ES2424298A1 - Method and system for contactlessly and anonymously accrediting groups with a minimum of users - Google Patents

Abstract

Each member in the group has an individually identifiable computing device with telecommunications capability, and the method proposes contactless interaction with the computing devices from a control centre, establishing conditions for a transaction, and determining the number of members by acquiring and counting a total number of partial digital signatures carried out by the members by means of a computer application in the computing device thereof which implements an identity-based digital signature scheme with a dynamic threshold, guaranteeing the anonymity of the members in the group. The system comprises the computing devices with an installed computer application, an accreditation station with means for interacting with the devices and a certification authority.

Description

Method and system of collection without contact, for the use of a road, for high occupancy vehicles

Technical sector

The present invention refers, in a first aspect, to a method of contactless charging, by the use of a road, in particular a toll road such as a highway, through which high-occupancy vehicles circulate.

The invention aims to facilitate the collection at a contactless toll station in a secure and personalized way, adapting the amount to be paid to the number of occupants or passengers of the vehicle, while ensuring their privacy.

The invention proposes two variants of the method for non-contact charging of a toll (for the use of a road), a first for the case in which the toll fee is calculated independently of the entry points on the highway (without a ticket) ) and another in the case where vehicles receive a ticket at the entrance of the highway and are charged according to the number of kilometers traveled (with ticket).

The invention also concerns, in a second aspect, a system for implementing the aforementioned non-contact charging method.

Background of the invention

Concerns about carbon dioxide emissions are motivating new toll collection schemes with the aim of offering lower rates for vehicles that transport more occupants (high occupancy vehicles or VAOs).

Some previous inventions disclose toll payment systems and / or methods that attempt to comply with the standards established for the use of lanes for shared vehicles.

US 2001/0137773 Al, 'Devices, Systems and methods for identifying and / or billing an individual in a vehicle' by Potts et al., Proposes a solution in which each occupant has a mobile device that transmits an identifier unique to some device of the vehicle that, by means of an antenna, determines according to its proximity who the driver is and communicates with the toll booth.

In US 2010/0106567 Al, 'System and method for electronic toll collection based on vehicle load' by McNew et al., The vehicle has an electronic card that transmits an identifier and the number of occupants in the vehicles. This number is obtained through the use of different methods, and the toll station will subsequently verify the accuracy of the data received.

US 7,091,880 B2, 'Licensed driver detection for high occupancy toll lane qualification' by Sorensen et al., Suggests that each vehicle has a driver's license reader. Once the license is read, the resulting data is encrypted and transmitted to the entity responsible for the toll. US 7,408,480 B2, 'Dual mode electronic toll collection transponder' by Sun Yee Woo et al., Proposes a system in which, through a transmitter installed in the vehicle, data such as license plate number, vehicle emissions, etc. they are transmitted in encrypted mode to an external system that will charge the amount to the vehicle.

S

US 4,303,904 A 'Universally applicable, in-motion and automatic toll paying system using microwaves' by Chasek et al., Proposes the use of an internal transceiver in the vehicle that transmits the necessary information to calculate the amount. JP 2000/172892 'A vehicle charge calculating system' proposes the use of external devices to determine vehicle emissions and calculate the amount to be paid.

US2010161392 (Al) proposes, in an exemplary embodiment (see paragraph [0028]), to count the number of occupants of a vehicle by detection, by an RFID reader implemented, for example, in a device of one of the occupant RFID tags of devices or elements carried by other occupants.

10

All the previous inventions only describe automated methods of managing a toll system in a collective transport lane with different devices to detect people or the carbon emissions generated by the vehicle through the use of additional devices in the vehicles themselves.

fifteen

In US20040049424Al proposes a method and system to promote shared travel (ridesharing) that describes (see paragraph [56]) determine the number of quot; participants traveling togetherquot; locating the mobile phones carried by them, and make a charge based on the number of occupants.

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Autonomous computing devices with telecommunication capabilities are also used in the present invention, such as a smart mobile phone (for example, a next-generation mobile phone or smartphone) for each occupant of the vehicle, but privacy is guaranteed as a relevant feature and the anonymity of the occupants, during their recount.

Exhibition of the invention

25 30 35

The present invention provides to achieve the objective explained, in a first aspect, a method of non-contact charging, by the use of a road, designed to manage high occupancy vehicles, in which as a premise it is established that each of the occupants of a vehicle that implements the charging method must have an autonomous computing device with telecommunication capability, identifiable by means of an individual identifier Id, or network address, such as a smart mobile phone comprising the method determining the number of occupants of a vehicle using information about said autonomous computing devices with telecommunication capability, through a contactless interaction with them from a track control center or charging station, to provide a payment amount for the use of the track, in function of the number of occupants of the vehicle. Such contactless interaction uses a known telecommunication technology, chosen among Bluetooth, Wifi, RFID, or any other, that supports autonomous computing devices with telecommunication capabilities of the vehicle's occupants.

   In contrast to the proposals of the aforementioned state of the art documents, the contactless collection method of this invention proposes that said determination of the number of occupants be carried out by the acquisition and counting of a total number of partial digital signatures made for each of the occupants of the vehicle through a computer application housed in their respective

35

Autonomous computing device with telecommunication capability, an application that implements a digital signature scheme based on identity, with dynamic threshold, which guarantees the anonymity of said occupants of the vehicle and the security of the interaction control center (or charging station / toll) -occupants.

For the implementation of the method, it is also foreseen that each occupant of the vehicle acquires before or at the time of the trip (but before making the payment) an amount as a credit that provides a payment code and the payment is made in said center of control, without contact, by one or more of the occupants, from their autonomous computing device with telecommunication capability, maintaining anonymity.

On the other hand, the aforementioned non-contact interaction control center-occupants includes the participation of a certifying authority that provides each of the occupants of the vehicle with a set of public keys and private keys to perform the said partial digital signatures.

In a second aspect the invention proposes a collection system, without contact, for the use of a road, for high-occupancy vehicles, which integrates the following elements:

-

a station for charging a variable rate for the use of the road, with telecommunication means;

-

an autonomous computing device, for each of the occupants, with telecommunication capability (for example a smart mobile phone), with an individual identifier Id or network address;

-

at least one application installable in autonomous computing devices with telecommunication capability, to implement the contactless charging method by means of said autonomous computing devices;

-

a certifying authority that provides a set of public keys and private keys to perform partial digital signatures using said autonomous computing devices; Y

-

means established in a control or collection center, such as said charging / toll station, for two-way contactless interaction of said control center for charging for use of the road, with said autonomous devices with telecommunication capability.

Said elements are intended to operate in combination to implement the proposed contactless charging method, which comprises counting said partial digital signatures of the vehicle occupants.

In an exemplary embodiment of the method of the present invention, said payment method is a variable rate toll road depending on the number of occupants of each vehicle crossing the toll, at least the following agents intervening in this scenario:

-

a toll collection station (with functions of said control center) with telecommunication means;

35

-

an autonomous computing device, for each of the occupants, with telecommunication capability, with an individual identifier Id or network address;

-

a certifying authority that provides a set of public keys and private keys for making said partial digital signatures; Y

-

at least one application installable in the autonomous computing devices to implement the method by means of said autonomous computing devices,

The proposed method is characterized by the following stages:

a) authentication to a certifying authority of each of the n occupants of the vehicle from said individual identifier that associates a unique Id number of the same length with the identity of the occupant of the vehicle;

b) generation for each occupant of a set of L public keys and the corresponding private keys by said certifying authority, where for i = l to L the i-th pair of keys is only a function of the value of the ith digit (or of the i-th group of digits) less significant of Id (in this way the i-th pair of keys is shared by all those occupants of the vehicle who share the same value for the i-th digit group of digits, with what when using said pair of keys does not reveal who of the users who share it has used it, which provides an effective anonymity)

e) transfer of said generated private keys to their respective occupant;

d) acquisition by each occupant of an amount by way of credit that provides a payment code (this acquisition can be made anonymously or by credit card);

e) one of the occupants of the vehicle Um (master) takes a leading role and each of the occupants of the vehicle establishes a digit / position or group of digits / positions of each of their personal identifiers Id, which is different for each of said occupants, be this j / th position (this stage can be carried out at any time of formation or consolidation of the group of occupants of the vehicle, at any given time);

f) the toll station provides for each vehicle next to the toll station a transaction identifier Ts with a time stamp (this stage can be carried out at the same time before a request for payment or detection of a vehicle by the toll station) ;

g) each of the occupants of the vehicle makes a partial signature with threshold n (where n is the number of occupants of the vehicle) with its jth private key of the message formed by Ts concatenated with the jth public keys of all occupants and said partial signatures are sent;

h)

acquisition or reception by said toll station of a final signature on behalf of the group, based on the aforementioned partial signatures;

S

i) verification by said toll station of said final group signature, which signature will only be valid if n occupants have participated in it, thereby allowing a safe and anonymous determination of the number of occupants of the vehicle, and

j)

application by the toll station of a preset amount according to tariff scales according to the number of occupants, and request of said amount to the occupants of the vehicle to enable a payment.

10

The referred submission of the partial signatures of stage g) is carried out by each of the occupants to an occupant Um, which combines the partial signatures and obtains a final group signature, representative of the n occupants, which is sent to the toll station, or it can be performed alternatively by each occupant of the vehicle to the toll collection station, where the partial signatures are combined and a final group signature is obtained, representative of the occupants.

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In general the payment will be assumed by one or more occupants of the vehicle that divide the amount to be paid that is transferred safely from one of the autonomous computing devices, in particular that of said Um.

As for the aforementioned transfer of said private keys of stage e), this is done by an office under a face-to-face scheme or by remote connection with it and secure identification by an occupant or potential occupant of the vehicle.

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In an example of execution to implement step f) the toll station detects the IDs of said autonomous computing devices with telecommunication capacity of the occupants of the vehicle, recognizes the number of devices traveling in the vehicle and sends them an identifier of transaction Ts with time stamp.

25

In another example of execution, it is foreseen that the toll station carries out a payment request to the occupant Um prior to said stage f).

30

Likewise, in the case of payment using tickets, an Msg time stamp and a reference toll locator, they are sent by an entry toll station to the occupants of the vehicle and each occupant of those who will collaborate on the payment sends said Msg concatenated with a payment code and encrypted with the public toll key to the occupant Um. The occupant Um or the toll station concatenates all the encrypted messages received from the occupants of the vehicle that they are going to pay along with the j-th public keys of the occupants, that is, Centryquot; the message resulting from said concatenation, and the toll station returns the message quot; Centryquot; Received from the occupants signed with the private toll key and the occupant Um stores Centry and the ticket on its autonomous computing device.

35

   The method also provides as an example of execution that at the exit of the toll, in step g) said occupant U m also sends quot; Centryquot; and the ticket.

Finally, the method verifies that at the time of payment the occupants who offered to pay at the entrance of the toll are agreed with those who pay at the exit, avoiding fraudulent changes of tickets.

Detailed description of the invention and examples of implementation

S The proposed system includes:

-

an application on an Appu mobile device for each occupant U of a vehicle that:

• allows the calculation of signatures with n on behalf of U, where n is a digital signature scheme with dynamic threshold and identity based (identity-based dynamic threshold digital signature scheme),

10 • allows the calculation of data encrypted with n ', a public key encryption scheme with the public key of the pkCA certification body,

•

It can be run in master or slave mode. In each of these modes Appu has a different role in the payment protocol,

•

includes a certificate that allows checking the validity of the public key pkCA

15 -a certification authority (CA), for example, the company responsible for the toll payment system, which distributes the applications for mobile devices, together with the necessary secret keys after the registration stage. The certification authority can sign messages

using the public key pkCA;

-

Prepaid cards available at gas stations, kiosks or similar. Each card 20 includes a unique code and the CA associates an account with the available credit to each Pay.Code code;

-

some system to penalize or prevent the abuse of the collective transport lane by vehicles, for example;

-

a penalty on the amount in the payment phase; Y

-

a mechanism in the collective transport lane that prevents access to vehicles that have committed some type of abuse.

Communication technologies used:

The mobile devices and in general the autonomous computing devices that the occupants of the vehicle can use must have some means of communication that allows them to communicate with each other and with the toll booth, either using communication technologies themselves known as 30 RFID , Bluetooth, Wi-Fi or others. Communication between mobile devices must include some mechanism that physically or logically limits the maximum communication distance. Bluetooth

35

It may be a natural technological solution for the proper functioning of the system, but others are not ruled out.

Preliminary Cryptographic Techniques

In identity-based public key cryptography, public keys correspond to arbitrary strings of specified length, which are known as 'identities'. Normally each public key chain is associated with an occupant and reflects some aspect of the identity of the occupant that identifies it only, for example, the email address. The secret key associated with the public key of an occupant U is calculated by some trusted entity, the CA certification authority, and is sent to U by some secure means. A feature of public key cryptography based on very interesting identity for the present invention is that public keys can be very short. The idea of identity-based cryptography is due to Shamir [3], who in 1984 proposed the idea of simplifying certificate management in traditional public key infrastructures.

In the threshold public key cryptography protocols some tasks are distributed among a group n of occupants so that at least t, the threshold, occupants have to cooperate to do the task satisfactorily. Normally, in these protocols n and t are decided at the beginning of the protocol and cannot be modified unless all the public information of the occupants is recalculated. The literature regarding distributed cryptographic protocols is very broad.

Dynamic threshold public key signatures (identity-based dynamic threshold or IBDT signatures) are as standard digital signatures except that: a) they are identity based, that is, public keys are arbitrary strings of specified length; b) they are threshold signatures, that is, at least t signatories outside the set S of n signatories must collaborate to produce a valid signature; and e) the threshold is dynamic, which means that the set of signers S and the threshold t can be chosen at the time of the signature calculation, that is, they can be different for each signature. A similar concept was considered in [1], but for encryption instead of signature and for the public key scenario instead of an identity-based scenario.

Informally, the security properties of an IBDT signature scheme ensure that at least t occupants of a set S have used the signature algorithm with their respective secret keys to calculate the signature. If the set S of n signers are the occupants of a vehicle and calculate a signature with threshold t = n, the signature can be considered as proof that there are at least n occupants in the car.

A signature with dynamic threshold based on identity consists of five algorithms:

IBDTS = (IBDT.Setup, IBDT.Keygen, IBDT.Sign, IBDT.Comb, IBDT. Verify). The first algorithm simply returns the parameters of the scheme. IBDT.Keygen is the algorithm that the certification authority uses to distribute the secret keys of the occupants. IBDT.Sign is an algorithm that is executed individually by the occupants and that returns a partial signature. At least t occupants of the set of signers S must execute it. The IBDT.Comb algorithm takes t of these partial signatures and returns the final signature for the set S and the threshold t. IBDT Verify is an algorithm that verifies if a given signature is valid for a certain set S and threshold t.

The various protocols used in the implementation of the exposed method are detailed below.

Protocols for charging a toll of high occupancy vehicles: case without entry ticket

The first protocol is executed by the certification authority and an occupant who wants to use the S automatic payment system. It is only necessary to execute it once for each occupant U.

Protocol 1, or registration protocol. At the beginning of the CA protocol choose a t-value that must be less than the length of the national identity document number nu. See Note 9.1 on the value

appropriate of t.

1. An occupant U with a national identity document number is not authenticated by an authority

10 CA certifier, in person or by any other acceptable means. The occupant receives a pinu personal identification number.

2. The CA associates a public key vector of ll with U,

where d¡, ..., of are the last / digits of nu and ll is a digitaiiBDT signature scheme. Public key

d

15 pki is a short string that encodes i and dj, for example by concatenating them:

i

d · =

pk¡ 1 = dL) •

3.

Using the private master key of the digital signature scheme ll, the CA calculates the secret keys associated with PK, which are:

Four.

Using the pinu personal identification number, the occupant can download the application with the associated keys SK and the public key pkCA of the certifying authority on their mobile device. The second protocol simply specifies how an occupant can buy so

Anonymous credit to pay tolls. 25 Protocol 2 Credit purchase

The occupant buys a prepaid card for the toll payment system, for example, a "scratch-scratch card"; (in which a code is hidden by a scratch removable layer).

• The card includes a Pay.Code code that must be entered in the mobile device application.

The following protocol is executed by the occupants of a vehicle before entering the toll payment lane.

S Protocol 3 Configuration.

1. An occupant U * between occupants U1, •••, A who travels together in the vehicle takes the leading role.

This occupant will be responsible for most of the communication with the toll booth. U * configures your application to run in master mode and the other occupants configure their applications to run in slave mode.

10 2. The occupants agree on an index j E {1,2, ..., t} such that the j-th least significant digit of the national identity document number is different for each occupant. The j-th least significant digit of the number of the national identity document nu of the occupant u.

i l

will be called hereafter d}.

The following protocol is executed when the vehicle enters a toll lane and makes the payment of the toll.

Protocol 4 Payment A: without ticket.

1. Automatic toll booth B detects the Bluetooth identifiers of the occupants of a vehicle and sends them a Time.Stmp time stamp.

2. Each occupant Ui executes the IBDT.Sign algorithm to calculate a signature of ll using its key

say sk. one .

20 secret 1, in the 1 message

d ~

Msg = <Time.Strnp 11 pk 1

¡¡

k ~ d} dj}

[{p ~ ·, ..., pkn for the public key group l and threshold n and where 11 is an operation of

concatenation. Next, send the resulting partial signature Ü • ¡• to U *.

3. U * receives (ü • t •, ..., (¡, quot; n ·) and executes the IBDT.Comb protocol to combine signatures

partial and obtain the resulting final signature (on behalf of U11 •••, Un. Subsequently, send message and signature to toll booth B:

• lt; Msgquot;, (quot; gt; quot ;.

4. The toll booth verifies the signature by executing

d1

(, pk] /

[IBDT. Verify (Msg. '·', N =

S

10

Note that this signature will only be valid if all Ul, ..., Un have collaborated in its elaboration, which shows that in the vehicle there are at least n occupants. If the signature is not valid, the vehicle will be penalized in any of the ways proposed above. Otherwise, the total amount is calculated that a vehicle must pay based on the number of occupants, that is, the higher n, the lower the amount.

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5. Each occupant U of the vehicle that is in the set P of occupants who want to collaborate in the payment of the toll sends their encrypted payment code to the toll booth via Bluetooth:

quot; Cquot; 1 "Uquot; •

quot; [quot; Enequot; Jl 1 ([quot; pkquot; JJ 1CA) quot; (Time.Stmpquot; / 1 [-Pay.Codequot; J1 1U),

where Pay.Codeu is the code that the occupant U obtains from the prepaid card and where Ene is the public key encryption algorithm of some public key encryption scheme n •.

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6. The toll booth deciphers the data {cu: U (P}) to obtain the payment codes of the occupants in P. received

7.

The toll booth subtracts the amount quot; amountnquot; divided by the cardinal of P of the accounts associated with the payment codes received.

Protocols for charging a toll of high occupancy vehicles: case with entrance ticket

25

Protocols 1 and 2 are identical to the case without a ticket and the only difference is in the payment phase. If the toll is charged using a ticket system, the payment phase is divided into two protocols: the first one is executed when the vehicles enter the lane for high-occupancy vehicles (VAO) and the second on its way out.

   Protocol 5 Payment B: entry.

l. An automatic toll 81 located at the entrance of the lane detects the Bluetooth identifiers of the occupants of a vehicle and sends them a time stamp and a location identifier

Loe

Msgentry = <Time. Stmpentr: and • LOcgt ;.

5 2. Each occupant U in subset P of vehicle occupants who want to collaborate

*

in the payment of the toll, it sends the message to the occupant who acts with the role of teacher U

where Pay. Codeu is the code that the occupant U obtains from the prepaid card and Jan is the encryption algorithm of some public key scheme n '.

*

10 3. U sends to the toll booth:

dquot;

p ~ l gt;

where P = {U¡] ····· U¡p} is the set of all occupants who want to collaborate in paying the toll.

4. The toll booth returns a ticket ticket = SignskcA (Centry), where Sign is some

1 15 public key signature algorithm of some digital signature scheme.

S. u * stores the Tictry Ticket Centry · Protocol 6 Payment B: departure.

l. An automatic toll 8 detects the Bluetooth identifiers of the occupants of a

vehicle and sends them a time stamp Time.Stmp.

20 2. Each occupant U executes the IBDT.Sign algorithm to calculate a den signature using d!

your secret key Sk¡, in the message

Msg = <Time. Stmp / J ---- == c = - :: -L :!

dl!

for the public key group {pk¡ '· - · pkn} and threshold n. Then send the

. *

resulting partial signature {J.I to U.

3. U * receives quot; (quot; (1quot; 1quot; • ···, (1quot; 1quot; quot;) quot; and executes the IBDT.Comb protocol to combine *

said signatures and get the final signature (on behalf of Ul, ..., Un. Then U sends the toll station B2 the message

quot; lt; Msg quot; (. · e 1entrv, quot; ticketgt;. ·

4. Each occupant U of the vehicle that is in the set P of occupants who want to collaborate in the payment of the toll sends to the toll booth via Bluetooth their payment code encrypted with the public toll key.

cu = EncpkCA (Time. Stmp // Pay. Codeu).

where Jan is the public key encryption algorithm of a public key encryption scheme.

S. The toll a2 penalizes the vehicle in any of the following cases:

-

The signature (from Msg or the Centry ticket signature is not valid.

15 - Payment codes encrypted within Centry differ from those encrypted in {Cu: U (P} ,,

-

The public keys specified in Msg differ from the public keys in Centry

6. Otherwise, the toll assumes that there are n occupants in the vehicle and proceeds as

in Protocol 4 to subtract the amountn divided by the cardinal of P of each account associated with each payment code received.

20 Several detailed issues of the protocols specified above are detailed below.

Diffusion range

As mentioned in the system description section, for protocol security it is important that in the communication between the toll booth and the mobile devices there are scope limitations, as well as in the communication between the mobile devices themselves in the Phase of

25 signature of the payment protocol. The extent of the diffusion of messages between mobile devices can be limited by technology, such as if the communication is done with RFID technology. In this case, no neighboring device would receive the messages.

Variants of the key pre-distribution scheme

35

The national identity document number can be replaced by any number or

string that uniquely identifies the occupant.

The protocol fails if there is no i ({1, ..., •} such that the j-th least significant digit of a different nusea

for all occupants of the vehicle (the probability of this happening is calculated in Subsection 9.2). To minimize this probability, a code could be associated with more than one digit of nu for example.

Communication in case of using Bluetooth technology

The toll should detect and communicate with the mobile devices of a vehicle via Bluetooth when they access the toll lane, so that they can receive the timestamp and perform the necessary encryption operations. In general, the discovery and communication phase between two devices can reach 20 seconds, which is not fast enough for the purposes of this invention. To accelerate it, it is enough that the toll that the other Bluetooth devices have to discover (the devices of the occupants of a vehicle) increases the frequency of identification request. According to [2], in this case the process can take only 1,075 seconds and can be accelerated to a time of 0.005 seconds following the optimizations proposed in that article. Note that this solution is not problematic in the present case since the toll booth can be a device with high calculation capacity and without energy restrictions.

Public toll keys

It could also be considered a variant of the protocol in which each toll booth had a different public key. For example, this might be necessary if the toll booths belonged to several collection companies. In this case, when the car enters the lane, the toll booth sends its occupants its public key along with a valid certificate. Both protocols (with ticket or without ticket) continue as detailed above, except that now the payment codes are encrypted with the

public key that the toll booth has issued instead of pkCA.

Below are some technical aspects of the protocols.

Correction

The correction ensures that any n occupants U1, ..., A who correctly follow the protocol can convince the toll booth that there are at least n occupants in the vehicle. The only step in which the test can fail is when for each of the last f digits of the numbers of the national identity document there is some repeated value among the occupants of the vehicle. In this

to dn

In this case, for each j (f1, ..., e}, the set of keys {Pk¡ J '..., pk¡} has at most n' different elements for some n'lt; n and it will only be possible to generate a signature that proves that there are at least n 'occupants in the car. The probability of this happening depends on f (the number of keys given to each occupant) and n (the number of occupants found in the vehicle) ; more specifically, assuming n ~ 10, said probability is:

25

1O (10-1) ... (10-n + 1)) 1

F (P, n) = 1-10n.

(

If the number of occupants n is close to 10, the probability of prior failure may be negligible for reasonable values of f. An option that allows to increase n even well above 10 is to associate each public key not with a single digit of the national identity document, but with m digits. In this case, assuming n ::; 10m the probability of failure is:

. . _ (10'quot; (10111 -1) ... (10m-n + l)) r

F (C, n, m) -1-10nm •

However, the price to be paid for choosing a higher m value is the reduction of anonymity, since if more digits are associated with each public key, fewer occupants share the same public key. If you want to admit a maximum of 9 occupants, taking m = 2 should be enough.

Security aspects

The registration phase ensures that each occupant U is associated with a single mobile device. On the other hand, the limitations in the scope of communications between the devices guarantee that only the devices that are in the vehicle have collaborated to calculate the final signature of (. Note that without the limitation in the scope of the communications, some occupant of a nearby vehicle could participate with its device in the signature protocol. Finally, the security properties of the scheme of

d1 dn signature guarantees that any signature of the signatories with the public keys Pk1t '· • · • P ~' and threshold n will only be verified correctly if at least n different occupants have collaborated in calculating it. Therefore, there must be at least n electronic devices registered in the vehicle, which means that there are also at least n different occupants unless a registered occupant who is not in the vehicle has lent their mobile device to the other occupants . The scheme proposed here does not detect this type of bad behavior, but we do not expect this attack to be common, since most people are reluctant to lend their mobile devices.

In a toll with a ticket, a possible attack would be for two vehicles to exchange their entrance tickets in order to pay less if they present the wrong ticket. This attack will only be successful if fraud is not detected at the exit toll, which would imply that the occupants of both vehicles had the same set of public keys and also that they exchange their Pay.Code payment codes (since they have to send them encrypted with the time stamp obtained at the exit). It does not seem expected that the occupants want to share their payment codes.

Anonymity

The exposed protocol guarantees the anonymity of the occupants in the sense that it is not possible for an intruder or even for the toll station itself to identify the occupants of the vehicle within a very large group of occupants. In fact, it should be noted that the only information that the toll booth sees about the occupants is their payment code, their network identifier (for example

Bluetooth identifier) and public key signature set. However:

roK = r .. • {pk ~~ \ ..., pk? ~} .: l¡ 1 . from lasoc1a as to a

Payment codes can be purchased anonymously (by paying the prepaid card in cash) and therefore the payment codes are not directly linked to any occupant.

S

The network identifiers can be chosen by the occupants arbitrarily and can be chosen so that there is no obvious relationship with the identity of the device owner.

10

On the other hand, any of the keys in the PJ set (it is shared with all the occupants who have the same digit in the position i of their national identity document number. For example, in the case of Spain, where the number of the National identity document has eight digits, for any pair i, d there can be up to 107 citizens (106 if we associate the keys with two digits) sharing the public key Pk1. In practice there will not be as many citizens sharing a public key because not all Numbers correspond to a national identity document issued and not everyone with a document will register their mobile device; even so the number of occupants with the same public key will remain high.

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References

[1] C. Delerablée and D. Pointcheval. Dynamic threshold public-key encryption. Cryptology-CRYPTO 2008, LNCS 5157, pp. 317-334, Springer, 2008.

In Advances in

[2] J-R. Jiang, B-R. Lin, and Y-C. Tseng A mechanism for quick Bluetooth device discovery. Proceedings of Mobile Computing 2004, Taichung, Taiwan, March 2004.

In

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   [3] A. Shamir. ldentity-based cryptosystems and signature schemes. In Advances in Cryptology CRYPTO 1984, LNCS 196, pp. 47-53, Springer, 1984. -

Claims (13)

S 10 15

1.-Non-contact charging method, for the use of a road, for high-occupancy vehicles, where each of the occupants of a vehicle that implements the charging method has an autonomous computing device with telecommunication capability, identifiable by means of an individual identifier Id or network address, the method comprising determining the number of occupants of a vehicle using information about said autonomous computing devices with telecommunication capability, through a contactless interaction with them from a control center of the route or charging station, to provide a payment amount for the use of the road, depending on the number of occupants of the vehicle, characterized in that said determination of the number of occupants is carried out by the acquisition and count of a total number of partial digital signatures made by each occupant through a hosted computer application and n its respective autonomous computing device with telecommunication capability, where said computer application implements a digital signature scheme based on identity, with dynamic threshold, which guarantees the anonymity of said vehicle occupants and the security of the control center interaction -occupants.

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2. Method according to claim 1, characterized in that each occupant of the vehicle acquires a credit-like amount that provides a payment code and payment is made at said control center, without contact, by one or more of the occupants, from their autonomous computing device with telecommunication capability, preserving anonymity.

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3. Method according to claim 1, characterized in that said non-contact interaction control center-occupants comprises the participation of a certifying authority that provides each of the occupants of the vehicle with a set of public keys and private keys to perform the said partial digital signatures.

30

4. Method according to claim 1, wherein said payment method is a variable charging toll road depending on the number of occupants of each vehicle crossing the toll, and in which at least the following agents intervene:

a toll collection station with telecommunication means;

an autonomous computing device, for each of the occupants, with the capacity to S telecommunication, with an individual identifier Id or network address; a certifying authority that provides a set of public keys and private keys to make said partial digital signatures; and at least one computer application installable on autonomous computing devices to implement the method by means of said autonomous computing devices, characterized by understanding the following stages: a) authentication to a certifying authority of each of the n occupants of the vehicle from said individual identifier that associates a unique Id number of the same length with the identity of the occupant of the vehicle; b) generation for each occupant of a set of L public keys and the corresponding private keys by said certifying authority, where for i = l to L the i-th pair of keys is only a function of the value of the ith digit (or from the i-th group of digits) least significant of Id; e) transfer of said generated private keys to their respective occupant; d) acquisition by each occupant of a credit-like amount that provides a payment code; e) one of the occupants of the vehicle Um (master) takes a leading role and each of the occupants of the vehicle establishes a digit / position or group of digits / positions of each of their personal identifiers Id, which is different for each of these occupants, this position / group is the jth; f) the toll station provides for each vehicle near the toll station a transaction identifier Ts with a time stamp; g) each of the occupants of the vehicle makes a partial signature with threshold n (where n is the number of occupants of the vehicle) with its jth private key of the message formed by Ts concatenated with the jth public keys of all occupants and said partial signatures are sent; h) acquisition or reception by said toll station of a final signature on behalf of the group, based on the aforementioned partial signatures; i) verification by said toll station of said final group signature, which signature will only be valid if n occupants have participated in it, thereby determining the number of occupants of the vehicle in a safe and anonymous manner, and j) application by the toll station of a prescribed amount in accordance with some tariff scales according to the number of occupants, and request of said amount to the occupants of the vehicle to enable a payment. 5. Method according to claim 4, characterized in that said sending of the partial signatures of step g) is carried out by each of the occupants to an occupant Um, which combines the partial signatures and obtains a final group signature , representative of the n occupants, which is sent to the toll station. 6. Method according to claim 4, characterized in that said sending of the partial signatures of step g) is carried out by each occupant of the vehicle to the toll collection station, where the partial signatures are combined and obtained a final group signature, representative of the occupants. 7. Method according to claim 4, characterized in that the payment is assumed by one or more occupants of the vehicle that divide the amount to be paid that is transferred safely from one of the autonomous computing devices, in particular from said U m. 8. Method according to claim 4, characterized in that said acquisition of a credit-like amount from step d) is carried out anonymously. 9. Method according to claim 4, characterized in that said acquisition of a credit-like amount from step d) is carried out through a credit card. 10. Method according to claim 4, characterized in that said transfer of said private keys of step e) is carried out by an office under a face-to-face scheme or by remote connection with it and secure identification by an occupant or potential occupant of the vehicle. 11. Method according to claim 4, characterized in that said step f) is carried out at the same time before a request for payment or detection of a vehicle by the toll station. 12. Method according to claim 4, characterized in that said step e) is carried out at any time of formation or consolidation of the group of occupants of the vehicle, at a given time. S 13.-Method according to claim 4, characterized in that to implement said stage f) the station toll detects the identifiers Id of said autonomous computing devices with capacity of telecommunication of the occupants of the vehicle, recognizes the number of devices traveling in the vehicle and sends them a transaction identifier Ts with time stamp. ' 14. Method according to claim 4, characterized in that the toll station previously carries out said step f) sending a payment request to the occupant Um. 15.-Method according to claim 5, characterized in that in the case of payment using tickets, a Msg timestamp and a reference toll locator are sent by a 15 entrance toll station for the occupants of the vehicle and each occupant of those who will collaborate on the payment sends said Msg concatenated with a payment code and encrypted with the public toll key to occupant Um. 16. Method according to claim 15, characterized in that the occupant Um or the toll station 20 concatenates all encrypted messages received from the occupants of the vehicle that they are going to pay along with the j-th public keys of the occupants, be `` Centry '' the message resulting from said concatenation, and the toll station returns as a ticket the message "Centry" received from occupants signed with the private toll key and the occupant Um stores Centry and the ticket on its autonomous computing device. 17. Method according to claim 16, characterized in that at the exit of the toll, in step g) said occupant Um also sends quot; Centryquot; and the ticket. 18.-Method according to claim 17, characterized in that at the time of payment must be 30 coincide the occupants who offered to pay at the entrance with those who pay at the exit, avoiding fraudulent changes of tickets.

19. Method according to claim 4, characterized in that said step a) of authentication of the n

occupants of the vehicle through its identifier Id, respective, it is only necessary to do it once, for

part of each of the occupants of the vehicle.

S

20.-Method according to any one of the preceding claims, characterized in that said

Contactless interaction uses a known telecommunication technology chosen among Bluetooth,

Wifi, RFID that support autonomous computing devices with telecommunication capability

of the occupants of the vehicle.

10

21.-Collection system, without contact, for the use of a road, for high occupancy vehicles, which integrates

the following elements:

a station for charging a variable rate for the use of the road, with means of

telecommunication;

an autonomous computing device, for each of the occupants, with the capacity to

fifteen

telecommunication, with an individual identifier Id or network address;

at least one computer application installable on autonomous computing devices

with telecommunication capability, to implement the method through said devices of

autonomous computing,

a certifying authority that provides a set of public keys and private keys

twenty

to make said partial digital signatures; Y

means established in a control center or collection center for bidirectional interaction without

contact of said station for charging for use of the road, with said autonomous devices with

telecommunication capability,

said elements being provided, which operate in combination, to implement the method of

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Contactless charging according to any one of claims 1 to 20.