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Does a SIM Card Store Data?

A SIM card is a microscopic chip that makes it possible to communicate on a mobile network. But in fact, the “SIM card” can do much more. Does a SIM card store data of users? Let’s consider the topic below.

What is a SIM Card?

A SIM card is a contact smart card with its own processor capable of registering on a mobile network. It is able to find the nearest transmitting station and store information: numbers, SMS and other data.

The SIM card has a permanent (non-volatile) and RAM. There is also a hardware encryption module and a hardware random number generator.

The SIM card processor operates at a frequency of up to 10 MHz. Permanent memory is divided into areas: about 60% is occupied by operator data, 20% is the operating system, and the rest is user data.

Do SIM cards store data? Sure! Read more below.

What Data Does a SIM Card Store?

First of all, the SIM card stores KI and IMSI numbers, as well as other information.

IMSI (International Mobile Subscriber Identity) is the international mobile subscriber number. It is forwarded to the network but only during authentication. When possible, instead of IMSI, the smartphone sends a TMSI-generated temporary ID based on IMSI.

KI (Key Identification) is a unique 128-bit user authentication key. You also need it to log in to the network. KI is generated using the A8 algorithm, authentication takes place using the A3 algorithm.

SIM cards store the information necessary for a successful connection to the cellular network: identification number, and technical data of the phone. Information supporting security: PIN and PUK codes. Network settings: internet settings, SMS service center number. There is also a certain amount of free space for storing phone service information: contacts, SMS, and numbers.

Subscriber Information

KI is the most important part of the card from a security point of view. It is this key that encrypts all data that is transferred from the card and back, so the key is stored in an area of memory that is not readable. Even if you connect the contacts of the SIM card to another processor and try to get all the data directly, it will not work.

PIN and PUK information is also stored here.

Network Information

ICCID (International Circuit Card Identity): A unique 19-20 digit serial number assigned to each SIM card. You can find it on the map itself or in the phone settings.

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IMSI is responsible for registering the card on the network — using it, the telecom operator understands which SIM card it is. Next, the operator looks into the database and determines which number is linked to it.

Contact Information

The SIM card can store a limited number of contacts (usually up to 250), including name and phone number.

SMS Messages

Some SIM cards have limited storage for SMS messages but in modern smartphones, messages are usually stored in the phone’s memory.

Other Data

Each SIM card contains a serial number and the number of the mobile phone linked to it. It also stores temporary information about the network in which the subscriber is located. Simply put data on which particular cell tower it is connected to at the moment or was connected to in the previous period.

The SIM cards also contain data from applications installed on the smartphone. In modern smartphones, such data is stored in the memory of “SIM cards” only by operator applications.