802.1X Port-Based Authentication HOWTO - Lars Strand (spicy books to read .TXT) 📗

802.1X Port-Based Authentication HOWTO

Lars Strand

2004-08-18

Revision History

Revision 1.0 2004-10-18 Revised by: LKS

Initial Release, reviewed by TLDP.

Revision 0.2b 2004-10-13 Revised by: LKS

Various updates. Thanks to Rick Moen for language

review.

Revision 0.0 2004-07-23 Revised by: LKS

Initial draft.

This document describes the software and procedures to set up and use IEEE

802.1X Port-Based Network Access Control using Xsupplicant as Supplicant with

FreeRADIUS as a back-end Authentication Server.

Table of Contents

Introduction

1.1. What is 802.1X?

1.2. What is 802.11i?

1.3. What is EAP?

1.4. EAP authentication methods

1.5. What is RADIUS?

Obtaining Certificates

Authentication Server: Setting up FreeRADIUS

3.1. Installing FreeRADIUS

3.2. Configuring FreeRADIUS

Supplicant: Setting up Xsupplicant

4.1. Installing Xsupplicant

4.2. Configuring Xsupplicant

Authenticator: Setting up the Authenticator (Access Point)

5.1. Access Point

5.2. Linux Authenticator

Testbed

6.1. Testcase

6.2. Running some tests

Note about driver support and Xsupplicant

FAQ

Useful Resources

Copyright, acknowledgments and miscellaneous

10.1. Copyright and License

10.2. How this document was produced

10.3. Feedback

10.4. Acknowledgments

A. GNU Free Documentation License

A.1. PREAMBLE A.2. APPLICABILITY AND DEFINITIONS A.3. VERBATIM COPYING A.4. COPYING IN QUANTITY A.5. MODIFICATIONS A.6. COMBINING DOCUMENTS A.7. COLLECTIONS OF DOCUMENTS A.8. AGGREGATION WITH INDEPENDENT WORKS A.9. TRANSLATION A.10. TERMINATION A.11. FUTURE REVISIONS OF THIS LICENSE A.12. ADDENDUM: How to use this License for your documents Introduction

This document describes the software and procedures to set up and use

802.1X: Port-Based Network Access Control using Xsupplicant with PEAP (PEAP/

MS-CHAPv2) as authentication method and FreeRADIUS as back-end authentication

server.

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.

[8021X-Overview]

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 component.

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 [[http://www.ietf.org/rfc/rfc1994.txt] 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.

See figure 802.1X for explanation.

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).

[8021X-Ports]

Figure port: The authorization state of the controlled port.

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?

1.2.1. WEP

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 [http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html] 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.

1.2.2. 802.11i

The new security standard, 802.11i, which was ratified in June 2004, fixes

all WEP weaknesses. It is divided into three main categories:

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) [[http://www.ietf.org/rfc/

rfc3610.txt] 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 authentication.

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, described next.

1.2.3. Key Management

1.2.3.1. 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.

[8021X-KeyManagement]

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 the AS.

Both the WN and the AS derive a new key, called the Pairwise Master Key

(PMK), from the Master Key.

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 traffic.

[8021X-KeyHierarchy]

Figure PKH: Pairwise Key Hierarchy

1.2.3.2. 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

"WPA".

The 256-bit PSK is generated from a given password using PBKDFv2 from

[[http://www.ietf.org/rfc/rfc2898.txt] 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! [http://www.wi-fi.org/]

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 + 802.1X.