Lantronix 900-560 manual Security Certificate Principles, RSA or DSA

16 Security in Detail

Security Certificate Principles

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 other’s 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 become one’s own CA. Tools exist to generate self-signed CA certificates or to sign other certificates.

A certificate before it is signed is known as a certificate request, which only contains the identifying information. Signing it makes it a certificate. One’s certificate is also used to sign any message transmitted to the peer to identify the originator and prevent tampering while transported.

In short:

￿When using HTTPS, SSL Tunneling in Accept mode, and/or EAP-TLS, the XPort Pro needs a personal certificate with 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(s) that can authenticate those it wishes to communicate with.

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.

Obtaining a Certificate and Private Key

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.

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