Private-Public Certificates - ZyXEL Communications P-793H v3 User Manual

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.
Advantages of Certificates
Certificates offer the following benefits.
• The P-79X 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.

14.3.2 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.
Tim wants to send a message to Jenny. He needs her to be sure that it comes from him, and that
1
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).
Tim keeps the private key and makes the public key openly available. This means that anyone who
2
receives a message seeming to come from Tim can read it and verify whether it is really from him
or not.
Tim uses his private key to sign the message and sends it to Jenny.
3
Jenny receives the message and uses Tim's public key to verify it. Jenny knows that the message is
4
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).
Additionally, Jenny uses her own private key to sign a message and Tim uses Jenny's public key to
5
verify the message.
Chapter 14 Certificates
P-79X Series User's Guide
156