SUBSCRIBER IDENTITY MODULE (SIM)

A key feature of the GSM standard is the Subscriber Identity Module (SIM) card. A SIM card contains information about the subscriber and must be plugged into the ME to enable the subscriber to use the network. With the exception of emergency calls, MSs can only be operated if a valid SIM is present. The SIM stores three types of subscriber related information:

• Fixed data stored before the subscription is sold: e.g. IMSI, authentication key and security algorithms

• Temporary network data: e.g. the location area of the subscriber and forbidden PLMNs

• Service data: e.g. language preference, advice of charge

GSM phase 1 SIMs contain all necessary network control information, while phase 2 SIMs include a large number of extra features such as a language identifier and a preferred language option.

TYPES OF SIM CARD

Two physical types of SIMs are specified. These are the ”ID-1 SIM” and the ”Plug-in SIM”. The logical and electrical interfaces are identical for both types of SIM.

ID-1 SIM

The format and layout of the ID-1 SIM comply with ISO standards for Integrated Circuit (IC) cards (i.e. credit card size).

ID-1 SIM card

Plug-in SIM

The plug-in SIM is smaller than the ID-1 SIM. It is intended for semi-permanent installation in the ME.

Plug-in SIM card

SECURITY FEATURES

GSM defines a number of security features to be supported by SIMs. These are:

• Authentication algorithm, A3

• Subscriber authentication key, Ki

• Ciphering key generation algorithm, A8

• Ciphering key, Kc

• Control of access to data stored and functions performed in SIM

SIM INFORMATION STORAGE REQUIREMENTS

A SIM contains information for GSM network operations. This information can be related to the mobile subscriber, GSM services or PLMN. The data storage requirements of a SIM are divided into two categories: mandatory and optional.

Mandatory storage

A SIM must provide storage capability for the following:

• Administrative information: describes the SIM’s mode of operation, e.g. normal or type approval

• IC card identification:

Unique information identifying the SIM and the card issuer

• SIM service table:

Indicates which optional services are provided by the SIM (e.g. last numbers dialled, call length indication, PLMN selection, etc.)

• International Mobile Subscriber Identity (IMSI):

 An identitynumber used by the network to identify the subscription

• Location information:

Comprising LAI, current value of periodic location updating timer and location update status

• Ciphering key (Kc) and ciphering key sequence number

• List of carrier frequencies to be used for cell selection

• Forbidden PLMNs

• Language preference:

Subscriber's preferred languages

The location information, Kc and the Kc sequence number may be updated at each call termination. In addition the SIM must be able to manage and provide storage in accordance with the security requirements:

• Personal Identification Number (PIN)

• PIN enabled / disabled indicator

• PIN error counter

• PIN Unlock Key (PUK)

• PUK error counter

• Subscriber authentication key (Ki)