Mobile and Wireless Communication Security

By Jason Gratto

WEP (Wired Equivalent Privacy)

Intended to provide confidentiality Key size:40 bits Key distribution: Manual Meant to protect wireless communication

from eavesdropping Also meant to prevent unauthorized access

to wireless network

Goals of WEP

Access Control Data Integrity Confidentiality

Protocol of WEP

Uses a secret key between the computer and the access point– The secret key is used to encrypt the packets– No standard for sharing the key but in practice a

single key is shared between all of the computers and access points.

WEP - Procedure

Generates a checksum Generates a keystream with a chosen IV

(Initialization Vector) v with RC4 XOR between message/checksum and the

keystring Transmits the v and the ciphertext

WEP – Procedure

WEP - Defenses

Integrity Check (IC)– Used to ensure packet wasn’t modified in transit

Initialization Vector (IV)– Used to avoid encrypting two ciphertexts with the

same key stream– Used to augment the shared key and produce a

different RC4 for each packet

WEP – Vulnerabilities

ICV insecure– ICV is a algorithm for creating the checksum, based on

CRC32 and can be modified to match the contents of the message.

IV key reuse– Because a small IV value is used, IV values end up being

reused, compromising the security.

Authentication forging– Using a recovered key stream and IV the authentication can

be forged.

WEP – Attack types

Passive– Eavesdropping on wireless traffic

Active– Constructing it’s own encrypted packets when plaintext is

known Active from both sides

– Constructing it’s own encrypted packets when only header is known by guessing.

Dictionary building– Computing the key stream using a decryption table

Wi-Fi Protected Access (WPA)

Key size: 128 bits Hash method: ICV, MICHAEL Key distribution: TKIP (Temporal Key Integral

Protocol) Inclusion of EAP certification for enterprise

versions of WPA

MICHAEL

MICHAEL generates a MIC (Message Integrity Code)– 8 bits long– Placed between the data and the ICV

TKIP

Made to address security problems with WEP

Looks to client’s configuration to determine what kind of key to use

Sets a unique default key for each client

TKIP - Defenses

Implements a key mixing function that combines a secret key with an IV before performing RC4 initialization

If packets are received out of order, they are rejected by the access point

Implements the MICHAEL integrity check to prevent forged packets from being accepted

Extensible Authentication Protocol (EAP)

Is a transmission method and framework for authentication protocols– Works with many other authentication protocols

such as RADIUS and Kerberos

Uses a variety of different transport methods

EAP

Originally designed for wired connections– To be used in a wireless environment, the

“tunneled” EAP method was created, wrapping the EAP in a stronger encrypted EAP

Common transport methods– EAP-TLS (Transport Layer Security)– EAP-TTLS (Tunneled Transport Layer Security)– PEAP (Protected EAP)– LEAP (Light EAP)

EAP Types

PEAP– Interior MSCHAPv2 inside a secure TLS tunnel

EAP-TTLS– Interior EAP-MD5 inside a secure TLS tunnel

LEAP– Modified version of MSCHAP– Vulnerable to dictionary attacks

WPA –Vulnerabilities

Denial of Service– Any time forged and unauthorized data is

detected, it shuts the access point down for 60 seconds

Because of this it is easy to shut down access points using little network activity

WPA2

Updated version of WPA Uses AES encryption and allows use of

RADIUS (Remote Authentication Dial In User Service) authentication protocol

RADIUS

Protocol for communication between Network Access Server (NAS) and a remote authentication server

Requires clients and servers

RADIUS

Data needed for authenticaiton– User data

IP Name or address Shared secret key

– User information Username and password

– Session information Speed, port, NAS ID

RADIUS – Database

The database can be stored in a number of different ways– A text file– Password file– Netware directory

The database can authenticate in a number of ways as well– Username/password– SecurID Token Card

RADIUS

After authentication is requested, the RADIUS server either accepts or rejects the NAS based on the following– Session timers– Filters– IP Address– IDSN Session Parameters

RADIUS

ISP User Database

ISP Modem Pool

User dials modem pool and establishes connection

UserID: bobPassword: ge55gep

UserID: bobPassword: ge55gepNAS-ID: 207.12.4.1

Select UserID=bob

Bobpassword=ge55gepTimeout=3600[other attributes]

Access-AcceptUser-Name=bob[other attributes]

Framed-Address=217.213.21.5

The Internet

ISP RADIUS Server

Internet PPP connection established

ISP User Database

ISP Modem Pool

User dials modem pool and establishes connection

UserID: bobPassword: ge55gep

UserID: bobPassword: ge55gepNAS-ID: 207.12.4.1

Select UserID=bob

Bobpassword=ge55gepTimeout=3600[other attributes]

Access-AcceptUser-Name=bob[other attributes]

Framed-Address=217.213.21.5

The Internet

ISP RADIUS Server

Internet PPP connection established

Sources

http://www.cs.fsu.edu/~yasinsac/group/slides/cubukcu.pdf

http://islab.oregonstate.edu/koc/ece478/05Report/Kalina.ppt

http://its.ndsu.edu/fileadmin/www.its.ndsu.edu/pdfs/Wireless_EAP.pdf

http://www.ceenet.org/workshops/lecture98/richard/2-radius/index.htm