ZyXEL ZyWALL USG 2000 User Guide - Page 450

Chapter 25 IPSec VPN Table 118 Configuration > VPN > IPSec VPN > VPN Connection > Edit (continued) LABEL DESCRIPTION Encryption This field is applicable when the Active Protocol is ESP. Select which key size and encryption algorithm to use in the IPSec SA. Choices are: NULL - no encryption key or algorithm DES - a 56-bit key with the DES encryption algorithm 3DES - a 168-bit key with the DES encryption algorithm AES128 - a 128-bit key with the AES encryption algorithm AES192 - a 192-bit key with the AES encryption algorithm AES256 - a 256-bit key with the AES encryption algorithm The ZyWALL and the remote IPSec router must both have at least one proposal that uses use the same encryption and the same key. Longer keys are more secure, but require more processing power, resulting in increased latency and decreased throughput. Authentication Select which hash algorithm to use to authenticate packet data in the IPSec SA. Choices are SHA1 and MD5. SHA1 is generally considered stronger than MD5, but it is also slower. Perfect Forward Secrecy (PFS) The ZyWALL and the remote IPSec router must both have a proposal that uses the same authentication algorithm. Select whether or not you want to enable Perfect Forward Secrecy (PFS) and, if you do, which Diffie-Hellman key group to use for encryption. Choices are: none - disable PFS DH1 - enable PFS and use a 768-bit random number DH2 - enable PFS and use a 1024-bit random number DH5 - enable PFS and use a 1536-bit random number Connectivity Check Enable Connectivity Check PFS changes the root key that is used to generate encryption keys for each IPSec SA. The longer the key, the more secure the encryption, but also the longer it takes to encrypt and decrypt information. Both routers must use the same DH key group. The ZyWALL can regularly check the VPN connection to the gateway you specified to make sure it is still available. Select this to turn on the VPN connection check. 450 ZyWALL USG 2000 User's Guide