entry time is not excessively prolonged. Preferably, for entering each character, a total of at least 8 vibrations are emitted, preferably at least 9 vibrations, and at least 10 vibrations. Thus, if the number of counting vibrations for entering a character is less than the total number of at least 8 vibrations, the counting vibrations are supplemented by decoy vibrations to reach this minimum number of vibrations. For example, if 7 counting vibrations are emitted to enter the number "7", then a decoy vibration is emitted. If at least 8 vibrations per character are emitted, this corresponds to at least 8 4combinations, or at least 4096 combinations. This number is at least 10000 combinations for a minimum of 10 vibrations per character.

[0027] - At least one decoy vibration is emitted before at least one step e) and at least one decoy vibration is emitted after step c) relating to a last character of the code.

[0028] - An audible signal is emitted for each character after step c) or at the end of the emission of the at least one decoy vibration. The user is thus notified that the character has been entered, and that he can, if necessary, resume the process at step a). Thus, it is not sufficient to detect when the finger has been lifted to identify the character entered. Preferably, the user is authorized to resume the process at step a) without waiting for the emission of the audible signal. Thus, the malicious person will not be able to determine which step of the process is in progress. It is understood that the audible signal is emitted by the electronic device which includes the touch surface (electronic payment terminal or telephone).

[0029] - In the case where several decoy vibrations are emitted consecutively during the same step of the process, the time interval between two consecutive decoy vibrations is less than a minimum time interval between two consecutive counting vibrations. For example, if the time interval between two counting vibrations can vary between 0.1 and 3 seconds, then the time interval between two consecutive decoy vibrations is less than 0.1 second. Thus, the code entry time is reduced.

[0030] - In at least one step a), at least two contacts made by a user on the touch-sensitive surface are detected. The at least two contacts are, for example, made by the user pressing at least two fingers on the touch-sensitive surface. Thus, by making several contacts, a character is entered more quickly because each contact triggers the emission of a series of at least one counting vibration. In addition to being faster, inputting using several contacts increases overall security, because there are thus several ways to enter a character. The at least two contacts are preferably simultaneous, so as not to lengthen the input time, or if the contact time is different, the briefest contact is made entirely during the longest contact. Advantageously, all contacts begin at the same time.In this embodiment, the touch-sensitive surface comprises at least two haptic actuators each coupled to at least one touch-sensitive key of the touch-sensitive surface. The vibration counter counts the vibrations emitted by the at least two haptic actuators. The input advantageously uses two or three contacts. It is understood that the at least two contacts are not necessarily exerted for the same duration of time. Thus, each contact triggers the emission of an independent number of counting vibrations. The number of counting vibrations required to input a character is thus easily emitted.

[0031] - The method further comprises, after step a) and before step b) relating to a first character of the code, a step during which a first vibration of constant amplitude is emitted, called the first calibration vibration, followed by a second vibration whose amplitude is decreasing, called the second calibration vibration. Thus, before entering the characters, the user is allowed to familiarize himself with vibrations emitted by the touch surface, and he is informed that the entry is about to begin. This step allows a “sensory calibration”, according for example to the work of the Acoustic Vibrations laboratory of INSA Lyon. This encourages the entry of a correct code. Advantageously, each of these calibration vibrations lasts approximately one second.Typically, the first calibration vibration has a frequency of 200 Hz with an amplitude of 100%, the second calibration vibration has a decreasing amplitude from 100% to 0%. The vibrations are typically emitted by a haptic actuator, for example a linear resonant actuator (LRA). For such an LRA actuator, the 100% amplitude is, for example, 1.2 g, i.e., 11.76798 m / s. 2 . For an LRA, the amplitude can range from 0.6 to 10 g depending on its size. Piezoelectric oscillators have acceleration amplitudes of up to several tens of g, depending on their size, and have a much wider frequency range.

[0032] - During at least one step b), the amplitude of the counting vibration increases to a maximum, then decreases. In one example, the amplitude increases linearly to the maximum, then decreases linearly. Advantageously, the increase from 0 to 100% is done as quickly as possible, as well as the decrease, so as not to be confused with the sensory calibration phase. In general, the maximum amplitude is defined so that it is perceptible by the user's finger (at least 0.3 g at the level of contact with the finger), but also so that it is not audible to a person located one meter from the electronic device.

[0033] - The touch surface is a touch surface of an electronic payment terminal. The code can be a confidential identification code.

[0034] - During step b), the counting vibrations are separated by a random time interval, between 0.1 and 2 seconds, preferably between 0.2 and 1.5 seconds. Thus, the time dedicated to entering the code is not too long but the intervals are long enough for the user to be able to release his pressure at the right time. This reduces the risk of input errors. User comfort is good while input efficiency is correct. Furthermore, the random duration parameter allows to gain entropy on the code, and thus reduce the possibilities for a potential hacker to guess the code. Finally, when the time interval can vary between 0.2 and 1.5 seconds, there is a multiplier of 7.5 between the smallest interval and the largest interval. A multiplier of 5, or even 10, allows to provide good entropy.This results in a large variation in input time, which complicates code identification. The higher the multiplier, the greater the entropy.

[0035] - In step b), the counting vibrations are emitted at a frequency ranging from 100 to 300 Hz, preferably 200 Hz.

[0036] - In step b), each counting vibration is emitted for a duration of between 0.1 and 2 seconds, preferably between 0.2 and 0.6 seconds, for example 250 ms.

[0037] The invention also relates to a method for entering a code on a touch-sensitive surface as described above, in which during step a), at least two contacts made by a user on the touch-sensitive surface are detected. However, this other subject according to the invention is not limited to a method in which at least one decoy vibration is emitted at the end of step c), while the contact is no longer detected.

[0038] The invention also relates to a payment method comprising the steps of the method for entering a confidential code as described above, further comprising at least one of the following steps: - prior to step a) relating to a first character of the code, vocal statement of the amount of the transaction, - after step e), transmission of a vocal message providing information on the outcome of the entry.

[0039] The invention also relates to an electronic payment terminal comprising a touch-sensitive surface configured to implement the method for entering a code as described above, the touch-sensitive surface being equipped with a haptic actuator configured to execute step b) of the method. The haptic actuator is for example a piezoelectric actuator, a linear resonant actuator (LRA), which uses a magnetic mass suspended by springs, or a vibrating motor with an eccentric rotating mass (ERM). The piezoelectric actuator has the advantage of being compact and having a wide frequency range (remains effective between 50 and 1000 Hz). Where appropriate, the haptic actuator is also configured to emit first and second calibration vibrations. Brief description of the figures

[0040] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0041] [The] illustrates different steps of a method of entering a code according to an embodiment of the invention;

[0042] Illustrates the evolution over time of vibrations emitted during a step illustrated on the;

[0043] Illustrates other steps of the process shown in the ;

[0044] Illustrates the evolution over time of vibrations emitted during stages illustrated on the. Detailed description

[0045] Figures 1 and 3 show different steps of a method for entering a code according to the method of the invention, during which an electronic payment terminal 10 is manipulated by a user. Prior to these steps, a transaction amount has been entered by a merchant. If necessary, the merchant has carried out the steps required for the entry to be made using the method according to the invention. More specifically, the merchant has launched an application allowing the implementation of the method. For use by a visually impaired person, the transaction amount can be spoken. When entering the code, the user can be guided vocally. The code to be entered comprises a first number of characters. For example, the code comprises 4 digits, and these digits are whole numbers ranging from 0 to 9.The PIN code entry by the blind person must be done ergonomically (for example, minimizing user errors), but also securely (a potential hacker must have great difficulty extracting the entered code).

[0046] The terminal 10 optionally comprises a contactless card reader, a smart card reader and a magnetic card reader, not shown. It also comprises a touch-sensitive surface 12, enabling in particular the viewing of information such as transaction amounts, and the entry of these same amounts as well as confidential customer identification codes. The terminal 10 also comprises electronic components assembled in one or more secure enclosures, not shown. All these components are included in a housing 14. The touch-sensitive surface 12 of the electronic payment terminal 10 according to the invention comprises at least one haptic actuator coupled to one or more keys of the touch-sensitive surface, not visible in the figures. The haptic actuator is configured to enable the emission by the touch-sensitive surface 12 of vibrations emitted during steps of the entry method.The terminal also includes a vibration counter emitted by one or more haptic actuators of the touch surface.

[0047] In Figures 1 and 3, the terminal 10 is shown in the hands 16 of a user. More precisely, during the various steps, the housing 14 of the terminal 10 rests in the hands 16 of the user.

[0048] The figure illustrates three steps in the input process, during which sensory calibration is performed. These steps take place before the code is entered.

[0049] First, the user takes hold of the terminal 10, step P, that is to say the housing 14 of the terminal 10 rests in his hands, and the hands 16 are in contact with the housing 14. During this step P, the hands 16 are not in contact with the touch surface 12. Alternatively, the method can be implemented on a fixed terminal or on an unattended payment terminal.

[0050] After launching the dedicated application, the user is asked to establish contact with the touch surface 12. The contact is established by means of a finger 18 of the user, step CC. It could be established by means of a stylus. The user can establish this contact anywhere on a touch key of the touch surface 12. The finger 18 therefore comes into contact with the touch surface 12, step CC, which is symbolized by the reference 20. The contact 20 is maintained during the step following step CC.

[0051] Following step CC, step a) of the method according to the invention is carried out, during which the contact exerted by the user on the touch key of the touch surface 12 is detected. The touch key is equipped with a sensor, itself coupled to a haptic actuator of the touch surface.

[0052] As soon as the contact 20 is detected, a first sensory calibration vibration 22 is emitted, followed by a second calibration vibration 24, during the VC step.

[0053] Illustrates the evolution over time, expressed in seconds, of the amplitude of vibrations 22 and 24, expressed in m / s 2 . As illustrated in the, the first calibration vibration 22 is continuous, that is to say that its amplitude is constant. The amplitude of the second calibration vibration 24 is decreasing, from 100%, down to 0%. Each of these vibrations 22, 24 lasts approximately one second. In the, the first vibration 22 has a frequency of 200 Hz and an amplitude of 100%, the second vibration 24 has a decreasing amplitude from 100%. Thus, before entering the characters, the user is allowed to familiarize himself with vibrations emitted by the touch surface, and he is informed that entry is about to begin.

[0054] After a random time, between 0.5 and 5 seconds (preferably 2 seconds), code entry can begin. This random time increases the entropy of the code.

[0055] La illustrates the entry of the numeric character “4” using the entry method according to the invention. La represents a case in which the number “4” is not the first character of the code. It follows another character that has already been entered. Also, the contact 20 has been stopped, step P. If, in another case not described, the number “4” was the first character of the code, its entry would be carried out directly after the sensory calibration step described in Figures 1 and 2, and the finger 18 would already be in contact 20 with the touch-sensitive surface 12, step C1 of contact between the user’s finger 18 and the touch-sensitive surface 12. In this other case, the contact 20 would have been maintained since the calibration, for 1 second as specified above.

[0056] In step C1, the contact 20 is established in the same way as in step CC. Step a) of the method according to the invention is then carried out, during which the contact 20 exerted by the user on the touch-sensitive surface 12 is detected.

[0057] Following detection of the contact 20, step b) of the method according to the invention is carried out, during which the touch surface 12 emits a series of at least one counting vibration 26 which can go up to a second number of vibrations. The counting vibrations are counted by the vibration counter. The counting vibrations 26 make it possible to code each character of the code, for example each digit from 0 to 9 of the code which comprises 4 digits. Each of these digits is coded by a determined number of vibrations. For example, the number of vibrations coding for a digit is equal to the digit it codes. Thus, "9" is for example coded by nine vibrations. In the example described, it is intended to code "0" by 10 vibrations. Thus, to code a digit, a series of at least one counting vibration is emitted, which can go in the example up to a second number of vibrations equal to 10.Thus, a third number of counting vibrations between 1 and 10 is emitted, corresponding to the character to be entered. In one embodiment, and this to allow a malicious person to be deceived, the number of vibration sequences can also be greater than 10. Thus, if the user lifts his finger at the 12th vibration, the number retained will be 2 (1 for 11 vibrations, 2 for 12, 3 for 13, etc.). Indeed, this makes it more difficult for a malicious person to guess the low-value numbers. Thus, the entropy is reinforced on all the numbers. The user can, for example, choose to stop at 23, to enter the number 3. Thus, in the case where a character of the code is a number, by number of counting vibrations which corresponds to a character of the code, it is understood that the number can be equal to the number of vibrations or to the number of vibrations modulo 10.

[0058] In the example of 1a, the number "4" is entered by proceeding as follows. In steps V1, V2, V3 and V4, a counting vibration 26, 28, 30 and 32 are emitted respectively. As shown in 1a, the counting vibrations 26, 28, 30 and 32 are separated by a time interval D1, D2 and D3. The time intervals D1, D2 and D3 each take place during a contact step, respectively C2, C3 and C4, during which the contact 20 is maintained but there is no vibration.

[0059] When the number of counting vibrations emitted corresponds to the third number, here “4”, the user stops the contact 20, step P, in which the hands 16 are not in contact with the touch surface 12. Step c) of the method according to the invention then proceeds, during which the stopping of the contact 20 is detected after the third number of vibrations.

[0060] We then proceed to step d) of the method, i.e. the third number of counting vibrations is recorded, here “4”, which corresponds to the character of the code entered, here “4”.

[0061] In an advantageous embodiment, and to increase the entropy of the code, the terminal can continue to emit a random number of vibrations, called "decoy vibrations", even after the user's finger is no longer in contact with the touch surface. Thus, at least one decoy vibration is emitted at the end of step c), while the contact is no longer detected. These decoy vibrations are not perceived by the user, only the terminal knows when the user removed his finger. Thus, the use of an accelerometer, stuck on the terminal, would not allow a malicious person to guess the entered code. In the variant described, the at least one decoy vibration is emitted before step e). Preferably, a total number of counting vibrations and decoy vibrations for entering a character before step e) is at most equal to 12, preferably at most equal to 10.This way, the time taken to enter the code is not excessively prolonged.

[0062] To enter the following characters of the code, repeat step a) until step d), until a number of characters equal to the first number is recorded, 4 characters in the example.

[0063] In a particularly advantageous variant of the embodiment involving decoy vibrations, the at least one decoy vibration is emitted after step c) relating to a last character of the code. The emission of these decoy vibrations is therefore done at the end of the transaction, and the presence of the user during the emission of these decoy vibrations is not required. This optimizes the entry time while ensuring improved security.

[0064] In a very advantageous variant of the embodiment involving decoy vibrations, for each character, a fourth average number of vibrations is emitted, which corresponds to the ratio of a total number of counting vibrations and decoy vibrations emitted during the input process, to the first number of characters included in the code. When the first number of characters included in the code is equal to 4, it is particularly advantageous for the fourth average number to be at least equal to 8.5, preferably greater than or equal to 9, even more preferably greater than or equal to 10, and preferably, it is equal to approximately 10. Under these conditions, the number of possible combinations is at least 8.5 to the power of 4, or more than 5000 combinations.In one variant, the total of the number of counting vibrations and the number of decoy vibrations emitted for each character is at least 8, preferably at least 9, and more preferably at least 10.

[0065] Thus, decoy vibrations are added depending on the character to be entered. For example, to obtain a fourth average number of 8.5 for a 4-character code, the number of decoy vibrations indicated is added to the following digits: - for the digit "1": between 3 and 7 decoy vibrations, - for the digit "2": between 3 and 5 decoy vibrations, - for the digit "3": between 2 and 5 decoy vibrations, - for the digit "4": between 0 and 5 decoy vibrations - for the digit "5" or a higher digit including 0: between 0 and 5 decoy vibrations.

[0066] In another embodiment, at least two contacts made by a user on the touch-sensitive surface are detected during step a). The at least two contacts are made by the user pressing at least two fingers on the touch-sensitive surface. Thus, by making several contacts, a character is entered more quickly because each contact triggers the emission of a series of at least one counting vibration. In addition to being faster, inputting using several contacts increases overall security, because there are thus several ways to enter a character.

[0067] For example, with one, two or three fingers, there are two ways to enter the number "1", and four ways to enter the number "2", as shown in the table below, when the number is equal to the number of counting vibrations or the number of vibrations modulo 10.

[0068] Character obtained based on the number of fingers and the number of vibrationsNumber of fingers presentNumber of vibrations123CharacterNumber of possibilities per character11231222462433693244824455055266286477417288648499879210000104

[0069] By increasing the number of vibrations, for example by accepting 12 vibrations triggered by a touch, the number of ways to enter numbers is further increased, as shown in the table below.

[0070] Character obtained based on the number of fingers and the number of vibrationsNumber of fingers presentNumber of vibrations123CharacterNumber of possibilities per character112313224626336933448245550552662865774172886484998792100001041112312246

[0071] Advantageously, the at least two contacts are not necessarily made for the same length of time. For example, to enter "8", the user can leave three fingers in contact for two vibrations, then leave only two fingers in contact for one additional vibration. Thus, with the time duration of four counting vibrations, and three contacts, a number between 0 and 9 can be entered. This increases the speed by 60% compared to a solution with a single contact and makes it more difficult for a malicious person to identify the code. In this embodiment, the use of decoy vibrations is reduced, even if they also increase the overall security of the code.

[0072] As shown in the, in the example the series of at least one counting vibration comprises at least two counting vibrations, more precisely four vibrations 26, 28, 30 and 32, and two consecutive counting vibrations are separated by a time interval D1, D2, D3 whose duration is random. Indeed, the durations D1, D2 and D3 are different from each other. Due to the interval of a random duration, the time required to enter a character is unknown and a malicious person cannot identify a character by simply timing the pressure time.

[0073] In the example, the counting vibrations 26, 28, 30 and 32 are separated by a time interval D1, D2, D3 of a duration of 1 second, 0.85 seconds and 3 seconds respectively.

[0074] In the example, during step b), each counting vibration 26, 28, 30 and 32 is emitted for a duration of between 0.8 and 1.6 seconds.

[0075] In the example, during step b), the amplitude of the counting vibration increases from 0 to 100%, then decreases to 0%. For better ergonomics, the amplitude of the vibration should increase from 0 to 100% in the shortest possible time.

[0076] The steps of the entry process are part of a payment process which also includes the following steps: - prior to step a), vocal statement of the transaction amount, - after step e), transmission of a vocal message informing about the outcome of the entry.

[0077] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. In particular, it is possible to implement the method without resorting to sensory calibration steps, or by having the sensory calibration at each digit entered, which is longer but easier. List of bibliographic references

[0078] - US10489567- CN107908936- Kamarushi et al., Proc. ACM Hum.-Comput. Interact., vol. 6, No. MHCI, art. 212, 2022- India Gesu https: / www.researchgate.net / publication / 329758413_TouchPIN_Numerical_Passwords_You_Can_Feel / link / 5c19371c92 851c22a33490ac / download?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6InB1YmxpY2F0aW9uIiwicGFnZSI6InB1YmxpY2F0aW9uIn19 List of numerical references in figures

[0079] 10: electronic payment terminal12: touch surface14: housing16: hands18: finger20: contact22: first calibration vibration24: second calibration vibration26: first counting vibration28: second counting vibration30: third counting vibration32: fourth counting vibrationP: gripping stepCC: contact step for calibrationVC: vibration step during calibrationC1, C2, C3, C4: contact steps during countingV1, V2, V3, V4: vibration steps during counting

Claims

Method for entering on a touch-sensitive surface (12) a code comprising a first number of characters, preferably four characters, comprising the following steps:a) detecting a contact made by a user on the touch-sensitive surface (12),b) emitting by the touch-sensitive surface (12) a series of at least one counting vibration (26, 28, 30, 32) which can go up to a second number of counting vibrations,c) detecting the stopping of the contact after a third number of counting vibrations included between 1 and the second number,d) recording the third number of counting vibrations which corresponds to a character of the code,e) repeating step a) up to step d), until recording a number of characters equal to the first number,method in which, when the series of at least one counting vibration comprises at least two counting vibrations (26, 28, 30, 32), two consecutive counting vibrations are separated by a time interval (D1, D2,D3) whose duration is random, characterized in that at least one decoy vibration is emitted at the end of at least one step c), while contact is no longer detected., Method for entering a code according to claim 1, wherein:- for each character, a fourth average number of vibrations is emitted, which corresponds to the ratio of a total number of counting vibrations and decoy vibrations emitted during the entry method, to the first number of characters included in the code,- the first number of characters included in the code is equal to 4, and- the fourth average number is at least equal to 8.5, preferably greater than or equal to 9, even more preferably greater than or equal to 10, and preferably, it is equal to approximately 10. A method of entering a code according to claim 2, wherein, for each character, the total number of counting vibrations and decoy vibrations is equal to the fourth average number of vibrations, for example equal to 10. Method for entering a code according to any one of claims 1 to 3, in which at least one decoy vibration is emitted only after step c) relating to a last character of the code. Method for entering a code according to any one of claims 1 to 3, in which at least one decoy vibration is emitted before at least one step e). A method of entering a code according to claim 5, wherein a total number of counting vibrations and decoy vibrations for entering a character before step e) is at most 12, preferably at most 10. Method for entering a code according to any one of claims 1 to 6, in which an audible signal is emitted for each character after step c) or at the end of the emission of the at least one decoy vibration. Method for entering a code according to any one of claims 1 to 7, in which during at least one step a), there is detection of at least two contacts made by a user on the touch surface. Method for entering a code according to any one of claims 1 to 8, further comprising after step a) and before step b) relating to a first character of the code, a step during which a first vibration of constant amplitude (22) is emitted, called the first calibration vibration, followed by a second vibration (24) whose amplitude is decreasing, called the second calibration vibration. A method of capturing according to any one of claims 1 to 9, wherein during at least one step b), the amplitude of the counting vibration increases to a maximum, then decreases. Payment method comprising the steps of the method for entering a confidential code according to any one of claims 1 to 10, further comprising at least one of the following steps: - prior to step a) relating to a first character of the code, vocal statement of the amount of the transaction, - after step e), transmission of a vocal message providing information on the outcome of the entry. Electronic payment terminal (10) comprising a touch surface (12) configured to implement the method of entering a code according to any one of claims 1 to 10, the touch surface (12) being equipped with a haptic actuator configured to execute step b) of the method.

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