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Glossary
IPSec
Spoofing, anti-
spoofing
Symmetrical
encryption
Port number
100 von 105
IP Security (IPSec) is a standard that makes it possible to ensure
the authenticity of the sender, the confidentiality and the integrity of
the data in IP datagrams by means of encryption. The components
of IPSec are the Authentication Header (AH), the Encapsulating
Security Payload (ESP), the Security Association (SA), the Security
Parameter Index (SPI) and the Internet Key Exchange (IKE).
When communication starts the computers involved clarify the
method used and its implications, e.g. Transport Mode or Tunnel
Mode.
In Transport Mode an IPSec header is inserted into each IP
datagram between the IP header and the TCP or UDP header. As
the IP header is not changed this mode is suitable only for a host-
to-host connection.
In Tunnel Mode an IPSec header and a new IP header are inserted
in front of the entire IP datagram. This means that the original
datagram is contained, encrypted as a whole, in the payload of the
new datagram.
The Tunnel Mode is used in the VPN: the devices at the tunnel
ends perform the encryption and decryption of the datagrams, while
the datagrams themselves remain completely protected as they
pass through the tunnel, i.e. during transmission via a public
network.
In Internet terminology, spoofing means giving a false address. By
giving a false Internet address someone is pretending to be an
authorised user.
Anti-spoofing refers to mechanisms designed to detect or prevent
spoofing.
With symmetrical encryption the data are encrypted and decrypted
using the same key. Examples of symmetrical encryption
algorithms are DES and AES. These are fast, but require complex
administration as the number of users increases.
The port number field is a 2-byte field in UDP and TCP headers.
Assigning port numbers serves to identify the different data streams
handled simultaneously by UDP/TCP. The entire data exchange
between the UDP/TCP and the application processes takes place
via these port numbers. The assignment of port numbers to
application processes takes place dynamically and randomly. Fixed
port number are assigned to certain frequently used application
processes. These are known as assigned numbers.
SINAUT MD740-1
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