802.11

Wireless, WEP and WPA

History

ALOHAnet - Hawaii

https://www.lib.utexas.edu/maps/us_2001/hawaii_ref_2001.jpg

ALOHAnet

June 1971

Version 1

Pure ALOHA

data.send

if network.collision {

do wait(time=random)

data.send

}

Pure ALOHA

http://upload.wikimedia.org/wikipedia/commons/thumb/3/35/Pure_ALOHA1.svg/800px-Pure_ALOHA1.svg.png

Slotted ALOHA

Only 18.4% of transmission time used for

successful frame transmissions

Version 2

Slotted ALOHA

Used discreet time slots

Station can only send at the beginning of a

time slot

All collisions at the beginning of a frame

Slotted ALOHA

http://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Slotted_ALOHA.svg/800px-Slotted_ALOHA.svg.png

Slotted ALOHA

Low-data-rate tactical satellite comms by

military

Subscriber based satellite comms networks

Mobile telephony call setup

Set top box comms

RFID

36.8% of transmission time used for

successful frame transmissions

Wireless

Range Max. Speed Frequency Year of release

Legacy 100m 2MB/s 2.4GHz 1997

802.11a 120m 54MB/s 5GHz 1999

802.11b 140m 11MB/s 2.4GHz 1999

802.11g 140m 54MB/s 2.4GHz 2003

802.11n 250m 150MB/s(per stream)

2.4GHz+5GHz 2009

802.11ac 866.7MB/s 5GHz 2014

Channels

http://en.wikipedia.org/wiki/File:2.4_GHz_Wi-Fi_channels_(802.11b,g_WLAN).svg

1-11 – Anywhere

12&13 – Anywhere except USA

14 – Japan only

WEP

Only used for legacy anymore

Neil still uses this at his home but shhhhh.

Very broken

WEP

How is a WEP connection made?

Probe request Client >>> AP

Probe response AP >>> Client

Authentication request Client >>> AP

Challenge AP >>> Client

Challenge Response Client >>> AP

Association request AP >>> Client

Association reponse Client >>> AP

How it works

24-bit IV (initialisation Vector)

Secret key (40Bit or 104Bit)

Result 64-Bit or 128-BitRC4 PRNG

Key StreamPlaintext Message

XOR’ed

CiphertextIV

Whys that broken?

• Only 16million possible IV’s

• On a 11MB/s link, with packets of 1500 bytes, can exhaust all possible IV’s in 5~ hours

• More collisions, easier for statistical attacks to calculate the original keystream

• Once you have keystream, you already have the IV, not hard to work out the secret key

WPA

• Replaced WEP

• Comes in 2 types, WPA and WPA2

• Each type has 2 flavours

– PSK (personal)

– Enterprise (802.1x + radius)

• WPA Had to use the same hardware as

WEP, only firmware updates allowed

• Used TKIP

WEP Vs. WPA

WEP WPA

Static session keys (always same key used for session start)

Dynamic session keys (different keys used for every session start)

WPA - PSK

Probe Request

Probe Response

Authentication Request

ANounce

Snounce + MIC

To Wireshark

CAPTURE FILE

The bigger picture

Pass phrase(8-63 chars)

Password Based Key Derivation Function (SSID)

Pre-shared Key (256-bit)

4-Way handshakeSnounceAnounceAP MAC

Client MAC

PTK (Pairwise transient key,

unique to session)

Pass phrase(8-63 chars)

Verify using MIC

Crackable?

Yes

BUT

Takes forever

Really need to be desperate

But there is one major flaw

WiFi Protected Setup

Security

Ease of UseFunctionality

WPS

• Simplifies WPA security for users

• Gives us a better in ;)

• Router breaks the key down into 2 sets of

4 numbers

• Tells client if a set it correct, even if the

other is wrong

• So, we have a lot fewer possibilities

Finally WPA-Enterprise