Mutual authentication with modified message authentication code

A subscriber identity module for a mobile station of a communications network, wherein said subscriber identity module is configured to process a plurality of authentication data parameters according to an authentication algorithm and generate first and second authentication parameters, and wherein said subscriber identity module is further configured to determine whether said first generated authentication parameter matches a first received authentication parameter, and whether said first received authentication parameter matches said second generated authentication parameter and to process a second received authentication parameter according to a predefined process when said first received authentication parameter matches said second generated authentication parameter.

A cellular communications network, comprising:

• a mobile station comprising a subscriber identity module configured to perform a predefined authentication algorithm using at least one authentication data parameter;
• a network element configured to generate a plurality of authentication data parameters for mutual authentication with said mobile station according to said predefined authentication algorithm, wherein said plurality of authentication data parameters includes at least a first authentication data parameter and a second authentication data parameter,
• wherein said subscriber identity module is configured to process said second authentication data parameter in a defined manner in response to a determination that said first authentication data parameter is different from a first authentication data parameter generated by said mobile station and equivalent to a second authentication data parameter generated by said mobile station.

In a mutual authentication system in which first and second communicating entities each authenticate the other, wherein said authentication comprises generating a message authentication code (MAC) at said first entity having a value dependent on a secret key shared by the first and second entities, wherein said MAC is received by said second entity with a plurality of additional data fields, a method of processing said received MAC value at said second entity comprising:

• generating a plurality of MAC values;
• comparing each of said plurality of MAC values to said received MAC value;
• processing at least a portion of one or more of said additional received data fields according to the results of said comparing.

In a communication network in which first and second communicating entities each authenticate the other, a method of a communicating entity authenticating itself to a receiving entity comprising:

• transmitting a message authentication code with at least a first additional data field, wherein said message authentication code authenticates the communicating entity and defines receiving entity interpretation of said additional data field.