ZyXEL Communications VMG3925-B30C User Manual page 300

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.
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.
Appendix B Wireless LANs
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