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Appendix C Wireless LANs
NWD-270N User’s Guide
78
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.