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laforge, 04/27/2022 05:19 PM
Manually Testing USIM Authentication¶
This page describes how you can use Osmocom tools to manually test USIM / ISIM authentication against a SIM card.
Prerequisites¶
- A USIM card of which you know the secret key K + OP/OPc
- A smart card interface device ("reader") supported by pysim (such as any pcsc-lite / libccid compatible reader)
osmo-auc-gen
program (part of libosmocore)pySim-shell
program (part of pysim)
Step-by-step guide¶
Generate a 16-byte random challenge¶
Let's use /dev/random
to generate 16 bytes of randomness; conver it to hexadecimal
$ dd if=/dev/random bs=16 count=1 2>/dev/null | xxd -p -l 100 8188388ad5cdd481b02298ff29827791
Generating the actual quintuple using osmo-auc-gen
¶
This process mimics what is happening inside the Authentication Centre part of the HLR/HSS of your 2G/3G/4G network: Deriving RES from K, OP/OPc and SEQ/SQN.
We use the card-specific K + OPc values we received from the card manufacturer, as well as the random value we generated in the previous step
$ osmo-auc-gen --3g --algorithm MILENAGE --key 77291F1E17132ADD86DC23A3AF601C89 --opc 831AFD01EF48692EC6FD18AEAB6CF381 --rand 8188388ad5cdd481b02298ff29827791 osmo-auc-gen (C) 2011-2012 by Harald Welte This is FREE SOFTWARE with ABSOLUTELY NO WARRANTY RAND: 8188388ad5cdd481b02298ff29827791 AUTN: 7f62c464f6d60000b77b88e0f6b9449c IK: 43c7bc1e8e193ed2e0e7e164126bbed5 CK: a0188b5f7724878b86b9a336d8f2e327 RES: b4013d66d107a2b6 IMS nonce: gYg4itXN1IGwIpj/KYJ3kX9ixGT21gAAt3uI4Pa5RJw= IMS res: tAE9ZtEHorY= SRES: 65069fd0 Kc: 8581751333a4e4ab SQN: 32 IND: 0This shows us the following information
- input data (RAND, IND, SQN)
- the challenge the network would send via radio interface to the UE/phone/modem (RAND, AUTN)
- the data the network keeps on the network side and does not send over radio:
- the A3 authentication result value (RES)
- the A8 generated keys for integrity protection and ciphering (IK, CK)
- the derived GSM values in case of fall-back to 2G (Kc, SRES)
Performing authentication with the card, using pySim-shell
¶
We now perform what the phone/modem does with the SIM card when it receives the RAND + AUTN values from the cellular network via a AUTHENTICATION REQUEST
.
For this, we use pysim, specifically the authentication
command in it. It takes two parameters: rand
and autn
(copy+pated from the above execution of osmo-auc-gen)
As we want to do UMTS-AKA against the USIM application on the card, we must first select ADF.USIM
.
$ ./pySim-shell.py -p0 Using PC/SC reader interface Waiting for card... Autodetected card type: sysmoISIM-SJA2 Info: Card is of type: UICC-SIM AIDs on card: USIM: a0000000871002ffffffff8907090000 (EF.DIR) ISIM: a0000000871004ffffffff8907090000 (EF.DIR) ADF.ISD: a000000003000000 ARA-M: a00000015141434c00 Detected CardModel: SysmocomSJA2 Welcome to pySim-shell! pySIM-shell (MF)> select ADF.USIM pySIM-shell (MF/ADF.USIM)> authenticate 8188388ad5cdd481b02298ff29827791 7f62c464f6d60000b77b88e0f6b9449c { "successful_3g_authentication": { "res": "b4013d66d107a2b6", "ck": "a0188b5f7724878b86b9a336d8f2e327", "ik": "43c7bc1e8e193ed2e0e7e164126bbed5", "kc": "8581751333a4e4ab" } }In this successful case, we see the card has accepted the AUTN nonce and generated the following output parameters:
- authentication result (RES); would be sent back to the network, where the network compares it with the expected RES value it has computed earlier. If it matches, authentication is OK.
- integrity protection (IK) and ciphering (CK) keys
- used for air interface protection on 3G/UMTS after a @CIPHERING MODE COMMAND
- used in derived forms for air interface protection and NAS protection in 4G/LTE
- GSM ciphering key (Kc); used for encryption on 2G/GSM/GPRS after a
CIPHERING MODE COMMAND
Updated by laforge about 2 years ago · 2 revisions