HP 10500 Series Configuration Manual page 311

Figure 114 Encapsulation by security protocols in different modes
Authentication algorithms and encryption algorithms
1. Authentication algorithms
IPsec uses hash algorithms to perform authentication. A hash algorithm produces a fixed-length
digest for an arbitrary-length message. IPsec peers respectively calculate message digests for each
packet. If the resulting digests are identical, the packet is considered intact.
IPsec supports the following hash algorithms for authentication:
MD5, which takes a message of arbitrary length as input and produces a 128-bit message
digest.
SHA- 1 , which takes a message of a maximum length less than the 64th power of 2 in bits as
input and produces a 160-bit message digest.
Compared with SHA-1, MD5 is faster but less secure.
2. Encryption algorithms
IPsec mainly uses symmetric encryption algorithms, which encrypt and decrypt data by using the
same keys. The following encryption algorithms are available for IPsec on the device:
Data Encryption Standard (DES), which encrypts a 64-bit plain text block with a 56-bit key. DES
is the least secure but the fastest algorithm. It is sufficient for general security requirements.
Triple DES (3DES), which encrypts plain text data with three 56-bit DES keys. The key length
totals up to 168 bits. It provides moderate security strength and is slower than DES.
Advanced Encryption Standard (AES), which encrypts plain text data with a 128-bit, 192-bit, or
256-bit key. AES provides the highest security strength and is slower than 3DES.
IPsec SA setup modes
There are two IPsec SA setup modes:
Manual mode. In this mode, you manually configure and maintain all SA settings. Advanced
•
features like periodical key update are not available. However, this mode implements IPsec
independently of IKE.
• ISAKMP mode. In this mode, IKE automatically negotiates and maintains IPsec SAs for IPsec.
If the number of IPsec tunnels in your network is small, use the manual mode. If the number of IPsec
tunnels is large, use the ISAKMP mode.
IPsec tunnel
An IPsec tunnel is a bidirectional channel created between two peers. An IPsec tunnel comprises one or
more pairs of SAs.
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