Vulnerabilities of Cellular and Satellite-based Voice and Data Networks

Vulnerabilities of Cellular and Satellite-based Voice and Data

Networks

Dan [email protected]

www.decodesystems.com/blackhat/bh-2.ppt

Black Hat BriefingsJuly 31, 2002

Vulnerabilities of Cellular and Satellite-based Voice & Data Networks

Page 2

Focus of this talk

• Practical security problems

• Industry responses

• Lessons (hopefully) learned from mistakes



Page 3

Practical Operator Considerations

• Getting paid– Prevent (limit) subscriber fraud– Ensure accurate clearing with other operators

• Reduce churn

• Ensure sufficient capacity

• Provide CALEA compliance

• Maintain public perception of security

• Provide additional features (marketing)



Page 4

Cellular

• Analog• Digital - TDMA• Digital - CDMA• Digital - GSM



Page 5

Cellular Signaling

• Control channel– Forward is continuous

– Reverse is shared

• Voice (Traffic) channel– Assigned for the call

– Shared in digital systems



Page 6

Analog Cellular

• Authentication is valid Electronic Serial Number (ESN) and Mobile Identification Number (MIN) pair

• Sent from mobile to base in the clear

• Early systems had just a “deny” list

• Not all systems initially available to each other for roaming verification



Page 7

Phone Theft

• Automobile “smash and grab”

• Use until service is canceled

• Call-sell operations



Page 8

Database Theft

• Dumpster diving

• Insider account maintenance

• Hack into authorization database

• Hack into switch maintenance port



Page 9

Rogue Base Station

• Forward link has no authentication

• Mobiles lock to false outbound

• Cell phone suppressor• Test equipment (ESN

readers)



Page 10

Network Interception

• Read pairs on link between base station and switch

• Microwave in many areas



Page 11

Tumbling

• ESN/MIN pair sent to home system

• Pre-call validation not available

• First call allowed to go through

• “Tumble” through random ESN/MIN pairs



Page 12

Cloning• Replace legit ESN with

snarfed ESN• Reprogram MIN• “Extension” phones• Rewrite phone firmware

• (Chip in lower left corner is conveniently socketed)



Page 13

Snarfing

• Tune scanner to control channel

• Decoder monitors inbound data

• Computer stores ESN/MIN pairs when the mobile registers

• AMPS data is simple FSK, in the clear



Page 14

Subscription Fraud

• Sign up for service under false identity

• “Identity Theft”



Page 15

Session Hijacking

• Overpower base station during legitimate call

• Use cell phone test mode to match Supervisory Audio Tone (SAT)

• Flashhook and place another call



Page 16

Fighting Analog Fraud• Legal

– Illegal to eavesdrop

– Illegal to clone

– Illegal to possess equipment that might be used to clone

• Technical– PINs

• Customers hated this

– Velocity checks• Good for roaming, not great for local clones

– Don’t allow more than one active at a time

– RF Fingerprinting



Page 17

2G Authentication• Generally, mobile is given a challenge and network

checks the response• US Digital Cellular

– Cellular Authentication and Voice Encryption (CAVE)– Control Message Encryption Algorithm (CMEA)– Voice Privacy Mask (VPM)

• GSM– A3 Authentication– A8 cipher key generation– A5 privacy



Page 18

Cellular Authentication and Voice Encryption

• A-key, 64 bits (20 digits plus 6 check digits)• RANDSSD: 56 bits• Electronic Serial Number (ESN): 32 bits• Shared Secret Data (SSD)

– SSD_A: 64 bits, for authentication– SSD_B: 64 bits, for encryption

• Authentication Result, AUTHx: 18 bits• Unique Challenge

– Uses voice channel during call attempts

• Global Challenge– Uses control channel, checks during registration, call attempt and

call delivery– All phones challenged with the same number



Page 19

Authentication• Phone attempts to access the

network– indicates authentication capability

• Serving MSC contacts HLR and AC– indicates whether it can do CAVE

• (if not, SSD cannot be shared, AC must do all the work)

– Gets profile• Includes whether authentication

should be done

– Generates random number RANDU and sends it to phone



Page 20

Authentication

• Phone runs CAVE ( RANDU, SSD, MIN, ESN )– Produces AUTHU– Sends AUTHU to MSC

• MSC runs CAVE ( RANDU, SSD, MIN, ESN ) – Produces local AUTHU

• At MSC, if received AUTHU matches local AUTHU, authentication is successful



Page 21

Shared Secret Data Update• Phone and AC update their SSD

– AC generates RANDSSD• Sends it to Serving MSC• Computes SSD from RANDSSD, ESN, A-key

– MSC sends RANDSSD to phone– Phone generates SSD from RANDSSD, ESN, A-key

• Phone authenticates Base Station (or AC)– Generates RANDBS– Calculates AUTHBS from RANDBS and new SSD– Sends RANDBS to Serving MSC– Either MSC or AC uses RANDBS and new SSD to calculate AUTHBS– MSC sends AUTHBS to phone– If phone AUTHBS and MSC AUTHBS match, phone stores new SSD– Another authentication process is performed

• If successful, AC stores new SSD



Page 22

Count

• Mobile maintains a 6-bit COUNT variable

• Incremented on instruction from AC

• AC maintains COUNT for each mobile• COUNT values must match in order for

mobile to gain access



Page 23

Weaknesses• Information sent in the

clear on interconnection networks (SS7, etc)

• Secret information held in vulnerable locations (HLR, VLR, etc)

• CMEA “broken”

• Small keysize

• Poor A-keys

• VPM fixed for the length of the call– XOR against known voice

(e.g. silence)



Page 24

Global System for Mobiles

• Handsets and SIMs• International Mobile

Equipment Identifier (IMEI)

• International Mobile Subscriber Identity (IMSI)



Page 25

GSM Network Elements• AuC: Authentication Center

• BTS: Base Transceiver Station

• BSC: Base Station Controller

• EIR: Equipment Identity Register (white, black, grey)

• HLR: Home Location Register

• ME: Mobile Equipment

• MSC: Mobile Switching Center

• OMC: Operations & Maintenance Center

• SIM: Subscriber Identity Module

• Visitor Location Register



Page 26

GSM Security GoalsThe objective of security for GSM system is to make the system as secure as the public switched telephone network. The use of radio at the transmission media allows a number of potential threats from eavesdropping the transmissions. It was soon apparent in the threat analysis that the weakest part of the system was the radio path, as this can be easily intercepted. The GSM MoU Group produces guidance on these areas of operator interaction for members. The technical features for security are only a small part of the security requirements, the greatest threat is from simpler attacks such as disclosure of the encryption keys, insecure billing systems or corruption ! A balance is required to ensure that these security processes meet these requirements.

At the same time a judgment must be made of the cost and effectiveness of the security measures.

Charles BrooksonChairman GSM MoU Security Group

Mercury one2one



Page 27

Anonymity

• Temporary identifiers.

• When a user first switches on his radio set, the real identity is used, and a temporary identifier is then issued.

• From then on the temporary identifier is used.



Page 28

Authentication• A random challenge is issued

to the mobile

• Mobile encrypts the challenge using the authentication algorithm (A3) and the key assigned to the mobile (Ki)

• Mobile sends response back (SRES)

• Network checks that the response to the challenge is correct.



Page 29

User data and signaling privacy

• A8 algorithm to compute Kc

• Used to encrypt the airlink

• A5 series privacy algorithms



Page 30

Cryptographic Algorithms

• A3 and A8 are in the SIM– Operators can choose their own A3/A8– COMP-128 provided as example algorithm– Can securely pass (RAND,SRES,Kc) while

roaming

• A5 is built into the hardware– A5/1 - more secure– A5/2 - less secure– Unencrypted



Page 31

GSM weaknesses• COMP-128 leaks Ki (April 1998)• A8 has effective security of 54 bits

– (last 10 bits set to 0)

• A5– 64-bit key (Kc) and 22-bit frame number, three shift registers– A5/1 (western Europe)– A5/2 (used in North America)– A5/0 (no encryption)

• Rogue base station• Unencrypted network links

– Eavesdropping– Query HLR/AuC for new triples

• Kc refreshed only occasionally



Page 32

Subscriber Identity Module• C1: Supply voltage

– (4.5 to 5.5 volts DC).

• C2: Reset signal• C3: Clock signal

– (1 to 5 MHz, external)

• C4: Reserved• C5: Ground• C6: Programming voltage

– (if available)

• C7: Input/Output– Baudrate is (clock

frequency) / 372.

• C8: Reserved



Page 33

Talking to a SIM

• Defined by ETSI document GSM 11.11• Five bytes:

– Class of instruction (CLA)• (always 0xA0 for GSM)

– Instruction Code (INS)– Parameter 1 (P1)– Parameter 2 (P2)– Parameter 3 (P3)

• (length of optional data segment)

• SIM card readers may require additional bytes



Page 34

Listening to a SIM

• Three fields:– Data

• (variable length)

– Status Word 1 (SW1)– Status Word 2 (SW2)

• 90 00 is normal response



Page 35

SIM CommandsCOMMAND INS P1 P2 P3SELECT A4 00 00 02STATUS F2 00 00 lengthREAD BINARY B0 offset (high) offset (low) lengthUPDATE BINARY D6 offset (high) offset (low) lengthREAD RECORD B2 record number mode lengthUPDATE RECORD DC record number mode lengthSEEK A2 00 type/mode lengthINCREASE 32 00 00 03VERIFY CHV 20 00 CHV number 08CHANGE CHV 24 00 CHV number 10DISABLE CHV 26 00 01 08ENABLE CHV 28 00 01 08UNBLOCK CHV 2C 00 00 (for CHV1) 10

02 (for CHV2) 10INVALIDATE 04 00 00 00REHABILITATE 44 00 00 00RUN GSM ALG 88 00 00 00SLEEP FA 00 00 00GET RESPONSE C0 00 00 length



Page 36

SIM ConversationSetup card for access

Activating card...01 Sending ATR 1...Sending Inverse ATR 1...3F 2F 00 80 69 AF 02 04 01 31 00 00 00 0E 83 3E 9F 16



Page 37

SIM ConversationRead Master File A0 A4 00 00 02 Select fileA4 ok3F 00 Master File9F 16 file access ok, 0x16 byte responseA0 C0 00 00 16 Read 0x16 byte responseC0 85 14 00 00 3F 00 01 80 FF FF FF 43 09 89 03 09 04 00 83 8A 83 8A 90 00

Master File Header [MF/DF] RFU: 85 14 Free Memory: 00 00 File ID: 3F 00 (MF) File Type: 01 (Master File) RFU: 80 FF FF FF 43 Length: 09 File characteristics: 89 Clock stop: Allowed, low level preferred Required speed: 13/8 CHV: Disabled Child DFs: 03 Child EFs: 09 CHVs, Unblock CHVs, etc: 04 RFU: 00 CHV1 Status: 83 (Initialized, 3 remaining) Unblock CHV1 Status: 8A (Initialized, 10 remaining) CHV2 Status: 83 (Initialized, 3 remaining) Unblock CHV2 Status: 8A (Initialized, 10 remaining)



Page 38

SIM ConversationRead Dedicated File A0 A4 00 00 02 Select fileA4 ok7F 20 GSM Dedicated File9F 16 access ok, 0x16 byte responseA0 C0 00 00 16 Read 0x16 byte responseC0 85 14 00 04 7F 20 02 00 FF FB FF 23 09 99 00 19 04 00 83 8A 83 8A 90 00

Dedicated File Header [MF/DF] RFU: 85 14 Free Memory: 00 04 File ID: 7F 20 (DF-GSM) File Type: 02 (Directory File) RFU: 00 FF FB FF 23 Length: 09 File characteristics: 99 Clock stop: Allowed, low level preferred Required speed: 13/8 CHV: Disabled Child DFs: 00 Child EFs: 19 CHVs, Unblock CHVs, etc: 04 RFU: 00 CHV1 Status: 83 (Initialized, 3 remaining) Unblock CHV1 Status: 8A (Initialized, 10 remaining) CHV2 Status: 83 (Initialized, 3 remaining) Unblock CHV2 Status: 8A (Initialized, 10 remaining)



Page 39

SIM ConversationRead Elementary File A0 A4 00 00 02 Select fileA4 ok6F 07 (GSM) EF-IMSI9F 0F access ok, 0x0F byte responseA0 C0 00 00 0F Read 0x0F byte responseC0 85 0D 00 09 6F 07 04 00 1B FF 1B 23 02 00 00 90 00

Elementary File Information [EF] RFU: 85 0D File Size: 00 09 File ID: 6F 07 ((GSM) EF-IMSI) File Type: 04 (Elementary File) RFU: 00 Access: 1B FF 1B Read/Seek: CHV1 Update: Admin 11 Increase: Never RFU: Never Rehabilitate: CHV1 Invalidate: Admin 11 Status: 23 (Not Invalidated) Length: 02 EF Structure: 00 (Transparent) Record Length: 00A0 B0 00 00 09 Read file, 9 bytesB0 08 39 01 13 10 00 43 98 44 90 00 IMSI



Page 40

SIM Conversation

Select GSM Dedicated FileA0 A4 00 00 02 Select FileA4 ok9F 16 GSM Dedicated File

Perform A3A8 computationA0 88 00 00 10 A3A8 with 0x10 bytes88 ok00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 RAND challenge 9F 0C ok, 0x0C bytes waitingA0 C0 00 00 0C get responseC0 D0 70 89 C4 8F 23 C4 EB 59 78 EC 00 90 00

Perform A3A8 computationA0 88 00 00 10 A3A8 with 0x10 bytes88 ok00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 RAND challenge 9F 0C ok, 0x0C bytes waitingA0 C0 00 00 0C get responseC0 9B 8E 05 84 FF 8A E8 60 45 A7 30 00 90 00



Page 41

SIM attacks

• Repeated authenticate, leaks Ki– (New SIMs have a limit (about 50k) on the

number of times the authentication algorithm can be run)

• Side-channel attacks– Power consumption– Timing– Electromagnetic emanations



Page 42

COMP-128 Updates• COMP128-2

– 54-bit Kc– Secret algorithm

• COMP128-3– 64-bit Kc– Secret algorithm

• Proposal for new A3A8 based on MILENAGE– Milenage based on Rijndael (AES)– Algorithm will be public

• New A3A8 requires– AuC software upgrade– New SIMs



Page 43

A5/3

• Based on the Kasumi algorithm– 3GPP confidentiality and integrity algorithms.

• Kasumi derived from the MISTY algorithm, created by Mitsubishi.

• Specifications are publicly available on the 3GPP web site (www.3gpp.org).



Page 44

Cellular Jamming• Low-power private base station transmits a forward link overhead

message• Mobiles register with base station• Base station never sends a page• The FCC view on this:• The Communications Act of 1934, as amended, and the Commission's rules do not permit the use of

transmitters designed to prevent or jam the operation of wireless devices in hospitals, theaters and other locations. Section 302(a) of the Communications Act, 47 USC 302(a), prohibits the manufacture, importation, sale, offer for sale, or use of devices that fail to comply with the regulations promulgated pursuant to this section.

• Based on the above, the operation of transmitters designed to jam wireless communications is a violation of 47 USC 301, 302(a), and 333. The manufacture, importation, sale or offer for sale, including advertising, of such transmitters is a violation of 47 USC 302(a). Parties in violations of these provisions may be subject to the penalties contained within 47 USC 501-510. Fines for a first offense can range as high as $11,000 for each violation or imprisonment for up to one year. The equipment can also be seized and forfeited to the U.S. Government. These regulations apply to all transmitters that are designed to cause interference to, or prevent the operation of, other radio communication systems.



Page 45

Satellite Networks• Big LEOs• Little LEOs• Mobile Satellite

Ventures• INTELSAT• INMARSAT• VSAT• GPS



Page 46

Big LEO

• Constellation of satellites in Low Earth Orbit (as opposed to geosynchronous)

• Base stations in the sky

• Linked to network of ground stations

• Voice as primary service

• 1610 to 1626.5 MHz up

• 2483.5 to 2500 MHz down



Page 47

Iridium• $5 billion

• 66 satellites (plus spares)

• TDMA, processing on-board

• 1621.35 to 1626.5 up and down

• 2.4 kbps data service

• Service start November 1998

• Bankruptcy in August 1999, only 55,000 customers



Page 48

Iridium Satellite LLC

• Paid $25M for Iridium assets• Relaunched commercial service in 2001• Large government contract ($72M/2 years via DISA)• Dedicated gateway earth station in Hawaii• Defense Information Systems Agency

– Department of Defense

– Department of State

– Inter-satellite links

• Enough money to replenish satellites?



Page 49

Globalstar

• Loral, Qualcomm

• 48 satellites in LEO

• Start of operations February 2000

• Currently under bankruptcy protection

• Bent-pipe

• CDMA service

• Underpowered satellites– Recharge over oceans

• 9.6 kbps data



Page 50

ICO

• $4.7 billion• Hughes-built satellites• 10 satellites in Medium

Earth Orbit (MEO)• GSM-based

• New ICO• Craig McCaw• Merged with Teledesic



Page 51

Orbcomm (Little LEO)

• 28 satellites• 14 earth stations• VHF operation• Data only• Store and Forward if

ground station not in view• “GlobalGrams” = X.400

e-mail• Latency



Page 52

Mobile Satellite Ventures

• Motient– AMSC-1 ($500M)– Spar Aerospace

• TMI– MSAT-1 (identical)

• Mobile satellite voice and data

• L-band• Digital voice



Page 53

Interception

• Gateways require tapping– FBI, CALEA requirements– Iridium agreement– Globalstar agreement– TMI on-demand access– National intelligence and police forces

• Test equipment

• Limited use of encryption

• Modifiable phone equipment



Page 54

INTELSAT

• Was a consortium of nations as signatories

• Now privatized

• Large fleet in geostationary orbit

• Primarily telephone and television traffic

• Carries unencrypted voice, data and fax

• Used by US DoD for UAV datalink



Page 55

INMARSAT

• International Maritime Satellite Organization

• AOR, POR, IOR coverage

• L-band



Page 56

Global Positioning System

• 24 satellites• Selective Availability

turned off May 2000• 30 meter accuracy• Can be jammed

(denial of service)• Can be spoofed



Page 57

GPS Frequencies

L1: 1575.42 MHz: Coarse Acquisition (C/A) code

L2: 1227.60 MHz: Precise (P) or Y (encrypted) code

L3: 1381.05 MHz: Nuclear burst detectors

L4: 1841.40 MHz: Ionospheric correction (under study)

L5: 1176.45 MHz: Civilian safety-of-life signal (proposed)



Page 58

GPS Enhancements

The new architecture also requires new user equipment and an upgraded ground control segment, as well as M-Code. All of those elements should be in place by 2008, when 18 satellites with M-Code - 12 IIRs and 6 IIFs - will be up.



Page 59

GLONASS

• Global Orbital Navigation Satellite System

• 1606 to 1616 MHz

• Full operational status achieved once



Page 60

Satellite Failures• PanAmSat Galaxy 4

– Attitude control and backup failed– Major supplier of service to paging towers

• AT&T Telstar 401– launched 1993, failed 11 January 1997– abrupt failure, solar activity? (large solar flare 6 January 1997)

• Galaxy 7– Primary control processor failed June1998. Secondary processor

failed November 2000. – Suspected electrical shorts in spacecraft control processor (SCP).

• Solidaridad 1– Primary SCP failed May 1999. Secondary SCP failed August

2000.• Anik E1

– 1996, Power Subsystem Failure, Partial Loss• EchoStar 4

– 1998, Solar Array Failed to Deploy, reduced electrical power available



Page 61

Questions?



Page 62

Satellite GlossaryBEACON Modulated oscillator, usually containing telemetry. Sometimes referred to as a “pilot.” Used to locate a satellite and determine received signal strength.

BEAM Uplink or downlink channel to or from the satellite. May cover a wide area, or be focused on a particular location (“spot beam”).

BENT PIPE Big repeater in the sky. Simply repeats uplinked signal on downlink side, with amplification. Also called non-processing.

DOWNLINK, UPLINK Downlink is signal from satellite to ground station. Uplink is signal from ground station to the satellite.



Page 63

Satellite Glossary (con’t)EOL End of Life. Satellite lifetimes, barring accident or other damaging incident, are determined by the amount of maneuvering fuel (typically hydrazine) on-board. When the fuel runs out the satellite can no longer be maneuvered to stay in it's assigned orbital location. The orbit then becomes inclined. Current satellites have an expected life of 10 - 15 years.

ECLIPSE Satellite's solar panels are blocked by the earth (22 days before and after spring and autumn equinox, maximum of 70 minutes) or the moon (irregular).

EIRP Effective Isotropic Radiated Power. A measure of satellite transmitter strength, usually in dBw (decibels above one watt).



Page 64

Satellite Glossary (con’t)

FDMA, TDMA, CDMA, DAMA Modulation schemes to allow resource (bandwidth) sharing. Frequency Division Muliple Access: standard for video. Time Division Multiple Access: standard for telephone, most data. Code Division Multiple Access: spread spectrum, originally military. Demand Assign Multiple Access: shared data systems, including VSAT.

FEEDERLINK Communications link between the ground station and the satellite. This link is distinct from the user links.

FOOTPRINT Geographic area on the earth covered by a particular satellite beam.



Page 65


INCLINED ORBIT When maneuvering fuel runs out. Requires tracker at ground station. Traces a figure-eight pattern above and below the equator over 24 hours.

INMARSAT International Maritime Satellite Organization. Covers Atlantic (AOR East and West), Pacific (POR) and Indian (IOR) Oceans. Has spares in orbit, not always in contact with TT&C.

LOOK ANGLE Elevation from a given location to a satellite. 90 degrees is directly overhead, 0 degrees is on the horizon.

PSEUDOLITE Pseudo-satellite. Ground-based or airborne transmitter emitting satellite-like signals.



Page 66


TRANSPONDER Discrete frequency slot assigned to an uplink/downlink.

TT&C Telemetry, Tracking and Command. Ground Station monitoring and controlling satellite operation.

TWT Traveling-Wave Tube amplifier. Has nearly flat response across a wide bandwidth. Newer satellites are using solid state amplifiers.

VSAT Very Small Aperture Terminal. Usually dedicated data links in a star configuration. Popular with gas stations for credit card verification; car dealers for sales information.

Documents

Vulnerabilities of Cellular and Satellite-based Voice and Data Networks