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IPSec General Operation, Components and Protocols
(Page 3 of 3)
IPSec Support Components
are commonly called protocols, though this is another case
where the validity of this term is debatable. They are not really distinct
protocols but are implemented as headers that are inserted into IP datagrams,
as we will see. They thus do the grunt work of IPSec, and
can be used together to provide both authentication and privacy. However,
they cannot operate on their own. For them to function properly they
need the support of several other protocols and services. The most important
of these include:
- Encryption/Hashing Algorithms: AH and
ESP are generic and do not specify the exact mechanism used for encryption.
This gives them the flexibility to work with a variety of such algorithms,
and to negotiate which is used as needed. Two common ones used with
IPSec are Message Digest 5 (MD5) and Secure Hash Algorithm
1 (SHA-1). These are also called hashing algorithms because
they work by computing a formula called a hash based on input
data and a key.
- Security Policies and Associations, and Management
Methods: Since IPSec provides flexibility in letting different devices
decide how they want to implement security, some means is required to
keep track of the security relationships between devices. This is done
in IPSec using constructs called security policies and security
associations, and by providing ways to exchange security association
information (see below).
- Key Exchange Framework and Mechanism:
For two devices to exchange encrypted information they need to be able
to share keys for unlocking the encryption. They also need a way to
exchange security association information. In IPSec, a protocol called
the Internet Key Exchange (IKE) provides these capabilities.
Key Concept: IPSec consists of a number of different components that work together to provide security services. The two main ones are protocols called the Authentication Header (AH) and Encapsulating Security Payload (ESP), which provide authenticity and privacy to IP data in the form of special headers added to IP datagrams.
Well, that's at least a start at
providing a framework for understanding what IPSec is all about and
how the pieces fit together. Well examine these components and
protocols in more detail as we proceed through this section.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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