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[SECURITY] [APP][WIP] IMSI Catcher/Spy Detector

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By E:V:A, Recognized Developer on 2nd January 2012, 03:30 AM
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UPDATE: 2015-01-14

Although this thread is still open, it is no longer updated with relevant info.
Please go to our official GitHub Site for the latest developer news and join
our development efforts in our back rooms...

For all the latest changes see our CHANGELOG.
For all the latest WIP alpha releases, see RELEASES.

The minimum supported AOS API version is 16, thus
AIMSICD will only work on Jelly Bean 4.1 or later.

Call for help to develop an IMSI catcher detector application for Android OS.

Q: What is an IMSI catcher?
A: It is a fake cell tower (aka. Base Transceiver Station, BTS) used to track and monitor specific (groups of) people in the near vicinity of that BTS.

In the light of last years highly publicized events in the many Arabic nations and the German state sponsored rootkit discovery, etc etc. It is of the highest priority to start developing anti/counter-spy applications for the people living in rogue states such as Syria, Iran etc. In addition, it may play an important role in finding (and preventing) other rogue applications that attempt to send silent SMS's to high-cost premium services.

Recently there have been some publicity surrounding the Osmocom BB's, application patch known as "Catcher Catcher" which is used to detect mobile phone tracking and spying, originating from the Mobile Phone Service Provider side. (I.e. something that generally can only be provided by state sponsored government and security forces.)

Relevant links include:

For a tutorial on how to compile and help populate the Gsmmap database, see here.

In the News:

This information started 2010 and was extended to last years 28C3 event...

How can you help?

I would very much like to have contact with anyone who can provide more in-depth knowledge how this could possibly be implemented on the AOS. There are several way you can help, eventhough you may not be an expert on HW or even android.

  • Help populate the Gsmmap database.
  • Follow and help/develop the OsmocomBB project.
  • Compile OsmocomBB for an Android phone, so that it can be used as a USB host. (Preferably for one of the more popular models like the Samsung galaxy S.)
  • Help mapping out the Android baseband AT command set or the internal RIL function, so that we can obtain as many GSM radio parameters as possible.
  • Reverse engineer the vendor RIL of the phone above.
  • Reverse engineer the Modem firmware so that we can use the phone as a native catcher-catcher.
  • Find provide documentation of the closed source modem(s) most used in androids.
  • Share other relevant experience you may have in this matter.
  • Find or provide links to documentation of anything baseband related, not already widely known!
  • Stay legal, or this project will close really quickly!

NOTE: This is not to prevent IMSI catchers, but to inform the "victims" that they are being subject to tracking/monitoring.

A few other items:
  • For the Software Change Log, our Github.
  • For Phone Support Log, see Post #7 below.
  • We have contacted EFF and The Guardian Project and hope to join their efforts and provide support to counter illegal tracking and tapping.
  • Thanks to SecUpwN, we now have our own GitHub HERE.
  • Have made a preliminary Developer Roadmap.
  • Added some important links.
  • Licensing Proposal: This will be a community project licensed under a GPLv3 license:
Glossary: (Harald Welte)

The BSS (Base Station Subsystem)
MS (Mobile Station): Your phone
BTS (Base Transceiver Station): The cell tower
BSC (Base Station Controller): Controlling up to hundreds of BTS
BP/CP (Baseband/Cellular Processor): Your phone radio/modem processor (usually an ARM 7/9)

The NSS (Network Sub System)
MSC (Mobile Switching Center): The central switch
HLR (Home Location Register): Database of subscribers
AUC (Authentication Center): Database of authentication keys
VLR (Visitor Location Register): For roaming users
EIR (Equipment Identity Register): To block stolen phones

Our Support:

We have as a goal to become a strong supporter of the EFF and The Guardian Project.
Part of all future donations will go to EFF. Intellectual and technological support will
also be given where possible.

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2nd January 2012, 03:35 AM |#2  
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The GSM Ciphering Indicator
According to the 3GPP GSM standards/specifications [1] for handsets,
there should be a Ciphering Indicator (CI) showing the user when the
GSM phone/data connection is not using encryption. Unfortunately for
many people in the rest of the world, this feature have not been
properly (if at all) implemented in the Android OS, AFAIK [2]. The
second culprit is the fact that your cellular service provider have
disabled showing this CI on the vast majority of SIM cards issued
around the world.

The only options for circumventing these privacy problems are:
  1. Write an application that present the current ciphering status. (Easy)
  2. Write an application that hijacks the baseband processor (modem)
    SIM binary-code (in the firmware) to force-enable CI and possibly
    also the use of A5/3. (Hard)
  3. Make and use a copy of your SIM card that has CI enabled. (Hard)
  4. Lobby your cellular service provider to always use A5/3 ciphering. (Hard)
    (A5/1 was never used and A5/2 can be cracked on-the-fly!)
  5. Force Google to fix the issue! This is hard, since the issue is
    already >2 years old at "medium priority", and in addition it
    does not resolve the service provider disabled CI in their SIM
As you can see the issue at hand does not look to be resolved
anytime soon. So I lobby for (1) or (2). But to do that we need
some background knowledge. Then I will show you how to read the
CI setting from your SIM card. Then we will figure out how to
write such an application!

[1] 3GPP GSM 02.07:
[2] Android Issue 5353:
[3] Dieter Spaar's Blog:
[4] 3GPP GSM 11.11: ???

Some 3GPP GSM Terminology:
EF      - Elementary Files 
AD      - Administrative (Data) Field
BCD     - Binary-Coded Decimal (compressed) 
CHV     - Card Holder Verification (usually your SIM code)
TLV     - Tag, Length, Value
BER-TLV - Object that conform to the Basic Encoding Rules (BER)
RFU     - Reserved for Future Use

[1] § B.1.26 Ciphering Indicator

The ciphering indicator feature allows the ME to detect that
ciphering is not switched on and to indicate this to the user,
as defined in GSM 02.09.

The ciphering indicator feature may be disabled by the home network
operator setting data in the "administrative data" field (EF-AD) in
the SIM, as defined in GSM 11.11.

If this feature is not disabled by the SIM, then whenever a
connection is in place, which is, or becomes unenciphered,
an indication shall be given to the user.

Ciphering itself is unaffected by this feature, and the user can
choose how to proceed.

[3] Ciphering Indicator in mobile phones

According to GSM 02.07 B.1.26, there should be a Ciphering Indicator
in the ME to allow a user to detect if ciphering is not switched on.
The Ciphering Indicator can be turned off by the network operator
clearing (what is formerly known as) the OFM (Operational Feature
Monitor) bit in the "administrative data" field of the SIM.
(See GSM 11.11, 10.3.18)

Usually the Ciphering Indicator is turned off, at least in those SIMs
I have seen so far. And you usually cannot modify the administrative
data in the SIM. But would a phone actually display something if the
Ciphering Indicator is enabled and ciphering is not on?

[4] § 10.2.18 The SIM Administrative Data field

All data on your SIM card is stored in a special filesystem hierarchy.
To not delve too far into the murky depths of SIM data storage, we
jump straight to the particular file we are interested in. It is an
elementary file (EF) called Administrative Data (AD), whose
filename/identifier is just a number, like always in the SIM-card
filesystem. In this case it is known '6FAD' (Hex for 28589).

This EF contains information concerning the mode of operation according
to the type of SIM, such as normal (to be used by PLMN subscribers for
GSM operations), type approval (to allow specific use of the ME during
type approval procedures of e.g. the radio equipment), cell testing
(to allow testing of a cellbefore commercial use of this cell),
manufacturer specific (to allow the ME manufacturer to perform specific
proprietary auto-test in its ME during e.g. maintenance phases).


Technical Summary:
Name:           EFAD (Administrative Data)
Identifier:     '6FAD' (28589)  
File size:      3+X bytes
Byte    Description
1       UE operation mode
2-3     Additional information (incl. cipher indication)
4       Length of MNC of IMSI
5-X     RFU
UE Operation Mode:              (byte 1)
This is the mode of operation for the MS.

Coding: (Initial value)
'00'    - normal operation
'80'    - type approval operations
'01'    - normal operation + specific facilities
'81'    - type approval operations + specific facilities
'02'    - maintenance (off line)
'04'    - cell test operation
NOTE: All other values are RFU (reserved for future) use 
Additional Information:         (byte 2-3)
- Specific facilities code              (if b1=1 in byte 1);
- ME manufacturer specific information  (if b2=1 in byte 1).

Ciphering indication is enabled by enabling both the specific 
facilities bit (b1) in byte-1 AND the cipher indicator bit (b1) 
in byte-3. Thus the administrative data field has to be:

Byte-1: 0x01    0000 0001
Byte-2: 0x00    0000 0000
Byte-3: 0x01    0000 0001
Byte-4: 0x02/3  0000 001x  
Length of MNC in the IMSI:      (byte 4)
The length indicator refers to the number of digits, 
used for extracting the MNC from the IMSI.

This value codes the number of digits of the MNC in
the IMSI. Only the values (b1-b2) '0010' and '0011' are
currently specified, all other values are reserved
for future use.
Relevant Documents:
TS 22.101
TS 31.102
TS 33.102
How to read the Ciphering Indicator in your SIM

Since there is no API call (AFAIK) for directly reading the SIM data
fields, we are going to use your modems standard AT commands. You can
normally do this in two ways. (1) By connecting your phone via USB to
your PC and use a terminal application to send AT commands (ATCs)
directly to the Baseband Processor (BP), aka "modem". (b) To connect
directly to the modem "device" via some terminal program within the
Android Operating System (AOS). For all the details surrounding this,
please see this thread.

Once you've got an AT command terminal session working, you are free
to issue the relevant AT commands to read from your SIM card. The
particular command we are interested in, is the +CRSM command. This
command can read/write various data directly from SIM card files.

If you know of any equivalent or valid AOS API call for reading
this type of SIM data, please let us know!


The +CRSM syntax is as follows:
AT+CRSM=<command>[,<fileid> [,<P1>,<P2>,<P3> [,<data> [,<pathid>]]]]

<command>       This is the operation to be performed:

        176 READ BINARY
        178 READ RECORD
        192 GET RESPONSE
        214 UPDATE BINARY
        220 UPDATE RECORD
        242 STATUS

<fileid>        This is an integer which is the identifier of a elementary
                datafile (EF) on SIM. Mandatory for every command except 
                STATUS and may be e.g.:

        Hex     Dec     File
        6F37    28471   ACMmax
        6F07    28423   IMSI
        6F39    28473   ACM 
        6F41    28481   PUKT
        6F42    28482   SMS

[CLA INS  P1  P2  P3 Data]

The bytes have the following meaning:

CLA             Is the class of instruction (ISO/IEC 7816-3 [25]), 'A0' is used in the GSM application;
INS             Is the instruction code (ISO/IEC 7816-3 [25]) as defined in this subclause for each command;
P1, P2, P3      Are parameters for the instruction. They are specified in table 9. 'FF' is a valid value for
                P1, P2 and P3. P3 gives the length of the data element. P3='00' introduces a 256 byte data transfer
                from the SIM in an outgoing data transfer command (response direction). In an ingoing data transfer
                command (command direction), P3='00' introduces no transfer of data.
SW1 and SW2     Are the Status Words indicating the successful or unsuccessful outcome of the command.

Dec.    <sw1> <sw2>     Description
144     0x90 0x00 normal entry of the command, indicating OK 

103     0x67 0xXX incorrect parameter P3
        0x6B 0xXX incorrect parameter P1 or P2
        0x6D 0xXX unknown instruction code given in the command
        0x6E 0xXX wrong instruction class given in the command
        0x6F 0xXX technical problem with no diagnostic given

        0x9F 0xXX length XX of the response data
        0x92 0x0X update successful but after using an internal retry routine X times
        0x92 0x40 memory problem
        0x94 0x00 no EF selected
        0x94 0x02 out of range (invalid address)
        0x94 0x04 file ID not found; pattern not found
        0x94 0x08 file is inconsistent with the command

        0x98 0x02 no CHV initialized
        0x98 0x04 Access condition not fullfiled / unsucc. CHV verify / authent.failed
        0x98 0x08 in contradiction with CHV status
        0x98 0x10 in contradiction with invalidation status
        0x98 0x40 Unsuccessful CHV-verification. Or UNBLOCK CHF / CHV blocked /UNBL.blocked
        0x98 0x50 Increase cannot be performed. Max. value reached
For example, you could also read your IMSI code from your SIM card,
but this is a little more tricky as that operation involves a parity
bit-field in the second byte, while using a compressed BCD coding.

Reading the AD field (containing cipher indication)
Also see +CSIM and +CSCS
+CRSM: 144,0,"000000"

==> Bytes: 1-3 = 00,00,00
    byte1: "MS operation mode" 
    byte2: "Specific facilities" B1
    byte3: "Specific facilities" B2 (+ cipher indication)
==> Ciphering indication is disabled

Note: a response like this "+CRSM: 103,3" indicates that there is 
      a problem with P3 and that the value for P3 should be 3.
How to write AD and enable the Cipher Indicator in your SIM

Now, this is the most tricky part while being poorly documented.
The problem is that since this is an "administrative operation", it
may require something called a "facility lock password". However it
is not clear to me what this is. Is it just a CHV PIN/PUK or is it
something only known to the OEM or cellular service provider?
Anyone who could provide proper guidance here, will be offered
a beer! (Also see: +CLCK, +CPWD, +CSIM for reference.)

Going through the reading hoops above, we guess that the
proper write command should be like this:

However, we know from reading other SIM files (IMSI) that sometimes
the data is returned in compressed BCD format. That is, it could be
that the 1st and last pairs of 01's should be swapped to 10's.
So that we have:

Any ideas?
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19th January 2012, 03:25 AM |#3  
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19th January 2012, 08:29 PM |#4  
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20th January 2012, 03:20 PM |#5  
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Wouldn't it help to use a Database like (I'm not allowed to link yet) to distinguish an IMSI-Catcher from a base station?
29th January 2012, 08:14 PM |#6  
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Originally Posted by XdxH62

Wouldn't it help to use a Database like (I'm not allowed to link yet) to distinguish an IMSI-Catcher from a base station?

been reading up on this.. quite fascinating.
29th January 2012, 09:08 PM |#7  
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Phone Support Log

This is a list of phones that have been claimed (but not verified) to work with AIMSICD. If you absolutely want to post success stories, do include exact phone model, API level (AOS version), and whether your using a special ROM, and the result from "uname -a" command.


This App is not even Beta version yet, so we don't expect it to work for anyone than
ourselves at the moment. As soon as this changes, you will find out here!

Current AIMSICD Version: 0.1.6-alpha

GT-I9100T  Android 4.1.2 Official stocked, rooted
Samsung Galaxy Nexus, CM 11.0 M5
HTC ONE M7 (PN0710000) AOKP M7 Generic (KitKat 4.4.2)


Old original post/message:

Originally Posted by XdxH62

Wouldn't it help to use a Database like (I'm not allowed to link yet) to distinguish an IMSI-Catcher from a base station?

Unfortunately not. If you had followed the links above, you would have seen gsmmap... It does help trying to map the likelyhood that someone outside an intelligence organization is using one, but you can technically fake any such valid BTS as well. You need other methods... See refs/docs.

29th January 2012, 09:14 PM |#8  
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Lightbulb ghost stations
Originally Posted by XdxH62

Wouldn't it help to use a Database like (I'm not allowed to link yet) to distinguish an IMSI-Catcher from a base station?

sure, that would make perfect sense. this way you would immediately spot "ghost base stations" that miraculously appear for one day only ...

*#0011# | Network Info
*#32489# | Cipher Info <--- does anybody get anything out of this (OFM-bit)
*#197328640# | General Service Mode GT-S5360 Galaxy Y : -1-7-3-1-1- in LA4 modem Fw.
*#745# | RIL Dump Menu
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29th January 2012, 09:40 PM |#9  
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Originally Posted by mai77

sure, that would make perfect sense. this way you would immediately spot "ghost base stations" that miraculously appear for one day only ...

That's partially correct, but you need to ensure (at least) two things.
1. That the "detector" you're using is not moving around!
2. That the database you're comparing with have not already been corrupted.

Therefore, you can (and should use a database), but you need a much more advanced algorithm for determining when and how this BTS appeared combined with other criteria.
29th January 2012, 09:47 PM |#10  
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in 97%+ of real cases, an IMSI catcher would be in operation for a short while only. this change should be detectable by comparing cell IDs and such of some area in a town, which hardly changes over time.

On an i9000 the code to access the engineering menu (*#197328640# in Dialer) worked – I’m assuming it’s standard across all recent Samsungs, not just the Galaxy S series.

Menu 1,8,3,1 displays the current ciphering status, i.e. whether or not your current call is currently encrypted.

from youtube :

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30th January 2012, 01:43 AM |#11  
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Originally Posted by mai77

On an i9000 but the code to access the engineering menu (*#197328640# in Dialer) worked just the same – I’m assuming it’s standard across all recent Samsungs, not just the Galaxy S series.

Menu 1,8,3,1 displays the current ciphering status, i.e. whether or not your current call is currently encrypted.

Right, and that's why I have been trying to reverse engineer the Service Mode application, to find out where all that info is coming from, including other parts needed from that app. But I'm new to all this Android stuff, so... Instead this led me to the RIL, but since the interesting parts of the RIL is closed source I tried to figure out what is happening in the modem. This finally led me to post this new thread:

"How to talk to the Modem with AT commands":

Any tips/ideas how to get this info would be great!

I suspect there will be several different way to get to this, but all may prove relevant...
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