ZyWALL 5/35/70 Series User’s Guide

19.8.3 Diffie-Hellman (DH) Key Groups

Diffie-Hellman (DH) is a public-key cryptography protocol that allows two parties to establish a shared secret over an unsecured communications channel. Diffie-Hellman is used within IKE SA setup to establish session keys. 768-bit (Group 1 - DH1) and 1024-bit (Group 2 – DH2) Diffie-Hellman groups are supported. Upon completion of the Diffie-Hellman exchange, the two peers have a shared secret, but the IKE SA is not authenticated. For authentication, use pre-shared keys.

19.8.4 Perfect Forward Secrecy (PFS)

Enabling PFS means that the key is transient. The key is thrown away and replaced by a brand new key using a new Diffie-Hellman exchange for each new IPSec SA setup. With PFS enabled, if one key is compromised, previous and subsequent keys are not compromised, because subsequent keys are not derived from previous keys. The (time-consuming) Diffie- Hellman exchange is the trade-off for this extra security.

This may be unnecessary for data that does not require such security, so PFS is disabled

(None) by default in the ZyWALL. Disabling PFS means new authentication and encryption keys are derived from the same root secret (which may have security implications in the long run) but allows faster SA setup (by bypassing the Diffie-Hellman key exchange).

19.9 X-Auth (Extended Authentication)

Extended authentication provides added security by allowing you to use usernames and passwords for VPN connections. This is especially helpful when multiple ZyWALLs use one VPN rule to connect to a single ZyWALL. An attacker cannot make a VPN connection without a valid username and password.

The extended authentication server checks the user names and passwords of the extended authentication clients before completing the IPSec connection (see Chapter 21 on page 366).

A ZyWALL can be an extended authentication server for some VPN connections and an extended authentication client for other VPN connections.

19.9.1 Authentication Server

A ZyWALL set to be a VPN extended authentication server can use either the local user database internal to the ZyWALL or an external RADIUS server for an unlimited number of users. The ZyWALL uses the same local user database for VPN extended authentication and wireless LAN security.

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Chapter 19 VPN Screens