Lantronix EDS4100, EDS32PR, EDS16PR, EDS8PR SSL RSA or DSA, SSL Certificates and Private Keys

12: Security Settings

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 EDS 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 EDS 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 EDS 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 EDS, 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 EDS 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 EDS.

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 EDS currently only accepts separate PEM files. The key needs to be unencrypted.

EDS User Guide 104