Method and devices for secure communications in a telecommunications network

1. A method for secure communications in a telecommunications network, the network comprising a group of servers S i (where i=1, 2, . . . , p, and p is a strictly positive integer), referred to as Authorization Servers, the method comprising, for a transaction between an entity A and an entity B of the network, the following steps:

a) the entity A sends to one of the Authorization Servers S i an authorization request (REQ) in which the entity A identifies and authenticates itself as the holder of an identifier ID A ;

b) the entity A declares to the Authorization Server S i its intention to communicate with the entity B; the Authorization Server S i determines an individual secret key K SiB which it shares with the entity B;

c) the Authorization Server S i generates a session key K N,Si AB which is a one-way function of the individual secret key K SiB , and which is also a function of an integer N, referred to as the transaction number, allocated to the transaction; the Authorization Server S i sends the session key K N,Si AB to the entity A;

d) the Authorization Server S i generates a filtering value IDTR N , which is a function dependent at least on the transaction number N in a non-invertible manner; the Authorization Server S i generates a transaction identifier IDTR N,Si , which is a function of the filtering value IDTR N , of the individual secret key K SiB , and of an identifier ID Si of the Authorization Server S i ;

e) the Authorization Server S i supplies the entity B with elements comprising at least the transaction identifier IDTR N,Si ;

f) using the transaction identifier IDTR N,Si , received during the step e), the entity B:

identifies the current filtering value IDTR N within a set of filtering values pre-calculated by the entity B and associated with at least one predicted value of the transaction number, and

obtains the Authorization Server identifier ID Si , and infers the corresponding individual secret key K SiB from the Authorization Server identifier ID Si ; and

g) the entity B generates the session key K N,Si AB .

2. The method for secure communications as claimed in claim 1 , wherein the entity B checks, during the step f), that the Authorization server S i has not already authorized a preceding transaction with the same number N for the entity B.

3. The method for secure communications as claimed in claim 1 , wherein the entity B checks, during the step f), that the value of the received transaction identifier IDTR N,Si is consistent with the individual secret key K SiB .

4. The method for secure communications as claimed in claim 1 , wherein the Authorization Servers use an algorithm common to all of the Authorization servers in the group to determine the successive transaction numbers N relating to a given entity B.

5. The method for secure communications as claimed in claim 4 , wherein the transaction number N determined, for a given entity B, by any given Authorization Server S i at a given time t d , is a predetermined function of the time t d and of a reference number N B , the value of which is a secret shared by the entity B and by all of the Authorization servers S i in the group.

6. The method for secure communications as claimed in claim 4 , wherein the transaction number N determined, for a given entity B, by any given Authorization Server S i is a predetermined sequencing function of the preceding transaction number, and wherein the Authorization Server S i sends a synchronization message to the entity B each time the Authorization Server S i determines a value of the transaction number belonging to a series of predetermined values for the entity B.

7. The method for secure communications as claimed in claim 1 , wherein the elements which the Authorization Server S i supplies to the entity B during the step e) also comprise a datum CHECK N,Si AB dependent on the transaction number N and inferred, by using a cryptographic function dependent on a secret key K SiB,check derived from the secret key K SiB , from a set of elements obtained from at least one of the authorization request (REQ) and the transaction number N.

8. The method for secure communications as claimed in claim 7 , wherein the entity A supplies the entity B with the identifier ID A of the entity A, or a derived identifier ID′ A .

9. The method for secure communications as claimed in claim 8 , wherein:

the set of elements from which the datum CHECK N,Si AB is inferred comprises the identifier ID A of the entity A or the derived identifier ID′ A , and

during the step f), the entity B checks, by using the secret key K SiB,check , the consistency between the datum CHECK N,Si AB and the elements comprising the identifier ID A or the derived identifier ID′ A .

10. An Authorization Server S i (where i=1, 2, . . . , p, and p is a strictly positive integer) configured to provide secure communications in a telecommunications network during a transaction between an entity A and an entity B, the Authorization Server programmed to:

identify and authenticate entity A holding an identifier ID A ,

determine an individual secret key K SiB which the Authorization Server S i shares with an entity B with which the entity A declares its intention to communicate,

generate a session key K N,Si AB and send it to the entity A, the session key K N,Si AB being a one-way function of the individual secret key K SiB and being a function of an integer N, referred to as the transaction number, allocated to the transaction,

generate a filtering value IDTR N , which is a function dependent at least on the transaction number N in a non-invertible manner,

generate a transaction identifier IDTR N,Si , which is a function of the filtering value IDTR N , of the individual secret key K SiB , and of an identifier ID Si of the Authorization Server S i so that the value of IDTR N corresponding to a predictable value for the transaction number N and subsequently the value of the session key K N,Si AB can be deduced therefrom by the entity B, and

supply the entity B with elements comprising at least the transaction identifier IDTR N,Si .

11. A device, referred to as entity B, configured to provide secure communications in a telecommunications network, wherein, during a transaction involving the entity B and an entity A, the entity B is configured to:

receive elements comprising at least a transaction identifier IDTR N,Si generated by an Authorization Server S i (where i=1, 2, . . . , p, and p is a strictly positive integer), wherein the transaction identifier IDTR N,Si is a function of a filtering value IDTR N , an individual secret key K SiB shared by the entity B and the Authorization Server S i , and an identifier ID Si of the Authorization Server S i , and wherein the filtering value IDTR N is a function dependent at least, in a non-invertible manner, on an integer N, referred to as the transaction number, allocated to the transaction,

use the transaction identifier IDTR N,Si to:

identify the current filtering value IDTR N within a set of filtering values pre-calculated by the entity B and associated with at least one predicted value of the transaction number, and

obtain the Authorization Server identifier ID Si , and infer the corresponding individual secret key K SiB from the Authorization Server identifier ID Si ; and

generate a session key K N,Si AB which is a function of the transaction number N and a one-way function of the individual secret key K SiB .

12. The device for secure communications as claimed in claim 11 , wherein the device is further configured to provide a correspondence table relating at least one predicted value of the transaction number with the associated pre-calculated filtering value.

13. A device, referred to as entity A, configured to provide secure communications in a telecommunications network, wherein, during a transaction involving the entity A and an entity B, the entity A is configured to:

identify itself and authenticate itself as the holder of an identifier ID A by communicating with an Authorization Server S i (where i=1, 2, . . . , p, and p is a strictly positive integer),

declare to the Authorization Server S i its intention to communicate with an entity B,

receive a session key K N,Si AB from the Authorization Server S i , wherein the session key K N,Si AB is a one-way function of an individual secret key K SiB shared by the Authorization Server S i and the entity B, and wherein the session key K N,Si AB is a function of an integer N, referred to as the transaction number, allocated to the transaction,

receive a transaction identifier IDTR N,Si from the Authorization Server S i , wherein the transaction identifier IDTR N,Si is a function of a filtering value IDTR N , the individual secret key K SiB , and an identifier ID Si of the Authorization Server S i , and wherein the filtering value IDTR N is a function dependent at least, in a non-invertible manner, on the transaction number N, so that the value of IDTR N corresponding to a predictable value for the transaction number N and subsequently the value of the session key K N,Si AB can be deduced therefrom by the entity B, and

send elements comprising at least the transaction identifier IDTR N,Si to the entity B.

14. A non-transitory data storage device comprising computer program code instructions that when executed perform the steps of the method for secure communications as claimed in claim 1 .

15. A non-transitory data storage device which is non-removable, or partially or totally removable, comprising computer program code instructions for allowing an Authorization Server to carry out the steps of a method for secure communications according to claim 1 .

16. A non-transitory data storage device which is non-removable, or partially or totally removable, comprising program code instructions for allowing an entity A to carry out the steps of a method for secure communications according to claim 1 .

17. A non-transitory data storage device which is non-removable, or partially or totally removable, comprising computer program code instructions for allowing an entity B to carry out the steps of a method for secure communications according to claim 1 .