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Wireless Security Research with focus on PEAP/TTLS Design and Implementation. Based on Nirmala Bulusu’s Master Thesis. Outline of the Talk. Introduction WLAN, RADIUS, EAP, TLS,TTLS, PEAP Design and Implementation of PEAP Module for Free RADIUS Performance Comparison of PEAP and TTLS

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wireless security research with focus on peap ttls design and implementation

Wireless Security Researchwith focus on PEAP/TTLS Design and Implementation

Based on Nirmala Bulusu’s Master Thesis

outline of the talk
Outline of the Talk
  • Introduction
  • Design and Implementation of PEAP Module for Free RADIUS
  • Performance Comparison of PEAP and TTLS
  • Conclusion and Future Work





Wireless Network

Wired Ethernet Network

Wireless Network

Access Point

Why Wireless Networking


  • No "plug ins"
  • Increased Productivity
  • Easier network expansion
  • Flexibility and
  • Lowers the cost of ownership
  • Use unlicensed band
  • Vulnerabilities
  • Unauthorized user access
  • Eavesdropping (network can be tapped using sniffing tools)
war driving
War Driving

A directional antenna fashioned from a Pringles can is used to search for unsecured access points.


Parking Lot Attack

secure tunnels
Secure Tunnels

The Extensible Authentication Protocol (EAP) uses encryption to create a “tunnel” for data confidentiality.






















IEEE 802.1x - Architecture

  • IEEE 802.1x is a port-based network access control solution to authenticate every network user accessing the LAN services.
  • It defines an encapsulation technique that allows for the transmission of EAP packets between the Supplicant and Authenticator in the LAN environment.

EAP- Tunneled Transport Layer Security (EAP- TTLS)

  • TTLS is a two-stage protocol - establish security in stage one, exchange authentication in stage two.
  • The user’s identity and password-based credentials are tunneled during authentication
  • Provides: mutual authentication, key generation , client identity privacy and data cipher suite negotiation
how peap works peap phase 1 establish tls tunnel
How PEAP WorksPEAP – Phase 1: Establish TLS Tunnel
  • Client/Supplicant associates with AP - EAPOL
  • Authentication Server is authenticated to the Supplicant using PKI certificate.
  • Supplicant sends machine credentials to authenticator over the established TLS channel
  • Authenticator checks Client’s validityand if valid, generates the WEP key
  • Authenticator delivers key to supplicant and transitions controlled port status to permit supplicant access to LAN
how peap works peap phase 2 authenticate client
How PEAP Works PEAP – Phase 2: Authenticate Client
  • Client is requested user identity
  • Supplicant responds by sending user credentials to authenticator
  • Authenticator checks validity by looking up the user database
  • If user id valid, authenticator extends controlled port status to permit supplicant full access to LAN
  • User is logged on to the domain and the network is open
the new proposed protocols eap ttls and peap
PEAP – developed by Microsoft, Cisco.

Windows XP is currently the only operating system that supports PEAP.

Only EAP - generic token card

TTLS - developed by Funk and Certicom,

Linux, Mac OS X, Windows 95/98/ME, and Windows NT/2000/XP.

Can use any Authentication Method - CHAP, PAP, MS-CHAP, MS-CHAPv2 and EAP

The New Proposed ProtocolsEAP-TTLS and PEAP

Research Goal : Design, Implement and perform a comparative analysis of the two protocols.

what is peap
What is PEAP ?
  • IETF Draft-standard proposed by RSA, Microsoft, Cisco
    • draft-josefsson-pppext-eap-tls-eap-02.txt.
  • PEAP is an 802.1x Authentication protocol typically designed for enhancing access control in wireless LANs (WLANs)
  • It is built on top of two well known protocols
    • Extensible Authentication Protocol (EAP)
    • Transport Layer Security (TLS)
ieee 802 1x how it works


Server System





Mostly Radius

IEEE 802.1x – How it Works
  • 802.1x is a port-based network access control method to authenticate and authorize users accessing Local Area Network (LAN) services.

The three elements in IEEE 802.1x





Host NIC

Services offered by


Ethernet 802.1,

the Authenticator


(Port Access Entity)

Wireless PC card,


EAP Messages





Port Unauthorized



The th

ree d





lements in



MAC Enable

802 1x communication protocols
802.1x Communication protocols
  • Protocols to transmit data between Supplicant and the Access Point:
    • EAP-over-LAN (EAPoL) encapsulated EAP messages in Ethernet frames
    • EAP over RADIUS (Remote Access Dial-in User Service) encapsulates EAP messages in RADIUS packets
remote access dial in user service radius
Remote Access Dial-in User Service (RADIUS)
  • RADIUS is a Client/server protocol and software that supports authentication, authorization, and accounting (AAA) for dial-up, virtual private network, and wireless network access.
  • Three major components of RADIUS
    • End User (Supplicant)
    • RADIUS Client (Access Point, Authenticator or Terminal Server)
    • RADIUS server (Authentication server).
  • All RADIUS messages are sent as User Datagram Protocol (UDP) messages on port 1812.
message exchanges between radius client and server
Message Exchanges Between RADIUS Client and Server

For PEAP, Password is not sent in this frame

802 1x authentication types
802.1X Authentication Types
  • EAP-TLS (EAP-Transport Layer Security)
    • Mutual authentication via PKI based client & server certificates
    • Supported in XP and soon other Windows versions
    • Imposes substantial administrative burden to generate, distribute and manage user certificates.
  • EAP-TTLS (EAP-Tunneled Transport Layer Security)
    • User authentication via user ID and password
    • Supported by Funk Software’s Odyssey
    • Supports both EAP and non-EAP kind of Authentication methods.
  • PEAP (Protected EAP)
    • User authentication via user ID and password
    • Supported by Cisco Aironet client adapters and Microsoft XP SP1
    • Supports only EAP authentication methods.
eap transport layer security
EAP–Transport Layer Security
  • EAP-TLS (RFC2716) defines a mechanism for exchange of messages with both client and server validating each other via certificates providing mutual authentication
  • Certificate management required for secure operation

No user-password kind of exchanges


Need for PEAP/TTLS

  • Wireless AP broadcasts all traffic hence can easily collect data if within the broadcast range
    • PEAP/TTLS answers this by transmitting user-sensitive data in an encrypted channel - the established TLS tunnel
  • Weak Wireless Encryption
    • Using PEAP/TTLS the data within the tunnel cannot be decrypted without the TLS master secret and the key is not shared with the Access point. Rogue/compromised access points cannot decrypt messages.
  • MAC address based access control does not work [NetStumbler]
    • Use TLS-based authentication mechanisms to tunnel user credentials.
  • EAP-TLS administrative overhead
    • With PEAP/TTLS only server side PKI infrastructure based digital certificates are used to authenticate EAP servers. No need to install and maintain Client side certificates.

EAP-Tunneled Transport Layer Security (EAP-TTLS)

  • Is a two-phase protocol - establish security in stage one, exchange authentication in phase two.
  • The user’s identity and password-based credentials are tunneled during authentication
  • The AAA server can proxy the user authentication to AAA/H (e.g., LDAP, Active Directory) server.

TTLS Architectural Model

protected eap peap
Protected EAP (PEAP)
  • Two Phase Protocol: Establish TLS connection, start a second EAP authentication process inside encrypted tunnel.
  • Client is authenticated in the second phase using any EAP authentication mechanism (Generic Token Card, One-Time-Password, MS-CHAPv2)
    • MS-CHAPv2 : Microsoft Challenge-Handshake Authentication Protocol
  • PEAP addresses the weaknesses of EAP by protecting user-credentials, standardizes key exchanges, supports fragmentation, fast reconnects and seamless transition.
    • Fast reconnection: Do quick re-authentication by passing only session keys. The session can be resumed without having to perform PEAP Phase 1 or 2.
    • Seamless transition: uses the connection re-establishment mechanism provided by the TLS handshake protocol.
phase 1 establish tls tunnel
Phase 1- Establish TLS Tunnel

AP only pass-through device from this point



Exchange Series of TLS messages

User Validates server certificate

RADIUS server sends Certificate chain to Client

phase 2 authenticate client
Phase 2- Authenticate Client

Challenge String

Response to challenge string & user password

EAP- Success message

Session key, encrypted WEP key

freeradius server code organization
FreeRADIUS Server Code Organization
  • Handles requests through a module interface Radius Load Module [RLM]
  • Module has four components that act on RADIUS requests at different stages of processing the request
      • Authorization: Process of obtaining information about the user from external source & determining the type of authentication protocol to be used.
      • Authentication: Process of validating a User’s Identity.
      • Pre-Accounting:Decides whether to proxy the request
      • Accounting :This records the request in the RADIUS log
  • A module declares which components it supports by putting function pointers in its "module_t rlm_* ” structure.

Free RADIUS Code Directory Structure

The new developed Software

module behavior
Module Behavior
  • Add module inside the modules{} block of the radiusd.conf file. module_name defined in the block is used to load the module.
  • Each configured module calls its own init() method.
  • The instantiate() method is called next. It is given a handle to the configuration block holding the parameters.
  • Finally a detach() method is called when server is shut- down to release the allocated resources.
example radiusd conf
Example - radiusd.conf

modules {

eap {

default_eap_type = peap


} …

peap {

default_eap_type = mschapv2


} …


# eap sets the authorize type as EAP

authorize { …



# eap authentication takes place.

authenticate { …


} …

the rlm eap peap module
The rlm_eap_peap module
  • Deals with the standard attach, detach, and authenticate interfaces.
  • The rlm_eap_peap module does not have an initiate() interface.
    • PEAP is a protocol on top of TLS, so before initiating PEAP we have to initialize the TLS session.

/* rlm_eap_peap.c - Contains interfaces called from the main module EAP */

 EAP_TYPE rlm_eap_peap = {

"eap_peap", /* module_name */

eappeap_attach, /* attach */

NULL, /* No peap initialization interface*/

NULL, /* No need for authorization interface*/

eappeap_authenticate, /* authentication */

eappeap_detach /* detach */


peap phase 1 implementation
PEAP Phase 1- Implementation
  • Handler is sent to the eaptls_process function which processes the EAP request & returns the status code.
  • If the status code returned is a Success then the PEAP module proceeds to decode the tunneled attributes
  • If the status code returned is a Fail then the PEAP module interprets it as a failure in establishing the TLS session and returns back to the eaptls_process method for ending the session.
the eap tlv method
The EAP-TLV Method
  • EAP-TLV is a payload with standard Type-Length-Value (TLV) objects.
    • Used to carry arbitrary parameters between the EAP peer and the EAP server.
  • The PEAP tunnel success/failure packet contains a Result TLV.
    • The Result TLV packet is used to indicate success or failure of the PEAP tunnel.
  • They are sent in the TLS channel - Phase 2.
    • Packets are protected from being spoofed by an attacker.
implementation eap tlv
Implementation – EAP-TLV
  • User credentials, the state of the message exchange and the Status i.e the Result TLV has to be passed through the encrypted channel.
    • A data structure to store these parameters is defined
    • Two functions for explicitly framing the result TLV packetshave been implemented

/* eap_peap.h - PEAP header file*/

#define TLV_SUCCESS 1

#define TLV_FAILURE 2

#define PW_EAP_TLV 33

typedef struct peap_tunnel_t {

VALUE_PAIR *username;

VALUE_PAIR *state;

int status; /* Checks for Result TLV status */

} peap_tunnel_t;

static int eappeap_success(EAP_HANDLER *handler, tls_session_t *tls_session)

static int eappeap_failure(EAP_HANDLER *handler, tls_session_t *tls_session)

peap phase 2 implementation
PEAP Phase 2- Implementation
  • Starts with the eappeap_authenticate () interface receiving the EAP_TLSOK status code from the eaptls_process function
  • The function proceeds to read and decrypt the tunneled data from the SSL session using the in built SSL functions .
  • Next it allocates a new request data structure and adds the tunneled attributes to the request.
  • It then calls the rad_authenticate () function with the new request packet as the parameter to handle the tunneled EAP-Type MS-CHAPv2.
peap phase 2 implementation1
PEAP Phase 2- Implementation
  • Next it reads the Response Packet received from the rad_authenticate function.
  • IF the status field = TLV_SUCCESS, then Phase two of the protocol has been successful and the server can proceed to generate the MPPE (Microsoft Point–to-Point Encryption) keys according to the RFC 2716 [EAP-TLS].
  • Any response messages in the VALUEPAIR format need to be converted to the tunneled data format.
client server machine configurations

Machine Spec

IP Address




1.8 Ghz, 1 GB RAM

RADIUS Server and DHCP server

RedHat 9.0

Running Linux 2.2.20-19.9 kernel



CVS snapshot radiusd-09.03.03.tar.gz


Access Point

Cisco Aironet 1200

RedHat 9.0 Running Linux 2.2.20-19.9 kernel

Cisco 1200 series


Toshiba – 366 Mhz, 512 MB

Wireless Client

Using Cisco Aironet 350 PC Card

Dynamic IP address


RedHat 6.2 running Linux 2.2.20-19.9 kernel

Open1x Xsupplicant

Version 9.0

Hobbit – 1 Ghz Dell Optiplex, 512 MB

Wireless Client

Using Cisco Aironet 350 PCI Card

Dynamic IP address


Windows XP-SP1

And RedHat 9.0 Running Linux kernel

Open1x Xsupplicant for Linux and built in Service Pack for XP

Client/Server Machine Configurations
performance impact of clients processor speed on peap ttls
Performance Impact of Clients’ Processor Speed on PEAP & TTLS
  • Purpose:

Investigate the impact of Client’s processor speed on the time taken to process the Client requests and to see the capacity of the server to handle multiple requests coming from the Clients.

  • Number of Tests Performed:

Three Tests performed - Toshiba machine – 366Mhz, Hobbit machine – 996 Mhz and with two clients having simultaneous access to the server.

peap vs ttls on toshiba machine
PEAP vs TTLS on Toshiba machine


Average 1046 949

Variance 8142 12060

peap vs ttls on hobbit machine
PEAP vs TTLS on Hobbit machine


Average 983 911

Variance 10 356

peap vs ttls simultaneous access of clients
PEAP vs TTLS Simultaneous Access of Clients


Average 1006 947

Variance 23707 12387

result analysis
Result Analysis
  • TTLS out performing PEAP on an average by 8%
  • At lower processor speeds - TTLS was outperforming PEAP by 10%
  • At higher processor speeds – the performance difference is around 7%
  • When running simultaneously with two clients it shows a performance difference of only 6%
  • TTLS and PEAP both show low data variance.
    • PEAP had almost negligible variance with a higher processor speed Client.
  • Processor speeds influencing PEAP relatively more as compared to TTLS
sensitivity study of peap ttls with client stationed at varying distances
Sensitivity study of PEAP & TTLS with Client stationed at varying distances
  • Purpose:

To study the impact on the performance of the two protocols by introducing packet loss or signal degradation with increasing distances between wireless Client and AP.

  • Number of Tests Performed:

Five Tests performed at distance ranges of approximately 25, 30, 45, 55 and 65 feet. Some tests were done behind walls and closed doors to see the impact of line of sight.

result analysis1
Result Analysis
  • As Client goes farther away from the access point the performance of both the protocols degrades.
  • At a lower distance range there is negligible performance difference between PEAP and TTLS – TTLS performing 1% better.
  • With increasing distance range average performance difference increases - TTLS performs 20 % better at ~65 feet range.
  • Data collected highly variant for PEAP as compared to TTLS at closer distances but at the farthest point of ~65 feet TTLS data showed higher variance than PEAP.
peap ttls resilience tests
PEAP & TTLS Resilience Tests
  • Purpose:

To study the tolerance capacity of the protocols towards network transient behavior.

  • Number of Tests Performed:

Five Tests performed. The network interface at the RADIUS server end is brought up and down over different time periods by running a Perl script.

  • Note: A constant downtime of 3 sec has been used in all tests.
    • At first this was chosen randomly. But later by changing downtime it seemed to be making less difference to the performance as compared to changing network uptime.
peap vs ttls network uptime 5 0 sec
PEAP vs TTLS Network Uptime 5.0 sec


Average 12 6

Variance 266 84

peap vs ttls network uptime 4 5 sec
PEAP vs TTLS Network Uptime 4.5 sec


Average 9 8

Variance 105 95

peap vs ttls network uptime 4 2 sec
PEAP vs TTLS Network Uptime 4.2 sec


Average 12 12

Variance 106 118

peap vs ttls network uptime 4 0 sec
PEAP vs TTLS Network Uptime 4.0 sec


Average 18 16

Variance 50 91

peap vs ttls network uptime 3 9 sec
PEAP vs TTLS Network Uptime 3.9 sec


Average 25 26

Variance 437 390

result analysis2
Result Analysis
  • Client performance degrades as the network interface uptime gets shorter.
  • At 3.8 sec uptime both PEAP and TTLS protocols failed to recover.
  • The average performance of TTLS as compared to PEAP is negligible
  • Where difference was large the variance difference between the two also has been relatively big.
peap ttls stress tests
PEAP & TTLS Stress Tests
  • Purpose:

To study the performance of the two protocols when run for a longer period of time.

  • Number of Tests Performed:

Two Tests performed – One for Each Protocol. Each test was run for over 15 hours

stress test ttls
Stress Test - TTLS

Average 1099

result analysis3
Result Analysis
  • Both protocols passed the stress tests. Both authenticated the Client all times.
  • The peaks can be attributed to the fact that in some of the cases the Client got authenticated in the second or third trial of authentication
  • The peaks reached by TTLS are much more frequent and higher as compared to PEAP - Over a longer time period TTLS shows more variance than PEAP
mac address spoofing test
MAC Address Spoofing Test
  • Purpose:

Investigate if by spoofing the MAC address an attacker can gain access to a wireless network that relies on tunneled encryption like PEAP/TTLS for authenticating wireless Clients.

  • Number of Tests Performed:

One test was performed with a Linux Client authenticating using PEAP. Attacker had Windows XP running AiroPeek software for sniffing MAC addresses.

I would like to thank Donovan Thorpe of Computer Services UCCS for his help in performing this test.

result analysis4
Result Analysis
  • The attacker could associate with the Access Point as it had a valid MAC address while eavesdropping the network. Thus passed the first line of defense – MAC address filtering.
  • The attacker was prompted for the user credentials. This stage could not be by-passed and the attacker could not access the network as the user credentials were in encrypted format and thus could not be sniffed.
  • Developed a Radius Server on Linux that supports both PEAP and TTLS.
  • PEAP is relatively more influenced by Client’s processor speeds, distance range and network transient nature as compared to TTLS.
  • Although the higher performance shown by TTLS over PEAP is negligible, it is worth noting that TTLS was outperforming PEAP on an average by 10% in all the tests.
  • The enhanced Radius Server can serve both Windows and Linux clients.
future work
Future Work
  • Study how to apply the PEAP/TTLS protocols in Mobile Ad-Hoc Networks.
  • Study the implications of providing Virtual Private Network (VPN) features in addition to encryption of PEAP/TTLS within the wireless Access Point devices.
  • Develop ways to protect user's identity that is passed in clear between the access point, the RADIUS server, and any other database-backend server by implementing firewalls or other such viable security techniques.