5G SIM and iSIM Technology

5G SIM and iSIM Technology

The evolution from 4G LTE to 5G introduces a new authentication framework, a redesigned SIMSIMApplicationSmart card for mobile network authentication.Click to view → architecture, and the integrated SIM (iSIMiSIMApplicationSIM integrated into device SoC.Click to view →) form factor. Understanding SUCI, 5G-AKA, and the GSMA iSIM specification is essential for device manufacturers, network operators, and enterprise IoT teams deploying 5G hardware.

5G Authentication: SUCI and 5G-AKA

SUPI and SUCI

In LTE, the subscriber identity (IMSI) was sent in cleartext during initial attach — a well-known vulnerability exploited by IMSI catchers. 5G replaces this with:

• SUPI (Subscription Permanent Identifier): The permanent identity, analogous to IMSI, stored only on the SIM and in the UDM (Unified Data Management) network function.
• SUCI (Subscription Concealed Identifier): A one-time, encrypted SUPI derived using the Home Network Public Key stored on the SIM.

SUCI generation uses an Elliptic Curve Integrated Encryption Scheme (ECIES) profile:

SUCI = Home Network Identifier || SUCI Protection Scheme || HN Public Key ID
       || Encrypted MSIN || MAC

The Home Network Private Key (held in the UDM) decrypts the SUCI to recover the SUPI. This protects subscriber privacy even if a rogue base station intercepts the initial registration request.

5G-AKA Authentication

5G-AKA (Authentication and Key Agreement) extends EPS-AKA with:

The SIM (now called USIM in 5G) stores the long-term key K and operator variant OPc. The SUPI and SUCI are generated entirely on the iSIM or USIM chip; K never leaves the secure element.

iSIM vs. eSIM vs. Physical SIM

The key distinction between eSIMeSIMApplicationProgrammable embedded SIM chip.Click to view → and iSIM is physical integration: an eSIM is a discrete IC soldered to the board, while an iSIM is a security domain within the application processor die, isolated by hardware TrustZone or equivalent partitioning.

GSMA Specifications

UICC Evolution Timeline

1991  SIM (ID-000, plug-in)
1996  SIM (mini-SIM, 2FF)
2003  USIM (3G authentication algorithms)
2010  micro-SIM (3FF) — iPhone 4
2012  nano-SIM (4FF) — iPhone 5
2016  eSIM (MFF2 soldered) — Apple Watch
2019  iSIM (integrated SoC) — Qualcomm Snapdragon X55
2022  5G-capable iSIM + SUCI — mass market IoT modules

Security Considerations

• SUCI privacy: SUCI provides unlinkability — each registration uses a fresh ephemeral key, so two SUCI values cannot be correlated to the same subscriber without the UDM's private key.
• Profile binding: iSIM profiles are cryptographically bound to the specific SoC; cloning attacks that worked on removable SIMs are computationally infeasible.
• Firmware attacks: The iSIM security domain must be isolated from the application processor even if the OS is compromised — verified by Common Criteria evaluation of the SoC.

Use the eSIM Checker to determine whether a device supports SGP.22 consumer RSP or the M2M SGP.02 profile, and the Cost Estimator to model 5G iSIM deployment costs.