ZyXEL Communications 792H manual Negotiation Mode, Diffie-Hellman DH Key Groups

Prestige 792H G.SHDSL Router

Choose a Diffie-Hellman public-key cryptography key group (DH1 or DH2).

Set the IKE SA lifetime. This field allows you to determine how long an IKE SA should stay up before it times out. An IKE SA times out when the IKE SA lifetime period expires. If an IKE SA times out when an IPSec SA is already established, the IPSec SA stays connected.

In phase 2 you must:

Choose which protocol to use (ESP or AH) for the IKE key exchange. Choose an encryption algorithm.

Choose an authentication algorithm

Choose whether to enable Perfect Forward Secrecy (PFS) using Diffie-Hellman public-key cryptography – see section 14.10.3. Select None (the default) to disable PFS.

Choose Tunnel mode or Transport mode.

Set the IPSec SA lifetime. This field allows you to determine how long the IPSec SA should stay up before it times out. The Prestige automatically renegotiates the IPSec SA if there is traffic when the IPSec SA lifetime period expires. The Prestige also automatically renegotiates the IPSec SA if both IPSec routers have keep alive enabled, even if there is no traffic. If an IPSec SA times out, then the IPSec router must renegotiate the SA the next time someone attempts to send traffic.

14.10.1Negotiation Mode

The phase 1 Negotiation Mode you select determines how the Security Association (SA) will be established for each connection through IKE negotiations.

Main Mode ensures the highest level of security when the communicating parties are negotiating authentication (phase 1). It uses 6 messages in three round trips: SA negotiation, Diffie-Hellman exchange and an exchange of nonces (a nonce is a random number). This mode features identity protection (your identity is not revealed in the negotiation).

Aggressive Mode is quicker than Main Mode because it eliminates several steps when the communicating parties are negotiating authentication (phase 1). However the trade-off is that faster speed limits its negotiating power and it also does not provide identity protection. It is useful in remote access situations where the address of the initiator is not know by the responder and both parties want to use pre-shared key authentication.

14.10.2Diffie-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.

14-14 VPN Screens