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Cell Phone Security


... for simple math Send or receive e-mail Get ... researchers claimed to have cracked this encryption in 10 hours by sending a large number of ... – PowerPoint PPT presentation

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Title: Cell Phone Security

Cell Phone Security
  • Linden Tibbets
  • Coen 150
  • 5/28/2004

  • Changed structure of our lives and the way we do
  • Hundreds of models and services
  • Potential for major annoyance

Endless Uses
  • Store contact information
  • Make task or to-do lists
  • Keep track of appointments and set reminders
  • Use the built-in calculator for simple math
  • Send or receive e-mail
  • Get news, entertainment, and stock quotes from
    the Internet
  • Browse regular Internet sites
  • Play simple games
  • Integrate other devices such as PDAs, MP3
    players, and GPS receivers
  • Use credit cards to buy products and services
  • Download ring tones, games, and other programs
    for the specific phone

Are They Secure?
  • Vast amounts of personal information
  • Personal Phone Book
  • Address
  • Credit Card Number
  • Email Password
  • Account Information

A Brief History
  • Concept Began in 1947
  • Researchers improve traffic of primitive car
    phones by reusing freq. in smaller areas called
  • Federal Communications Commission (FCC) hinders
    cell phone progress
  • Only enough channels for 23 conversations per
  • Not practical

The Cell Phone Boom
  • 1967 FCC expands available frequencies
  • 1973 Dr. Martin Cooper at Motorola makes first
    cell phone call to his rival Joel Engel at Bell
  • 1983 First cell phone network in US (Chicago)
  • 1987 Over a million users
  • 2004 If you dont have a cell phone your in the

How Do They Work?
Inside the Cell Phone
  • Inner workings not much different than a personal
  • RAM
  • CPU
  • Input
  • Output
  • Power Source

The Cellular Approach
  • At first only one tower per city (around 25
  • Now a provider has 832 freq. in each city
  • One cell uses 1/7 of these
  • Share freq. Between cells
  • Cell Phones are two way devices so they use two
    separate channels

Frequency Breakdown
  • Provider has 395 total voice channels (more when
    it goes digital)
  • 42 control channels for system signals
  • 395 x 2(in/out) 42 832 Frequencies

  • Electronic Serial Number (ESN) - a unique 32-bit
    number programmed into the phone when it is
  • Mobile Identification Number (MIN) - a 10-digit
    number derived from your phone's number
  • System Identification Code (SID) - a unique
    5-digit number that is assigned to each carrier
    by the FCC

  • When you first power up the phone, it listens for
    an SID on the control channel. The control
    channel is a special frequency that the phone and
    base station use to talk to one another about
    things like call set-up and channel changing. If
    the phone cannot find any control channels to
    listen to, it knows it is out of range and
    displays a "no service" message.

  • When it receives the SID, the phone compares it
    to the SID programmed into the phone. If the SIDs
    match, the phone knows that the cell it is
    communicating with is part of its home system.
  • Along with the SID, the phone also transmits a
    registration request, and the MTSO (Mobile
    Telephone Switching Office) keeps track of your
    phone's location in a database -- this way, the
    MTSO knows which cell you are in when it wants to
    ring your phone.

  • The MTSO gets the call, and it tries to find you.
    It looks in its database to see which cell you
    are in.
  • The MTSO picks a frequency pair that your phone
    will use in that cell to take the call.
  • The MTSO communicates with your phone over the
    control channel to tell it which frequencies to
    use, and once your phone and the tower switch on
    those frequencies, the call is connected.

  • As you move toward the edge of your cell, your
    cell's base station notes that your signal
    strength is diminishing. Meanwhile, the base
    station in the cell you are moving toward (which
    is listening and measuring signal strength on all
    frequencies, not just its own one-seventh) sees
    your phone's signal strength increasing. The two
    base stations coordinate with each other through
    the MTSO, and at some point, your phone gets a
    signal on a control channel telling it to change
    frequencies. This hand off switches your phone to
    the new cell.

Analog to Digital
  • Early phones were purely analog radios
  • To increase security and channel use efficiency
    converted all calls to digital, encrypted and
    spread over the frequencies
  • Three methods to do this FDMA, TDMA, CDMA

  • Frequency division multiple access
  • Much like analog control except now calls are
  • Insecure since a call is set to specific

  • Frequency division multiple access
  • Splits calls up into different time slots.
  • Allocates only a certain amount of time on any
    given freq.
  • Introduces data encryption
  • Basis for GSM (Global System for Mobile
    Communications). Used everywhere except USA.

  • Code division multiple access
  • Uses unique code in phone to encrypt the data
    then break it up into packets that are sent on a
    broad range of freq.
  • Further scrambles information

What Makes Cellular Insecure?
Physical Problems
  • Small and easily lost
  • Most phones have a password lock but they are
    easy to get around and nobody uses them
  • Easy target for stealing personal information

Common Wireless Problems
  • Analog and FDMA phones easy to listen in on
  • Needed 200 scanner and some technical skills
  • Overcome by CDMA and TDMA
  • Still possible to crack yet much harder
  • Cell network is much the same as a WLAN
  • Lack security physical wires provide, anybody can
    pick up the signal

Common Wireless Security contd.
  • The level of protection is limited
  • Slow data rates
  • Availability
  • High error rates due to the mobility of user
  • Limited computational power
  • Limited battery power

Encryption Problems
  • The limitations of the cell phone and its network
    disable the encryption and authentication process
  • Number of bits in the key must be low
  • Number of handshakes or checks the authentication
    scheme allowed is low as well
  • Despite these limitations cell phones remain more
    secure than most wireless networks due to the
    fast pace changes and the scrambling of data over
    multiple frequencies

Attacks, Interference, Other problems
Should We Still Worry
  • In order to listen in to a modern cell phone
    conversation an organization must be well funded
    and posses considerable technical skill
  • Even grabbing a credit card number would not
    enable you to turn a profit
  • Yet there remain problems with everyday cell
    phone usage

  • Early days quite simple
  • Figure out the ESN, MIN, SID
  • Program other phones with these numbers and all
    calls would be billed to one users account
  • Harder to do today
  • Still costs cellular providers over 500 million
    dollars a year

Cloning in the Digital Age
  • Most phones carry all of the critical info on a
    SIMM card much like a smart card
  • Group of Berkeley researchers claimed to have
    cracked this encryption in 10 hours by sending a
    large number of challenges to the authorization
    module in the phone, compromising the security
    behind the GSM standard

Cloning in the Digital Age contd.
  • Claim the A5 cipher that keeps conversations
    private was made intentionally weaker by
    replacing the leading 10 bits of a 64-bit key
    with zeros
  • Blame the NSA for forcing the weakness in order
    to monitor cell phone traffic

SMS Attacks
  • Many phones use SMS messaging service
  • Can send and receive messages to phones or the
  • Programs created to bomb a specific phone with
    thousands of messages (DOS attack)
  • Jams the phones service
  • Uses up the users predetermined text limit

They Know Where You Are
  • Providers can pinpoint your location to within
    100 feet if your phone is on
  • The constant check for signal strength creates
    the side effect of tracking locations and
  • A huge market for more invasive advertising
  • Track the consumers location
  • Send tailored ads to a cell phone based on the
    location of the user
  • Consider how bad it is on the Internet and this
    doesnt seem so far fetched

Turn It Off in the Airplane
  • Signals have been proven to disrupt the workings
    of sensitive equipment
  • A single phone in a plane causes no problems, but
    a whole cabin full of phone users really could
    change the readings in some equipment
  • Other reports of cellular traffic having an
    effect on the payment systems at pay-at-the-pump
    gas stations

  • Simple device used to send a signal on all
    available freq. in an area causing a cell phone
    to show no service bars
  • Already in use to protect the President from
    cellular phone bomb calls (similar to the bomb in
    Spain) while he is traveling
  • Illegal in the USA
  • Restaurants and Movie theaters lobbying for such
    devices to keep their places of business cell
    phone free

  • Just like secure computer networks, cell phones
    must make use of current data encryption schemes,
    authentication methods and physical security
  • In order for the cell phone to become a more
    useful tool in everyday lives it must first
    secure its current features and gain the trust of
    the millions of users who still watch what they
    say or do over the phone
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