Chapter 14 Certificates; Certificates Overview; Advantages Of Certificates - ZyXEL Communications ZyWALL 5 User Manual

This chapter gives background information about public-key certificates and explains how to

14.1 Certificates Overview

The ZyWALL can use certificates (also called digital IDs) to authenticate users. Certificates are based
on public-private key pairs. A certificate contains the certificate owner's identity and public key.
Certificates provide a way to exchange public keys for use in authentication.
A Certification Authority (CA) issues certificates and guarantees the identity of each certificate owner.
There are commercial certification authorities like CyberTrust or VeriSign and government
certification authorities. You can use the ZyWALL to generate certification requests that contain
identifying information and public keys and then send the certification requests to a certification
authority.
In public-key encryption and decryption, each host has two keys. One key is public and can be made
openly available; the other key is private and must be kept secure. Public-key encryption in general
works as follows.
1. Tim wants to send a private message to Jenny. Tim generates a public key pair. What is
encrypted with one key can only be decrypted using the other.
2. Tim keeps the private key and makes the public key openly available.
3. Tim uses his private key to encrypt the message and sends it to Jenny.
4. Jenny receives the message and uses Tim's public key to decrypt it.
5. Additionally, Jenny uses her own private key to encrypt a message and Tim uses Jenny's
public key to decrypt the message.
The ZyWALL uses certificates based on public-key cryptology to authenticate users attempting to
establish a connection, not to encrypt the data that you send after establishing a connection. The
method used to secure the data that you send through an established connection depends on the type of
connection. For example, a VPN tunnel might use the triple DES encryption algorithm.
The certification authority uses its private key to sign certificates. Anyone can then use the
certification authority's public key to verify the certificates.
A certification path is the hierarchy of certification authority certificates that validate a certificate. The
ZyWALL does not trust a certificate if any certificate on its path has expired or been revoked.
Certification authorities maintain directory servers with databases of valid and revoked certificates. A
directory of certificates that have been revoked before the scheduled expiration is called a CRL
(Certificate Revocation List). The ZyWALL can check a peer's certificate against a directory server's
list of revoked certificates. The framework of servers, software, procedures and policies that handles
keys is called PKI (public-key infrastructure).

14.1.1 Advantages of Certificates

Certificates offer the following benefits.
Certificates
ZyWALL 5 Internet Security Appliance
Chapter 14
Certificates
use them.
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