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This chapter gives background information about public-key certificates and explains how to use
15.1 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ZyWALL does not trust a certificate if any certificate on its path has expired or been revoked.
Certificates
them. This chapter is only applicable to the ZyWALL 2.
ZyWALL 2 Series User's Guide
Chapter 15
Certificates
15-1
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