• Beyond Traditional IEEE 802.11 Security

Marie Waldrick May 5, 2003

Outline

• Characterizing Wireless Networks

• Wireless technology, 802.11 currently

• 802.1X

• EAP Architecture

• 802.1X/EAP

• Future Trends-802.1X/EAP/TKIP

• Conclusion-802.11i

Characterizing Wireless Networks

• Adhoc only requires wireless devices on each computer.

• Infrastructure requires wireless devices on each computer AND a base station (with built in DHCP server and firewall)

Peer-to-Peer (Adhoc)Wireless devices have no access point connection and each device communicates with each other directly

Client/Server (infrastructure networking)Extends an existing wired LAN to wireless devices by adding an access point (bridge and central controller)

Advantages to Infrastructure Mode

• Automatic use of Network Address Translation (NAT) firewall –blocks all outside port requests

• Local reserved IP addresses only used by clients. Those IP addresses will not show up on the internet.

• The DCHP server (gateway) that is built into this NAT firewall does not require that any one computer be on (and functioning) in order to use the connection.

Wireless Networks

• By nature, wireless networks need to advertise their beacons to show their existence

•Service set identifier (SSID) Beacons frames broadcast network parameters are sent unencrypted•Media Access Control (MAC) address filtering 802.11 uses 48 bit station identifiers in the frame headers -check mac address to insure station has access not part of 802.11 standard but used anyway to identify Wired Equivalent Privacy (WEP) Was supposed to provide authentication and privacy Secret 40 bit keys, but unsafe at any length Static-manually-configured keys Weakness due to long life of keys and they are shared among many users

The IEEE 802.11 standard

802.1X Standard

-Solves user authentication problem-Standard for passing EAP over a wired or

wireless LAN-EAP messages are packaged in Ethernet frames

and don’t use PPP.-It is only authentication-Provides a security framework for port-based

access control-Resides in the upper layers to enable new

authentication and key management methods without changing current network devices.

-The latest security technology should still work with your existing infrastructure

802.1X architecture overview

APClient

AuthenticatorSupplicant Authentication Server

Concrete Authentication Protocol

EAP carries concrete authentication protocol between Supplicant and Authentication Server

802.1: carries EAP over 802 LAN between Supplicant and Authenticator

RADIUS/UDP/IP: carries EAP between Authenticator and Authentication Server

802.1x connection• A client device connects to a port on an 802.1x

switch and AP• The switch port can determine the authenticity of

the devices• The services offered by the switch can be made

available on that port• Only EAPOL frames can be sent and received on

that port until authentication is complete. • When the device is properly authenticated, the

port switches traffic as through it were a regular port.

Authentication Server

Access point

Laptop

5

1

3

2

4

1 -Client Associates with Blocked Access Point2 -User Provides Login Authentication Credentials3 a)-Server<->user authentication

b)-Server delivers Unicast WEP key to Access Point4 -Access point delivers broadcast WEP key Encrypted with Unicast WEP key to client5 -Client and Access Point activate WEP and Use Unicast and

Broadcast WEP keys for transmission

EAP Transport “Authentication” Protocol

Unicast-communication single host single receiver

packets sent to a unicast address are delivered to the interface identified by that address

Multicast is communication between a single host and multiple receivers

Multicast Sends Packets to a Subnet, and defined devices listen for Multicast

Packets

What is EAP• Beyond simple user names and passwords• Easily encapsulated within any data link protocol• Provides a generalized framework for all sorts of

authentication methods.• Simpler interoperability and compatibility across

authentication methods• For example, when you dial a remote access

server(RAS) and use EAP as part of your PPP connection, the RAS doesn’t need to know any of the details about your authentication system. Only you and the authentication server have to be coordinated.

• The RAS server gets out of the business and just re-packages EAP packets to hand off to a RADIUS server to make the actual authentication decision.

EAPoL packet structure

EAP messages are packaged in ethernet frames and don’t use PPP

Source Ethernet Addr

Destination Ethernet Addr

Ether type = 888E

Vers | Type

Body Length

Body

(e.g. EAP frame)

A typical EAPOL protocol runSupplicant Authenticator

EAPOL start

EAP request/identity

EAP response/identity

EAP request/MD5-challenge

EAP response/MD5-challenge

EAP success

Temporal key

MAC addr

SEQ #

Integrity key

Shared secret key

P1 P2 RC4

IV/SEQ

RC4

S | D | body

hash

ciphertext

| |

| MIC

TKIP

WEP IV

IV | ciphertext

| | S | D | body | IC

V

CRC-32

TKIP(Temporal Key Integrity Protocol)

• Addresses weak IVs, IV collisions• Firmware upgrade deployable to existing

802.11 hardware• Components

-Cryptographic message integrity code-Packet sequencing-Per-packet key generation-Re-keying mechanism

TKIP-MIC

• Sender and receiver share 64-bit secret integrity key

• MIC = H(src MAC|dst MAC|frame body)K

• If receivers computation matches the MIC sent, then message presumed authentic

• If 2 forgeries in a second, then assume under attack-Delete keys, disassociate, and reassociate

TKIP-Packet Sequencing

• Reuse 16-bits of WEP IV packet field for sequence number

• Initialize sequence # to 0 for new encryption key

• Increment sequences # by 1 on each packet

• Discard any packet out of sequence

TKIP-Per-packet Key

• Phase 1:– Key_mix(128-bit temporal key, 48-bit MAC)=128-bit

result• Ensures unique key if clients share same temporal key

• Phase 2:Key_mix(phase 1 result, seq #) = 128-bit per-packet key

Incrementing seq# ensures unique key for each packet

• Keystream=RC4(128-bit per-packet key)

TKIP-Rekeying

• Key hierarchy– Master key

• Established via 802.1x or manually• Used to securely communicate key encryption

keys- Key encryption keys (2)

• Secure messages containing keying material for deriving temporal keys

• Key 1: encryption Key 2: integrity– Temporal keys(2)

• Key 1: encrypting data Key 2: data integrity

TKIP

• If master key compromised, then TKIP is voided

• The lack of PKI represents a huge issue on the AP side.

Standard EAP with TKIP WLAN Design Attack Mitigation Roles for Standard EAP WLAN Design

802.1X/EAP with TKIPThreats mitigated

• Wireless packet sniffers

-per packet keying

-key rotation• Unauthenticated access

-only authenticated users are able to access the wireless and wired network

-optional access control on the Layer 3 switch limits wired network access

• MITM

-the mutual authentication nature of several EAP authentication types combined with the MIC can prevent hackers from inserting themselves in the path of wireless communications.

• IP spoofing

-have to first authenticate to WLAN

-layer 3 switch restricts any spoofing to the local subnet range

• ARP spoofing

-have to first authenticate to WLAN• Network topology discovery

-have to first authenticator to WLAN

-know network exist by SSID, but cannot access the network.

802.1X/EAP with TKIPAdditional Threats mitigated

802.1X/EAP with TKIPThreats not mitigated

Password attack-passive monitoring 802.1X/EAP exchanges between client and the access point

-Protected EAP mitigates this by establishing a TLS tunnel from the client to the server before asking for user authentication credentials.

IETF-802.11i

Back End (EAP)Server

EAP Method

CipherSuite

Client

Laptop

Network Access Server (NAS)

Trust

EAP method

CipherSuite

EAP Conversation (over PPP, 802.11, etc.)

Determines authentication encryption and MAC algorithms. Select by Server Default Cipher Suite

TLS_DHE_CSS_WITH_3DES_EDE_CBC_SHA

Keys for Link Layer CipherSuites

IEEE 802.11iEmbraces 802.1x and TKIP

Replaces RC4 with AES for encryption and integrity

48-bit sequence counter, 128-bit key

Requires coprocessor, therefore new hardware deployment

Summary

• Mobile communication technology will continue to grow encouraged by switching to packet-switched 3G cellular phones

• Results in natural progression to accessing the internet without wires

• Results in requiring more privacy/security protection mechanisms

• Standards/vendor products eventually evolve to meet customers’ needs

The Alliance announced the first certified products with WPA

April 29, 2003 • The Wi-Fi Alliance created Wi-Fi

Protected Access (WPA) in October of 2002 as a stepping stone between the sullied Wired Equivalent Privacy (WEP) encryption that has long been part of the 802.11 specifications, and the upcoming 802.11i standard that will bring IEEE endorsed security to WLANs.

http://www.80211planet.com/news/

• P. Nikander, Authorization and charging in public WLANs using FreeBSD and 802.1x, Ericsson Research NomadicLab, pekka.nikander@ericsson.com

• IEEE Draft P802.1X/D11: Standard for Portbased Network Access Control, LAN MAN StandardsCommittee of the IEEE Computer Society,March 27, 2001.

• L. Blunk and J. Vollbrecht, RFC2284, PPP ExtensibleAuthentication Protocol (EAP), IETF,March 1998.

• C. Rigney, S. Willens, A. Rubens, W. Simpson, RFC2865, Remote Authentication Dial In User Service (RADIUS), IETF, June 2000.

• http://www.cisco.com/warp/public/cc/so/cuso/epso/sqfr/safwl_wp.htmns?• Cisco Networking Academy Program: Second-Year Companion Guide, Cisco

Systems, Inc., Cisco Press 2001.• Glen Fleishman, “Key to Wi-Fi security”, http://www.infoworld.com

/article/ /03/01/10/030113newifisec_1.html• H.Anderson,“Protected Extensible Authentication Protocol (PEAP),

http://www.globecom.net/ietf/draft/draft-josefsson-pppex-eap-tls-eap-02.html • Rob Flickenger, “Using SSH Tunneling”,

http://www.oreillynet.com/pub/a/wireless/2001/02/23/wep.html• http://www.ietf.org/ietf/lid-abstracts.txt• www.inetdevgrp.org/20020618/WLANSecurity.pdf• http://www.prism.gatech.edu/~gt0369c/802_11%20Security%20Survey_slides.pdf

References:

Thank You

Notes:

• If access is approved, the authenticator hands over a unique per-supplicant master key from which the supplicant's network adapter derives the TKIP key, the packet integrity key, and other cryptographic necessities. The user can then be authenticated

• EAP is used to frequently refresh the master key, reducing the window of opportunity for intercepting packets for cracking.