Guide: Enabling 5G SUCI

SUPI/SUCI Concealment is a feature of 5G-Standalone (SA) to encrypt the IMSI/SUPI with a network operator public key. 3GPP Specifies two different variants for this:

  • SUCI calculation in the UE, using data from the SIM

  • SUCI calculation on the card itself

pySIM supports writing the 5G-specific files for SUCI calculation in the UE on USIM cards, assuming that your cards contain the required files, and you have the privileges/credentials to write to them. This is the case using sysmocom sysmoISIM-SJA2 cards (or successor products).

In short, you can enable SUCI with these steps:

  • activate USIM Service 124

  • make sure USIM Service 125 is disabled

  • store the public keys in SUCI_Calc_Info

  • set the Routing Indicator (required)

If you want to disable the feature, you can just disable USIM Service 124 (and 125).

Technical References

This guide covers the basic workflow of provisioning SIM cards with the 5G SUCI feature. For detailed information on the SUCI feature and file contents, the following documents are helpful:

For specific information on sysmocom SIM cards, refer to Section 9.1 of the sysmoUSIM User Manual.

Admin PIN

The usual way to authenticate yourself to the card as the cellular operator is to validate the so-called ADM1 (admin) PIN. This may differ from card model/vendor to card model/vendor.

Start pySIM-shell and enter the admin PIN for your card. If you bought the SIM card from your network operator and don’t have the admin PIN, you cannot change SIM contents!

Launch pySIM:

$ ./pySim-shell.py -p 0

Using PC/SC reader interface
Autodetected card type: sysmoISIM-SJA2
Welcome to pySim-shell!
pySIM-shell (00:MF)>

Enter the ADM PIN:

pySIM-shell (00:MF)> verify_adm XXXXXXXX

Otherwise, write commands will fail with SW Mismatch: Expected 9000 and got 6982.

Key Provisioning

pySIM-shell (00:MF)> select MF
pySIM-shell (00:MF)> select ADF.USIM
pySIM-shell (00:MF/ADF.USIM)> select DF.5GS
pySIM-shell (00:MF/ADF.USIM/DF.5GS)> select EF.SUCI_Calc_Info

By default, the file is present but empty:

pySIM-shell (00:MF/ADF.USIM/DF.5GS/EF.SUCI_Calc_Info)> read_binary_decoded
missing Protection Scheme Identifier List data object tag
9000: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff -> {}

The following JSON config defines the testfile from TS 31.121 Section 4.9.4 with test keys from TS 33.501 Annex C.4. Highest priority (0) has a Profile-B (identifier: 2) key in key slot 1, which means the key with hnet_pubkey_identifier: 27.

{
     "prot_scheme_id_list": [
        {"priority": 0, "identifier": 2, "key_index": 1},
        {"priority": 1, "identifier": 1, "key_index": 2},
        {"priority": 2, "identifier": 0, "key_index": 0}],
     "hnet_pubkey_list": [
        {"hnet_pubkey_identifier": 27,
         "hnet_pubkey": "0272DA71976234CE833A6907425867B82E074D44EF907DFB4B3E21C1C2256EBCD1"},
        {"hnet_pubkey_identifier": 30,
         "hnet_pubkey": "5A8D38864820197C3394B92613B20B91633CBD897119273BF8E4A6F4EEC0A650"}]
}

Write the config to file (must be single-line input as for now):

pySIM-shell (00:MF/ADF.USIM/DF.5GS/EF.SUCI_Calc_Info)> update_binary_decoded '{ "prot_scheme_id_list": [ {"priority": 0, "identifier": 2, "key_index": 1}, {"priority": 1, "identifier": 1, "key_index": 2}, {"priority": 2, "identifier": 0, "key_index": 0}], "hnet_pubkey_list": [ {"hnet_pubkey_identifier": 27, "hnet_pubkey": "0272DA71976234CE833A6907425867B82E074D44EF907DFB4B3E21C1C2256EBCD1"}, {"hnet_pubkey_identifier": 30, "hnet_pubkey": "5A8D38864820197C3394B92613B20B91633CBD897119273BF8E4A6F4EEC0A650"}]}'

WARNING: These are TEST KEYS with publicly known/specified private keys, and hence unsafe for live/secure deployments! For use in production networks, you need to generate your own set[s] of keys.

Routing Indicator

The Routing Indicator must be present for the SUCI feature. By default, the contents of the file is invalid (ffffffff):

pySIM-shell (00:MF)> select MF
pySIM-shell (00:MF)> select ADF.USIM
pySIM-shell (00:MF/ADF.USIM)> select DF.5GS
pySIM-shell (00:MF/ADF.USIM/DF.5GS)> select EF.Routing_Indicator
pySIM-shell (00:MF/ADF.USIM/DF.5GS/EF.Routing_Indicator)> read_binary_decoded
9000: ffffffff -> {'raw': 'ffffffff'}

The Routing Indicator is a four-byte file but the actual Routing Indicator goes into bytes 0 and 1 (the other bytes are reserved). To set the Routing Indicator to 0x71:

pySIM-shell (00:MF/ADF.USIM/DF.5GS/EF.Routing_Indicator)> update_binary 17ffffff

You can also set the routing indicator to 0x0, which is valid and means “routing indicator not specified”, leaving it to the modem.

USIM Service Table

First, check out the USIM Service Table (UST):

pySIM-shell (00:MF)> select MF
pySIM-shell (00:MF)> select ADF.USIM
pySIM-shell (00:MF/ADF.USIM)> select EF.UST
pySIM-shell (00:MF/ADF.USIM/EF.UST)> read_binary_decoded
9000: beff9f9de73e0408400170730000002e00000000 -> [2, 3, 4, 5, 6, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 25, 27, 28, 29, 33, 34, 35, 38, 39, 42, 43, 44, 45, 46, 51, 60, 71, 73, 85, 86, 87, 89, 90, 93, 94, 95, 122, 123, 124, 126]
From TS31.102

Service No.

Description

122

5GS Mobility Management Information

123

5G Security Parameters

124

Subscription identifier privacy support

125

SUCI calculation by the USIM

126

UAC Access Identities support

129

5GS Operator PLMN List

If you’d like to enable/disable any UST service:

pySIM-shell (00:MF/ADF.USIM/EF.UST)> ust_service_deactivate 124
pySIM-shell (00:MF/ADF.USIM/EF.UST)> ust_service_activate 124
pySIM-shell (00:MF/ADF.USIM/EF.UST)> ust_service_deactivate 125

In this case, UST Service 124 is already enabled and you’re good to go. The sysmoISIM-SJA2 does not support on-SIM calculation, so service 125 must be disabled.

USIM Error with 5G and sysmoISIM

sysmoISIMs come 5GS-enabled. By default however, the configuration stored in the card file-system is not valid for 5G networks: Service 124 is enabled, but EF.SUCI_Calc_Info and EF.Routing_Indicator are empty files (hence do not contain valid data).

At least for Qualcomm’s X55 modem, this results in an USIM error and the whole modem shutting 5G down. If you don’t need SUCI concealment but the smartphone refuses to connect to any 5G network, try to disable the UST service 124.