WIRELESS TECHNOLOGYEXCERPTS FROM CWNA/CWSP

A QUICK INTRODUCTION

OUTLINE OF THIS PRESENTATION▸ Components▸ Measurements▸ Communication / Signal▸ Security▸ Questions and/or Applause

RADIO FREQUENCY CREATION

HOW A SIGNAL IS CREATED1. Data is sent to the Transmitter, which creates the wireless

medium.

2. Transmitter is responsible for the modulation of the signal (carrier signal) and the signal strength (Amplitude/Power).

3. The Antenna radiates the carrier signal in a pattern specific to the type of antenna and receive signals from air to propagate it back to the transmitter

SIGNAL DEMYSTIFIED

MEASUREMENTS▸ Equivalent Isotropic Radiated Power (EIRP) - Highest

signal strength that is transmitted from a particular antenna.▸ Antennas tend to focus the RF signal, altering the

effective output.▸ Decibel (dB) - a unit of comparison, NOT a unit of

power.▸ identifies the difference between 2 values.▸ A relative expression and a measurement in change

of power

SIGNAL DEMYSTIFIED

MEASUREMENTS CONTINUED▸ Decibel notations:

▸ dBi (decibel isotropic) - comparison of an antenna to an isotropic radiator (think antenna gain).

▸ dBd (decibel dipole) - comparison of an antenna to a dipole antenna (omnidirectional).

▸ dBi = dBd + 3▸ dBm - a signal comparison to 1 milliwatt of power.

SIGNAL DEMYSTIFIED

MEASUREMENTS MATH EXAMPLES▸ Problem: 2.4GHz AP transmitting at 100mW, Laptop is

100m (0.1Km) from AP. ▸ Solution: Laptop receives 0.000001mW or if we use

FSPL formula -> dB = 32.4 + (20log10(2400)) + (20log10(0.1)) or 80.004dB ~ 80dB of signal loss.

▸ dBm: 0dBm = 1mW then what would 100mW be?▸ dBm = 10 X log10(PmW) or +20dBm▸ the reverse formula is: PmW = 10(dBm/10)

RF SIGNAL

UNDERSTANDING SOME KEY METHODS AND WAVE FUNCTIONS▸ Manipulation of signal is called Keying Method.

▸ Aptitude Shift-Keying (ASK)▸ Frequency Shift-Keying (FSK)▸ Phase Shift-Keying (PSK)

RF SIGNAL

UNDERSTANDING SOME KEY METHODS AND WAVE FUNCTIONS▸ All RF signals will experience some type of degradation.

▸ Absorption - loss of attenuation due to various materials▸ Reflection - diversion or bouncing of a signal▸ Scattering - multiple reflections of signal in various directions▸ Refraction - bending of a signal as it passes through a medium of

different density.▸ Diffraction - bending of a signal around an object▸ Free Space Path Loss - loss of signal strength caused by natural

broadening of the waves (Beam Divergence)

SIGNAL PROPAGATION

RF TRANSMISSION METHODS▸ Narrowband

▸ uses very little bandwidth▸ more susceptible to interference and intentional

jamming▸ Spread Spectrum

▸ wide range of bandwidth▸ less susceptible to jamming and interference

SIGNAL PROPAGATION

TYPES OF SPREAD SPECTRUM▸ Frequency Hopping Spread Spectrum (FHSS)

▸ Components:▸ Hopping sequence - predefined pattern of

frequencies▸ Dwell time - measure of time of signal

transmission▸ Hop time - measure of time between transmission

signal change▸ Modulation (Gaussian Frequency Shift-Keying)

GFSK

FREQUENCY HOPPING SPREAD SPECTRUM COMPONENTS

SIGNAL PROPAGATION

TYPES OF SPREAD SPECTRUM▸ Direct Sequence Spread Spectrum (DSSS)

▸ Signal transmission is spread across the range of frequencies that make up that channel.

▸ The process of spreading the data is known as: Data Encoding.

▸ Modulation▸ Differential Binary Phase Shift-Keying (DBPSK)▸ Differential Quadrature Phase Shift-Keying (DQPSK)

SIGNAL PROPAGATION

ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM)▸ Most popular and used in either 5GHz or 2.4GHz range▸ Looks like Spread Spectrum, but it uses subcarriers

(52 separate closely and precisely spaced frequencies)

▸ More resistant to ISI and negative effects from multi-path interference.

▸ Utilizes harmonics overlap to cancel unwanted signals.▸ Modulation is BPSK or QPSK (at higher rates uses 16-

QAM or 64-QAM).

OFDM

2.4GHZ CHANNEL OVERLAY DIAGRAM

2.4GHZ CHANNEL OVERLAY DIAGRAM

SECURITY

THE CHALLENGE▸ Unauthorized access

▸ open systems for customers and consumers▸ data and information is in the open and easy to

view both in promiscuous mode and in attack mode

▸ Rogue AP’s▸ redirect traffic▸ out-signal the original transmission

CONNECTIVITY

PROCESS OF GETTING CONNECTED▸ It’s a 4 step process

1. Authentication‣ Open - no verification of identity (null

authentication)‣ Varied - open to join but data encrypted to outside‣ Private - some type of encryption / shared key

2. Association‣ becoming a part of the BSS

SECURITY

TYPES OF PROTECTION▸ Access Control

▸ MAC address filtering▸ Restrictions

▸ Encryption▸ Wireless Equivalent Protection (WEP)▸ Wi-Fi Protected Access (WPA)▸ Wi-Fi Protected Access v2 (WPA2)

▸ SSID Cloaking

SECURITY

VULNERABILITIES AND ATTACKS▸ Leaving the Default access (Passwords, set-up)▸ open Authentication and/or Authorization▸ Use of SNMP-managed devices (Simple Network

Management Protocol) in unsecured mode▸ Improper configuration of gateways, extenders, bridged

devices, etc.▸ MAC Spoofing and MAC Layer Attacks

▸ session hijacking, MITM, DoS and Disassociation(s)

SECURITY

ENCRYPTION TYPES AND DEFINITION▸ Static WEP

▸ Layer 2 encryption using RC4 streaming cipher▸ 64-bit and 128-bit encryption (24-bit IV)

▸ Weakness▸ IV Collision attacks - 24-bit IV is in clear text and repeats itself after

16 million.▸ RC4 Key-scheduling Algorithm uses 24-bit IV▸ Reinjection Attack▸ Bit-Flip Attack - ICV considered weak and packet can be

compromised

SECURITY

ENCRYPTION TYPES AND DEFINITION CONT.▸ Wi-Fi Protected Access (WPA)

▸ Temporal Key Integrity Protocol (TKIP) - 40-bit encryption and 128-bit key. Generates keys dynamically for each packet, avoiding some collisions.

▸ Message Integrity Check (MIC) - avoids the capturing, changing and resending the packets. Also uses the MIC as a seed for the mathematic encryption keys.

SECURITY

ENCRYPTION TYPES AND DEFINITION CONT.▸ Wi-Fi Protected Access 2 (WPA2)

▸ Advanced Encryption Standard (AES)▸ AES-CCMP

▸ Counter Mode with Cipher Block Chaining Authentication Code Protocol (CCMP)

▸ Message Integrity Check (MIC) - avoids the capturing, changing and resending the packets. Also uses the MIC as a seed for the mathematic encryption keys.