Prestige 794M User’s Guide

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.

 

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Chapter 7 VPN