ZyXEL Communications P-660 series Guia do Utilizador descarregar pdf (Página 138)

Chapter 9 Certificates

P-660R-F1 Series User’s Guide

138

Advantages of Certificates

Certificates offer the following benefits.

• The ZyXEL Device only has to store the certificates of the certification authorities that you decide

to trust, no matter how many devices you need to authenticate.

• Key distribution is simple and very secure since you can freely distribute public keys and you

never need to transmit private keys.

Self-signed Certificates

You can have the ZyXEL Device act as a certification authority and sign its own certificates.

9.6.2 Private-Public 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 message, no-one can

have altered it (because they cannot re-sign the message with Tim’s private key).

5 Additionally, Jenny uses her own private key to sign a message and Tim uses Jenny’s public key to

verify the message.

9.6.3 Verifying a Trusted Remote Host’s Certificate

Certificates issued by certification authorities have the certification authority’s signature for you to

check. Self-signed certificates only have the signature of the host itself. This means that you must

be very careful when deciding to import (and thereby trust) a remote host’s self-signed certificate.

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ZyXEL Communications P-660 series Guia do Utilizador Página 138