ZyXEL Communications P-2612HW Series User Manual page 292

Chapter 15 Certificates
Public and Private Keys
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. Public-key encryption in general works as follows.
Tim wants to send a private message to Jenny. Tim generates a public-private key
1
pair. What is encrypted with one key can only be decrypted using the other.
Tim keeps the private key and makes the public key openly available.
2
Tim uses his private key to encrypt the message and sends it to Jenny.
3
Jenny receives the message and uses Tim's public key to decrypt it.
4
Additionally, Jenny uses her own private key to encrypt a message and Tim uses
5
Jenny's public key to decrypt the message.
The ZyXEL Device uses certificates based on public-key cryptology to authenticate
users attempting to establish 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.
Certification Path
A certification path is the hierarchy of certification authority certificates that
validate a certificate. The ZyXEL Device does not trust a certificate if any
certificate on its path has expired or been revoked.
Certificate Directory Servers
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 A directory of certificates that have been revoked before the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 ZyXEL
Device 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).
Advantages of Certificates
Certificates offer the following benefits.
292
P-2612HW Series User's Guide