SIM (Subscriber Identity Module)

The Subscriber Identity Module is the tamper-resistant smart card that stores the long-term subscriber key Ki/K, the IMSI/SUPI, network selection data, and a small file system. It executes the AKA authentication algorithm so the secret key never leaves the card. The SIM exists today as a removable UICC, an embedded eSIM with remote provisioning, and an integrated iSIM inside the modem chipset. SIM security underpins all subscriber authentication, making SIM swap and cloning attacks among the highest-impact threats in mobile.

Categories: Identity and SubscriberSecurity ControlsThreats and Attacks

SIM in context

Subscriber identifiers (IMSI, SUPI, MSISDN, IMEI) are the anchor for authentication, charging, lawful interception and fraud analytics. Any protocol or interface that leaks a permanent identifier is treated as a serious privacy defect, which is why 5G introduced SUCI concealment on the air interface.

Security controls in telecom span signaling firewalls (SS7/Diameter/GTP screening at the network edge), transport encryption (IPsec, TLS, PRINS), identity and access on OSS/BSS, and monitoring at both the packet and log level. Controls are audited against GSMA FS.11/FS.19/FS.20/FS.36 and, in Europe, NIS2 sectoral rules.

To place SIM in the wider telecom-security picture, review SNMP, Event Logging, IMSI, TMSI Reallocation, UDM and USIM.

Related terms

Equipment

SIM, eSIM and provisioning (UICC, eUICC, SM-DP+, OTA)

Articles in the P1 mobile network security guide

Related topic hubs

  • SIM Swap Attack SIM swap fraud, port-out and account takeover risk.
  • Diameter Attacks S6a IDR/PUR/CLR abuse, subscriber tracking, LTE signaling attacks.
  • 5G Security 5G SBA, SEPP, SUCI, 5G-AKA, N32 and service-based interface security.
  • VoLTE Security IMS/VoLTE signaling risk: SIP, IMS-AKA, media plane attacks.

More from the TelcoSec Glossary

Browse the full TelcoSec Glossary, the Ultimate Guide to Mobile Network Security, or the P1 Arsenal of telecom-security tools.