ZyXEL Communications ZyWall USG 50-H Series, Руководство пользователя

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ZyWALL USG 50-H User’s Guide
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Certificates
34.1 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.
34.1.1 What You Can Do in the Certificate Screens
• Use the My Certificate screens (see Section 34.2 on page 492 to Section 34.2.3 on page
499 ) to generate and export self-signed certificates or certification requests and import the
ZyWALL’s CA-signed certificates.
• Use the Trusted Certificates screens (see Section 34.3 on page 500 to Section 34.3.2 on
page 504 ) to save CA certificates and trusted remote host certificates to the ZyWALL. The
ZyWALL will trust any valid certificate that you have imported as a trusted certificate. It
will also trust any valid certificate signed by any of the certificates that you have imported
as a trusted certificate.
34.1.2 What You Need to Know About Certificates
When using public-key cryptology for authentication, 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.
These keys work like a handwritten signature (in fact, certificates are often referred to as
“digital signatures”). Only you can write your signature exactly as it should look. When
people know what your signature looks like, they can verify whether something was signed by
you, or by someone else. In the same way, your private key “writes” your digital signature and
your public key allows people to verify whether data was signed by you, or by someone else.
This process works as follows.
1 Tim wants to send a message to Jenny. He needs her to be sure that it comes from him,
and that the message content has not been altered by anyone else along the way. Tim
generates a public key pair (one public key and one private key).
2
Tim keeps the private key and makes the public key openly available. This means that
anyone who receives a message seeming to come from Tim can read it and verify
whether it is really from him or not.
3 Tim uses his private key to sign the message and sends it to Jenny.
4
Jenny receives the message and uses Tim’s public key to verify it. Jenny knows that the
message is from Tim, and that although other people may have been able to read the