ZyXEL Communications MAX-306, Руководство пользователя, Страница: 199 / 405

Chapter 15 The Certificates Screens
User’s Guide
199
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 she knows 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.
The WiMAX Device 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 WiMAX Device does not trust a certificate if any
certificate on its path has expired or been revoked.
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 A directory of certificates that have been revoked before the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 WiMAX
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).
15.4.1.1 Advantages of Certificates
Certificates offer the following benefits.