Wireless LAN Security

Presented by:

Pallavi PriyadarshiniStudent ID 003503527

Agenda

Brief background on Wireless LAN Basic security mechanisms in 802.11 WEP Vulnerabilities Enhancing wireless security with

WPA Comparing WEP and WPA Conclusion

Brief Background A local area network (LAN) with no wires Several Wireless LAN (WLAN) standards

802.11 - 1-2 Mbps speed, 2.4Ghz band 802.11b (Wi-Fi) – 11 Mbps speed, 2.4Ghz band 802.11a (Wi-Fi) - 54 Mbps speed, 5Ghz band 802.11g (Wi-Fi) – 54 Mbps speed, 2.4Ghz band

Wireless network components

Security Challenges and Solutions

Challenges Beyond any physical boundaries Encryption, Authentication and Integrity

Basic Security Mechanisms in 802.11 Service Set ID (SSID) – Acts like a shared

secret, but sent in clear. MAC Address Lists – Modifiable and also sent in

clear. The WEP Algorithm

More on WEP Stands for Wired Equivalent Privacy Designed to encrypt data over radio

waves Provides 3 critical pieces of security

Confidentiality (Encryption) Authentication Integrity

Uses RC4 encryption algorithm Symmetric key stream cipher 64-bit shared RC4 keys, 40-bit WEP key, 24-

bit plaintext Initialization Vector (IV)

WEP Encryption and Integrity

IV

Secret Key

Seed PRNGXOR

IV

Ciphertext

PlaintextCRC-32

Algorithm

Integrity Check value

Plaintext

KeySequence

Message

PRNG – RC4 Pseudorandom number generation algorithm

Data payload

WEP Authentication

2 levels of authentication “Open” : No authentication “Shared secret” :

Sta

tion

A

Sta

tion

B

Nonce N

E(N, KA-B)

Request for shared key auth.

Authentication response

WEP – The “flawed” Solution Weakness in key management

Single key for all access points and client radios Static unless manually changed Authentication and encryption keys are the same

Shared key authentication failure No knowledge of secret to gain network access WEPPR=C P (where C, P are passively recorded)

Atta

cker

AP

Authentication request

Challenge R

WEPPR R

Success

WEP – The “flawed” Solution (contd.) Weakness in Encryption

Short 24-bit IV, reuse mandatory Weak per-packet key derivation - exposes RC4

protocol to weak key attacks. Given c1 and c2 with same IV, c1 c2= p1p2 [p1 S p2 S], leading to statistical attacks to recover plaintexts

Short 40-bit encryption scheme No forgery protection

Using CRC-32 checksum possible to recompute matching ICV for changed data bits

Given C= RC4(IV, key) <M, ICV(M)>, can find C’ that decrypts to M’=M+Δ such that C’= RC4(IV, key) <M’, ICV(M’)>

WEP – The “flawed” Solution (contd.)

No protection against replays Optional, mostly not turned on by

users

Design Constraints

WEP patches will rely entirely on software upgrade

Access points have little spare CPU capacity for new functions

Encryption functions are hard-wired in the access points

Enhancing WLAN Security with WPA WPA - Wireless Protected Access Strong, standards based, interoperable

security for Wi-Fi Addresses all known weaknesses of WEP Subset of forthcoming IEEE 802.11i

standard Designed to run as a software upgrade

on most Wi-Fi certified products.

Security Mechanisms in WPA - TKIP Uses TKIP (Temporal Key Integrity Protocol)

Encryption. Suite of algorithms wrapping WEP Adds 4 new algorithms to WEP:

1. New cryptographic message integrity code (MIC) called Michael - to defeat forgeries

2. New IV sequencing discipline - to remove replay attacks

3. A re-keying mechanism – to provide fresh encryption and integrity keys

More on TKIP

4. A per-packet key mixing function • Phase 1 (Eliminates same key use by all links) -

Combines MAC address and temporal key. Input to S-box to produce intermediate key

• Phase 2 (De-correlates IVs and per-packet keys) - Packet sequence number encrypted under the intermediate key using a fiestel cipher to produce 128-bit per packet key.

TKIP leverages 802.1X/EAP framework for key management

802.1X/EAP Architecture

Supplicant(wireless client)

Authenticator(AP)

AuthenticationServer (RADIUS)

EAP-start

EAP-identity request

EAP-identity response

EAP success/reject

EAP success/reject

WPA Modes of Operation - Pre-shared key vs. Enterprise Pre-shared Key Mode for home/SOHO

users Does not require authentication server “Shared Secret” or password entered

manually in the AP and wireless client. WPA takes over automatically. Only the clients with matching passwords are

allowed to join the network. The password automatically kicks off the TKIP

encryption process. Enterprise Mode for corporate users

Requires an authentication server like RADIUS Centralized management of user credentials

WPA modes of operation – Enterprise Mode

Wired Network Services

Internet

Authentication server

Access Point

WEP vs. WPA

WEP WPAEncryption Flawed Fixes all WEP flaws

40-bit keys 128-bit keys

Static-same keys used by everyone on network

Dynamic session keys. Per-user, per-session, per-packet keys

Manual distribution

Automatic Distribution

Authentication

Flawed, uses WEP key itself

Strong user authentication using 802.1X and EAP

Comparing WPA and 802.11i

802.11i

802.1X

Key management

Cipher & Authentication negotiation

TKIP

AES

WPA

Conclusion WPA is not an ideal security protocol

design… However, it is a dramatic improvement in

Wi-Fi security. Has not been broken (yet). Protects the original hardware investment. If hardware constraint removed, a more

robust security solution possible. Such a solution is being developed based

on a even stronger cryptographic cipher - Advanced Encryption Standard (AES).

References

[1] Bruce Potter & Bob Fleck, “802.11 Security”, O-Reilly, December 2002

[2]James larocca & Ruth larocca, “802.11 Demystified”, McGraw-Hill Telecom, 2002

[3]Whitepaper on Wireless LAN Security on http://www.wi-fi.org

[4]http://www.ieee802.org/1/pages/802.1x.html