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ZyXEL AG-200 User’s Guide
Appendix A i
Appendix A
Types of EAP Authentication
This appendix discusses the five popular EAP authentication types: EAP-MD5, EAP-TLS, EAP-TTLS,
PEAP and LEAP. The type of authentication you use depends on the RADIUS server. 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.
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.