Zyxel P-870HN-51b Router Manual PDF (Setup & Configuration Guide)

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Appendix D Wireless LANs

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IEEE 802.1x

In June 2001, the IEEE 802.1x standard was designed to extend the features of

IEEE 802.11 to support extended authentication as well as providing additional

accounting and control features. It is supported by Windows XP and a number of

network devices. Some advantages of IEEE 802.1x are:

•

User based identification that allows for roaming.

•

Support for RADIUS (Remote Authentication Dial In User Service, RFC 2138,

2139) for centralized user profile and accounting management on a network

RADIUS server.

•

Support for EAP (Extensible Authentication Protocol, RFC 2486) that allows

additional authentication methods to be deployed with no changes to the access

point or the wireless clients.

RADIUS

RADIUS is based on a client-server model that supports authentication,

authorization and accounting. The access point is the client and the server is the

RADIUS server. The RADIUS server handles the following tasks:

• Authentication

Determines the identity of the users.

• Authorization

Determines the network services available to authenticated users once they are

connected to the network.

• Accounting

Keeps track of the client’s network activity.

RADIUS is a simple package exchange in which your AP acts as a message relay

between the wireless client and the network RADIUS server.

Types of RADIUS Messages

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

and the RADIUS server for user authentication:

• Access-Request

Sent by an access point requesting authentication.

• Access-Reject

Sent by a RADIUS server rejecting access.

• Access-Accept

Sent by a RADIUS server allowing access.

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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 116

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

WPA improves data encryption by using Temporal Key Integrity Protocol (TKIP),

Message Integrity Check (MIC) and IEEE 802.1x. WPA2 also uses TKIP when

required for compatibility reasons, but offers stronger encryption than TKIP with

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

chaining Message authentication code Protocol (CCMP).

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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