1 Wireless Security Update Mark Ciampa Western Kentucky University [email protected].

1

Wireless Security Update

Mark Ciampa

Western Kentucky University

[email protected]

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Oxymoron Government organization Same difference Pretty ugly Working vacation Tax return

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Oxymoron Jumbo shrimp Adult male Act naturally Microsoft Works Wireless security

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Wireless Advantages

Mobility Increased productivityEasier installationLess expensive installation

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Wireless Disadvantages

Radio signal interference

Health risksSecurity

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Wireless Security Vulnerabilities

Unauthorized users access the wireless network

Attackers view transmitted data Employees install rogue access

points Weaknesses in original IEEE 802.11

wireless security and new WPA

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Wireless Attack Tools

NetStumbler – Discover wireless network

Airopeek & Airmagnet – Packet sniffers

Kismet & Airsnort – Break security

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Wireless Security Attitudes

“It doesn’t matter if someone uses my wireless LAN”

“You can’t make a wireless LAN secure”

“I don’t know what to do”

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Does Wireless Security Matter?

Get into any folder set with file sharing enabled

See wireless transmissions Access to network behind

firewall can inject malware Download harmful content

linked to unsuspecting owner

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Does Wireless Security Matter?

Legal implications Security begins at home

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Can Make Wireless Secure

Significant improvement wireless security

New IEEE wireless standard ratified

Common non-technical wireless security language now used

Vendors making wireless security easier

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Wireless security that doesn’t work and why

Wireless security that does work How to secure a home WLAN Contents of wireless curriculum How to secure an enterprise

WLAN

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WLAN Defenses That Do Not Work

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Common WLAN Defenses

Encrypt transmissions (WEP) Hide my network (Disable

SSID beaconing) Restrict who can join my

network (MAC address filtering)

Use advanced security (WPA)*

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WLAN Defenses That Don’t Work





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WEP Wired equivalent privacy (WEP)

intended to guard confidentiality of data through cryptography

WEP relies on a secret key that is “shared” between device and access point (AP)

Using same (shared) secret key to both encrypt and decrypt is private key cryptography or symmetric encryption

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WEP Objectives

Efficient - Algorithm must be proficient enough to be implemented in either hardware or software

Exportable - Must meet the guidelines set by the U.S. Department of Commence so wireless device using WEP can be exported overseas

Optional - The implementation of WEP in wireless LANs is an optional feature

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WEP Objectives

Reasonably strong - Security of the algorithm lies in the difficulty of determining the secret keys through attacks, which is related to the length of the secret key and the frequency of changing keys. WEP was to be “reasonably” strong in resisting attacks.

Self-synchronizing - Each packet must be separately encrypted (prevents a single lost packet from making subsequent packets indecipherable)

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WEP Keys WEP keys must be a minimum

of 64 bits in length Most vendors add an option to

use a larger 128-bit WEP key for added security (a longer key is more difficult to break)

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WEP Key Creation

64-bit WEP key created by entering 5 ASCII characters (5y7js) or 10 hexadecimal characters (456789ABCD)

128-bit WEP key created by entering 13 ASCII characters (98jui2wss35u4) or 26 hexadecimal characters (3344556677889900AABBCCDDEE)

Passphrase created by entering 16 ASCII characters (marchspringbreak)

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How WEP Works1. Information has cyclic redundancy

check (CRC) checksum value calculated (WEP calls this integrity check value (ICV)) and appends it to end of text

2. WEP default shared secret key combined with initialization vector (IV), a 24-bit value that changes each time a packet is encrypted

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How WEP Works

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How WEP Works3. Default shared secret key and IV are

then entered into an RC4 pseudo-random number generator (PRNG) that creates a random number (output is keystream)

4. Text + ICV and keystream combined through exclusive OR (XOR) to create ciphertext

5. IV pre-pended to ciphertext

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How WEP Works

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WEP Won’t Work WEP creates a detectable pattern for

attackers (weak keys) Attacker who captures packets for

length of time can see the duplication and use it to crack the code

Weakness is with initialization vector (IV), 24-bit value that changes each time a packet is encrypted

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WEP Won’t Work IV is 24-bit number = 16,777,216 possible

values “Expanded” WEP not increase IV AP transmitting at only 11 Mbps can send and

receive 700 packets each second Since different IV used for each packet IVs

start repeating in less than 7 hours Ways to reduce time needed to minutes Some WLANs always start with the same IV

after the system is restarted and then follow the same sequence of incrementing IVs

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WEP Won’t Work RC4 uses a pseudo-random number

generator (PRNG) to create keystream PRNG does not create true random

number but what appears to be (pseudo) random number

First 256 bytes of the RC4 cipher can be determined by bytes in the key itself

RC4 cipher is not considered the most effective cipher for the task

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SSID Beaconing Service Set Identifier (SSID) is

“beaconed” from AP Provides information to wireless

devices wanting to join network Beaconing SSID is default mode Some users disable SSID beaconing

so network not appear on Windows list of available wireless networks

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Disable SSID Beaconing

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Disable SSID Beaconing Won’t

Work SSID is initially transmitted in

cleartext when device negotiating with AP

Attacker only has to watch for any authorized device to negotiate

If attacker cannot capture initial negotiation process can force one to occur

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Force Renegotiation

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Work If SSID suppressed from beacon

frames, still transmitted in other management frames sent by the AP Windows can’t see it Netstumbler can see it

Many users do not change default SSID and these well known; an attacker can try default SSIDs until a connection is accepted

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Work Steps to manually enter SSID on

wireless device that not receive beaconed SSID are inconvenient

Turning off SSID beaconing prevents wireless devices from freely roaming from one wireless network to another

Many access points prohibit or discourage turning off SSID beaconing

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Discourage Turning Off SSID Beaconing

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Work Not uncommon to detect multiple

wireless signals at home or work May received signal with broadcast

SSID and signal where broadcast SSID turned off

If using Windows XP the device will always connect to the access point that is broadcasting its SSID

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MAC Address Filtering

Access control - Intended to limit a user’s admission to the AP (only those authorized able to become part of wireless LAN)

Most common type of access control is Media Access Control (MAC) address filtering (not part IEEE standard)

MAC address is unique 48-bit number “burned” into the network interface card adapter when manufactured

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MAC Address

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MAC Address

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Access to the wireless network can be restricted by entering the MAC address of approved or denied devices

Once the MAC addresses are entered, only specific devices can be authenticated based on MAC address

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MAC Filtering

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MAC Address Filtering Won’t Work

MAC addresses initially exchanged in cleartext between device and access point

MAC address can be “spoofed” Some wireless NICs allow for a

substitute MAC address to be used Programs available that allow users to

spoof MAC address

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MAC Address Filtering Won’t

Work

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WPA Won’t Work* Wi-Fi Protected Access (WPA) Intended to provide enhanced

security using older wireless equipment

Must enter same passphrase on access point and wireless device

Passphrases less than 20 characters subject to offline dictionary attacks

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Wireless Security Solutions

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802.11i By IEEE organization Designed specifically

address WLAN vulnerabilities

Ratified June 2004

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Common Security Models

By Wi-Fi organization Personal Security Model

WPA – Personal WPA2 - Personal

Enterprise Security Model WPA - Enterprise WPA2 - Enterprise

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Personal Security Model - WPA

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Personal Security Model

Designed for single users or small office home office (SOHO) settings of < 10 devices and authentication server unavailable

Personal security model has 2 options WPA – Legacy hardware WPA2 – Newer hardware

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Wi-Fi Protected Access (WPA)

Wi-Fi Alliance introduced Wi-Fi Protected Access (WPA) in October 2003

Subset of 802.11i Addresses encryption &

authentication Designed to enhance security on

older WLAN devices

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Temporal Key Integrity

Protocol (TKIP) WPA replaces WEP with new encryption

Temporal Key Integrity Protocol (TKIP)

TKIP uses 128-bit per-packet key (dynamically generates a new key for each packet and prevents collisions)

TKIP distributes key to client and AP, setting up automated key hierarchy and management system

TKIP dynamically generates unique keys to encrypt every data packet

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TKIP Encryption TKIP strong substitution WEP encryption Instead of replacing WEP engine TKIP

designed to fit into the existing WEP procedure with a minimal amount of change

Device starts with 2 keys, a 128-bit encryption key (temporal key) and 64-bit MIC

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TKIP Encryption1. Temporal key XORed with sender’s MAC

address to create an intermediate Value 1

2. Value 1 then mixed with a sequence number to produce Value 2 (the per-packet key) and then entered into the (PRNG), just as with normal WEP

3. Sender’s MAC address and receiver’s MAC address are all run through a MIC function and creates text with MIC key appended; value is then XORed with keystream to create ciphertext

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TKIP Encryption

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TKIP Key Mixing

WEP constructs a per-packet RC4 key by concatenating a key and packet IV

TKIP per-packet key construction (TKIP key mixing) substitutes temporary (temporal) key for WEP base key and constructs a per-packet key that changes with each packet

Temporal keys have fixed lifetime and are replaced frequently

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IV Sequencing

TKIP reuses the WEP IV field as a sequence number for each packet

Both the transmitter and receiver initialize the packet sequence space to zero whenever new TKIP keys are set, and the transmitter increments the sequence number with each packet it sends

Length of the sequence number (IV) has been doubled, from 24 bits to 48 bits.

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Message IntegrityCheck (MIC)

WPA replaces Cyclic Redundancy Check (CRC) with Message Integrity Check (MIC), designed to prevent an attacker from altering packets

Attacker can modify a packet and the CRC, making it appear that the packet contents were the original

Receiver and transmitter each compute and then compare the MIC

If not match, the data is assumed to have been tampered with and the packet is dropped

Optional countermeasure all clients are de-authenticated and new associations are prevented for one minute if MIC error occurs

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Pre-Shared Key (PSK) Authentication

WPA authentication can be accomplished by either authentication server or pre-shared key (PSK)

Passphrase (the PSK) is manually entered to generate encryption key on AP and devices in advance

PSK not used for encryption but instead serves as the starting point (seed) for generating the encryption keys

Disadvantage of key management: key must be created and entered in any device (“shared”) prior to (“pre”) communicating

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Wi-Fi Protected Access (WPA)

Designed to enhance security on older WLAN devices

Should only be used if devices cannot support WPA2

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Personal Security Model – WPA2

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Wi-Fi Protected Access 2 (WPA2)

Wi-Fi Alliance introduced Wi-Fi Protected Access 2 (WPA2) in September 2004

WPA2 based on the final IEEE 802.11i WPA2 uses AES for data encryption and

supports authentication server or PSK technology

WPA2 allows both AES and TKIP clients to operate in the same WLAN; IEEE 802.11i only recognizes AES

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AES AES algorithm processes blocks of 128 bits,

yet the length of the cipher keys and number of rounds can vary, depending upon the level of security that is required

Available key lengths are of 128, 192 and 256 bits, and the number of available rounds are 10, 12, and 14

Only the 128-bit key and 128-bit block are mandatory for WPA2

It is recommended that AES encryption and decryption be performed in hardware because of the computationally intensive nature of AES

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AES Security

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How To Make a Home Wireless LAN

Secure

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Steps Protect Personal Wireless

Install Microsoft Hot Fix (KB893357) Turn on WPA2

On older equipment use WPA MUST use 20+ character WPA passphrase

Turn on wireless VLAN If want to deter “casual” users

Use MAC address filtering Use unidentifiable SSID Turn off SSID beaconing

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Set WPA2 on AP

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Set WPA2 on AP

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Set WPA2 on Device

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Show WPA2

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Turn on VLAN

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Secure Easy Setup

Collaboration between Linksys and Broadcom Activate WPA security “at the push of a button” Automatically configures custom SSID and

enables WPA dynamic key encryption settings No need to manually enter a passphrase or key Two step process

Push the SES button on access point Click the START SES button on client

To add more wireless devices to network simply push the button on the router again to repeat process

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Secure Easy Setup

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Contents of Wireless Curriculum

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Wireless Curriculum CompTIA dropped proposed

Wireless+ certification Most popular wireless certifications

from CWNA (Planet3) Wireless# Certified Wireless Network Administrator Certified Network Security Professional

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Course Technology Wireless Textbooks

Guide to Wireless Communications 2ed (Wireless#) – May 2006

CWNA Guide to Wireless LANs 2ed (CWNA) – August 2005

CWSP Guide to Wireless Security 1st (CWSP) – August 2006

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Enterprise Security Model – WPA &

WPA2

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Enterprise Security Model

Designed for medium to large-size organizations such as businesses, government agencies, and universities with authentication server

The personal security model has 2 options: WPA & WPA2 (older equipment may be forced to implement WPA, while newer equipment can support WPA2)

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802.1x IEEE 802.11i authentication and key

management uses IEEE 802.1x (originally developed for wired networks)

802.1x port security (device requests access to network prevented from receiving any traffic until its identity can be verified)

802.1x blocks all traffic on port-by-port basis until the client is authenticated using credentials stored on authentication server

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802.1x Authentication

The supplicant is device which requires secure network access and sends request to an authenticator that serves as an intermediary device (authenticator can be an access point on a wireless network or a switch on a wired network)

The authenticator sends request from supplicant to authentication server, which accepts/rejects the supplicant’s request and sends that information back to the authenticator, which in turn grants or denies access to the supplicant

Strength of the 802.1x protocol is that supplicant never has direct communication with authentication server

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802.1x1. Device requests from AP permission to join

WLAN 2. AP asks device to verify its identity3. Device sends identity information to AP,

which passes encrypted information to authentication server

4. Authentication server verifies/rejects client’s identity and returns information to AP

5. Approved client now join the network

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802.1x

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802.1x Supplicant Supplicant, required on the wireless device,

is software that is installed on the client to implement the IEEE 802.1x protocol framework

Supplicant software may be included in client operating system, integrated into device drivers, or installed as third-party “standalone” software

Some vendors of wireless NICs supply supplicant with their cards

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Authentication Server

Authentication server stores the list of the names and credentials of authorized users

Wireless user credentials may also be stored in an external database, such as Structured Query Language (SQL), Lightweight Directory Access Protocol (LDAP), or Microsoft Active Directory

Typically a Remote Authentication Dial-In User Service (RADIUS) server is used

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RADIUS Request is first sent to authenticator, which

relays the information (username, password, type of connection) to RADIUS server

Server first determines if AP itself is permitted to send requests

RADIUS server attempts to find the user’s name in its database

Then applies the password to decide whether access should be granted to this user

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Encryption Once authenticated by IEEE 802.1x

same protocol next provides the wireless device a unique encryption key called the MK

From single key all the necessary encryption keys for encrypted communication can then be created

Keys can also be changed during a session

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Encryption Eliminates difficulties and potential

dangers associated with PSK Each user has a unique key Keys remain strong and require no

management Adding additional APs only requires

that the newly installed APs connect to the existing authentication server

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Extensible Authentication Protocol (EAP)

EAP-Transport Layer Security (EAP-TLS) - Requires the use of certificates to validate a supplicant and supported by Microsoft and included in Microsoft Windows XP and Windows Server 2003

Lightweight EAP (LEAP) - Propriety standard supported by Cisco; LEAP provides authentication based on the Windows username and password logon (certificates are not required)

EAP-TunneledTLS (EAP-TTLS) - Supports advanced authentication methods such as using tokens

Protected EAP (PEAP) - Uses certificates similar to Secure Sockets Layer (SSL) with Web browsers; supplicant presents a certificate to the authentication server (via the authenticator) but does not require a certificate from the server in return

Flexible Authentication via Secure Tunneling (FAST) - Most recent variation; can set up a tunnel without checking digital certificates and also support tokens

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Enterprise Security Model

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Mark Ciampa

Western Kentucky University

[email protected]

1 Wireless Security Update Mark Ciampa Western Kentucky University [email protected].

Documents

wireless security easier

wireless security matter

wireless security attitudes

wireless device

wireless lans

wireless network attackers

wireless transmissions

strong security