Wireless Networking

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Outline

• Wireless Network Communications– Background– Security Issues– WEP / WPA

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Hardening Wireless Local Area Networks (WLAN)

• By 2007, >98% of all notebooks will be wireless-enabled

• Serious security vulnerabilities have also been created by wireless data technology:– Unauthorized users can access the wireless signal

from outside a building and connect to the network

– Attackers can capture and view transmitted data

– Employees in the office can install personal wireless equipment and defeat perimeter security measures

– Attackers can crack wireless security with kiddie scripts

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IEEE 802.11 Standards

• A WLAN shares same characteristics as a standard data-based LAN with the exception that network devices do not use cables to connect to the network

• RF is used to send and receive packets• In September 1999, a new 802.11b High Rate was

amended to the 802.11 standard. It added two higher speeds, 5.5 and 11 Mbps to original speeds of 1, 2 Mbps

• Communications distance varies with bandwidth to a maximum range of up to 300 ft.

• With faster data rates, 802.11b quickly became the standard for WLANs

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IEEE 802.11 Standards

• At same time, the 802.11a standard was released

• 802.11a has a maximum rated speed of 54 Mbps and also supports 48, 36, 24, 18, 12, 9, and 6 Mbps transmissions at 5 GHz

• 802.11g added in 2003. It adds transmission rates of 18, 36, and 54 Mbps to the rates available under 802.11b.

• 802.11n draft product in 2007, standardized in 2009. Added rates up to 600 mbps

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Data Rates / Range• 802.11b

• 1 Mbps / 90+ m.• 2 Mbps / 75 m.• 5.5 Mbps / 60 m.• 11 Mbps / 50 m.

• 802.11g

• All of 802.11b• 18 Mbps / 50 m.• 36 Mbps / 35 m.• 54 Mbps / 20 m.

• 802.11n – per stream• (4 streams max)

• 20 MHz band– 7.2, 14.4 … 72.2 Mbps

• 40 MHz band– 15, 30 … 150 Mbps

• “Twice the distance of 802.11g”

• Typical configurations 2 transmit / receive streams

• Can transmit on 2.4 or 5 GHz

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WLAN Components

• Each network device must have a wireless network interface card installed

• Wireless NICs are available in a variety of formats:– Type II PC card – Mini PCI– CompactFlash (CF) card – USB device– USB stick

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WLAN Components (cont)

• An access point (AP) consists of three major parts:– An antenna and a radio transmitter/receiver to

send and receive signals– An RJ-45 wired network interface that allows it

to connect by cable to a standard wired network

– Special bridging software

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Basic WLAN Security

• Two areas: – Basic WLAN security – Enterprise WLAN security

• Basic WLAN security uses two new wireless tools and one tool from the wired world:– Service Set Identifier (SSID) beaconing– MAC address filtering– Wired Equivalent Privacy (WEP)

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Service Set Identifier (SSID) Beaconing

• A service set is a technical term used to describe a WLAN network

• Three types of service sets:– Independent Basic Service Set (IBSS)– Basic Service Set (BSS)– Extended Service Set (ESS)

• Each WLAN is given a unique SSID

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MAC Address Filtering

• Another way to harden a WLAN is to filter MAC addresses

• The MAC address of approved wireless devices is entered on the AP

• A MAC address can be spoofed• When wireless device and AP first exchange

packets, the MAC address of the wireless device is sent in plaintext, allowing an attacker with a sniffer to see the MAC address of an approved device

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MAC Address Filtering

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Wired Equivalent Privacy (WEP)

• Optional configuration for WLANs that encrypts packets during transmission to prevent attackers from viewing their contents

• Uses shared keys―the same key for encryption and decryption must be installed on the AP, as well as each wireless device

• Keys:– 40 bit (5 byte) key + 24 bit IV = 64 bits– 104 bit (13 byte) key + 24 bit IV = 128 bit

• No data integrity function

WEP - Shared Key Authentication

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Client Access Point

Authentication Request

Challenge Text

Encrypt Challenge w/key

Compare

AuthenticationFrame

WEP Encryption

Text CRC Text ICV

ICV = Integrity Check Value

IV = initialization Vector

IVSecret Key

PRNG Keystream

XOR

CiphertextIV

+

=

=

1

2

34

5

WEP Frame layout

IV Data >=1 ICV

encrypted

Inititialization Vector Key ID3 bytes 1 byte

ICV = Integrity check value (CRC)

4 bytes

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(WEP) (cont)

WEP Weaknesses

• IV sent as cleartext. Since key never changes, once we know two packets share the same IV, we know their keys are identical– XOR the two ciphertext messages– XOR of plaintext will have same value as XOR of

ciphertext!– We will know some of the transmitted data

• ARP requests• DNS• Etc.

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Untrusted Network

• The basic WLAN security of SSID beaconing, MAC address filtering, and WEP encryption is not secure enough for an organization to use

• One approach to securing a WLAN is to treat it as an untrusted and unsecure network

• Requires that the WLAN be placed outside the secure perimeter of the trusted network

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Untrusted Network (continued)

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Trusted Network

• It is still possible to provide security for a WLAN and treat it as a trusted network

• Wi-Fi Protected Access (WPA) – Developed by WECA in 2002 as interim solution – Intended to be a software upgrade for WEP (use RC4)

• WPA-2 – 802.11 standard• Has two Domains:

– Personal Wireless Security– Enterprise Wireless Security

Personal Wireless SecurityWPA -1

• Authentication – Based on Pre-Shared Key• Encryption – Temporal Key Integrity Protocol

– Mixes IV and Extended IV with secret key– EIV includes sequence counter– Adds 8 byte Message Integrity Check– Uses RC4 as encryption mechanism– Includes ICV for backward compatibility

IV Data >=1 ICV

encrypted

EIV MIC FCSMAC h.

Personal Wireless SecurityWPA -2

• Authentication – Based on Pre-Shared Key• Encryption – AES – CCMP

– Counter mode-CBC MAC Protocol– Mixes IV and Extended IV with secret key– EIV includes sequence counter– Adds Message Integrity Check– Uses AES as encryption mechanism

IV Data >=1

encrypted

EIV MIC FCSMAC h.

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Enterprise Wireless Security

• Network supporting the 802.1x protocol consists of three elements:– Supplicant: client device, such as a desktop

computer or personal digital assistant (PDA), which requires secure network access

– Authenticator: serves as an intermediary device between supplicant and authentication server

– Authentication server: receives request from supplicant through authenticator

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IEEE 802.1x

Enterprise Authentication

• Extensible Authentication Protocol – Used to pass information from supplicant to

AS

WN AP AS

Security Capabilities Discovery

Authentication

Key management Key Distribution

Data protection

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IEEE 802.1x (cont)

• Several variations of EAP can be used with 802.1x:– EAP-Transport Layer Security (EAP-TLS)– Lightweight EAP (LEAP)– EAP-Tunneled TLS (EAP-TTLS)– Protected EAP (PEAP)– Flexible Authentication via Secure Tunneling

(FAST)

Enterprise Wireless Security

• Data Encryption – WPA 1– TKIP

• Data Encryption – WPA 2– AES - CCMP

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Wireless Security Summary

• Broadcast nature of Wireless LAN makes communication more vulnerable than wired networks

• Several mechanisms can be used to limit access

• Encryption used to protect data transmission (and access).

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References:

• Wireless Security– 802.1x - tldp.org/HOWTO/802.1X-HOWTO– IPSec – tldp.org/IPSec-HOWTO

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Summary

• Wireless Network Communications– Background– Security Issues– WEP / WPA