10: Security Settings
XPort Pro User Guide
89
SSL Certificates
The goal of a certificate is to authenticate its sender. It is analogous to a paper document that
contains personal identification information and is signed by an authority, for example a notary or
government agency.
The principles of Security Certificate required that in order to sign other certificates, the authority
uses a private key. The published authority certificate contains the matching public key that allows
another to verify the signature but not recreate it.
The authority’s certificate can be signed by itself, resulting in a self-signed or trusted-root
certificate, or by another (higher) authority, resulting in an intermediate authority certificate. You
can build up a chain of intermediate authority certificates, and the last certification will always be a
trusted-root certificate.
An authority that signs another certificates is also called a Certificate Authority (CA). The last in
line is then the root-CA. VeriSign is a famous example of such a root-CA. Its certificate is often
built into web browsers to allow verifying the identity of website servers, which need to have
certificates signed by VeriSign or another public CA. Since obtaining a certificate signed by a CA
that is managed by another company can be expensive, it is possible to have your own CA. Tools
exist to generate self-signed CA certificates or to sign other certificates.
A certificate request is a certificate that has not been signed and only contains the identifying
information. Signing it makes it a certificate. A certificate is also used to sign any message
transmitted to the peer to identify the originator and prevent tampering while transported.
When using HTTPS, SSL Tunneling in Accept mode, and/or EAP-TLS, the XPort Pro needs a
personal certificate with a matching private key to identify itself and sign its messages. When using
SSL Tunneling in Connect mode and/or EAP-TLS, EAP-TTLS or PEAP, the XPort Pro needs the
authority certificate that can authenticate users with which it wishes to communicate.
SSL RSA or DSA
As mentioned above, the certificates contain a public key. Different key exchange methods require
different public keys and thus different styles of certificate. The XPort Pro supports key exchange
methods that require a RSA-style certificate and key exchange methods that require a DSA-style
certificate. If only one of these certificates is stored in the XPort Pro, only those key exchange
methods that can work with that style certificate are enabled. RSA is sufficient in most cases.
SSL Certificates and Private Keys
You can obtain a certificate by completing a certificate request and sending it to a certificate
authority that will create a certificate/key combo, usually for a fee. Or generate your own. A few
utilities exist to generate self-signed certificates or sign certificate requests. The XPort Pro also
has the ability to generate its own self-signed certificate/key combo.
You can use XML to export the certificate in PEM format, but you cannot export the key. Hence the
internal certificate generator can only be used for certificates that are to identify that particular
XPort Pro.
Certificates and private keys can be stored in several file formats. Best known are PKCS12, DER
and PEM. Certificate and key can be in the same file or in separate files. The key can be encrypted
with a password or not. The XPort Pro currently only accepts separate PEM files. The key needs
to be unencrypted.
