Description
An Elementary File (EF) is a basic, addressable data container residing within the file system of a UICC (Universal Integrated Circuit Card), which includes SIM, USIM, and ISIM applications. The UICC's file system is hierarchically organized, starting with a Master File (MF) as the root, under which are Dedicated Files (DFs) representing applications (like the GSM or USIM application), and within these DFs reside the Elementary Files. Each EF is identified by a unique file identifier (FID) and can be selected using standard ISO/IEC 7816-4 commands. EFs store a wide variety of data, structured as either transparent (a simple sequence of bytes), linear fixed (records of fixed length), cyclic (a fixed number of records where the oldest is overwritten), or BER-TLV (data objects encoded in Tag-Length-Value format).
How an EF works is central to the operation of the UICC. When the mobile device (ME) needs specific data, such as the IMSI for network registration or the authentication key (Ki) for security procedures, it sends a command (e.g., READ BINARY or READ RECORD) to the UICC, specifying the FID of the target EF. The UICC's operating system locates the file, performs any necessary access condition checks (e.g., verifying a PIN), and returns the requested data. For example, the EF_IMSI (file identifier '6F07') stores the International Mobile Subscriber Identity. The ME reads this file during initial registration to identify itself to the network. Similarly, EF_LOCI stores the Location Information, which is updated by the network to allow for efficient paging.
Key components of the EF concept include the file structure, the access conditions, and the associated metadata defined in the EF's header. The header specifies the file type, size, record length (if applicable), and access conditions (e.g., always allowed, PIN1 required, ADM required). EFs are the backbone for storing both mandatory network parameters (like EF_KC for ciphering key in GSM) and optional user data (like EF_PBR for phonebook references). Their role is to provide a standardized, secure, and persistent storage mechanism that is independent of the mobile device, enabling subscriber mobility and secure authentication across different handsets and networks.
Purpose & Motivation
The Elementary File exists to provide a standardized, secure, and organized method for storing critical subscriber and application data on the smart card used in mobile telecommunications (the UICC). It solves the problem of how to persistently manage a wide variety of data—from secret cryptographic keys to public phonebook entries—in a way that is accessible to the mobile equipment but protected from unauthorized access. The motivation for its creation dates back to the original GSM SIM specification, which needed a file system model derived from ISO smart card standards to replace the simple memory storage used in earlier cellular technologies.
The historical context is that prior to the standardized UICC file system, subscriber data and network parameters were often stored in proprietary formats on the mobile device itself, hindering interoperability and subscriber mobility. The introduction of the EF, along with the DF/MF hierarchy, created a universal 'data cabinet' where every piece of information had a known, standardized location and access method. This allowed any compliant mobile device to interact with any compliant SIM card, a cornerstone of GSM's global success. It addressed limitations by separating the subscriber's identity and service profile from the handset, enabling easy swapping of phones while retaining one's number and services, and by enforcing security through file-level access conditions, protecting sensitive data like authentication keys.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (45 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-4, normative work from Rel-15.
In Release 15, several new Elementary Files (EFs) were introduced to support 5G and IoT capabilities. These included an EF for 5G UAC Access Identity Information, an EF for 5G NSI (Network Slice Instance), and an EF containing keys generated by the ME from CK and IK. The release also brought updates such as modifying the structure of the SUCI Calc EF to introduce a Routing Indicator and extending the EF ACL to include DNN.
- Introduce an EF that contains list of EARFCNs and the geographical areas associated with the EARFCNs for enabling cell search of MTC carrier or NB-IOT carrier. TS 31.102CR0771
- Introduce an EF that contains keys generated by ME from CK and IK. TS 31.102CR0774
- Introduce an EF that contains 5G UAC Access Identity Information TS 31.102CR0780
- USIM Service Table update for PDU session call control support TS 31.102CR0786
- Allow configuration of MCS (Access Identity 2) via USIM. TS 31.102CR0794
- Modify structure of SUCI Calc EF and introduce Routing Indicator TS 31.102CR0797
+ 10 more changes
In Release 16, the USIM's Elementary File (EF) functionality was expanded to support new configuration lists for network selection and access control, including the RLOS PLMN list, a Trusted non-3GPP access networks list, and a PS Data Off list for home and roaming. It also introduced new storage capabilities, such as for URSP rules and a potentially separate KSEAF for non-3GPP access, while providing clarifications and corrections to existing file reading procedures and formats.
- Support for USIM configuration of RLOS PLMN list TS 31.102CR0847
- URSP storage in USIM TS 31.102CR0861
- Specify storage for a potentially separate KSEAF for non-3gpp access on the USIM TS 31.102CR0864
- USIM configuration of RLOS allowed MCC list TS 31.102CR0881
- Support for Trusted non-3GPP access networks list by USIM TS 31.102CR0891
- Dedicated AID for USIM Applications with non-IMSI based SUPI Types TS 31.102CR0897
+ 4 more changes
In Release 17, new Elementary Files (EFs) were introduced in the USIM to store configurations for several key 5G capabilities. These include files for pre-configured Closed Access Group (CAG) information, Secure Onboarding Roaming Connectivity Management Control Information (SOR-CMCI), and parameters for Non-Seamless WLAN Offload (NSWO) and extended Discontinuous Reception (eDRX) for NG-RAN. Additionally, new EFs were defined for disaster roaming settings, warning message reception in SNPNs, and an indicator to prevent E-UTRA disabling in 5GS.
- Introduce a USIM file to store pre-configured CAG information list TS 31.102CR0904
- SOR-CMCI storage in USIM TS 31.102CR0917
- Addition of USIM files for the indication of whether disaster roaming is enabled in the UE, disaster roaming wait range, disaster return wait range and applicability indicator for disaster roaming PLMNs list provided by VPLMN. TS 31.102CR0938
- Adding eDRX parameters in the USIM for NG-RAN TS 31.102CR0943
- 5G NSWO (Non-Seamless WLAN Offload) configuration support in the USIM compromised proposal. TS 31.102CR0946
- Support of 'No E-UTRA Disabling In 5GS' in USIM TS 31.102CR0947
+ 4 more changes
In Release 18, the Elementary File (EF) function was expanded to include new storage for parameters supporting SENSE (Service and Network Slicing Enhancements), Access Control for GBA_U_APIs, and IMS Data Channel configuration on both the USIM and ISIM. The release also mandated that enabling Service n°133 requires Service n°123 for extended 5G security parameter storage and added a pre-configured list of PLMNs for MINT (Mission Critical Services) parameters within the EFDRI for disaster roaming. These additions enhance the USIM/ISIM's role in storing subscription data, security parameters, and service-specific configurations as defined for 3G access and security.
- Addition of EF to store parameters for SENSE TS 31.102CR0978
- 5G Security Parameters extended storage on USIM (Mandating Service n°133 to be enabled when Service n°123 is enabled) Rel18. TS 31.102CR1014
- Add EF of Access Control to GBA_U_APIs to the USIM TS 31.102CR1007
- Add EF of IMS Data Channel configuration to the USIM TS 31.102CR1006
- Addition of pre-configured list of PLMNs, provided by HPLMN for MINT related parameters in EFDRI (Disaster roaming information EF). TS 31.102CR1001
- Add EF of Access Control to GBA_U_APIs for the ISIM TS 31.103CR1
+ 2 more changes
In Release 19, a specific enhancement was introduced for the EF_5GAuthKeys Elementary File to ensure backward compatibility for USIMs that lack extended security parameter storage. This change provides handling procedures for such legacy USIMs during authentication and key establishment protocols. The update ensures these USIMs can still operate within the enhanced security framework defined for variable-length security parameters.
- Backward compatibility handling of USIM without extended security parameter storage in EF_5GAuthKeys - Rel19 TS 31.102CR1074
Explore further
Broader topics and technologies where EF plays a role.
Defining Specifications
3GPP specifications that define or reference EF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 21.111 vj00 | USIM and UICC Requirements for 3G | Rel-19 |
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 22.022 vj00 | ME Personalisation Features for GSM/3G | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |
| TS 31.103 vj00 | ISIM Application Specification | Rel-19 |
| TS 31.105 vj10 | Slice Subscriber Identity Module (SSIM) Application | Rel-19 |
| TS 31.121 vi50 | UICC-terminal interface test specification | Rel-18 |
| TS 31.131 vj00 | C Language Binding for (U)SIM API | Rel-19 |
| TS 31.829 vd00 | ISIM Conformance Requirements Technical Report | Rel-13 |
| TR 31.900 vj00 | 3GPP TS 31.900: Security Interworking Guidance | Rel-19 |
| TS 34.131 vj00 | SIM API C Language Test Specification | Rel-19 |
| TS 34.229 vj21 | IMS SIP/SDP UE Conformance Testing for 5GS | Rel-19 |