Avaya Business Secure Router 222 Configuration - Basics Manual de usuario descargar pdf (Pagina 240)

240 Chapter 13 VPN

NN47922-500

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 known by the responder and both parties want to

use preshared key authentication.

Preshared key

A preshared key identifies a communicating party during a phase 1 IKE

negotiation. It is called preshared because you have to share it with another party

before you can communicate with the party over a secure connection.

Diffie-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), 1 024-bit (Group 2 – DH2) and 1 536-bit (Group 5 - DH5)

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 preshared keys.

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.

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Avaya Business Secure Router 222 Configuration - Basics Manual de usuario Pagina 240