Wireless SecurityWireless Security

CS 551: Information Systems Security

presented by

The Dining Philosophers

November 25, 2002

The Dining PhilosophersThe Dining Philosophers

Eugene LebanidzeHao LiangImran ShahAdrian Kao

Thanks to Steve Tropello

AgendaAgenda

IntroductionOverview of wireless technology

– Cellular phones– WLANs– Bluetooth

Security issuesSolutionsConclusions

Wireless DevicesWireless Devices

Mobile/Cell phones Pagers WLAN (Wireless Local Area Network) Bluetooth Radio stations Cordless phones Garage door openers Handheld devices (infrared)

Electromagnetic SpectrumElectromagnetic Spectrum

ModulationModulation

Encoding information so it’s suitable for transmission

Analog Modulation– Traditional AM & FM (Radio stations)

Digital Modulation– More cost effective than analog– Greater noise immunity– More robust to channel impairment– Error control– Security (i.e. encryption)

Digital Modulation MethodsDigital Modulation Methods

Amplitude Shift Keying (ASK)– On-off keying– “On” means 1, “off”

means 0.

Frequency Shift Keying (FSK)– f1 means 1, f2 means 0

– Less efficient

Phase Shift Keying– Binary (BPSK)– Differential (DPSK)– Quadrature (QPSK)– Offset QPSK– /4 QPSK– and many more

ASKASK

FSKFSK

BPSKBPSK

Issues in WirelessIssues in Wireless

Modulation techniques Handoff / Tracking ISI (Intersymbol Interference) Fading “Line of Sight”

– Reflections– Obstacles

Noise Efficiency, capacity

Cell Phones: HandoffCell Phones: Handoff

Base Station

Device IssuesDevice Issues Mobility: size and weight

– Enough storage?– Enough processing power?– Practical?

Power consumption– More computation requires more power– More circuitry requires more power

Price– Memory, processor, and battery costs

Technology– Does it do what we want? Does it do it right?

Security IssuesSecurity Issues

Information is open and in the air Signals can be affected by noise or EM radiation Mobile devices are small (small storage, slow, low

power consumption) Many, many devices

– Key distribution (pseudo random)– Interference

Networks– Centralized/distributed systems and ad-hoc networks

SolutionsSolutionsEncrypt data

– Don’t have to worry about eavesdropping– But still have to worry about noise and ISI

Directional antennas– SDMA– Doesn’t work very well, not as efficient

Power/distance control– Hard to do, requires lots of computing power,

not practical for mobile devices

Cell PhonesCell Phones

Scrambler

More privacy then securityCan we implement better security?

Speech Encoder +

Pseudo Random

Modulator

WAPWAP Wireless Application Protocol Standard created by a forum to provide more

optimized content for mobile wireless devices

Security flaws in transport layer

WTLSWTLS Wireless Transport Layer Security Similar to TLS or SSL in conventional networks WAP gateway must first decrypt and then encrypt with less

secure scheme– Optimized for wireless, hence less secure– Not compatible with TSL

WLANWLAN

Wireless Local Area NetworkMost common standard: IEEE 802.11In addition to worrying about issues in

networks, must also worry about issues in wireless

Does not focus on security, just the physical standard

Security is focused in other standards

802.1x802.1x

Port based network access controlNew Wi-Fi security protocol wireless

standards, but has already been cracked.– “Session hijacking”– “Man-in-the-middle”

Can add WEP on top to provide more security

Cracking 802.1xCracking 802.1x Session hijacking

– Occurs because of race conditions in 802.1x and 802.11 state machines

– Hacker waits for successful authentication– Break user connection and impersonate user– Can exploit user’s session until timeout (~1 hr)

Man-in-the-Middle– Works since 802.1x uses only one-way authentication– Hacker acts as Access Point to user and user to AP– APs are trusted entities bad design

WEPWEP Wireless Equivalent Privacy IEEE 802.11b Uses RC4 stream cipher developed by RSA

– Known to be weak and can be easily cracked– Developed in 1987– 40-bit secret key

Design Criteria– Reasonably Strong – Computationally Efficient – Self-synchronizing – Exportable– Optional

WEP Encryption ArchitectureWEP Encryption Architecture

How WEP worksHow WEP works Secret key to maintain privacy (RC4)

– 24-bit IV (Initialization Vector)– 40-bit secret key– Concatenated and 64-bit value used as seed for PRNG

32-bit ICV (Integrity Check Value) to ensure no manipulated data transmitted (CRC-32)– Based on plaintext from Integrity Algorithm– Concatenated with original plaintext

XOR key with plaintext– IV concatenated in front of ciphertext and final message is

sent

Cracking WEPCracking WEP

You don’t need toOpen-source software available to take

advantage of RC4 weaknesses– Airsnort

Hours to days, depending on traffic

– WEPCrack Several Perl programs

– Search on Google yields numerous programs

Solutions for WLANsSolutions for WLANs

802.1x with WEP is not enoughPut lots of things together for securityNeed another encryption protocol on top to

provide securityProblems

– Need hardware acceleration– Optimize for speed and efficiency– Tradeoff in security scheme

BluetoothBluetooth Ad hoc, personal networks (piconets)

– PDA or laptop to cell phone Short range, low power consumption, and cheap!

– 1mW ~ 100mW– 0.1m ~ 100m– $5 ~ $25

Frequency hopping– Involves periodic change of transmission frequency

Sequence of data bursts Time-varying, pseudorandom carrier frequencies

– Not so much security as interference avoidance scheme

Bluetooth SecurityBluetooth Security Issues in dist’d systems, ad hoc networks

– Availability– Authorization and key management– Confidentiality and Integrity

Security modes– Mode 2: service level enforced security– Mode 3: link level enforced security

Device initiates sec. procedure before channel is established

Device security levels– Trusted device – Untrusted device

Service security levels– Authentication only – Open to all– Authorization and Authentication

Bluetooth Link Level SecurityBluetooth Link Level Security Link Keys (no encryption key)

– Combination key Derived from information from two devices, new for each pair

– Unit key Generated in single device when it is installed

– Master key Temp key replaces current key, used by Master to broadcast to many

– Initialization key Before there are any combination or unit keys, used only for install

48-bit unique Bluetooth Device Address defined by IEEE 128-bit random Private Authentication Key 8 ~ 128-bit Private Encryption Key 128-bit (pseudo-)random number generated by device

Bluetooth Security ProblemsBluetooth Security Problems 128-bit key stream cipher can be broken in O(264), but

so short it can’t happen (FH) Usability: need to input PIN twice, very annoying Initialization key is not trustworthy

– Based on PIN only, and if 4-bits, then only 10,000 possibilities

– 50% of PINs are “0000” Unit key assumed to be shared secret, but can be

obtained and identity can be forged Device Address can be used to track and monitor Battery draining denial of service attack

Solutions for BluetoothSolutions for Bluetooth

Application level key agreement in software Problems with implementing better security

– More hardware, more storage, more power, more $$– Defeats the whole purpose of Bluetooth

Or, forget about security altogether (not likely)– Let Bluetooth be only physical and technical standard– Security left to users who can use software (not smart)

Spread SpectrumSpread Spectrum Other modulation techniques strive for greater power

and/or bandwidth efficiency SS modulation has transmission bandwidth orders of

magnitude greater than message bandwidth Multiple users without interfering CDMA (Code Division Multiple Access)

– 3G cell phones– Military communications

“Spread” message across entire bandwidth, below noise level

Controlled by pseudo-noise (PN) code

Concluding RemarksConcluding Remarks

Wireless security is hard– Power and size compromise– Must optimize for wireless devices

Each situation is different, so no one method will work

State of the art: cause for concern– Absolutely no encryption for most mobile

devicesPerhaps ECC (Elliptic Curve Cryptograph)?

Questions?