Manually Testing USIM Authentication » History » Revision 2
Revision 1 (laforge, 04/27/2022 05:17 PM) → Revision 2/4 (laforge, 04/27/2022 05:19 PM)
h1. Manually Testing USIM Authentication
This page describes how you can use Osmocom tools to manually test USIM / ISIM authentication against a SIM card.
h2. 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:]])
h2. Step-by-step guide
h3. Generate a 16-byte random challenge
Let's use @/dev/random@ to generate 16 bytes of randomness; conver it to hexadecimal
<pre>
$ dd if=/dev/random bs=16 count=1 2>/dev/null | xxd -p -l 100
8188388ad5cdd481b02298ff29827791
</pre>
h3. 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
<pre>
$ 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: 0
</pre>
This 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)
h3. 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@.
<pre>
$ ./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"
}
}
</pre>
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@
