ZyXEL Communications Network Card unified security gateway Manuel d'utilisateur télécharger pdf (Page 417)

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Chapter 23 IPSec VPN

ZyWALL USG 20/20W User’s Guide

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keys for the IKE SA and IPSec SA. In main mode, this is done in steps 3 and 4, as

illustrated next.

Figure 246 IKE SA: Main Negotiation Mode, Steps 3 - 4: DH Key Exchange

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 247 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.

Note: The ZyWALL and the remote IPSec router must use the same pre-shared key.

Diffie-Hellman key exchange

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

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