ZyXEL Communications Prestige 662HW Series, User Manual

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Prestige 662HW Series User’s Guide
Introduction to IPSec 15-1
Chapter 15
Introduction to IPSec
This chapter introduces the basics of IPSec VPNs.
15.1 VPN Overview
A VPN (Virtual Private Network) provides secure communications between sites without the expense
of leased site-to-site lines.
A secure VPN is a combination of tunneling, encryption, authentication,
access control and auditing technologies/services used to transport traffic over the Internet or any
insecure network that uses the TCP/IP protocol suite for communication.
15.1.1 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.
15.1.2 Security Association
A Security Association (SA) is a contract between two parties indicating what security parameters,
such as keys and algorithms they will use.
15.1.3 Other Terminology
Encryption
Encryption is a mathematical operation that transforms data from "plaintext" (readable) to "ciphertext"
(scrambled text) using a "key". The key and clear text are processed by the encryption operation,
which leads to the data scrambling that makes encryption secure. Decryption is the opposite of
encryption: it is a mathematical operation that transforms “ciphertext” to plaintext. Decryption also
requires a key.