Zyxel P-2601HN-F1 Router Manual PDF (Setup & Configuration Guide)

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• Access-Challenge

Sent by a RADIUS server requesting more information in order to allow access.

The access point sends a proper response from the user and then sends another

Access-Request message.

The following types of RADIUS messages are exchanged between the access point

and the RADIUS server for user accounting:

• Accounting-Request

Sent by the access point requesting accounting.

• Accounting-Response

Sent by the RADIUS server to indicate that it has started or stopped accounting.

In order to ensure network security, the access point and the RADIUS server use a

shared secret key, which is a password, they both know. The key is not sent over

the network. In addition to the shared key, password information exchanged is

also encrypted to protect the network from unauthorized access.

Types of EAP Authentication

This section discusses some popular authentication types: EAP-MD5, EAP-TLS,

EAP-TTLS, PEAP and LEAP. Your wireless LAN device may not support all

authentication types.

EAP (Extensible Authentication Protocol) is an authentication protocol that runs on

top of the IEEE 802.1x transport mechanism in order to support multiple types of

user authentication. By using EAP to interact with an EAP-compatible RADIUS

server, an access point helps a wireless station and a RADIUS server perform

authentication.

The type of authentication you use depends on the RADIUS server and an

intermediary AP(s) that supports IEEE 802.1x. .

For EAP-TLS authentication type, you must first have a wired connection to the

network and obtain the certificate(s) from a certificate authority (CA). A certificate

(also called digital IDs) can be used to authenticate users and a CA issues

certificates and guarantees the identity of each certificate owner.

EAP-MD5 (Message-Digest Algorithm 5)

MD5 authentication is the simplest one-way authentication method. The

authentication server sends a challenge to the wireless client. The wireless client

‘proves’ that it knows the password by encrypting the password with the challenge

and sends back the information. Password is not sent in plain text.

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However, MD5 authentication has some weaknesses. Since the authentication

server needs to get the plaintext passwords, the passwords must be stored. Thus

someone other than the authentication server may access the password file. In

addition, it is possible to impersonate an authentication server as MD5

authentication method does not perform mutual authentication. Finally, MD5

authentication method does not support data encryption with dynamic session

key. You must configure WEP encryption keys for data encryption.

EAP-TLS (Transport Layer Security)

With EAP-TLS, digital certifications are needed by both the server and the wireless

clients for mutual authentication. The server presents a certificate to the client.

After validating the identity of the server, the client sends a different certificate to

the server. The exchange of certificates is done in the open before a secured

tunnel is created. This makes user identity vulnerable to passive attacks. A digital

certificate is an electronic ID card that authenticates the sender’s identity.

However, to implement EAP-TLS, you need a Certificate Authority (CA) to handle

certificates, which imposes a management overhead.

EAP-TTLS (Tunneled Transport Layer Service)

EAP-TTLS is an extension of the EAP-TLS authentication that uses certificates for

only the server-side authentications to establish a secure connection. Client

authentication is then done by sending username and password through the

secure connection, thus client identity is protected. For client authentication, EAP-

TTLS supports EAP methods and legacy authentication methods such as PAP,

CHAP, MS-CHAP and MS-CHAP v2.

PEAP (Protected EAP)

Like EAP-TTLS, server-side certificate authentication is used to establish a secure

connection, then use simple username and password methods through the

secured connection to authenticate the clients, thus hiding client identity.

However, PEAP only supports EAP methods, such as EAP-MD5, EAP-MSCHAPv2

and EAP-GTC (EAP-Generic Token Card), for client authentication. EAP-GTC is

implemented only by Cisco.

LEAP

LEAP (Lightweight Extensible Authentication Protocol) is a Cisco implementation of

IEEE 802.1x.

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Dynamic WEP Key Exchange

The AP maps a unique key that is generated with the RADIUS server. This key

expires when the wireless connection times out, disconnects or reauthentication

times out. A new WEP key is generated each time reauthentication is performed.

If this feature is enabled, it is not necessary to configure a default encryption key

in the wireless security configuration screen. You may still configure and store

keys, but they will not be used while dynamic WEP is enabled.

Note: EAP-MD5 cannot be used with Dynamic WEP Key Exchange

For added security, certificate-based authentications (EAP-TLS, EAP-TTLS and

PEAP) use dynamic keys for data encryption. They are often deployed in corporate

environments, but for public deployment, a simple user name and password pair

is more practical. The following table is a comparison of the features of

authentication types.

WPA and WPA2

Wi-Fi Protected Access (WPA) is a subset of the IEEE 802.11i standard. WPA2

(IEEE 802.11i) is a wireless security standard that defines stronger encryption,

authentication and key management than WPA.

Key differences between WPA or WPA2 and WEP are improved data encryption and

user authentication.

If both an AP and the wireless clients support WPA2 and you have an external

RADIUS server, use WPA2 for stronger data encryption. If you don't have an

external RADIUS server, you should use WPA2-PSK (WPA2-Pre-Shared Key) that

only requires a single (identical) password entered into each access point, wireless

gateway and wireless client. As long as the passwords match, a wireless client will

be granted access to a WLAN.

Table 92

Comparison of EAP Authentication Types

EAP-MD5

EAP-TLS

EAP-TTLS

PEAP

LEAP

Mutual Authentication

No

Yes

Certificate – Client

No

Yes

Optional

No

Certificate – Server

No

Yes

No

Dynamic Key Exchange

No

Yes

Credential Integrity

None

Strong

Moderate

Deployment Difficulty

Easy

Hard

Moderate

Client Identity

Protection

No

Yes

No

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If the AP or the wireless clients do not support WPA2, just use WPA or WPA-PSK

depending on whether you have an external RADIUS server or not.

Select WEP only when the AP and/or wireless clients do not support WPA or WPA2.

WEP is less secure than WPA or WPA2.

Encryption

Both WPA and WPA2 improve data encryption by using Temporal Key Integrity

Protocol (TKIP), Message Integrity Check (MIC) and IEEE 802.1x. WPA and WPA2

use Advanced Encryption Standard (AES) in the Counter mode with Cipher block

chaining Message authentication code Protocol (CCMP) to offer stronger

encryption than TKIP.

TKIP uses 128-bit keys that are dynamically generated and distributed by the

authentication server. AES (Advanced Encryption Standard) is a block cipher that

uses a 256-bit mathematical algorithm called Rijndael. They both include a per-

packet key mixing function, a Message Integrity Check (MIC) named Michael, an

extended initialization vector (IV) with sequencing rules, and a re-keying

mechanism.

WPA and WPA2 regularly change and rotate the encryption keys so that the same

encryption key is never used twice.

The RADIUS server distributes a Pairwise Master Key (PMK) key to the AP that

then sets up a key hierarchy and management system, using the PMK to

dynamically generate unique data encryption keys to encrypt every data packet

that is wirelessly communicated between the AP and the wireless clients. This all

happens in the background automatically.

The Message Integrity Check (MIC) is designed to prevent an attacker from

capturing data packets, altering them and resending them. The MIC provides a

strong mathematical function in which the receiver and the transmitter each

compute and then compare the MIC. If they do not match, it is assumed that the

data has been tampered with and the packet is dropped.

By generating unique data encryption keys for every data packet and by creating

an integrity checking mechanism (MIC), with TKIP and AES it is more difficult to

decrypt data on a Wi-Fi network than WEP and difficult for an intruder to break

into the network.

The encryption mechanisms used for WPA(2) and WPA(2)-PSK are the same. The

only difference between the two is that WPA(2)-PSK uses a simple common

password, instead of user-specific credentials. The common-password approach

makes WPA(2)-PSK susceptible to brute-force password-guessing attacks but it’s

still an improvement over WEP as it employs a consistent, single, alphanumeric

password to derive a PMK which is used to generate unique temporal encryption

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keys. This prevent all wireless devices sharing the same encryption keys. (a

weakness of WEP)

User Authentication

WPA and WPA2 apply IEEE 802.1x and Extensible Authentication Protocol (EAP) to

authenticate wireless clients using an external RADIUS database. WPA2 reduces

the number of key exchange messages from six to four (CCMP 4-way handshake)

and shortens the time required to connect to a network. Other WPA2

authentication features that are different from WPA include key caching and pre-

authentication. These two features are optional and may not be supported in all

wireless devices.

Key caching allows a wireless client to store the PMK it derived through a

successful authentication with an AP. The wireless client uses the PMK when it tries

to connect to the same AP and does not need to go with the authentication

process again.

Pre-authentication enables fast roaming by allowing the wireless client (already

connecting to an AP) to perform IEEE 802.1x authentication with another AP

before connecting to it.

Wireless Client WPA Supplicants

A wireless client supplicant is the software that runs on an operating system

instructing the wireless client how to use WPA. At the time of writing, the most

widely available supplicant is the

WPA patch for Windows XP, Funk Software's

Odyssey client.

The Windows XP patch is a free download that adds WPA capability to Windows

XP's built-in "Zero Configuration" wireless client. However, you must run Windows

XP to use it.

WPA(2) with RADIUS Application Example

To set up WPA(2), you need the IP address of the RADIUS server, its port number

(default is 1812), and the RADIUS shared secret. A WPA(2) application example

with an external RADIUS server looks as follows. "A" is the RADIUS server. "DS" is

the distribution system.

1

The AP passes the wireless client's authentication request to the RADIUS server.

2

The RADIUS server then checks the user's identification against its database and

grants or denies network access accordingly.

3

A 256-bit Pairwise Master Key (PMK) is derived from the authentication process by

the RADIUS server and the client.

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