ZyXEL ZyWALL USG 50 User Manual - Page 407

Chapter 23 IPSec VPN If you enable PFS, the ZyWALL and remote IPSec router perform a DH key exchange every time an IPSec SA is established, changing the root key from which encryption keys are generated. As a result, if one encryption key is compromised, other encryption keys remain secure. If you do not enable PFS, the ZyWALL and remote IPSec router use the same root key that was generated when the IKE SA was established to generate encryption keys. The DH key exchange is time-consuming and may be unnecessary for data that does not require such security. Additional Topics for IPSec SA This section provides more information about IPSec SA in your ZyWALL. IPSec SA using Manual Keys You might set up an IPSec SA using manual keys when you want to establish a VPN tunnel quickly, for example, for troubleshooting. You should only do this as a temporary solution, however, because it is not as secure as a regular IPSec SA. In IPSec SAs using manual keys, the ZyWALL and remote IPSec router do not establish an IKE SA. They only establish an IPSec SA. As a result, an IPSec SA using manual keys has some characteristics of IKE SA and some characteristics of IPSec SA. There are also some differences between IPSec SA using manual keys and other types of SA. IPSec SA Proposal using Manual Keys In an IPSec SA using manual keys, you can only specify one encryption algorithm and one authentication algorithm. You cannot specify several proposals. There is no DH key exchange, so you have to provide the encryption key and the authentication key the ZyWALL and remote IPSec router use. Note: The ZyWALL and remote IPSec router must use the same encryption key and authentication key. Authentication and the Security Parameter Index (SPI) For authentication, the ZyWALL and remote IPSec router use the SPI, instead of pre-shared keys, ID type and content. The SPI is an identification number. Note: The ZyWALL and remote IPSec router must use the same SPI. ZyWALL USG 50 User's Guide 407