ZyXEL Communications NWA-3550, User Manual

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Chapter 18 Certificates
NWA-3500/NWA-3550 User’s Guide
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18.4 Technical Reference
This section provides technical background information about the topics covered in
this chapter.
18.4.1 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.
18.4.2 Certification Authorities
A Certification Authority (CA) issues certificates and guarantees the identity of
each certificate owner. There are commercial certification authorities like
CyberTrust or VeriSign and government certification authorities. You can use the
NWA to generate certification requests that contain identifying information and
public keys and then send the certification requests to a certification authority.