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YggdraSIM

ETSI UICC

ETSI TS 102 221 defines the UICC's physical, logical, and administrative interface. The filesystem model, access conditions, and SELECT semantics used by every admin shell come from this specification. The vendored copy lives in docs/ts_102221v160200p.md.

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Filesystem anatomy

flowchart TB
    MF["MF
Master File"] --> DFTelecom["DFTELECOM"]
    MF --> DFGSM["DFGSM"]
    MF --> ADFUSIM["ADFUSIM"]
    MF --> ADFISIM["ADFISIM"]
    DFTelecom --> EFAdn["EFADN"]
    ADFUSIM --> EFImsi["EFIMSI"]
    ADFUSIM --> EFLoci["EFLOCI"]
    ADFUSIM --> DFAuthn["DFAUTHN"]

Figure: ETSI UICC filesystem anatomy — MF, DFs, ADFs, and key EFs

  • MF is the Master File. It is the root of the tree.
  • DF is a Dedicated File. It groups related EFs and subordinate DFs.
  • ADF is an Application Dedicated File. It is the root of a NAA such as USIM or ISIM.
  • EF is an Elementary File. It is where actual data lives.

Each EF carries a structure that determines the right access verb.

EF structure Access
Transparent READ BINARY / UPDATE BINARY
Linear fixed READ RECORD / UPDATE RECORD by record number
Cyclic READ RECORD / UPDATE RECORD with ring behavior
BER-TLV TLV tag-based access

SELECT semantics

SELECT addresses a file by FID, by AID, by path, or by application template depending on P1/P2. The card returns a FCP template with size, structure, access conditions, lifecycle, and proprietary tags.

The file-identifier space uses 2-byte FIDs, and the common ones are well known:

  • 3F00 is the MF
  • 7FFF is the reserved value
  • 7F10 is historical DF TELECOM
  • 7F20 is historical DF GSM
  • ADFs for USIM and ISIM are addressed by AID rather than fixed FID

Access conditions

Every EF carries access conditions per operation (READ, UPDATE, DEACTIVATE, ACTIVATE, INCREASE, etc.). Common values include:

  • ALW always allowed
  • PIN requires verified CHV1
  • PIN2 requires verified CHV2
  • ADM requires administrative authentication (for example GP SCP03)
  • NEV never allowed

The UICC enforces these before it answers. The admin shell surfaces them in filesystem listing output.

PIN and authentication

CHV1 (PIN) and CHV2 (PIN2) are the user-level authentication credentials. Blocking counters apply, and PUK values reset a blocked CHV. The commands are VERIFY, CHANGE, DISABLE, ENABLE, and UNBLOCK.

APDU pathing

Since 3F00 is addressable explicitly, YggdraSIM's SCP03 shell uses path strings such as 3F00/7FFF/6F07 when a verb needs an unambiguous target.

[A0...] > SELECT 3F00
[A0...] > SELECT 7FFF
[A0...] > SELECT 6F07
[A0...] > READ

Toolkit

ETSI TS 102 223 defines the Card Application Toolkit that lets the card initiate actions toward the terminal. YggdraSIM surfaces toolkit interactions indirectly through SCP80 OTA flows that install or update toolkit applets.

Where to look in YggdraSIM