AU2841399A

AU2841399A - Mobile telephone system with prepaid card

Info

Publication number: AU2841399A
Application number: AU28413/99A
Authority: AU
Inventors: Bruno Basquin
Original assignee: Gemplus SCA; Gemplus Card International SA
Current assignee: Gemplus SA
Priority date: 1998-03-20
Filing date: 1999-03-17
Publication date: 1999-10-18
Also published as: EP1064777A1; JP2002508633A; WO1999049647A1; CN1293861A; BR9908904A; CA2323002A1; FR2776454B1; FR2776454A1

Description

1 A MOBILE TELEPHONY SYSTEM WITH A PREPAYMENT CARD The invention relates to mobile telephones used with prepayment cards. 5 A mobile telephone network, whether it is of the GSM or DCS type, corresponding respectively to the English acronyms "Global System for Mobiles" and "Digital Cellular System", can be represented as comprising two 10 parts: - a part accessible to the user: the mobile telephone and card, 15 - a part under the control of the network operator: the infrastructure.

2 With this representation, prepayment systems can be classified in three major categories depending on whether the pre-payment functions are performed 5 (a) solely by the infrastructure, (b) partly by the infrastructure and partly by the mobile telephone and card, 10 (c) solely by the mobile telephone and the card. The systems in categories (a) and (b) exist in commercial use but have the following drawbacks: 15 - they require a heavy investment entirely borne by the operator, - they require a large amount of maintenance, and hence an ongoing cost, 20 - they make it necessary to modify certain functions of the network, - they must be sized according to the number of users, 25 requiring continuous updating. To mitigate these various drawbacks, the aim of the invention is to produce a system in category (c) in which all the operations for charging for the services 3 are performed by the mobile telephone and memory card in a completely autonomous manner. However, it should be noted that there exists a system 5 in which the infrastructure supplies to the mobile telephone and card a cost advice, more usually known by the English acronym AoC, standing for "Advice of Charge". Such an AoC system has the following drawbacks: 10 - for each call, the charge to be applied is sent by the network infrastructure, which means that the latter must be designed for this purpose. Currently a few installed networks include this function; 15 - the charging tables are housed in the network so that the charging is fixed, which does not correspond to the wish of the network operators; 20 - the payment units account is managed through the mobile telephone/card interface by the exchange of standard commands without any particular security measure. 25 The aim of the invention is to guarantee that the user of the network unavoidably pays for his communications by means of his prepaid card. The principle of the invention consists in proposing 30 means for making secure all the operations related to 4 the management of the units of payment, to charging and to debiting proper, and means for triggering the authentication of the mobile and/or card at times chosen by the operator. 5 Another object of the invention is to propose means affording interoperability between all the mobiles, the prepayment cards (cards with or without an internal charging table) or standard subscription cards. 10 To this end, the mobile has a mechanism for selecting the operating mode appropriate to the above card type. The aim of the invention is achieved by a system in 15 which: - the mobile telephone and card have specific functionalities for implementing the prepayment application according to the invention; 20 - the mobile telephone/card assembly autonomously determines the invoicing for the service; - the mobile telephone/card assembly manages the user 25 account, - the payment units counter is located in the card, and - the exchanges of information between the mobile 30 telephone and card are protected against any fraud.

5 As an option, a server can be provided, connected to the network to send recharging or parameter management instructions to the mobile telephone/card assembly. 5 The invention relates to a mobile telephony system with a prepayment card in which a prepayment card is associated with a mobile telephone connected to a telephone network, characterised in that: 10 - the prepayment card comprises at least one microprocessor for effecting cryptographic calculations with a view to ciphering and/or deciphering digital messages and a payment unit counter, containing the 15 prepaid value, - the mobile telephone comprises at least one microprocessor for making debit calculations according to the characteristics of the telephone call and the 20 user of the telephone as well as cryptographic calculations with a view to ciphering and/or deciphering digital messages, and a recording and reading device for the prepayment card in order to exchange the said ciphered digital messages or not with 25 the said prepayment card, and - each digital message recorded or read in the prepayment card is ciphered and/or deciphered by means of a cryptographic certificate contained in the digital 30 message.

6 In a preferred example embodiment of the system, the prepayment card also comprises a memory for recording the parameters of the charging applied to the user. 5 To record the cryptographic certificate of each ciphered digital message, the mobile telephone and the prepayment card each also comprise a memory for this purpose. 10 To increase the security of the ciphering and deciphering, the mobile telephone and the prepayment card each also comprise a counter which is loaded with a random code supplied by the network and which is 15 incremented by the same number of units at given times. The invention also relates to a method for implementing the telephony system with prepayment card, characterised in that it comprises the following steps 20 consisting in: (a) powering up the mobile telephone, (b) recognising the presence or absence of a prepaid 25 card connected to the mobile telephone, and - going to step (c) in the event of absence of the card, or 7 - going to step (d) et seq in the event of presence of the card, (c) operating the mobile telephone in a conventional 5 manner in the event of absence of a prepaid card, (d) reading in the prepaid card the international identification number of the user of the prepayment card, 10 (e) registering in the mobile telephone the user of the prepayment card as a user of the network under the international identification number, 15 (f) authenticating, at the request of the network, the mobile telephone as an authorised user of the prepayment card, (g) reading in the prepayment card the charging 20 parameters for the call from the user as well as the payment credit remaining on the payment unit counter, (h) passing the call if the remaining payment credit is sufficient, and 25 (i) calculating in the mobile telephone, as the telephone connection continues, the number of payment units to be debited, 8 (j) debiting the payment unit counter by a number of units corresponding to the current telephone connection. 5 Other characteristics and advantages of the present invention will emerge from a reading of the following description, the said description being given in relation to the accompanying drawings, in which: 10 - Figure 1 is a diagram showing the operations to be performed with a view to obtaining security of the exchanges or transactions between the mobile telephone and the card, 15 - Figure 2 is a diagram showing the operations to be performed with a view to recognising and activating a prepayment card with an authorised mobile telephone, - Figure 3 is a diagram showing the operations to be 20 performed with a view to periodically authenticating the mobile telephone by means of the card, and - Figure 4 is a diagram showing the operations to be performed with a view to choosing the charging rate and 25 debiting the card. Each figure has been divided into three vertical parts I, II and III separated by two broken lines 10 and 12 to indicate the three components of the system, namely 30 a network or infrastructure 14, a mobile telephone 16 9 and a prepayment card 18 often referred to as an SIM card, SIM being the English acronym for Subscriber Identification Module, that is to say the module identifying the user or subscriber. The operations 5 indicated in each vertical part I, II or III are performed by the corresponding component and the exchanges of information by the elements are represented by horizontal arrows connecting the parts to which the exchange relate. 10 In order to ensure the security of the exchanges of information against fraud, the invention provides for these exchanges to be made by implementing the cryptographic methods according to the diagram in 15 Figure 1. In this Figure 1, the mobile telephone 6 produces a command 20 which, if it is critical for security, is ciphered by means of a cryptographic calculation 20 operation 22. It is a case of a critical command or message which has an impact on the management of the payment units, notably invoicing, reading the charging rate and 25 accounting for the units of payment, but also on the mutual authentication between the card and the mobile. Certain commands which are not critical from the point of view of security are not ciphered.

10 The command, ciphered or not, is transmitted to the card 18. The ciphered command can contain a cryptographic certificate which allows its certification by the card 18. According to a preferred 5 variant depicted in Figure 1, the command is transmitted without ciphering (24) but, in parallel, a cryptographic certificate is transmitted (26) to the card and is recorded by the telephone in a file in the card referred to as a "mailbox". The advantage of 10 proceeding thus is to use messages or commands to a standard format. This certificate is used for making cryptographic calculations so as to check that it is a case of a ciphered command (28) provided by the system. 15 If the verification or certification is not valid (30), the card transmits an error signal (32) to the mobile telephone. If the certification is validated, the command is executed (34) . Execution of the command gives rise to the production of the response from the 20 card (operation 36), a response which is preferably ciphered (operation 38), particularly if it is a case of responses to critical commands as referred to above with the recording of a cryptographic certificate in the mailbox (operation 40). The response is 25 transmitted to the mobile telephone (operation 42) whilst the cryptographic certificate is read by the mobile telephone in the mailbox (operation 44) to be used for the cryptographic processing (verification) (operation 46) in the mobile telephone. 30 11 It should be noted that access to the mailbox is effected by means of conventional commands without security. As described above, the protection of the bilateral exchanges between mobile telephone and card 5 is based on a cryptographic calculation made by the part which transmits and verified by the part which receives, this calculation being effected at each data transmission between the mobile telephone and the card. 10 To avoid the result of the cryptographic calculation being identical for two commands identical in their content, the invention provides an anti-replay mechanism which consists in introducing into the cryptographic calculation an arbitrary variable data 15 item which has a very low probability of taking the same value twice. This variable data item can be obtained by means of a counter in the mobile telephone and the card, a counter 20 which is updated independently by each party to the exchange and which is incremented by one unit at each cryptographic calculation. However, such a counter value must be kept from one session to another, which means that a given prepayment mobile telephone 25 functions only with a given prepayment card and has the drawback of being limitative. To mitigate this drawback, the invention uses a random number, referred to as "random". Preferably, for 30 reasons of ease of implementation, use is made of the 12 "random" which is situated in the authentication request sent in conventional manner by the network. Thus, at each authentication request by the network, the mobile telephone and card each record the value of 5 the "random" as a new initial value of the counter and at each new certified command or response that must be exchanged between the mobile telephone and the card, each part will use the value of its counter as it is and then will increment it by the same fixed number of 10 units at each data or command exchange. For a mobile telephone without prepayment not to be capable of generating a request for registration on the network with a prepayment card, the invention makes 15 provision for deactivating certain functions of the card (operation 50, Figure 2) after it is powered up (operation 52) by the mobile telephone and to activate it only by an authorised mobile telephone. 20 For the mobile telephone to be able to function both with prepayment cards and normal subscription cards, it is necessary to set up a mutual recognition procedure. To this end, every session begins with a recognition of the card by the mobile telephone (operation 54) by 25 inspecting the card configuration data without any particular security since a card which would claim to be what it is not would be rejected during the subsequent procedures. If this recognition fails (operation 58) , the system functions in a conventionnal 30 manner without prepayment (operation 60). If the card 13 is recognised as being a prepayment card, the mobile telephone transmits to the card a command for reading (operation 62) the international code of the subscriber, better known by the English acronym IMSI, 5 standing for International Mobile Subscriber Identification. This command to read the code IMSI is effected with certification, a certification which is validated or not by the card (operation 64). 10 If the command to read the IMSI code is not validated, the card transmits an error signal (operation 66) to the mobile telephone. In the contrary case, the card is fully activated and goes into standby (operation 72) ; it transmits its IMSI code (operation 70) to the 15 mobile telephone, which registers the subscriber on the network and waits for an authentication request (operation 72). This certified reading of the IMSI code prevents a 20 mobile telephone from operating without prepayment and then activating a prepayment card and generating a request for registration on the network. The prepayment card transmits its IMSI code only if the read command is correctly certified. 25 It is then necessary to verify that the mobile telephone is authorised to use a prepayment card in order to guarantee that the management of the payment units is correctly effected. To this end, the 30 invention provides that, at the periodic request of the 14 network, the mobile telephone preferably repetitively proves to the card and vice versa that it is authorised to operate a prepayment card. Advantageously, this verification of the authenticity of the mobile and/or 5 of the card is triggered externally and in a manner unpredictable to the user by means of a procedure existing at the level of the network. In particular, the request for authentication of the card by the network is suitable as an external procedure which 10 forces an interaction between the mobile and the card. Thus (Figure 3) the network transmits an authentication request (operation 80) to the mobile telephone, which transmits it to the card (operation 84) after 15 cryptographic calculation (operation 82) in a ciphered form with a cryptographic certificate as described above. The card performs a cryptographic calculation to 20 authenticate the request (operation 86). If the certification is not validated (operation 88), the card transmits an error signal (operation 90) to the mobile telephone, which retransmits it (operation 25 92) to the network. The latter then rejects the mobile telephone (operation 94). If the certification is validated, the card transmits its response to the mobile telephone (operation 96), 30 which retransmits it to the network (operation 98).

15 According to the invention, the charging parameters are calculated by the card according to the characteristics of the call such as the number requested, the time, the 5 location zone, etc. These calculations are made from charging tables recorded in files internal to the card. The format of the parameters transmitted by the card to the mobile telephone and the manner of processing them by the latter can be of the AoC (Advance of Charge) 10 type and are described in the operating standard for the GSM system. Thus, using the GSM AoC charging standards in the mobile telephone, it is possible to process both 15 chargings supplied by the card and chargings supplied by the network. The choice between one or other charging is made in particular by a protected detection of the presence of the charging files in the card. 20 The charging parameters are processed by the mobile telephone in order to determine the manner of debiting the payment unit counter during the call. For example, an all-in debit when the line is picked up, then a debiting of units of payment according to the time. In 25 this case, the periodicity with which the mobile debits the counter in the card is defined by the charging parameters. The credit remaining in the payment unit counter of the 30 card is checked by the mobile telephone at the time of 16 granting the service to the user, and then at each debiting operation during the call. The decisions taken by the mobile telephone according 5 to the state of the counter are preferably in accordance with what is described for the AoC in the GSM standard. The operations performed for choosing the charging and 10 debiting of units in the prepayment card will be described in relation to Figure 4. When the user requests a call (operation 100), the mobile telephone transmits the parameters of the call 15 (operation 114) to the card, preferably in a form protected by cryptographic calculation (operation 112) with a cryptographic certificate. The card checks the certification (operation 116) and, if this check is valid, transmits, preferably in protected form 20 (operation 120), the charging parameters and the credit remaining to the mobile telephone. The mobile telephone checks the remaining credit (operation 122) and authorises or not the passing of 25 the call to the network (operation 132) . When the connection is established (operation 124), the mobile telephone transmits in protected form to the card the debit in units of payment as the telephone connection progresses (operation 126). The card responds with an 30 acknowledgement, also protected (operation 128), with 17 an amount of credit remaining which is checked by the mobile telephone (operation 130). Where the card does not contain any charging 5 parameters, the mobile telephone deduces therefrom (operation 102) that the tariff is that of the network and allows the call to pass (operation 104) . The network responds by transmitting to the mobile telephone the parameters of the AoC (operation 106) 10 with which the latter calculates the cost to be debited. After checking the credit remaining in the card (operation 108), the mobile telephone authorises the connection or not (operation 110) and performs operations 126 and 128 with the card in order to debit 15 the card. The description of Figure 4 shows that all the debiting commands and the acknowledgements are protected by means of the protection method described in relation to 20 Figure 1. By means of this method, it is ensured that the debiting effected in the card is authentic, complete and correctly performed in a valid prepayment card. 25 As indicated above, the acknowledgement can contain the updated value of the payment unit counter, thus avoiding the mobile generating a separate command for knowing the value remaining in the counter.

18 At the start of the session, the mobile telephone is capable of reading, in a secure manner, the value of the counter in the card and transmitting a nil debit command. 5 The description which has just been given in relation to Figures 1 and 4 defines the different steps for a method for implementing the mobile telephony system, these steps consisting in: 10 (a) powering up the mobile telephone 16, (b) recognising the presence or absence of a prepaid card 18 connected to the mobile telephone, and 15 - going to step (c) in the event of absence of the card, or - going to step (d) et seq in the event of 20 presence of the card, (c) operating the mobile telephone in a conventional manner in the event of absence of the prepaid card, 25 (d) reading in the prepaid card the international identification number of the user of the prepayment card, 19 (e) registering in the mobile telephone the user of the prepayment card as a user of the network under the international identification number, 5 (f) causing a mutual authentication procedure between the mobile and the prepayment card, (g) reading in the prepayment card the charging parameters for the call from the user as well as the 10 payment credit remaining on the payment unit counter, (h) passing the call if the remaining payment credit is sufficient, and 15 (i) calculating in the mobile telephone, as the telephone connection continues, the number of payment units to be debited, (j) debiting the payment unit counter by a number of 20 units corresponding to the current telephone connection. Step (f) is triggered at the request of the network, at the time of a request for registration on the network 25 (connection) under the identification number read in the card and is preferably repeated from time to time during a connection session in order to renew the authentication and thus prevent a possible replacement of the module and/or card during the session. 30 20 Step (j) is also repeated in order to debit the payment unit counter so as to check the credit remaining. In order to prevent fraud, at least one or even all of 5 the steps (d) , (e) , (f) , (g) and (j) are added, which are performed in a protected form in accordance with the principles described in relation to Figure 1: (A) effecting cryptographic calculations on the 10 digital message to be transmitted by means of a cryptographic key and/or a code (number) contained in a counter of the message transmitter, (B) transmitting the ciphered digital message and the 15 cryptographic certificate to the message receiver, (C) effecting cryptographic calculations on the ciphered digital message by means of the cryptographic certificate and a code contained in a counter of the 20 receiver. In order to improve this security, the counter of the transmitter of the digital message and that of the receiver of the digital message are loaded by means of 25 the same random code, referred to as the "random", supplied by the network. The step (f) of authentication of the mobile telephone associated with the prepayment card comprises the 30 following intermediate steps consisting in: 21 (f 1 ) effecting by means of the network an authentication request to the mobile telephone, 5 (f 2 ) ciphering, in the mobile telephone, this authentication request, (f 3 ) transmitting to the prepayment card a digital message containing this encrypted authentication 10 request, (f 4 ) deciphering, in the prepayment card, the digital message transmitted by the mobile telephone, 15 (fs) determining, in the prepayment card, whether or not the network authentication request transmitted by the mobile telephone is valid, and - going to steps (f 6 ) and (f 7 ) if there is no 20 validation, - going to steps (f 8 ) and (fs) if there is validation, 25 (f 6 ) transmitting an error signal to the network by means of the mobile telephone, and (f 7 ) rejecting the mobile telephone as a user of the network with the associated prepayment card, 30 22 (f 8 ) transmitting a validation signal to the network by means of the mobile telephone, and (f 9 ) recognising the mobile telephone as a user of the 5 network with the associated prepayment card. The description which has just been given of the invention shows that it involves only the mobile telephones and the prepayment cards. The result is: 10 - a minimal investment for the operator, - no installation requirements, 15 - an increase in the total number of mobiles limited only by the capacity of the network, - no additional cost. 20 Moreover, all the exchanges between the mobile telephone and the card and in particular those relating to the charging rates are protected so that the possibility of fraud is related to the resistance of the cryptographic algorithm to attacks rather than to 25 the ability to filter the commands at the mobile telephone/card interface. Finally, the charging rates are calculated by the card by means of internal tables contained in the card so 30 that the charging tables can be modified by 23 personalisation or by remote management. As a result an operator can implement his own commercial charging strategies by acting at the level of the cards.

Claims

1. A mobile telephony system with a prepayment card (18) having an international identification number for 5 the user of the said card, a payment unit counter containing a prepaid value, in which a prepayment card (18) is associated with a mobile telephone (16) connected to a telephone network (14), characterised in that: 10 - the prepayment card (18) comprises at least one microprocessor for effecting cryptographic calculations on critical messages, 15 - the mobile telephone (16) comprises at least one microprocessor for making debit calculations according to telephone charges (AoC) as well as cryptographic calculations on critical messages, and a recording and reading device for the prepayment card in order to 20 exchange the said ciphered digital messages or not with the said prepayment card (18), and - each of the said critical messages being ciphered or associated with a cryptographic certificate transmitted 25 separately with a view to protecting the message exchanges produced between the mobile and the card.

2. A system according to Claim 1, characterised in that the prepayment card also comprises a memory for 30 recording the parameters of the charging rate applied 25 to the user, the said parameters being read in the card by the mobile telephone.

3. A system according to Claim 1, characterised in 5 that the parameters of the charging rate applied to the user are supplied by the network (AoC).

4. A system according to Claim 1, 2 or 3, characterised in that the prepayment card (18) and the 10 mobile telephone (16) each also comprise a memory for recording the said cryptographic certificate.

5. A system according to Claim 1, 2, 3 or 4, characterised in that the prepayment card (18) and the 15 mobile telephone (16) each also comprise a counter provided for increasing by the same number of units at each cryptographic calculation and able to be initialised by a random number supplied by the network (14). 20

6. A method for implementing the telephony system with prepayment card according to one of the preceding claims, characterised in that it comprises the following steps consisting in: 25 (a) powering up the mobile telephone (16), (b) recognising the presence or absence of a prepaid card (18) connected to the mobile telephone, and 30 26 - going to step (c) in the event of absence of the card, or - going to step (d) et seq in the event of the 5 presence of the card, (c) operating the mobile telephone in a conventional manner in the event of absence of the prepaid card, 10 (d) reading in a protected manner in the prepaid card the international identification number of the user of the prepayment card, (e) registering in the mobile telephone the user of 15 the prepayment card as a user of the network under the international identification number, (f) causing a mutual authentication procedure between the mobile and the prepayment card in order to request 20 registration on the network under the identification number read in the card, (g) reading in the prepayment card the charging parameters for the call from the subscriber as well as 25 the payment credit remaining on the payment unit counter, (h) passing the call if the remaining payment credit is sufficient, and 30 27 (i) calculating in the mobile telephone, as the telephone connection continues, the number of payment units to be debited, 5 (j) debiting the payment unit counter by a number of units corresponding to the current telephone connection.

7. A method according to Claim 6, characterised in 10 that steps (f) and (j) are repeated from time to time during a telephone connection.

8. A method according to Claim 6 or 7, characterised in that steps (d), (e), (f), (g) and (j) are performed 15 in protected form.

9. A method according to Claim 8, characterised in that the operations for protecting steps (d), (e) , (f), (g) and (j) consist in: 20 (A) effecting cryptographic calculations on the digital message to be transmitted by means of a cryptographic key and/or a code (number) contained in a counter of the message transmitter, 25 (B) transmitting the ciphered digital message and the cryptographic certificate to the message receiver, (C) effecting cryptographic calculations on the 30 ciphered digital message by means of the cryptographic 28 certificate and a code contained in a counter of the receiver, the counter of the transmitter and the counter of the 5 receiver previously being positioned to the same code value and being advanced by the same number of units at given times.

10. A method according to Claim 9, characterised in 10 that the code contained in the counter of the message transmitter and in the counter of the message receiver is a random code supplied by the network.

11. A method according to either one of Claims 9 or 15 10, characterised in that step (f) consists of the following intermediate steps consisting in: (fi) effecting by means of the network an authentication request to the mobile telephone, 20 (f 2 ) ciphering, in the mobile telephone, this authentication request, (f 3 ) transmitting to the prepayment card a digital 25 message containing this encrypted authentication request, (f 4 ) deciphering, in the prepayment card, the digital message transmitted by the mobile telephone, 30 29 (f 5 ) determining, in the prepayment card, whether or not the network authentication request transmitted by the mobile telephone is valid, and 5 - going to steps (f 6 ) and (f 7 ) if there is no validation, - going to steps (f 8 ) and (f9) if there is validation, 10 (f 6 ) transmitting an error signal to the network by means of the mobile telephone, and (f 7 ) rejecting the mobile telephone as a user of the 15 network with the associated prepayment card, (f 8 ) transmitting a validation signal to the network by means of the mobile telephone, and 20 (f 9 ) recognising the mobile telephone as a user of the network with the associated prepayment card.