Intro

Wireless communication uses electromagnetic (EM) waves to transfer information between two or more nodes without a conducting path

The complete range of frequencies of EM radiation

EM waves are carried by photons which oscillate with a specific frequency 𝑓 (in [Hz]), independent of the medium

For the purpose of information transfer, the region below the visible light spectrum is preferred

Transceivers can be much more easily constructed than for Terahertz radiation

The penetrative properties of RF allow communication through obstacles and much higher range than with infrared

Infrared (𝑓 [𝑇𝐻𝑧], 𝜆 ~ 700𝑛𝑚 … 1𝜇𝑚)

Terahertz radiation(𝑓 [𝑇𝐻𝑧 … 𝐺𝐻𝑧], 𝜆 ~ 30𝜇𝑚 … 1𝑚𝑚)

Radio Frequency (𝑓 [𝐺𝐻𝑧 … 𝐻𝑧], 𝜆 > 1𝑚𝑚

The microwave range, which contains the shortest wavelengths/ highest frequency (𝑓 ~ 300𝑀𝐻𝑧 … 300𝐺𝐻𝑧, 𝜆 ~ 1𝑚𝑚 … 1𝑚) and is used for most wireless communication technologies

The Very High Frequency (VHF) range, which is (was) used for radio and television broadcasting

The High Frequency (HF) and Medium Frequency (MF) ranges which are used for wide-range and intercontinental communication

defined by the ITU in Radio Regulations articles and (mostly) internationally agreed on

no licence costs are necessary for their usage

most common used 2.4 – 2.5GHz

structure that converts between a guided plane wave on a line and a spherical free-space wave

converts currents on a wire into RF photons, and vice versa

matched to a certain wavelength

• Dipole

• Meander

• Yagi-Uda

• Dish

• Cantenna

downsized versions of the classical BNC-type connectors for coaxial cables, called Subminiature Version A (SMA)

Typically, male connectors are used on antennas, female connectors are used on boards/dongles

Male: Inner-threaded barrel and inner pin

Female: Outer-threaded barrel and inner receptable

Male: Inner-threaded barrel and inner receptable (!)

Female: Outer-threaded barrel and inner pin (!)

RF signal sent out by an antenna gradually loses energy, with the loss proportional to the square of the distance

The weakening of a RF signal due to distance alone is termed the Free-Space Path Loss (FSPL)

assuming direct line-of-sight transmission in vacuum and that sender and receiver use ideal omnidirectional antennas

Additional losses from other factors (e. g. absorption, interference) must be considered

Superposition by other, stronger RF signals

can be mitigated by sophisticated transmission schemes

By matter in the propagation path

(e. g. water molecules in air, walls, conducting structures

Reflection in multiple directions due to small (e. g. Rayleigh scattering: d > 𝜆) or uneven objects

(e. g. dust, snow storm)

Bending of the signal path on sharp edges of objects

(e. g. buildings)

Splitting up into multiple path components due to reflections (e. g. on walls) with possible destructive interference by the delayed path components at receiver

Can be exploited for higher data rates!

Undefined range: in principle unlimited range

Shared medium: Wireless devices communicate over the same medium, wireless transmission is half-duplex only

Variable link quality: Overall quality can change rapidly in short time

Mobility of devices

All this makes the need for different routing protocols

Fokus auf Wlan, Bluetooth, Zigbee und NFC

Confidentiality

Integrity

Availability

Authentication

Authorisation

Replay Protection

Key Management

Non-Repudiation

Protection of data in transit and at rest from unwanted disclosure

Typically achieved via Encryption

Protection of data in transit and at rest from undetected modification

Enabling use of services for legitimate (!) users, when needed

Proving the identity of devices, persons and services

Enforces access control for protected resources, dependent on proper Authentication

Detection of deliberately repeated transmissions

Establishment, Distribution and Update of cryptographic material

Proving that a transmission originated from a specific sender

Uses a shared Secret Key which must never be disclosed

Encryption and Decryption use the same key

Uses a pair of Public and Private Keys, requires only Private Key to be secret

Encryption is performed with the Public Key of the receiver,

Decryption with the Private Key of the receiver

Reconnaissance

Eavesdropping (also: Capturing, Sniffing)

Cryptanalysis

Injection

Replay attack

Impersonation

Denial of Service

Gain information about target network, computers and users

Passive attack, capturing data in transit

Recovering the plaintext and/or key from captured data

Unauthorised sending of crafted messages

Spoofing … forging the origin of messages

Fuzzing … sending messages with invalid or unusual content

Re-sending previously captured messages

Assuming the identity of legitimate devices/users/services

Disrupting services, preventing access for legitimate users

Physical access is MUCH easier than with wired networks

Significantly lowers the effort and risk for an attacker

Attacker can engage over long distances

Mobile attacker is much harder to detect and capture

Wireless network lies at the edge of the network infrastructure

Limited computing power and energy

High effort for Key Management

Huge number of possible configurations

Market pressure leads to compromises regarding security

Physical DoS via RF interference

Logical DoS via forged messages

No effective way to mitigate DoS attempts