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Prestige 794M User’s Guide
83 Chapter 7 VPN
7.3 IPSec
Internet Protocol Security (IPSec) is a standards-based VPN that offers flexible solutions for
secure data communications across a public network like the Internet. IPSec is built around a
number of standardized cryptographic techniques to provide confidentiality, data integrity and
authentication at the IP layer.
7.3.1 AH (Authentication Header)
AH protocol (RFC 2402) was designed for integrity, authentication, sequence integrity (replay
resistance), and non-repudiation but not for confidentiality, for which the ESP was designed.
In applications where confidentiality is not required or not sanctioned by government
encryption restrictions, an AH can be employed to ensure integrity. This type of
implementation does not protect the information from dissemination but will allow for
verification of the integrity of the information and authentication of the originator.
7.3.2 ESP (Encapsulating Security Payload)
The ESP protocol (RFC 2406) provides encryption as well as the services offered by AH. ESP
authenticating properties are limited compared to the AH due to the non-inclusion of the IP
header information during the authentication process. However, ESP is sufficient if only the
upper layer protocols need to be authenticated.
An added feature of the ESP is payload padding, which further protects communications by
concealing the size of the packet being transmitted.
Table 43 ESP and AH
ESP AH
Encryption DES (default)
Data Encryption Standard (DES) is a
widely used method of data encryption
using a secret key. DES applies a 56-bit
key to each 64-bit block of data.
3DES
Triple DES (3DES) is a variant of DES,
which iterates three times with three
separate keys (3 x 56 = 168 bits),
effectively doubling the strength of DES.
AES
Advanced Encryption Standard is a
newer method of data encryption that
also uses a secret key. Various secret
key lengths (128, 192 and 256 bits) are
implemented. AES is faster than 3DES.
Select NULL to set up a phase 2 tunnel
without encryption.