GB2444302A

GB2444302A - Transmission of encrypted location information

Info

Publication number: GB2444302A
Application number: GB0623773A
Authority: GB
Inventors: Nicholas James Olivier
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2006-11-28
Filing date: 2006-11-28
Publication date: 2008-06-04
Anticipated expiration: 2026-11-28
Also published as: GB2444302B; GB0623773D0

Abstract

There is described a mobile communication system having base stations which communicate with mobile communication devices within range of that base station. At least one base station is arranged to transmit encrypted location information indicative of the location of a mobile communication device within range of that base station, and authorized mobile communication devices include means for decrypting said encrypted location information. This allows only certain mobile users to receive the location information, for example those that pay a subscription to use such a service.

Description

* 2444302 MOBILE COMIvIUNTCATION SYSTEM This invention relates to a

mobile communication system in which mobile communication devices are in communication with fixed base stations, and in particular relates to the provision by a fixed base station of location information indicative of the location of that fixed base station.

The possibility of downloading location-dependent information to a mobile communication device, such as a mobile phone, has atiracted significant interest recently. However, in order to download location-dependent information, the location of the mobile communication device must be known.

Mobile communication devices are already available which incorporate a GPS receiver which allows the position of the mobile station to be determined using signals broadcast by a network of satellites. However, such GPS receivers are expensive and also significantly increase the size of the mobile communication device.

According to the present invention, a mobile communication system has a plurality of geographically-spaced base stations with each base station communicating with mobile communication devices within range of that base station. Each base station transmits encrypted location information indicative of the location of a mobile communication device, and the mobile communication device decrypts the encrypted location information.

In an embodiment, the location information indicative of the location of the mobile conununjcatjori device is the location of the base station, or a perturbed version of the location of the base station. Although the recovered location information does not then precisely correspond to the location of the mobile communication device, the recovered location information is sufficiently accurate for most location-dependent information services.

The encrypted location information may be provided in the form of a subscription service in which users of the mobile communication devfce pay to receive the cryptographic key for decrypting the encrypted location information.

Preferably, the cryptographic key is intermittently updated to improve security. Further, preferably the location information transmitted by the base station is perturbed, with the perturbation being intermittently altered. In this way, knowledge of the location information for a base station at one time is of little use in any attempt to cryptoanalyse the broadcast encrypted location information to determine the cryptographic key at a later time when the cryptographic key has changed.

An exemplary embodiment of the invention will now be described with reference to the attached drawings in which: Figure 1 schematically shows the main components of a mobile con-miunication system forming a first embodiment of the invention; Figure 2 schematically shows the main components of a subscription server forming part of the mobile communication system illustrated in Figure 1; Figure 3 schematically shows the contents of an entry in a client database forming part of the subscription server illustrated in Figure 2; Figure 4 schematically shows the main components of a Base Transceiver Station forming part of the mobile communication system illustrated in Figure 1; -Figure 5 schematically shows data stored in the Base Transceiver Station illustrated in Figure 4; and Figure 6 schematically shows the main components of a mobile phone forming part of the mobile communication system illustrated in Figure 1.

OVERVIEW

The exemplary embodiment of the mobile communication system of the invention complies with the GSM (Global System for Mobile Communications) standard. As schematically shown in Figure 1, a plurality of mobile phones la-le are in radio communication with respective Base Transceiver Stations (BTSs) 3a, 3b. In particular, in Figure 1 three mobile phones la-Ic are shown in communication with a first BTS 3a, and two mobile phones id-I e are shown in Communication with a second BTS 3b.

The first BTS 3a and the second BTS 3b are connected, together with other BTSs which are not shown for clarity, to a common Base Station Controller (BSC) 5 which is in turn connected to a Packet Control Unit (PCU) 7. The BSC 5 together with the attached BTSs 3 and the attached PCU 7 form a Base Station System (BSS) 9.

The BSS 9 is connected to a circuit-switched network via the BSC 5 and a packet-switched network via the PCU 7. The BSC 5 sends data received from the circuit-switched network and the packet-switched network to the appropriate BTS 3, and processes data received from the BTSs 3 and forwards data to be sent via the packet-switched network to the PCU 7.The circuit-switched network includes a plurality of mobile switching centres (MSCs) 11, only one of which is shown for clarity, which are each connected to a plurality of BSSs 9. The circuit-switched network also includes one or more Gateway MSCs (GMSCs) 13 which are connected to external networks. In this embodiment, a GMSC is connected to the Public Switched Telephone Network (PSTN) 15 to allow communication with landline telephones 17, only one of which is shown for clarity, and a Short Message Service Centre (SMSC) 19 which is used in the sending of text messages using the Short Message Service (SMS) of the GSM specification.

The packet-switched network implements the General Packet Radio Service (GPRS), and includes a plurality of Serving GPRS Support Nodes (SGSNs) 21, only one of which is shown for clarity, which are each connected to one or more BSSs 9. The packet-switched network further includes one or more Gateway GPRS Support Nodes (GGSNs) 23 via which the packet-switched network is connected to other networks such as the Internet 25. As shown in Figure 1, in this embodiment the SMSC 19 is also connected to the Internet 25.

According to the present invention, each BTS 3 transmits encrypted location information indicative of the location of that BTS 3. In order to S obtain the decryption key to allow decryption of the encrypted location information, the user of a mobile phone I subscribes to a service which is managed by a subscription server 27 connected to the Internet 25.

The subscription server 27, a BTS 3 and a mobile phone I will now be described in more detail. In this embodiment the BSCs 5, the PCUs 7, the MSCs 11, the GMSC 13, the SGSNs 21 and the GGSN are all conventional components.

SUBSCRIPTION SER VER

The main components of the subscription server 27 will now be described with reference to Figures 2 and 3. As shown in Figure 2, the subscription server 27 includes a processor 41, a network interface 43, an operator interface 45 and memory 47 interconnected by a bus system 49.

The net-work interface 43 receives network signals 51 from, and sends network signals 53 to, the Internet 25. The operator interface 45 allows an operator at the subscription server 27 to change data and/or program routines stored in the subscription server 27 including adding new data and/or program routines, deleting data and/or program routines and amending data and/or program routines. In this embodiment, the operator interface 45 includes a CD-ROM reader/writer allowing data to be read from, or stored in, a CD-ROM 53.

The memory 47 includes a region 55 storing program routines, a region 57 storing a client database and a region 59 providing working memory. As shown, the program routines stored include: -a Master Control routine 61 which controls the operation of the subscription server; -a Register Client sub-routine 63 which is initiated to rejister a new client; -a Log_Payment sub-routine 65 which is initiated in response to receipt of a subscription payment by a client; -a Check Status sub- routine 67 which periodically checks the payment status of each client; and -an Update_Keys sub-routine 69 which is periodically initiated to change the cryptographic keys used for encryption and decryption.

It will be appreciated that memory 47 is formed by various memory devices, each having different memory access times. Conventional caching techniques are performed during operation to move data which is most likely to be required to fast access memory.

The client database 57 includes entries for all clients of the subscription server 27. As schematically shown in Figure 3, an entry 79 in the client database 57 includes: -a Username field 81 storing a unique usernarne for the client; -a Telephone Number field 83 storing the telephone number of the mobile station 1 of the client; -a Payment Status field 85 storing the current payment status for the client, which is either paid' or owing'; -a Next Payment Due field 87 which stores the date when the next subscription payment is due from the client; and -a Bank Account Details field 89 which stores the bank account details for the client.

Returning to Figure 2, the processor 41 processes data received by the network interface 43 or the operator interface 45, and/or data stored in the client database 57, in accordance with the program routines, and either outputs data via the network interface 43 or the operator interface 45, and/or changes the data stored in the client database 57. It will be appreciated that the program routines themselves could be pre-stored in the subscription server 27 during manufacture, or input via the network interface 43 or the operator interface 45.

The main routines performed by the subscription server 27 will now be discussed.

In this embodiment, a prospective client of the subscription server 27 applies to join by entering a form on a web page provided by a web server (not shown) forming part of the subscription server 27. The form requests a username, the telephone number of the mobile phone I of the prospective client, and bank account details. In response to receipt of the completed form data, the Master Control routine 61 initiates the Register_Client sub-routine 63 which creates a new entry in the client database 57, sets the payment status as owing', sets the next payment due date to the current date, and initiates obtaining payment using the bank details.

In response to a signal 51 indicating a payment has been made by a client, the Master Control routine 61 initiates the Log_Payment sub-routine which sets the payment status in the entry in the client database for that client to paid' and amends the next payment due date in the entry For the client to a date one month in the future.

At a predetermined time each day, the Master_Control routine 61 initiates the Check_Status sub-routine 67 which checks for each client entry 79 if the present date is after the next payment due date, and if it is sets the payment status in the entry for that client to owing'. Following execution of the Check_Status sub-routine 67, the Master_Control routine 61 initiates the Update_Keys sub-routine which generates a new cryptographic key using a random number generator (not shown), and sends the new cryptographic key to all the BTSs 3 and also to all clients whose payment status is paid'. In this embodiment, the new cryptographic key is sent by the subscription server 27 to the BTSs 3 via the Internet 25, the GGSN 23 and the appropriate SGSN 21, and the new cryptographic key is sent to the mobile phone 1 of each subscriber by requesting the SMSC 19 to send SMS messages to the subscribers conveying the cryptographic key.

BASE TRANSCEIVER STATION

A BTS 3 according to the present invention will now be described with reference to Figures 4 and 5.

As schematically shown in Figure 4, a BTS 3 includes a processor 101, a network interface 103, an operator interface 105, memory 107 and an RF transceiver 109 interconnected by a bus system 111.

The network interface 103 receives network signals 51 from, and sends network signals 113 to, the corresponding BSC 5. The operator interface 105 allows an operator at the BTS 3 to change data and/or program routines stored in the BTS 3 including adding new data and/or program routines, deleting data and/or program routines and amending data and/or program routines. In this embodiment, the operator interface 105 includes a CD-ROM reader/writer allowing data to be read from, or stored in, a CD-ROM 115.

The memory 107 includes a region 117 storing program routines, a region 119 storing a client database and a region 121 providing working memory. As shown, the program routines stored include: -a Master_Control routine 123 which controls the operation of the BTS 3; and -an Update_Key sub-routine 125 which updates the cryptographic key used to encrypt location data.

As shown in Figure 5, the data store 119 includes: -a Location Data field 131 storing the location of the BTS 3; and -an Encryption Key field 133 storing the cryptographic key currently being used to encrypt the location data.

It will be appreciated that memory 107 is formed by various memory devices, different memory access times. Conventional caching techniques are performed during operation to move data which is most likely to be required to fast access memory.

Returning to Figure 4, the processor 101 processes data received by the network interface 103 or the operator interface 105, and/or data stared in the client data store 119, in accordance with the program routines, and either outputs data via the network interface 103 or the operator interface 105, and/or changes the data stored in the data store 119. It will be appreciated that the program routines themselves could be pre-stored in the BTS 3 during manufacture, or input via the network interface 103 or the operator interface los.

The RF transceiver 109 is connected to an aerial 127 which broadcasts radio signals for reception by mobile phones I within range of the BTS 3, and receives radio signals from mobile phones I within range of the BTS 3.

During operation, among other tasks including the handling of comniunication with mobile phones 1, the Master Control routine 123 causes the aerial 127 to broadcast encrypted location data. In particular, in this embodiment the encrypted location data is generated by first perturbing the location data stored in the Location Data field 131, and then encrypting the perturbed location data using the Data Encryption Standard (DES) symmetric encryption algorithm and the cryptographic key stored in the Encryption Key

field 133.

Periodically, the BTS 3 receives a new cryptographic key from the subscription server 27. Following receipt of the new cryptographic key, the Master Control routine 123 initiates the Update_Key sub-routine 125 which stores the new cryptographic key in the Encryption Key field 133. In this embodiment, at the same time as updating the cryptographic key, the perturbation applied to the location data is altered. In this way, if a usèr of a mobile phone 1 stops subscription payments after storing location data for one BTS 3 from previous transmissions, then as the location data has changed it is more difficult to cryptoanalyse the new encrypted location data to determine the new cryptographic key to allow the location of all BTSs 3 to be determined.

A MOBILE PHONE

A mobile phone I according to the present invention will now be described with reference to Figure 6. As schematically shown in Figure 6, the mobile phone I has a controller 151 which is connected to an RF transceiver 153, an audio CODEC 155, a display driver 157, a SIM (subscriber identification module) card 159 and memory 161.

The RF transceiver 153 converts radio signals detected by an aerial 163 into digital signals in a format which is recognised by the controller 151, and converts digital signals from the controller 151 into radio signals in a format which is recognised by the BTS 3. The audio CODEC 155 converts analogue signals corresponding to sound detected by a microphone 165 into digital signals which are recognised by the controller 151, and converts digital signals from the controller 151 into analogue signals which produce desired sounds when input to a loudspeaker 167. The display driver 157 converts digital signals from the controller 151 into drive signals for producing a desired image on a display 169.

The SIM card 159 is a conventional SIM card providing infoination about the user of the mobile phone 1.

The memory 161 includes a region 171 storing program routines, a region 173 storing data and a region 175 providing working memory. As shown, the stored program routines include, among others: -an operating system 177; -a WAP (Wireless Access Protocol) browser 179; -a location identifier 181; and -akeyupdater 183.

The stored data includes: -a Location Data field 185 storing location data; and -a Decryption Key field 187 storing a cryptographic key.

In addition to conventional call handling functions, the mobile phone 1 monitors location by decrypting the encrypted location data received from the nearest BTS 3. In particular, the location identifier 181 of the mobile phone I decrypts received encrypted location data using the DES cryptographic algorithm with the cryptographic key stored in the Decryption Key data field 187, and stores the decrypted location data in the Location Data field 185.

Periodically, the mobile phone I receives an SMS message conveying a new cryptographic key. Following receipt of such an SMS message, the key updater 183 extracts the new cryptographic key from the SMS message and stores the extracted cryptographic key in the Decryption Key data field 187.

The location data stored in the Location Data data field 185 allows location dependent data to be downloaded using WAP services. In this embodiment, the location data is provided to applications in the mobile phone 1 using the JSR179 J2M1E API.

In particular, location data may be appended to a URL (Uniform Resource Locator) for a web site, and the web site can then reply with information specific to the location of the mobile phone 1. For example, a web site may provide details of local services such as the location of the nearest dry cleaner or the nearest Indian restaurant. Alternatively, the web site may provide local weather or traffic information.

MODIFICATIONS AND FURTHER EMBODIMENTS

Although the illustrated embodiment involves a Public Land Mobile Network (PLMJS.1) conforming to the GSM specification, it will be appreciated that the invention could equally apply to other mobile communications networks in which mobile communication devices communicate with fixed terrestrial base stations.

I

Mobile phones, sometimes referred to as cellular phones, are used in the illustrated embodiment. It will be appreciated that the invention could also apply to other mobile communication devices such as PDAs (Personal Digital Assistants) with teleconmnmication facilities.

In the illustrated embodiment, the location information is encrypted using the DES encryption algorithm. It will be appreciated that other symmetric encryption algorithms could be used. Alternatively, an asymmetric algorithm, such as the RSA algorithm, in which the encryption key is drfferent from the decryption key could be used.

The cryptographic key could be communicated to the BTSs in a number of different ways to that used in the illustrated embodiment, for example via an ATM network. Similarly, the cryptographic key could be transmitted to the mobile phone in a number of different ways to that used in the illustrated embodiment, for example using the WAP protocol.

In the illustrated embodiment, the cryptographic key itself is transmitted to the mobile phone. In an alternative embodiment, data is transmitted which may be combined with data already stored in the mobile phone to derive the cryptographic key. For example, a bitwise exclusiveOR operation may be performed on the received data and the IMEI number of the mobile phone to derive the cryptographic key.

While it is preferred to perturb the location information prior to encryption and to regularly change cryptographic keys, it will be appreciated that these features are not essential.

O

In the illustrated embodiment, the BTS 3 stores location information and a cryptographic key, and encrypts the location information using the cryptographic key prior to broadcast. In an alternative embodiment, the BSC S stores location information for each BTS 3 connected to the BSC 5 and the cryptographic key, and sends encrypted location information to each connected BTS 3. As such, the term base station covers the entire BSS 9.

The embodiment described with reference to the drawings comprises computer apparatus and involve processes performed in the computer apparatus. The invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate to source code and object code such as in partially compiled form, or in any other form suitable for using in the implementation of the processes according to the invention.

The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a ROM, for example a CD-ROM or a semiconductor ROM, or a magnetic recording medium, for example a floppy disc or a hard disc, or an optical recording medium. Further, the carrier may be a transmissible carrier such as an electronic or optical signal which may be conveyed via electrical or optical cable or by radio or other means.

The carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

Although in the described embodiment the invention is implemented S by software, it will be appreciated that alternatively the invention could be implemented by hardware devices or a combination of hardware devices and software.

Claims

1. A mobile communication system comprising a plurality of geographically-spaced terrestrial base stations and a plurality of mobile communication devices, with each base station being operable to communicate with mobile communications devices within range of that base station via respective wireless communications links, wherein each base station is operable to transmit location inforthation, indicative of the location of a mobile communication device within range of that base station, encrypted using a first cryptographic key, wherein the communication system comprises key distribution means operable to distribute data associated with a second cryptographic key for decrypting the encrypted location information to one or more of the plurality of mobile communication devices, and wherein following receipt of the data associated with the second cryptographic key, a mobile communication device is operable to decrypt the encrypted location information using the second cryptographic key.

2. A mobile communication system according to claim 1, further comprising a key generator operable to generate the first cryptographic key and the second cryptographic key, wherein the key distribution means is operable to distribute the first cryptographic key to the plurality of base stations, and wherein each base station comprises means for encrypting location information indicative of the location of that base station following receipt of the first cryptographic key.

3. A mobile communication system according to claim 1 or 2, wherein the first and second cryptographic keys are identical.

4. A mobile communication system according to claim 2 or 3, herein the key distribution means is operable to update the first and second cryptographic keys.

5. A mobile communication system according to any of claims 2 to 4, wherein each base station comprises: a data store storing position data indicative of the location of the base station; and means for generating said location information by perturbing the position data stored in the data store.

6. A mobile communication system according to claim 5, wherein the generating means is operable to vary the perturbation applied to the position data.

7. A mobile communications system according to any preceding claim, wherein the mobile communications device comprises one or more applications which are operable to retrieve data in dependence on the recovered location information.

8. A terrestrial base station for a mobile communications network, the base station comprising: a data store for storing position data indicative of the positioii of the base station; means for generating encrypted location information using position data stored in the data store; and means for transmitting the encrypted location information.

9. A base station according to claim 8, wherein said generating means comprises: means for perturbing position data stored in the data store; and means for encrypting said perturbed position data.

10. A base station according to claim 9, wherein said perturbing means is arranged to change the perturbation intermittently.

11. A mobile communication device operable to communicate with a terrestrial base station of a mobile communication network, the mobile communication device comprising: a data store for storing a cryptographic key; a receiver for receiving encrypted location information transmitted by a base station; and means for decrypting the received encrypted location information to recover location information.

12. A mobile communication device according to claim 11, further comprising a receiver for receiving data associated with a new cryptographic key, and means for replacing the cryptographic key in the data store with the new cryptographic key.

13. A mobile conimunication device according to claim 11 or 12, further comprising means for accessing location dependent information via the mobile communication network using the recovered location information.

14. A subscription server operable to communicate with terrestrial base stations and mobile communication devices of a mobile communications network, the subscription server comprising: a database for storing details of subscribers including addressing information for addressing network communications to the respective mobile communication devices for the subscribers; and means for transmitting cryptographic key data to the base stations and the mobile communication devices corresponding to subscribers.

iS. A computer program comprising computer-implementable instructions for programming a programmable apparatus to operate as a subscription server as claimed in claim 14.

16. A computer program comprising computer-implementable instructions for programming a base station of a mobile communications network to operate as a base station as claimed in any of claims 8 to 10.

17. A computer program comprising computer-implementable instructions for programming a mobile communications device to operate as a mobile communications device as claimed in any of claims 11 to 13.

18. A mobile communication system having base stations which are each operable to communicate with mobile communication devices within range of that base station, wherein at least one base station is arranged to transmit encrypted location information indicative of the location of a mobile communication device within range of that base station, and said mobile

S

communication device comprises means for decrypting said encrypted location information.