and eliminates the need for a public-key
infrastructure (PKI) to manage the certificates. -
Phase 2: In Phase 2, the RADIUS server authenticates the
user credentials with EAP-GTC, which is protected by the TLS
tunnel that is created in Phase 1.
EAP-FAST
Authentication
Figure illustrates how the wireless
client associates with an access point using open
authentication: - The access point restricts all
traffic from the client until the client has authenticated to
the RADIUS server.
- The client sends an EAP over LAN
(EAPOL)-start frame to the access point.
- The access
point returns a Request/Identity to the client.
- The
client sends a network access identifier (NAI) e-mail format
address to the access point, which passes the NAI to the RADIUS
server.
- The server and the client mutually
authenticate each other using Phase 1 and Phase 2 of the
EAP-FAST process.
- The RADIUS server sends the session
key to the access point in a Success packet. The RADIUS server
and client negotiate and derive the session encryption key.
This process varies based on whether the client is using WEP or
IEEE 802.11i.
- The client and the access point use the
keys during the session.
- At the end of the session,
the client sends an EAPOL-logout packet, and the access point
returns to the preauthentication state (filtering all but EAPOL
traffic)
Content 6.2
Introducing Wireless Security 6.2.8
EAP-TLS EAP-TLS is one of the original authentication
methods that the IEEE specified when 802.1x and EAP were
initially proposed and established as a standard. TLS is used
in many environments and is intended to be an alternative,
standardized version of the widely deployed Secure Sockets
Layer (SSL) encryption mechanism. EAP-TLS uses a message
authentication code that is derived from a certificate to
authenticate a user. Certificates are issued to users and
computers by a certificate authority (CA) and are used to
validate identity. The maintenance of the CA (which is part of
a PKI) can be a barrier to EAP-TLS deployment for some
customers. All clients (users) must have their own certificates
personally issued and installed on their machines in order to
perform TLS authentication. Each AAA server must also have
unique certificates. EAP-TLS has native support on Microsoft
Windows 2000, Windows XP, Windows CE, and Windows Vista.
Third-party supplicants can be used for non-Windows support.
Meetinghouse has supplicant software that supports EAP-TLS.
With the Cisco (and Microsoft) implementation of EAP-TLS, it is
possible to tie the Microsoft credentials of the user with the
certificate of that user in a Microsoft database, which permits
one-time sign-on to a Microsoft domain. EAP-TLS
Authentication
Figure illustrates the 802.1x EAP
authentication process with EAP-TLS as the authentication
protocol. The process takes part in many steps: - The
wireless client associates with the access point using open
authentication.
- The access point restricts all
traffic from the client until the client has authenticated to
the RADIUS server.
- The client sends an EAPOL-start
frame to the access point.
- The access point returns a
Request/Identity to the client.
- The client sends an
NAI (e-mail format) address to the access point, which passes
the address on to the RADIUS server.
- The server and
the client mutually authenticate each other using an exchange
of digital certificates.
- The RADIUS server sends the
session key to the access point in a Success packet. The RADIUS
server and client negotiate and derive the session encryption
key. This process varies based on whether the client is using
WEP or 802.11i.
- The client and the access point use
the keys during the session.
- At the end of the
session, the client sends an EAPOL-logout packet, and the
access point returns to the preauthentication state (filtering
all but EAPOL traffic).
Content
6.2 Introducing Wireless Security
6.2.9 PEAP PEAP is an authentication protocol that
was jointly proposed and developed by Cisco, Microsoft, and RSA
Security. The purpose of PEAP is to protect the
authentication transaction with a TLS-secured connection, much
as you might secure a connection to an e-commerce website when
performing an online transaction. Note that there are two
implementations of PEAP: - PEAP-GTC
-
PEAP-Microsoft Challenge Handshake Authentication Protocol
version 2 (MSCHAPv2)
The PEAP-GTC authentication
mechanism allows generic authentication to a number of
databases—Novell Directory Service (NDS), Lightweight Directory
Access Protocol (LDAP), OTP, and so on. The PEAP-MSCHAPv2
authentication mechanism allows authentication to databases
that support the MSCHAPv2 format, including Microsoft NT and
Microsoft Active Directory. As with other 802.1x and EAP types,
dynamic encryption can be used with PEAP. A CA certificate must
be used at each client to authenticate the server to each
client before the client submits authentication credentials.
Figure summarizes and expands on these points. EAP-PEAP
Authentication
Figure illustrates the 802.1x EAP
authentication process with EAP-PEAP as the authentication
protocol, a multistep exchange: - The wireless client
associates with the access point using open
authentication.
- The access point restricts all
traffic from the client until the client has authenticated to
the RADIUS server.
- The initial handshake between the
client and the access point is a TLS handshake, as seen
earlier.
- The client authenticates the server using a
CA to verify the digital certificate of the server. Then the
client and the server establish an encrypted tunnel. The client
submits client credentials inside the tunnel using either
MSCHAPv2 or GTC.
- The RADIUS server sends the session
key to the access point in a Success packet. The RADIUS server
and client negotiate and derive the session encryption key.
This process varies based on whether the client is using WEP or
802.11i.
- The client and the access point use the keys
during the session.
At the end of the session, the
client sends an EAPOL-logout packet, and the access point
returns to the preauthentication state (filtering all but EAPOL
traffic).
Content 6.2 Introducing
Wireless Security 6.2.10 Wi-Fi Protected
Access WPA Characteristics
WPA is the Wi-Fi
Alliance standards-based mechanism that creates secure and
interoperable WLAN networks. WPA provides a mechanism to
authenticate keys for use in 802.11 environments as well as
providing enhancements to WEP encryption to increase the
robustness of the security protocol. WPA was an interim
solution proposed by the wireless industry consortium to create
a WLAN standard in advance of the IEEE standard for security,
IEEE 802.11i, which was ratified in June 2004. WPA addressed
vulnerabilities of standard 802.11 WEP security and permitted a
path for migration of users to this new security mechanism
through a software upgrade. Components of WPA
WPA is
a standard that describes a combination of security
capabilities. These capabilities were available before WPA
became an industry standard (note that WPA was not an IEEE
standard as of late 2003), but WPA pulls the capabilities into
one definition. The following, listed in Figure , are the most
important aspects of WPA: - Authenticated key
management: Either using 802.1x authentication or a
preshared key, the user is authenticated prior to
authentication of the keys that are used.
- Unicast
and broadcast key management: The keys that are derived
after user authentication are authenticated through a
handshake process between the access point and client.
- TKIP (per-packet keying) and MIC.
- IV
space expansion: The IV space is expanded from 24 bits, as