Transcript Wireless Networking / Instant Messenging

Wireless Networking
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 wirelessenabled
• 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.
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• 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
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WEP - Shared Key
Authentication
Client
Access Point
Authentication
Request
Challenge
Text
Encrypt
Challenge
w/key
Compare
Authentication
Frame
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WEP Encryption
1
Text
CRC
Secret
Key
PRNG
=
Text
ICV
2
IV
+
=
Keystream
3
4
IV
5
ICV = Integrity Check Value
IV = initialization Vector
XOR
Ciphertext
WEP Frame layout
encrypted
IV Data >=1
ICV
4 bytes
Inititialization Vector Key ID
3 bytes
ICV = Integrity check value (CRC)
1 byte
(WEP) (cont)
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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.
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
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Personal Wireless Security
WPA -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
encrypted
MAC h. IV EIV Data >=1
MIC ICV FCS
Personal Wireless Security
WPA -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
encrypted
MAC h. IV EIV Data >=1
MIC FCS
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
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Enterprise Authentication
• Extensible Authentication Protocol
– Used to pass information from supplicant to
AS
WN
AP
AS
Security Capabilities Discovery
Authentication
Key management
Data protection
Key Distribution
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)
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Enterprise Wireless Security
• Data Encryption – WPA 1
– TKIP
• Data Encryption – WPA 2
– AES - CCMP
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
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