D-Link DFL-1600 - Security Appliance, User Manual

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2. Client to LAN connection - Where many remote clients need to connect to an internal
network over the Internet. In this case, the internal network is protected by the NetDefend
Firewall to which the client connects and the VPN tunnel is set up between them.
9.1.2. VPN Encryption
Encryption of VPN traffic is done using the science of cryptography. Cryptography is an umbrella
expression covering 3 techniques and benefits:
Confidentiality No one but the intended recipients is able to receive and
understand
the communication. Confidentiality is
accomplished by encryption.
Authentication and Integrity Proof for the recipient that the communication was actually
sent by the expected sender, and that the data has not been
modified in transit. This is accomplished by authentication,
and is often implemented through the use of cryptographic
keyed hashing.
Non-repudiation Proof that the sender actually sent the data; the sender cannot
later deny having sent it. Non-repudiation is usually a
side-effect of authentication.
VPNs are normally only concerned with confidentiality and authentication. Non-repudiation is
normally not handled at the network level but rather is usually done at a higher, transaction level.
9.1.3. VPN Planning
An attacker targeting a VPN connection will typically not attempt to crack the VPN encryption
since this requires enormous effort. They will, instead, see VPN traffic as an indication that there is
something worth targeting at the other end of the connection. Typically, mobile clients and branch
offices are far more attractive targets than the main corporate network. Once inside those, getting to
the corporate network then becomes easier.
In designing a VPN there are many issues that need to be addressed which aren't always obvious.
These include:
• Protecting mobile and home computers.
9.1.2. VPN Encryption Chapter 9. VPN
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