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Chapter 16 Certificates
FMG3024-D10A / FMG3025-D10A Series User’s Guide
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The 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The Device does not trust a certificate if any certificate on its path has expired or been revoked.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A directory of certificates that have been revoked before the scheduled expiration is called a CRL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 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 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.
Certificate File Formats
The certification authority 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 64 ASCII characters 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. The 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 64 ASCII
characters to convert a binary PKCS#7 certificate into a printable form.
Note: Be careful not to convert a binary file to text during the transfer process. It is easy
for this to occur since many programs use text files by default.
16.1.3 Verifying a Certificate
Before you import a trusted CA or trusted remote host certificate into the Device, you should verify
that you have the actual certificate. This is especially true of trusted CA certificates since the Device
also trusts any valid certificate signed by any of the imported trusted CA certificates.