ZyXEL Communications NBG334SH - Manual (Page 245)

Appendix F Wireless LANs
ZyXEL NBG-334SH User’s Guide
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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 Authentication
This appendix discusses some popular authentication types: EAP-MD5, EAP-TLS, EAP-
TTLS, PEAP and LEAP.
The type of authentication you use depends on the RADIUS server or the AP. Consult your
network administrator for more information.
EAP-MD5 (Message-Digest Algorithm 5)
MD5 authentication is the simplest one-way authentication method. The authentication server
sends a challenge to the wireless station. The wireless station ‘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.
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 stations
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.