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Overview of SSL Certificates and Keys

Nessus supports authentication protocols based on the OpenSSL toolkit (please see for more details about the toolkit). This provides cryptographic protection and secure authentication. This section provides an overview of the certificates and keys necessary for SSL communication with Nessus. In the example described in this document, there are three key system components: the Certificate Authority, the Nessus Server and the Nessus client, which in this case is SecurityCenter. It is necessary to generate the keys required for the SSL communication and copy them to the appropriate directories.

Certificate Authority

The Certificate Authority (CA) ensures that the certificate holder is authentic and not an impersonator. The Certificate Authority holds a copy of the certificates for registered users to certify that the certificate is genuine. When the Certificate Authority receives a Certificate Signing Request (CSR), it validates and signs the certificate. In the example provided in this document, the Certificate Authority resides on the Nessus server, but this is not the recommended method for a production environment. In proper PKI deployments, the Certificate Authority would be a separate system or entity, such as Thawte or Verisign.

Nessus Server

In the example described in this document, the Nessus server is the same physical system that holds the Certificate Authority, but this will not likely be the case in a production environment. The Nessus server is the target of the secure communication and its keys must be generated locally and copied to the systems that will need to communicate with it using the SSL protocol. The Nessus server has users defined that authenticate to it either by simple login and password or via SSL. These users will also have keys associated with them.

Nessus Client

The Nessus client, which is SecurityCenter in this case, communicates with the Nessus server via SSL. It uses keys generated for a Nessus client and stores these keys and the certificate for the Certificate Authority in the /opt/sc/daemons directory. These keys must be owned by the “tns” userid.

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