ZyXEL Communications 200 Series - Manual (Page 375)

Chapter 20 IPSec VPN
ZyWALL USG 100/200 Series User’s Guide
375
DH public-key cryptography is based on DH key groups. Each key group is a fixed number of
bits long. The longer the key, the more secure the encryption, but also the longer it takes to
encrypt and decrypt information. For example, DH2 keys (1024 bits) are more secure than
DH1 keys (768 bits), but DH2 keys take longer to encrypt and decrypt.
Authentication
Before the ZyWALL and remote IPSec router establish an IKE SA, they have to verify each
other’s identity. This process is based on pre-shared keys and router identities.
In main mode, the ZyWALL and remote IPSec router authenticate each other in steps 5 and 6,
as illustrated below. The identities are also encrypted using the encryption algorithm and
encryption key the ZyWALL and remote IPSec router selected in previous steps.
Figure 263 IKE SA: Main Negotiation Mode, Steps 5 - 6: Authentication (continued)
You have to create (and distribute) a pre-shared key. The ZyWALL and remote IPSec router
use it in the authentication process, though it is not actually transmitted or exchanged.
"
The ZyWALL and the remote IPSec router must use the same pre-shared key.
Step 5:
pre-shared key
ZyWALL identity, consisting of
- ID type
- content
Step 6:
pre-shared key
Remote IPSec router identity, consisting of
- ID type
- content