ZyXEL VSG1432 User Guide - Page 253

Chapter 21 IPSec Table 87 Settings > Add/Edit: Auto(IKE) LABEL DESCRIPTION Encryption Algorithm Select DES, 3DES, AES-128, ES-192 or AES-256 from the dropdown list box. Integrity Algorithm Select DiffieHellman Group for Key Exchange Key Life Time (Seconds) When you use one of these encryption algorithms for data communications, both the sending device and the receiving device must use the same secret key, which can be used to encrypt and decrypt the message or to generate and verify a message authentication code. The DES encryption algorithm uses a 56-bit key. Triple DES (3DES) is a variation on DES that uses a 168-bit key. As a result, 3DES is more secure than DES. It also requires more processing power, resulting in increased latency and decreased throughput. This implementation of AES uses a 128-bit, 192-bit or 256-bit key. AES is faster than 3DES. Select SHA1 or MD5 from the drop-down list box. MD5 (Message Digest 5) and SHA1 (Secure Hash Algorithm) are hash algorithms used to authenticate packet data. The SHA1 algorithm is generally considered stronger than MD5, but is slower. Select MD5 for minimal security and SHA1 for maximum security. You must choose a key group for key exchange in SA setup. 768bit refers to Diffie-Hellman Group 1 a 768 bit random number. 1024bit refers to Diffie-Hellman Group 2 a 1024 bit (1Kb) random number. Other options include 1536, 2048, and 3072 bit Diffie-Hellman groups. Define the length of time before an IKE or IPSec SA automatically renegotiates in this field. It may range from 1 to 2,000,000,000 seconds. Apply Cancel A short SA Life Time increases security by forcing the two VPN gateways to update the encryption and authentication keys. However, every time the VPN tunnel renegotiates, all users accessing remote resources are temporarily disconnected. Click Apply/Save to save your changes and return to the IPSec screen. Click Cancel to exit this screen without saving. 21.3.1.2 Manual Key Setup Manual key management is useful if you have problems with Auto(IKE) key management. 21.3.1.3 Security Parameter Index (SPI) An SPI is used to distinguish different SAs terminating at the same destination and using the same IPSec protocol. This data allows for the multiplexing of SAs to a single gateway. The SPI (Security Parameter Index) along with a destination IP address uniquely identify a particular Security Association (SA). The SPI is transmitted from the remote VPN gateway to the local VPN gateway. The local VPN gateway then uses the network, encryption and key values that the administrator associated with the SPI to establish the tunnel. VSG1432-B101 Series User's Guide 253