Enhanced short message and method for synchronizing and ensuring security of enhanced short messages exchanged in a cellular radio communication system

Claim 2

Enhanced message of the type transmitted by a message service center (C-SMS) to a mobile station (MS) of a cellular radio communication system, said enhanced message including a header ( 1 ) and a body ( 2 ), said body ( 2 ) containing in particular a first field ( 3 ) storing remote commands belonging to an application remote from said mobile station, said mobile station constituting a terminal cooperating with a subscriber identification module, said terminal including means for receiving said enhanced message, said subscriber identification module including means for storing and processing said enhanced message received by the terminal, said subscriber identification module serving to support said remote application and including means for executing said remote commands, said enhanced message being characterized in that said body ( 2 ) also includes a second field ( 4 ) for storing the current value of a synchronization counter, said current value of the synchronization counter being intended to be compared to a previous value of the synchronization counter stored in the subscriber identification module such that said enhanced message is accepted or rejected by the subscriber identification module depending on the result of comparing the current with the previous value of the synchronization counter, said previous value being updated with said current value only once the enhanced message has been accepted by the subscriber identification module.

Claim 3

Enhanced message according to claim 1 , characterized in that body ( 2 ) of said enhanced message also includes a third field ( 5 ) storing a first piece of information pinpointing the location of said previous synchronization counter value in said subscriber identification module data storage means.

Claim 4

Enhanced message according to claim 2 , wherein said subscriber identification module data storage means have a hierarchical structure with at least three levels including at least the following three types of files: master file (MF); dedicated file (DF) or dedicated file placed under said master file, elementary file (EF) placed under one of said dedicated files, known as parent dedicated file, or directly under said master file, known as parent master file, an elementary system file (EF SMS System) specific to each remote application containing a second piece of information pinpointing the location of said previous synchronization counter value in said subscriber identification module data storage means, said enhanced message being characterized in that said first piece of locating information contained in said third storage field ( 5 ) is an identifier of a dedicated file (DF) or master file (MF) to which said elementary system file (EF SMS System) relates according to a predetermined search strategy in the data storage means.

Claim 5

Enhanced message according to claim 1 , characterized in that said body also includes a fourth field ( 6 ) storing a cryptogram, known as transmitted cryptogram, calculation of which at least partially involves the content of the second field storing the current synchronization counter value, said transmitted cryptogram being intended to be compared with another cryptogram, known as local cryptogram, calculated by the subscriber identification module so that said enhanced message is accepted by the subscriber identification module if the transmitted and local cryptograms are identical, and rejected if they are not.

Claim 6

Enhanced message according to claim 4 , characterized in that calculation of said transmitted and verification cryptograms also involves, at least partially, the content of the first field ( 3 ) storing the remote commands.

Claim 7

Enhanced message according to claim 5 , characterized in that calculation of said transmitted and local cryptograms involves at least the entire content of the second field ( 4 ) storing the current synchronization counter value and the entire content of the first field ( 3 ) storing the remote commands.

Claim 8

Enhanced message according to claim 1 , characterized in that said transmitted and local cryptograms are calculated with a cryptographic function belonging to the group including: the secret key cryptographic functions; and the public key cryptographic functions.

Claim 9

Enhanced message according to claim 1 , whereby said subscriber identification module stores, in said subscriber identification module data storage means, a cryptographic function and an associated key which are specific to said remote application and enables said local cryptogram to be calculated, said enhanced message being characterized in that the body of said enhanced message also includes a fifth field ( 5 ) storing a third piece of information pinpointing the location in said data storage means where said cryptographic function and said associated key specific to said remote application are stored.

Claim 10

Enhanced message according to claim 1 , characterized in that said third field ( 5 ) also constitutes said fifth field, and said first piece of locating information also constitutes said third piece of locating information.

Claim 11

Enhanced message according to claim 1 , characterized in that said body ( 2 ) also includes a sixth field ( 7 ) storing a checksum, known as transmitted checksum, calculation of which involves, at least in part, the contents of the first field ( 3 ) storing remote commands, said transmitted checksum being intended for comparison with another checksum known as local checksum, calculated by the subscriber identification module, so that said enhanced message is accepted by the subscriber identification module if the transmitted checksum and local checksum are identical, and rejected if they are not.

Claim 12

Enhanced message according to claim 1 , said subscriber identification module including an input/output line over which it receives local commands belonging to an application local to said mobile station, characterized in that said remote commands contained in said first field ( 3 ) of said enhanced message are substantially identical to said local commands received over the input/output line.

Claim 13

Method for synchronizing and ensuring security of enhanced messages exchanged between a message service center (C-SMS) and a mobile station (MS) of a cellular radio communication system, each enhanced message including a header ( 1 ) and a body ( 2 ), said body ( 2 ) containing in particular a first field ( 3 ) for storing remote commands belonging to a remote application of said mobile station, said mobile station constituting a terminal cooperating with a subscriber identification module, said terminal including means for receiving said enhanced message, said subscriber identification module including means for storing and processing said enhanced message received by the terminal, said subscriber identification module serving to support said remote application and including means for executing said remote commands, said method being characterized by having in particular the following steps: said message service center transmits ( 61 ) to said mobile station an enhanced message whose body also includes a second field in which the current value of a synchronization counter is stored; the subscriber identification module of the mobile station compares ( 65 , 85 ) said current synchronization counter value contained in said enhanced message with a previous synchronization counter value stored in the subscriber identification module; the subscriber identification module accepts ( 67 ) or rejects ( 66 ) said enhanced message depending on the result of comparing the current with the previous synchronization counter values; if the enhanced message has been accepted, the subscriber identification module updates ( 86 ) said previous value with said current value.

Claim 14

Method for synchronizing and ensuring security of enhanced messages exchanged between a message service center (C-SMS) and a mobile station (MS) of a cellular radio communication system, each enhanced message including a header ( 1 ) and a body ( 2 ), said body ( 2 ) containing in particular a first field ( 3 ) for storing remote commands belonging to a remote application of said mobile station, said mobile station constituting a terminal cooperating with a subscriber identification module, said terminal including means for receiving said enhanced message, said subscriber identification module including means for storing and processing said enhanced message received by the terminal, said subscriber identification module serving to support said remote application and including means for executing said remote commands, said method being characterized by having in particular the following steps: said message service center transmits ( 61 ) to said mobile station an enhanced message whose body also includes a second field in which the current value of a synchronization counter is stored; the subscriber identification module of the mobile station compares ( 65 , 85 ) said current synchronization counter value contained in said enhanced message with a previous synchronization counter value stored in the subscriber identification module; the subscriber identification module accepts ( 67 ) or rejects ( 66 ) said enhanced message depending on the result of comparing the current with the previous synchronization counter values; if the enhanced message has been accepted, the subscriber identification module updates ( 86 ) said previous value with said current value.

Claim 15

Method according to claim 12 , characterized in that, for each new enhanced message of said remote application transmitted by said message service center, the current synchronization counter value is incremented by a predetermined step, and in that said enhanced message is accepted by the subscriber identification module only if said current synchronization counter value is higher than said previous value.

Claim 16

Method according to claim 12 , characterized in that said step in which the previous synchronization counter value is updated with said current value is carried out only if the difference between said current and previous values is less than a maximum predetermined increment.

Claim 17

Method according to claim 12 , characterized by also including the following step: when said enhanced message is rejected ( 66 ) by the subscriber identification module, the latter sends back ( 87 ) to the message service center an enhanced message containing a specific error code telling the message service center that said enhanced message that it previously transmitted was rejected due to a counter synchronization problem.

Claim 18

Method according to claim 12 , characterized in that the body ( 2 ) of said enhanced message transmitted by the message service center to the mobile station also includes a third field ( 5 ) storing a first piece of information pinpointing the storage location, in said subscriber identification module data storage means, of said previous synchronization counter value, and in that said comparison step ( 85 ) by the subscriber identification module of the current and previous synchronization counter values is preceded by the following steps: the subscriber identification module reads ( 82 ) said first piece of locating information contained in the third field of said enhanced message; the subscriber identification module deduces ( 83 ) therefrom the storage location of the previous synchronization counter value; the subscriber identification module reads ( 84 ), in said storage location, the previous synchronization counter value.

Claim 19

Method according to claim 12 , characterized in that the body ( 2 ) of the enhanced message transmitted by the message service center to the mobile station also includes a fourth field ( 6 ) storing a cryptogram, known as transmitted cryptogram, calculated using at least part of the contents of the second field ( 4 ) storing the current synchronization counter value, and in that said method also includes the following steps: the subscriber identification module calculates ( 92 ) a local cryptogram, using at least in part the contents of the second field ( 4 ) of said enhanced message; the subscriber identification module compares ( 93 ) said transmitted cryptogram to said local cryptogram so that said enhanced message is accepted if the transmitted and local cryptograms are identical and rejected if they are not.

Claim 20

Method according to claim 12 , whereby said subscriber identification module stores, in said subscriber identification module data storage means, a cryptographic function and an associated key that are specific to said remote application enabling said local cryptogram to be calculated, characterized in that the body of said enhanced message transmitted by the message service center to the mobile station also includes a fifth field ( 5 ) storing a third piece of information pinpointing the storage location, in said data storage means, of said cryptographic function and said associated key, and in that said step ( 92 ) in which the subscriber identification module calculates said local cryptogram is divided into the following steps: the subscriber identification module reads ( 94 ) said third piece of locating information contained in the fifth field ( 5 ) of said enhanced message; the subscriber identification module ( 95 ) deduces from this the storage location of said cryptographic function and said associated key; the subscriber identification module calculates ( 96 ) said local cryptogram, using said cryptographic function, said associated key, and at least part of the contents of the second field ( 4 ) of said enhanced message.

Claim 21

Method according to claim 18 , whereby said subscriber identification module data storage means possess a hierarchical structure with at least three levels having at least the following three types of files: master file (MF); dedicated file (DF), or dedicated file placed under said master file, elementary file (EF) placed under one of said dedicated files, known as parent dedicated file, or directly under said master file, known as parent master file, said method being characterized in that an elementary system file (EF SMS System) specific to each remote application, contains a second piece of information pinpointing the location, in said subscriber identification module data storage means, of said previous synchronization counter value, of said cryptographic function, and of said associated key, and in that said third field ( 5 ) also constitutes said fifth field with said first piece of locating information also constituting said third piece of locating information, and characterized in that said first piece of locating information contained in said third storage field ( 5 ) is an identifier of a dedicated file (DF) or master file (MF) to which said elementary system file (EF SMS System) relates according to a predetermined search strategy in the data storage means.

Claim 22

Method according to claim 12 , characterized in that body ( 2 ) of said enhanced message transmitted by the message service center to the mobile station also includes a sixth field ( 7 ) storing a checksum, known as transmitted checksum, calculation of which involves at least in part the contents of the first field ( 3 ) storing remote commands, and in that said method also includes the following steps: the subscriber identification module calculates ( 72 ) a local checksum, using at least in part the contents of the first field ( 3 ) of said enhanced message, the subscriber identification module compares ( 73 ) said transmitted checksum to said local checksum so that said enhanced message is accepted if the transmitted and local checksums are identical and rejected if they are not.