Wireless Network Security
Dr. Mana Khatua
Assistant Professor
Dept. of CSE, IIT Guwahati
Email: manaskhatua@iitg.ac.in
Wireless Security Overview
Security requirements for wireless are the same with wired environment.
Confidentiality
Integrity
Availability
Authenticity
Accountability
Key Factors Contributing to Risks
Channel: broadcast communication; more susceptible to eavesdropping and jamming
Mobility: contributes additional risks
Resources: advanced OS, but limited resources (memory, processing)
Accessibility: Certain devices (sensors, robots) may be left unattended for long time
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Wireless Network Threats
Lack of
central
point of
control
e.g. Bluetooth,
Barcode reader,
Handhold PDAs
Bogus reconfiguration
commands to routers
/switches exposed to
nonfiltered traffic
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Wireless Security Measures
wireless security measures dealing with three components -
Securing wireless transmission
Signal hiding technique (for hiding wireless AP)
Turn off SSID broadcasting by AP
Assign cryptic name to SSID
Reduce signal strengths
Directional antennas
Encryption of wireless transmission
Securing wireless access point (AP) Securing wireless networks
Access control policy Enable anti-virus, anti-spyware, firewall
o it is typically based on the identity of the user Turn off SSID broadcasting by routers
who requests access to a resource
Change default identifier on router
Authentication mechanism
o to make sure the identity is who they say they Change router’s pre-set password
are. Apply MAC-filtering
Use encryption for traffic
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IEEE 802.11 Wireless LAN
• IEEE 802 committee responsible for LANs
• In 1990, IEEE 802.11 WG was formed
Aims:
• To develop a protocol & transmission specifications for Wireless LAN
• Developed IEEE 802.11i WLAN Security Specification
•The Wi-Fi alliance formed in 1999. This is an industry consortium.
First standard became popular is 802.11b in 1999
Developed a certification procedure for 802.11 security standards
Wi-Fi Protected Access (WPA)
Recent version in WPA2 – it incorporates all features of 802.11i spec
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IEEE 802.11 Protocol Stack
LLC:
keeps track of frame transmissions
handle frame retransmissions
MAC layer
Addressing
MAC framing from data
Medium Access
Physical layer
encode/decode signals
Bit transmission/reception
Transmission medium
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MAC Frame (MPUD)
MAC protocol data unit (MPUD)
MSDU
CRC: Cyclic Redundancy Check. Also known as Frame Check Sequence (FCS).
This is an error-detecting code, such as that which is used in other data-link
control protocols.
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IEEE 802.11 BSS, ESS
BSS (basic service set):
the smallest building
block.
BSS consists of a set of
stations controlled by a
single coordination
function.
BSSs connected via
APs. APs functions as
bridges.
ESS: two or more BSSs are connected via Distribution System (DS)
IBSS (independent BSS): When all stations in the BSS are mobile stations that
communicate directly with one another (not using an AP)
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IEEE 802.11 Services
Service Provider Used to support
Association Distribution system MSDU delivery
Disassociation Distribution system MSDU delivery
Re-association Distribution system MSDU delivery
Authentication Station LAN access and security
De-authentication Station LAN access and security
Distribution Distribution system MSDU delivery
Integration Distribution system MSDU delivery
MSDU delivery Station MSDU delivery
Privacy Station LAN access and security
Re-association: Enables an established association to be transferred from one AP to another
Distribution: when the MPDUs must traverse the DS to get destination STA
Integration: transfer of data between a STA on an 802.11 LAN and a STA on an 802.x LAN.
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Wireless LAN Security Protocols
Wired Equivalent Privacy (WEP) algorithm
The original native security
o 802.11 privacy by 802.11 work group
mechanism for WLAN.
Disadvantage: very week w.r.t. security & privacy • Used to protect wireless
communication from
802.11 Task Group i is formed to address the issue. eavesdropping (confidentiality)
• Prevent unauthorized access to a
Wi-Fi Protected Access (WPA) wireless network (access control)
o eliminates most of the 802.11 security issues
• Prevent tampering with
o it was based on the current state of the 802.11i standard transmitted messages (integrity)
Final form of the standard • Provide users with the equivalent
level of privacy inbuilt in wireless
Robust Security Network (RSN) networks (User’s role)
Wi-Fi Protected Access 2 (WPA2)
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How WEP Works
IV original unencrypted packet checksum
RC4
key
IV encrypted packet
IV (initialization vector) WEP Flaws and Vulnerabilities
There are 224 different IVs Weak keys for encryption
IV reuse and small size
RC4 is an Encryption Algorithm
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Wi-Fi Protected Access (WPA)
New security technique WPA in the year 2002-03
Replacement of security flaws in WEP
Improved data encryption
Strong user authentication
Because of many attacks related to static key, WPA minimize shared secret
key in accordance with the frame transmission
Use the RC4 algorithm in a proper way and provide fast transfer of the data
before someone can decrypt the data.
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WPA2
Based on the IEEE 802.i standard
The primary enhancement over WPA is the use of the AES (Advanced
Encryption Standard) algorithm
The encryption in WPA2 is done by utilizing either AES or TKIP (Temporal
Key Integrity Protocol)
2 versions: Personal & Enterprise
The Personal mode uses a PSK (Pre-shared key) & does not require a
separate authentication of users
The enterprise mode requires the users to be separately authenticated by
using EAP (Extensible Authentication Protocol)
WPA3 has been proposed, not used extensively till now.
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WEP vs WPA vs WPA2
WEP WPA WPA2
Year introduced 1999 2003 2004
TKIP (Temporal Key Integrity CCMP (Counter Mode CBC-
Encryption protocol Fixed-key
Protocol) MAC Protocol)
Session key size 64-bit/128-bit 256-bit 256-bit
Cipher type RC4 stream cipher TKIP (RC4-based) AES
Cyclic Redundancy
Data integrity Message Integrity Check CCMP
Check
Authentication Open system /Shared PSK + PMK (Pairwise Master
Pre-Shared Key (PSK)
method key Key)
Symmetric key
Key management WPA + WPA-PSK PMK + PSK
encryption
Pros Better than no security i) TKIP encryption i) Stronger encryption
ii) 256-bit key for encryption method: AES
ii) Solves prior issues
Cons i) Fixed-key encryption Many security Require more processing
ii)many vulnerabilities vulnerabilities still exist power
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Services in RSN
Latest Security
Standard by IEEE
802.11 Task Group I
Access Control (as Security Function) – It works with any authentication protocol and key exchange
Authentication – It is mutual authentication. Also do secret key exchange for secured communication
Privacy with message integrity – MAC-level data encryption and message integrity code (MIC) are used
to ensure confidentiality, integrity, origin authentication, etc.
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Cryptographic Algorithms in RSN
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Types of Configuration
802.11i security is
limited to BSS STA IBSS STA
End-to-end security is
provided by upper layer
STA
STA
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802.11i Phases of Operations
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(1) Discovery Phase
Purpose of Discovery Phase:
For an STA and an AP
to recognize each other,
agree on a set of security capabilities,
establish an association for future communications
Security Capabilities:
Confidentiality & Integrity protocols (Cipher suite)
TKIP
CCMP
Vendor specific
Authentication & Kay management approach
(AKM suite)
IEEE 802.11X (Port based network access control)
Vendor specific
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Discovery Phase
Discovery Procedure:
AP uses
• Beacon & Probe Response to advertise its 802.11i
security policy
STA uses the above messages
• to identify an AP
• to associate with the AP
Open system authentication
Only to maintain backward compatibility with the IEEE
802.11 state machine
STA & AP simply exchanges IDs
Association
STA & AP agree on a set of security capabilities to be
used.
Using Association Request, STA informs its selection from
the set declared by AP (using Beacon / Probe Response)
AP can refuse association request
STA also can block rogue AP
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(2) Authentication Phase
This is mutual authentication
◦ Between STA & AS located in a DS
IEEE 802.11i makes use of IEEE 802.11X Port-
based Network Access Control
◦ Extensible Authentication Protocol (EAP)
◦ Supplicant ~STA
◦ Authenticator ~AP
◦ Authentication server (AS)
Consists of three steps:
Connect to AS
◦ By request-Response, AP STA AS
EAP exchange
◦ authenticates the STA and AS to each other
◦ STA-to-AP message flow uses EAP over LAN (EAPOL)
protocol,
◦ AP-to-AS message flow uses Remote Authentication
Dial In User Service (RADIUS) protocol
Secure key delivery
◦ the AS generates a master session key (MSK)
◦ sends it to the STA secretly
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(3) Key Management Phase
In this phase, a variety of
cryptographic keys are
generate and distributed to
STAs.
There are two types of keys:
• pairwise keys used for
communication between an
STA and an AP
• group keys used for multicast
communication.
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IEEE 802.11i Keys
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IEEE 802.11i Keys
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Key Distribution
4-way handshake:
The upper part of the
Figure shows the MPDU
exchange for distributing
pairwise keys.
Group Key Handshake
the AP generates a GTK and
distributes it to each STA in
a multicast group.
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(4) Protected Data Transfer Phase
IEEE 802.11i defines two schemes for this:
Temporal Key Integrity Protocol (TKIP) – for older WiFi devices using WEP
Counter Mode-CBC MAC Protocol (CCMP) – for new WiFi devices using WPA / RSN
TKIP and CCMP both provides two services:
Message integrity
In TKIP: using message integrity code (MIC) generated by algorithm Michael
In CCMP: using cipher block chaining message authentication code (CBC-MAC)
Data confidentiality
In TKIP: using RC4 based encryption
In CCMP: using AES for encryption
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EAP Layered Context
RFC RFC RFC RFC
5216 5281 5433 5106
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EAP Protocol Exchanges
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IEEE 802.1X Access Control
Until the AS authenticates a
supplicant (i.e. client),
the 802.1X control channel is
unblocked, but the 802.11 data
channel is blocked.
Once a supplicant is authenticated
and authorised, the data channel
becomes unblocked
802.1X uses the concepts of
controlled and uncontrolled ports.
Ports are logical entities defined
within the authenticator and refer to
physical network connections,
Each logical port is mapped to one
these two types of physical ports
(controlled /uncontrolled)
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Cont
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