4 Overview of Security System

03.483GPPRelease 1999Security mechanisms for SIM application toolkitStage 2TS

An overview of the secure communication related to the SIM Application Toolkit together with the required security mechanisms is given in TS 02.48 [2], (see figure 1).

Figure 1: System Overview

The Sending Application prepares an Application Message and forwards it to the Sending Entity, with an indication of the security to be applied to the message.

The Sending Entity prepends a Security Header (the Command Header) to the Application Message. It then applies the requested security to part of the Command Header and all of the Application Message, including any padding octets. The resulting structure is here referred to as the (Secured) Command Packet.

Under normal circumstances the Receiving Entity receives the Command Packet and unpacks it according to the security parameters indicated in the Command Header. The Receiving Entity subsequently forwards the Application Message to the Receiving Application indicating to the Receiving Application the security that was applied. The interface between the Sending Application and Sending Entity and the interface between the Receiving Entity and Receiving Application are proprietary and therefore outside the scope of the present document.

If so indicated in the Command Header, the Receiving Entity shall create a (Secured) Response Packet. The Response Packet consists of a Security Header (the Response Header) and optionally, application specific data supplied by the Receiving Application. Both the Response Header and the application specific data are secured using the security mechanisms indicated in the received Command Packet. The Response Packet will be returned to the Sending Entity, subject to constraints in the transport layer, (e.g. timing).

Although there is no direct acknowledgement to an SMS-CB message in TS 04.12 [12], the Sending Application may have requested a response. In this case a (Secured) Response Packet could be sent using a different bearer by the Receiving Application.

In some circumstances a security related error may be detected at the Receiving Entity. In such circumstances the Receiving Entity shall react according to the following rules:

1) nothing shall be forwarded to the Receiving Application. i.e. no part of the Application Message, and no indication of the error.

2) if the Sending Entity does not request a response (in the Command Header) the Receiving Entity discards the Command Packet and no further action is taken

3) if the Sending Entity does request a response and the Receiving Entity can unambiguously determine what has caused the error, the Receiving Entity shall create a Response Packet indicating the error cause. This Response Packet shall be secured according to the security indicated in the received Command Packet.

4) if the Sending Entity does request a response and the Receiving Entity cannot determine what has caused the error, the Receiving Entity shall send a Response Packet indicating that an unidentified error has been detected. This Response Packet is sent without any security being applied.

5) If the Receiving Entity receives an unrecognisable Command Header (e.g. an inconsistency in the Command Header), the Command Packet shall be discarded and no further action taken.