Wireless Networking Designing and Implementing WLAN Security Module-11 Jerry Bernardini Community College of Rhode Island 6/28/20151Wireless Networking

Wireless Networking

Designing and Implementing WLAN Security

Module-11

Jerry BernardiniCommunity College of Rhode Island

04/18/23 1Wireless Networking J. Bernardini

Presentation Reference Material• CWNA Certified Wireless Network Administration

Official Study Guide, Fourth Edition, Tom Carpenter, Joel Barrett– Chapter-10, pages475-525

• Cisco White Paper - A Comprehensive Review of 802.11 Wireless LAN Security and the Cisco Wireless Security Suite

www.cisco.com/warp/public/cc/pd/witc/ao1200ap/prodlit/wswpf_wp.htm

• Your 802.11 Wireless Network has No Clothes¤– William A. Arbaugh, Narendar Shankar, Y.C. Justin Wan, Department of

Computer Science University of Maryland College Park, Maryland 20742 March 30, 2001

– http://www.cs.umd.edu/~waa/wireless.pdf

04/18/23 Wireless Networking J. Bernardini 2

http://www.cisco.com/warp/public/cc/pd/witc/ao1200ap/prodlit/wswpf_wp.htm

http://www.cisco.com/warp/public/cc/pd/witc/ao1200ap/prodlit/wswpf_wp.htm

http://www.cs.umd.edu/~waa/wireless.pdf

Early IEEE 802.11 Security

• Referred to as: Pre-RSNA Security– RSNA=Robust Security Network Association

• Pre-RSNA Security includes– Open System Authentication– Share Key Authentication– Wired Equivalent Privacy

• This technology has many flaws and should not be considered for new systems

• But we should understand Pre-RSNA to appreciate WLAN vulnerabilities


CCRI J. Bernardini 4

Open Authentication

• Open authentication allows any device network access.

• If no encryption is enabled on the network, any device that knows the SSID of the access point can gain access to the network.

• With WEP encryption enabled on an access point, the WEP key itself becomes a means of access control.


802.11 client authentication process• 1. Client broadcasts a probe request frame on every channel• 2. Access points within range respond with a probe response frame• 3. The client decides which access point (AP) is the best for access and sends an

authentication request• 4. The access point will send an authentication reply• 5. Upon successful authentication, the client will send an association request frame to the

access point• 6. The access point will reply with an association response• 7. The client is now able to pass traffic to the access point


Open Authentication Vulnerabilities

• No way for the access point to determine whether a client is valid.

• A major security vulnerability if WEP or better encryption is not implemented– Cisco does not recommend deploying wireless LANs without WEP encryption.

• When WEP encryption is not needed or is not feasible to deploy - such as public WLAN deployments

• Higher-layer authentication can be provided by implementing a Service Selection Gateway (SSG).


Shared Key Authentication1. The client sends an authentication request to the access point requesting shared

key authentication2. The access point responds with an authentication response containing challenge

text3. The client uses its locally configured WEP key to encrypt the challenge text and

reply with a subsequent authentication request4. If the access point can decrypt the authentication request and retrieve the original

challenge text, then it responds with an authentication response that grants the client access


Vulnerability of Shared Key Authentication

Wired Equivalent Privacy-WEP

• Wired Equivalent Privacy, a security protocol for WLANs defined in the 802.11b standard.

• A secret key is shared between STAs and an AP• The secret key is used to encrypt packets (MSDU)

before they are transmitted.• LANs are inherently more secure than WLANs• WLANs are over radio waves and can be intercepted

WEP uses RC4

• It is reasonably strong:• It is self-synchronizing:• WEP is self-synchronizing for each message. This property is

critical for a• data-link level encryption algorithm, where “best effort”

delivery is assumed and packet loss rates may be high.• It is efficient:• The WEP algorithm is efficient and may be implemented in

either hardware or software.• It may be exportable:


What is RC4

• RC4 is a stream cipher designed by Ronald L. Rivest (MIT Professor) for RSA Data Security (now RSA Security).

• It is a variable key-size stream cipher with byte-oriented operations.

• The algorithm is based on the use of a random permutation. Analysis shows that the period of the cipher is overwhelmingly likely to be greater than 10100.

• Eight to sixteen machine operations are required per output byte, and the cipher can be expected to run very quickly in software.

• Independent analysts have scrutinized the algorithm and it is considered secure.



Correct WEP Key Required

• If a device does not have the correct WEP key, even though authentication is successful, the device will be unable to transmit data through the access point.

• Neither can it decrypt data sent from the access point

WEP Encryption Process

PRNG

Integrity Algorithm

Ciphertext

IVInitializationVector (IV)

Secret Key

Seed

Plaintext

IntegrityCheck

Value (ICV)

C1

C2Exclusive-OR

Key Stream

What is Transmitted

Pseudorandom Number

Generator

802.11 recommends IV change per-framesame packet is transmitted twice resulting cipher-text will be different


Initialization Vector• The IV is a 24-bits that augments a 40-bit WEP key to 64 bits and

a 104-bit WEP key to 128 bits. • The IV is sent in the clear in the frame header so the receiving

station knows the IV value and is able to decrypt the frame • Although 40-bit and 104-bit WEP keys are often referred to as 64-

bit and 128-bit WEP keys, the effective key strength is only 40 bits and 104 bits, respectively, because the IV is sent unencrypted.


1 0 1 1 1 0 0 1 0 1 1 1 0 1 0 1 1 0 0 1 1 1 1 0 1

1 1 1 1 0 1 1 0 0 1 1 1 1 0 1 0 1 0 1 0 1 1 1 0 1

0 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 0

Data

Key Stream

Cipher Stream (Transmitted and Received)

1 1 1 1 0 1 1 0 0 1 1 1 1 0 1 0 1 0 1 0 1 1 1 0 1

Key Stream

1 0 1 1 1 0 0 1 0 1 1 1 0 1 0 1 1 0 0 1 1 1 1 0 1

Data


IV4

Data PDU>=1

ICV4

Init. Vector3

The WEP Encrypted Frame Body

1 OctetPad

6-bitsKey ID2-bits

Encrypted

WEP Keys

• 802.11b – 64-bit shared RC4 Key. 24-bit IV plus a 40-bit Secret Key.

• 128-bit shared RC4 Key24-bit IV plus a 104-bit Secret Key.

• 152-bit shared RC4 Key24-bit IV plus a 128-bit Secret Key.

IV24 - bits

Secret Key40 - bits

PRNG Seed

0 23|24 63

WEP Weaknesses• Key management and key size.

40-bit• The IV is too small. 24-bit = 16,777,216 different cipher streams.• The ICV algorithm is not appropriate

Uses CRC-32 when MD5 or SHA-1 would be better.

• Authentication messages can be easily forged.


Initialization Vector Replay Attacks• 1. A known plain-text message is sent to an

observable wireless LAN client (an e-mail message)

• 2. The network attacker will sniff the wireless LAN looking for the predicted cipher-text

• 3. The network attacker will find the known frame and derive the key stream

• 4. The network attacker can "grow" the key stream using the same IV/WEP key pair as the observed frame

• This attack is based on the knowledge that the IV and base WEP key can be reused or replayed repeatedly to generate a key stream large enough to subvert the network.


Block Cipher Operation

• Block ciphers deal with data in defined blocks• The block cipher fragments the frame into blocks of predetermined size and performs the

XOR function on each block. • Each block must be the predetermined size, and leftover frame fragments are padded to the

appropriate block size


Electronic Code Book Encryption

• The process of encryption described stream ciphers and block ciphers is known as Electronic Code Book (ECB) mode encryption.

• With ECB mode encryption, the same plain-text input always generates the same cipher-text output. • The Figure illustrates, the input text of "FOO" always produces the same cipher-text. • This is a potential security threat because eavesdroppers can see patterns in the cipher-text and start

making educated guesses about what the original plain-text is.

There are two encryption techniques to overcome this issue:•Initialization vectors•Feedback modes


Feedback Modes Encryption Process

• Feedback modes are modifications to the encryption process to prevent a plain-text message from generating the same cipher-text during encryption.

• Feedback modes are generally used with block ciphers, and the most common feedback mode is known as cipher block chaining (CBC) mode.

• The premise behind CBC mode is that a plain-text block has the XOR function performed with the previous block of cipher-text.

• Because the first block has no preceding cipher-text block, an IV is used to change the key stream.


"Growing" a Key Stream Attack • Once a key stream has been derived for a given

frame size, it can be "grown" to any size required. • 1. The network attacker can build a frame one

byte larger than the known key stream size; an Internet Control Message Protocol (ICMP) echo frame is ideal because the access point solicits a response

• 2. The network attacker then augments the key stream by one byte

• 3. The additional byte is guessed because only 256 possible values are possible

• 4. When the network attacker guesses the correct value, the expected response is received: in this example, the ICMP echo reply message

• 5. The process is repeated until the desired key stream length is obtained

RSNA Security

• Robust Security Network Association• IEEE 802.11. Clause 8 (previously IEEE 802.11i)• TKIP and RC4• CCMP and AES• IEEE 802.1X• Preshared Keys• Certificates and PACs• Four way Handshake• Key Hierarchies• Transition Security Network04/18/23 Wireless Networking J. Bernardini 24

IEEE 802.11, Clause 8


Discusses and defines the following issues

Temporal Key Integrity Protocol - TKIP• Part of the IEEE 802.11i encryption standard for wireless LANs

(Pronounced tee-kip )

• TKIP is the next generation of WEP (initially call WEP2). • Provides per-packet key mixing, a message integrity check and

a re-keying mechanism, thus fixing the flaws of WEP. • TKIP Process

– begins with a 128-bit "temporal key" shared among clients and access points– Combines the temporal key with the client's MAC address and then adds a relatively

large 16-octet initialization vector to produce the key that will encrypt the data. – This procedure ensures that each station uses different key streams to encrypt the data.

• Older WEP based devices can be upgraded to TKIP and not processor intensive

CCMP and AES

• Counter Mode with Cipher Block Chaining-Message Authentication Code (CCMP)

• CCMP uses Advanced Encryption Standard (AES) instead of RC4 algorithm

• CCMP/AES uses 128-bit encryption, encrypts 128-bit blocks, uses 8-bytes integrity check

• AES is very processor intensive• Not upgradable for older devices


Advanced Encryption Standard - AES

• Relatively new U.S. National Institute of Standards and technology (NIST) for single-key encryption; approved in 2002.

• 16-byte Block Cipher based on Rijndael – (pronounced “Rain Doll”)

• Key Lengths of 128, 192, and 256-bit• Time to brute-force break an AES 256-bit key… several years.• AES Encryption is a four step process

http://en.wikipedia.org/wiki/Advanced_Encryption_Standard

AES Four Steps


1

2

3

4

http://en.wikipedia.org/wiki/Advanced_Encryption_Standard

802.1X and EAP• IEEE’s 802.1X Port Based Network Access Control

standard provides strong authentication and network access control for 802.11 networks.

• Extensible Authentication Protocol (EAP) is used to pass authentication information between the supplicant and the AS.

1

Supplicant Authenticator Authentication Server


802.1X Requires Three Entities:• The supplicant-—Resides on the wireless LAN client• The authenticator-—Resides on the access point• The authentication server—Resides on the RADIUS server


Cisco Wireless Security Suite and 802.1X

• authentication framework—The IEEE 802.1X standard provides a framework for many authentication types and the link layer

• Extensible Authentication Protocol (EAP) Cisco authentication algorithm—The EAP Cisco Wireless authentication type, also called Cisco LEAP supports centralized, user-based authentication with the ability to generate dynamic WEP keys

• Temporal Key Integrity Protocol (TKIP)—Cisco has implemented two components to augment WEP encryption:

– Message Integrity Check (MIC)—The MIC function provides effective frame authenticity to mitigate man-in-the-middle vulnerabilities

– Per-Packet Keying—Per-packet keying provides every frame with a new and unique WEP key that mitigates WEP key derivation attacks

• Broadcast Key Rotation—Dynamic key rotation

Four-Way Handshake


•Used to establish temporary transient keys with AP•Four-packet exchange

1.Number used once (Anounce)2.Supplicant nounce (Snounce)3.Authenticator Nounce4.Message Integrity Check (MIC)

IPsec VPN (Secure Your Wireless with Ipsec by Dan Langille 10/21/2004 )

• IPsec is short for IP security• It is a set of protocols for securely exchanging packets at the

IP layer. – VPNs frequently use it. can use the same approach to secure our wireless network.

• uses shared secrets to encrypt data. • uses security policies to decide what types of traffic to

encrypt between which hosts.• IPsec can create a point-to-point tunnel between two hosts. • IPsec cannot exist on its own -need to have IPsec at both ends• IPsec uses a database to decide how to treat traffic.

– The two main types of rules are policy and association.– Security Policy Database (SPD) determines what traffic IPsec should handle. – Security Association Database (SAD) specifies how to encrypt that traffic.


http://www.onlamp.com/pub/au/1422

http://beta.freebsddiary.org/pipsecd.php

Wireless VPNs

• Virtual Private Networks, or VPNs, use publicly accessible or wireless network infrastructures combined with private connections to securely exchange private applications and data.

• All VPN systems use encryption and other security mechanisms to ensure that only authorized users can access the network, so that the data cannot be intercepted.

Wireless Gateways

• A network device or base station, usually providing shared network access, firewall security and encryption.

• An Access Point, LAN Switch, Firewall, and WAN Interface in one enclosure.

WPA

• There are 2 modes of WPA and WPA2 certification—Enterprise and Personal

WPA WPA2Enterprise Mode(Business & Government)

Authentication: IEEE 802.1X/EAP

Encryption: TKIP/MIC

Authentication: IEEE 802.1X/EAP

Encryption: AES-CCMP

Personal Mode(Personal & SOHO)

Authentication: PSK

Encryption: TKIP/MIC

Authentication: PSK

Encryption: AES-CCMP

WPA & WPA2, 7-steps

• The 7 steps are: • Step 1: Security Mechanism and Credentials • Step 2: User Authentication Database • Step 3: Client Operating Systems • Step 4: Supplicants • Step 5: EAP Types (EAP-TTLS) • Step 6: Authentication Server • Step 7: Access Points and Client NIC Cards

Example of a WPA2

• Windows 1. Security Credentials: Digital Certificate X.509 2. Database: Microsoft Active Directory 3. Client OS: Windows XP 4. Supplicant: Built into Windows XP for EAP-TLS 5. Authentication EAP Type: EAP-TLS 6. Authentication Server: Cisco Secure Access Control Server (RADIUS server) 7. Access Points and Client Devices: WPA2-Enterprise Wi-Fi CERTIFIED

WPA Deployment

Access Points

Wired LAN

1 2

AuthenticationDatabase

WirelessClients

AP-1

Radius Server802.1X EAP Type

Support for802.1X EAP TypeTKIP

WiFi Cert with WPA802.1X EAP TypeSupplicant for EAP & OSTKIP Encryption

Corporate Security Policy

• Develop a wireless security policy to define what is and what is not allowed with wireless technology.

• Know the technologies and the users that use the network.

• Measure the basic field or illumination coverage of the wireless network.

• Physical Security

Corporate Security Policy

• Set base lines and perform audits/monitoring of the network.

• Harden AP’s, servers, and gateways.• Determine level of security protocols

and standards.• Consider using switches, DMZ, RADIUS

servers, and VPN.• Update firmware and software.

To Secure the WLAN

• If possible, put the wireless network behind its own routed interface so you can shut it off if necessary.

• Pick a random SSID that gives nothing about your network away.

• Use WPA or have your broadcast keys rotate every ten minutes.

• Use 802.1X for key management and authentication – Look over the available EAP protocols and decide which is

right for your environment. – Set the session to time out every ten minutes or less.

Security Solutions

802.1XAuthentication

MICMessage Integrity

Checking

TKIPTemporal Key Integrity

Protocol

Cipher andAuthentication

Negotiation

KeyManagement

AESAdvanced Encryption

Standard

WPA / WPA2Wi-Fi Protected

Access

802.11i


Service Set Identifier Myth

• The SSID is a construct that allows logical separation of wireless LANs.

• A client must be configured with the appropriate SSID to gain access to the wireless LAN.

• The SSID does not provide any data-privacy functions, nor does it truly authenticate the client to the access point.


MAC Address Authentication

• MAC address authentication is not specified in the 802.11 standard• Many vendors—including Cisco—support it. • MAC address authentication verifies the client's MAC address against a locally configured list

of allowed addresses or against an external authentication server

• MAC authentication is used to augment the open and shared key authentications provided by

802.11


MAC Address Authentication Vulnerabilities Myth

• MAC addresses are sent in the clear as required by the 802.11 specification. • In wireless LANs that use MAC authentication, a network attacker might be

able to subvert the MAC authentication process by "spoofing" a valid MAC address.

• MAC address spoofing is possible in 802.11 network interface cards (NICs) that allow the universally administered address (UAA) to be overwritten with a locally administered address (LAA).

• A network attacker can use a protocol analyzer to determine a valid MAC address in the business support system (BSS) and an LAA-compliant NIC with which to spoof the valid MAC address.


Authentication Vulnerabilities with SSID

• The SSID is advertised in plain-text in the access point beacon messages Although beacon messages are transparent to users

• Eavesdropper can easily determine the SSID with WLAN packet analyzer• Some access-point vendors, offer the option to disable SSID broadcasts in the beacon

messages. • The SSID can still be determined by sniffing the probe response frames from an access point• Disabling SSID broadcasts might have adverse effects on Wi-Fi interoperability for mixed-

client deployments.


Wireless Security SummarySecurity Model Authentication Encryption Security

Level

Transitional (only a temporary

solution)

Shared Key – Up to four WEP keys should be rotated between clients

SSID Beaconing – turn off if AP permits and or cryptic name SSID

MAC Address Filtering – Pre-approved at the AP and no guests

WEP – Even 128-bit WEP has vulnerabilities. 16 ASCII passphasing generate predictable keys and should be discouraged. Only secure against Script-kiddies and casual eavesdroppers.

Low

WPA Personal (ten or fewer devices)

PSK – Manually entered and used as starting seed for encryption generation

Must be entered in both the AP and client

TKIP – Is strong than WEP but uses same hardware. TKIP has three components. MIC to prevent forgeries; the IV is increased from 24 to 48-bits and changed for each packet; TKIP key mixing generates keys that are replaced frequently.

Medium

WPA2 Personal PSK – Keys are automatically changed after set number of packets.

AES-CCMP – Superior to TKIP and based on the 802.11i standard. Produces 128-bit blocks with 128 to 256-bits. Computation intensity strongly suggests hardware processing.

Med/High

WPA Enterprise 802.1x – Port based authentication employing a Supplicant (client), an Authenticator (server isolating client and RADIUS) and Authentication Server (RADIUS).

TKIP – Same as WPA2 Personal High/Med

WPA2 Enterprise 802.1x – Same as WPA Enterprise AES-CCMP - Same as WPA2 Personal High/High


Wireless Security Terms

• SSID –Service Set Identifier• WPA –Wi-Fi Protected Access• WEP- Wired Equivalent Privacy• PSK –Pre-Shared Key• TKIP –Temporal Key Integrity Protocol• MAC –Media Access Control• MIC –Message Integrity Check• AES –Advanced Encryption Standard• CCMP -Counter Mode CBC-MAC Protocol• RADIUS –Remote Dial-In User Service

Documents

Wireless Networking Designing and Implementing WLAN Security Module-11 Jerry Bernardini Community College of Rhode Island 6/28/20151Wireless Networking