ZyXEL Communications P-334W - Manual (Page 228)

Prestige 334W User’s Guide
16-18 VPN Screens
16.11.3 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 Prestige. 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).
16.12 Configuring Advanced IKE Settings
Select Advanced at the bottom of the Rule Setup IKE screen. This is the Rule Setup IKE- Advanced
screen as shown next.