If another authentication mechanism than PEAP is preferred, e.g.,
EAP-TLS or EAP-TTLS, only a small number of configuration options
needs to be changed. PEAP/MS-CHAPv2 are also supported by Windows XP
SP1/Windows 2000 SP3.
1.1. What is 802.1X?
The 802.1X-2001 standard states:
"Port-based network access control makes use of the physical
access characteristics of IEEE 802 LAN infrastructures in order to
provide a means of authenticating and
authorizing devices attached
to a LAN port that has point-to-point connection characteristics,
and of preventing access to that port in cases
which the authentication and authorization fails. A port in this
context is a single point of attachment to the LAN
infrastructure." --- 802.1X-2001, page 1.
Figure 802.1X: A wireless node must be authenticated before it
can gain access to other LAN resources.
When a new wireless node (WN) requests access to a LAN resource,
the access point (AP) asks for the WN's identity. No
other traffic than EAP is allowed before the WN is authenticated
(the "port" is closed).
The wireless node that requests authentication is often called
Supplicant, although it is more correct to
say that the wireless node contains a
Supplicant. The Supplicant is responsible for responding to
Authenticator data that will establish its credentials. The same
goes for the access point; the
Authenticator is not the access point. Rather,
the access point contains an Authenticator. The Authenticator does
not even need to be in the access point; it can be an external
EAP, which is the protocol used for authentication, was originally
used for dial-up PPP. The identity was the username, and either
PAP or CHAP authentication [RFC1994] was
used to check the user's password. Since the identity is sent in
clear (not encrypted), a malicious sniffer may learn the user's
identity. "Identity hiding" is therefore used; the
real identity is not sent before the encrypted TLS tunnel is up.
After the identity has been sent, the authentication process
begins. The protocol used between the Supplicant and the
Authenticator is EAP, or, more correctly, EAP encapsulation over
LAN (EAPOL). The Authenticator re-encapsulates the EAP messages to
RADIUS format, and passes them to the Authentication Server.
During authentication, the Authenticator just relays packets
between the Supplicant and the Authentication Server. When the
authentication process finishes, the Authentication Server sends a
success message (or failure, if the authentication
failed). The Authenticator then opens the
"port" for the Supplicant.
After a successful authentication, the Supplicant is granted
access to other LAN resources/Internet.
Why is it called "port"-based authentication? The
Authenticator deals with controlled and
uncontrolled ports. Both the controlled and the
uncontrolled port are logical entities (virtual ports), but use the
same physical connection to the LAN (same point of attachment).
Figure port: The authorization state of the controlled
Before authentication, only the uncontrolled port is
"open". The only traffic allowed is EAPOL; see
Authenticator System 1 on figure port. After the Supplicant has been
authenticated, the controlled port is opened, and access to other LAN
resources are granted; see Authenticator System 2 on figure port.
802.1X plays a major role in the new IEEE wireless standard 802.11i.
1.2. What is 802.11i?
Wired Equivalent Privacy (WEP), which is part of the original
802.11 standard, should provide confidentiality. Unfortunately WEP
is poorly designed and easily cracked. There is no authentication
mechanism, only a weak form of access control (must have the
shared key to communicate). Read more here.
As a response to WEP broken security, IEEE has come up with
a new wireless security standard named 802.11i. 802.1X plays a
major role in this new standard.
The new security standard, 802.11i, which was ratified in June
2004, fixes all WEP weaknesses. It is divided into three main
Temporary Key Integrity Protocol (TKIP) is
a short-term solution that fixes all WEP weaknesses. TKIP can be
used with old 802.11 equipment (after a driver/firmware upgrade)
and provides integrity and confidentiality.
Counter Mode with CBC-MAC Protocol (CCMP) [RFC2610]
is a new protocol, designed from ground up. It uses AES [FIPS
197] as its cryptographic algorithm, and, since this is
more CPU intensive than RC4 (used in WEP and TKIP), new 802.11
hardware may be required. Some drivers can implement CCMP in
software. CCMP provides integrity and confidentiality.
802.1X Port-Based Network Access Control:
Either when using TKIP or CCMP, 802.1X is used for
In addition, an optional encryption method called "Wireless
Robust Authentication Protocol" (WRAP) may be used instead
of CCMP. WRAP was the original AES-based proposal for 802.11i, but
was replaced by CCMP since it became plagued by property
encumbrances. Support for WRAP is optional, but CCMP support is
mandatory in 802.11i.
802.11i also has an extended key derivation/management,
1.2.3. Key Management
126.96.36.199. Dynamic key exchange and management
To enforce a security policy using encryption and integrity
algorithms, keys must be obtained. Fortunately, 802.11i implements
a key derivation/management regime. See figure KM.
Figure KM: Key management and distribution in 802.11i.
When the Supplicant (WN) and Authentication Server (AS)
authenticate, one of the last messages sent from AS, given that
authentication was successful, is a Master Key
(MK). After it has been sent, the MK is known only to the
WN and the AS. The MK is bound to this session between the WN and
Both the WN and the AS derive a new key, called the
Pairwise Master Key (PMK), from the Master
The PMK is then moved from the AS to the Authenticator (AP). Only
the WN and the AS can derive the PMK, else the AP could
make access-control decisions instead of the AS. The PMK is a fresh
symmetric key bound to this session between the WN and the AP.
PMK and a 4-way handshake are used between the WN and the AP to
derive, bind, and verify a Pairwise Transient Key
(PTK). The PTK is a collection of operational keys:
Key Confirmation Key (KCK), as the name
implies, is used to prove the posession of the PMK and to bind
the PMK to the AP.
Key Encryption Key (KEK) is used to
distributed the Group Transient Key (GTK). Described below.
Temporal Key 1 & 2 (TK1/TK2) are used
for encryption. Usage of TK1 and TK2 is ciphersuite-specific.
See figure PKH for a overview of the
Pairwise Key Hierarchy.
The KEK and a 4-way group handshake are then used to send the
Group Transient Key (GTK) from the AP to the
WN. The GTK is a shared key among all Supplicants connected to the
same Authenticator, and is used to secure multicast/broadcast
Figure PKH: Pairwise Key Hierarchy
188.8.131.52. Pre-shared Key
For small office / home office (SOHO), ad-hoc networks or home
usage, a pre-shared key (PSK) may be used. When using PSK, the whole
802.1X authentication process is elided. This has also been called
"WPA Personal" (WPA-PSK), whereas WPA using EAP (and
RADIUS) is "WPA Enterprise" or just
The 256-bit PSK is generated from a given password using PBKDFv2
from [RFC2898], and is
used as the Master Key (MK) described in the key management regime
above. It can be one single PSK for the whole network (insecure), or
one PSK per Supplicant (more secure).
1.2.4. TSN (WPA) / RSN (WPA2)
The industry didn't have time to wait until the 802.11i standard
was completed. They wanted the WEP issues fixed now! Wi-Fi Alliance felt the
pressure, took a "snapshot" of the standard
(based on draft 3), and called it Wi-Fi Protected Access
(WPA). One requirement was that existing 802.11
equipment could be used with WPA, so WPA is basically TKIP +
WPA is not the long term solution. To get a Robust
Secure Network (RSN), the hardware must support and use
CCMP. RSN is basically CCMP + 802.1X.
RSN, which uses TKIP instead of CCMP, is also called Transition
Security Network (TSN). RSN may also be called WPA2, so that the
market don't get confused.
TSN = TKIP + 802.1X = WPA(1)
RSN = CCMP + 802.1X = WPA2
In addition comes key management, as described in the previous
1.3. What is EAP?
Extensible Authentication Protocol (EAP) [RFC 3748] is just
the transport protocol optimized for authentication, not the
authentication method itself:
[EAP is] an authentication framework which supports multiple
authentication methods. EAP typically runs directly over data link
layers such as Point-to-Point Protocol (PPP) or IEEE 802, without
requiring IP. EAP provides its own support for duplicate
elimination and retransmission, but is reliant on lower layer
ordering guarantees. Fragmentation is not supported within EAP
itself; however, individual EAP methods may support this."
--- RFC 3748, page 3
1.4. EAP authentication methods
Since 802.1X is using EAP, multiple different authentication
schemes may be added, including smart cards, Kerberos, public key,
one time passwords, and others.
Not all authentication mechanisms are considered secure!
EAP-MD5: MD5-Challenge requires
username/password, and is equivalent to the PPP CHAP protocol
method does not provide dictionary attack resistance, mutual
authentication, or key derivation, and has therefore little use in a
wireless authentication enviroment.
Lightweight EAP (LEAP): A username/password
combination is sent to a Authentication Server (RADIUS) for
authentication. Leap is a proprietary protocol developed by
Cisco, and is not considered secure. Cisco is phasing out LEAP in
favor of PEAP. The closest thing to a published standard can be
EAP-TLS: Creates a TLS session within EAP,
between the Supplicant and the Authentication Server. Both the
server and the client(s) need a valid (x509) certificate, and
therefore a PKI. This method provides authentication both
ways. EAP-TLS is described in [RFC2716].
EAP-TTLS: Sets up a encrypted TLS-tunnel for
safe transport of authentication data. Within the TLS tunnel,
(any) other authentication methods may be used. Developed by Funk
Software and Meetinghouse, and is currently an IETF draft.
Protected EAP (PEAP): Uses, as EAP-TTLS, an
encrypted TLS-tunnel. Supplicant certificates for both EAP-TTLS
and EAP-PEAP are optional, but server (AS) certificates are
required. Developed by Microsoft, Cisco, and RSA Security, and is
currently an IETF draft.
EAP-MSCHAPv2: Requires username/password, and
is basically an EAP encapsulation of MS-CHAP-v2 [RFC2759].
Usually used inside of a PEAP-encrypted tunnel. Developed by
Microsoft, and is currently an IETF draft.
1.5. What is RADIUS?
Remote Authentication Dial-In User Service (RADIUS) is defined in
(with friends), and was primarily used by ISPs who authenticated
username and password before the user got authorized to use the
802.1X does not specify what kind of back-end authentication
server must be present, but RADIUS is the "de-facto" back-end
authentication server used in 802.1X.
There are not many AAA protocols available, but both RADIUS and
(including their extensions) conform to full AAA support. AAA
stands for Authentication, Authorization, and Accounting (IETF's
AAA Working Group).