ZyXEL Communications ZyXEL ZyWALL 35 - Manual (Page 258)

ZyWALL 35 User’s Guide
256 Chapter 14 VPN Screens
14.11.4 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).
14.12 Configuring Advanced VPN Rule
Select Advanced at the bottom of the Edit VPN Rule screen. This is the VPN Rule - Edit-
Advanced screen as shown next.
Figure 120 Edit VPN Rule: Advanced