Different parts of a SIM card

A SIM - short for Subscriber Identity Module - is a piece of plastic that slots into mobile phone that acts as your unique ID, so that you can connect to, make calls over and be charged for using a particular mobile phone network. It contains the integrated
circuit to store the International Mobile Subscriber
Identity or IMSI and the keys to identify and
authenticate the subscribers on the communication
system.
Following image shows parts of the SIM card


The most important part of the SIM card is its
Microcontroller. It is a paper sized chip which is a
typical ROM with a size between 64 KB to 512 KB. The
RAM size ranges between 1KB to 8KB while the
EEPROM size is in between 16KB to 512 KB. The ROM
contains the OS or operating system for the card,
while the EEPROM contains data called
personalization that includes security keys, phone
book, SMS settings etc. The operating voltage of SIM
maybe, 1.8V, 3V or 5V but the operating voltages of
most of the modern SIM support 5V, 3V and 1.8V.
Key functionalities of a SIM card :
1.Integrated Circuit Card Identifier or ICCID – It is
the Primary account number that has 19 digit long.
The number has sections like Issuer Identification
Number or IIN, Individual Account Identification,
Check digit etc.
2. International Mobile Subscriber Identity or IMSI
– It is used to identify the individual operator net
work. Normally it has 109 digits. Its first 3 digits
represent Mobile Country Code or MCC, the next 2 to
3 digits represents the Mobile Network Code or MNC,
The next digits represents the Mobile Subscriber
Identification Number or MSIN.
3. Authentication Key or Ki – It is a 128 bit used to
authentication of the SIM card on the Mobile
Network. Each SIM has a unique Authentication key
assigned by the operator during personalization. The
Authentication Key is also stored in the data base of
the carrier’s network. When the mobile phone first
activates using the SIM card, it gets the International
Mobile Subscriber Identity or IMSI from the SIM card
and transfers it to the mobile operator for
authentication. The data base in the operator system
then searches for incoming IMSI and the associated
Authentication key. The operator data base then
generates a Random Number or RAND and signs it
with the IMSI and gives another number called
Signed Response 1(SRES_ 1). The RAND will be sending
to the mobile phone and the SIM then signs it with
the Authentication Key and produces the SRES_ 2
which then passes into the operator network. The
operator net work then compares the SRES_1 it
produced and the SRES_2 from the mobile phone. If
both match, the SIM is authenticated.
4. Location Area Identity or LAI– This the
information stored in the SIM about the local network
available. The operator network is divided into
different small areas each having a LAI.
5. SMS messages – SIM card can store many SMS
6. Contacts – SIM can store around 250 contacts.


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