Method for determining a key for securing communication between a user apparatus and an application server

A determining method for determining a key to secure a communication between a user equipment and an application server, said method comprising:

• authenticating the user equipment by an authentication server a mobile communication network, a secret master key being generated, during said authenticating, by the user equipment and the authentication server;
• after the secret master key is generated by the user equipment and the authentication server, receiving by the authentication server a key request that was sent by the user equipment with a view to communicating with the application server;
• sending a random variable by the authentication server to the user equipment after receiving the key request from the user equipment;
• and
• computing said key by using a key derivation function applied to at least the random variable, a user identifier and an identifier of the application server and using the master key.

A user equipment, arranged to communicate with an application server via a mobile communication network, said equipment comprising:

• at least one processor;
• and
• at least one non-transitory computer-readable medium comprising instructions stored thereon which when executed by the at least one processor configure the user equipment to:
• authenticate the user equipment with an authentication server of the mobile communication network, a secret master key being generated, during said authentication, by the user equipment and the authentication server;
• after the secret master key is generated by the user equipment and the authentication server, send, to the authentication server, a key request with a view to communicating with the application server;
• and
• compute a key to make a communication between the user equipment and the application server secure by using a key derivation function applied to at least a random variable, a user identifier and an identifier of the application server and using the master key, said random variable having been received by the user equipment from the authentication server after sending the key request to the authentication server.

An authentication server of a mobile communication network, said authentication server comprising:

• at least one processor;
• and
• at least one non-transitory computer-readable medium comprising instructions stored thereon which when executed by the at least one processor configure the user equipment to:
• perform an authentication of a user equipment, a secret master key being generated, during said authentication, by the user equipment and the authentication server;
• after the secret master key is generated by the user equipment and the authentication server, receive a key request that was sent by the user equipment with a view to communicating with an application server;
• send a random variable to the user equipment after receiving the key request from the user equipment;
• and
• compute a key to make a communication between the user equipment and the application server secure, said key being computed by using a key derivation function applied to at least the random variable, a user identifier and an identifier of the application server and using the master key.

A non-transitory computer-readable storage medium, on which is stored a program comprising program-code instructions which are executable by a processor of a user equipment arranged to communicate with an application server via a mobile communication network, wherein the instructions configure the user equipment to:

• authenticate the user equipment with an authentication server of the mobile communication network, a secret master key being generated, during said authentication, by the user equipment and the authentication server;
• after the secret master key is generated by the user equipment and the authentication server, send, to the authentication server, a key request with a view to communicating with the application server;
• and
• compute a key to make a communication between the user equipment and the application server secure by using a key derivation function applied to at least a random variable, a user identifier and an identifier of the application server and using the master key, said random variable having been received by the user equipment from the authentication server after sending the key request to the authentication server.

A non-transitory computer-readable storage medium, on which is stored a program comprising program-code instructions which are executable by a processor of an authentication server of a mobile communication network, wherein the instructions configure the an authentication server to:

• perform an authentication of a user equipment, a secret master key being generated, during said authentication, by the user equipment and the authentication server;
• after the secret master key is generated by the user equipment and the authentication server, receive a key request that was sent by the user equipment with a view to communicating with an application server;
• send a random variable to the user equipment after receiving the key request from the user equipment;
• and
• compute a key to make a communication between the user equipment and the application server secure, said key being computed by using a key derivation function applied to at least the random variable, a user identifier and an identifier of the application server and using the master key.