ZyXEL Communications NWA Series User Manual page 155

Additionally, Jenny uses her own private key to sign a message and Tim uses Jenny's public key to verify
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the message.
The Zyxel 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.
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
Zyxel Device does not trust a certificate if any certificate on its path has expired or been revoked.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directory of certificates that have been revoked before the scheduled expiration is called a CRL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 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.
• 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.
Factory Default Certificate
The Zyxel Device generates its own unique self-signed certificate when you first turn it on. This certificate
is referred to in the GUI as the factory default certificate.
Certificate File Formats
Any certificate that you want to import has to be in one of these file formats:
• Binary X.509: This is an ITU-T recommendation that defines the formats for X.509 certificates.
• PEM (Base-64) encoded X.509: This Privacy Enhanced Mail format uses lowercase letters, uppercase
letters and numerals to convert a binary X.509 certificate into a printable form.
• Binary PKCS#7: This is a standard that defines the general syntax for data (including digital signatures)
that may be encrypted. A PKCS #7 file is used to transfer a public key certificate. The private key is not
included. The Zyxel Device currently allows the importation of a PKS#7 file that contains a single
certificate.
• PEM (Base-64) encoded PKCS#7: This Privacy Enhanced Mail (PEM) format uses lowercase letters,
uppercase letters and numerals to convert a binary PKCS#7 certificate into a printable form.
Chapter 16 Certificates
NWA/WAC/WAX Series User's Guide
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