The server is authenticated with a digital signature based on a DSA or RSA public-key algorithm. At the beginning of the connection, the server sends its public key to the client for validation.

The key pair used for server authentication is defined on the server in the ssh-server-config.xml file with the following elements:

<params>
  <hostkey>      
    <private file="/etc/ssh2/hostkey" />
    <public file="/etc/ssh2/hostkey.pub" />
  </hostkey>
...
</params>

Giving the public key in the configuration file is not mandatory. It will be derived from the private key if it is not found otherwise. Specifying the public key will, however, decrease start-up time for the software, as deriving the public key is a somewhat time-consuming operation.

During the installation process, one RSA key pair (with the file names hostkey and hostkey.pub) is generated and stored in the /etc/ssh2 directory on Unix and in the "C:\Program Files\SSH Communications Security\SSH Tectia\SSH Tectia Server" directory on Windows. By default this key pair is used for server authentication.

Each SSH Tectia Server can have multiple host keys. You could have, for example, the following set of parameters in your ssh-server-config.xml file:

<params>
  <hostkey>      
    <private file="/etc/ssh2/hostkey_dsa" />
    <public file="/etc/ssh2/hostkey_dsa.pub" />
  </hostkey>

  <hostkey>      
    <private file="/etc/ssh2/hostkey_rsa" />
    <public file="/etc/ssh2/hostkey_rsa.pub" />
  </hostkey>
...
</params>

Both keys are stored in memory when the ssh-server-g3 process is started, which means that either one of them can be used to authenticate the server.

We recommend that you use a maximum of one DSA and one RSA key pair. If also certificates are used in server authentication, an additional two host key pairs (DSA with certificate and RSA with certificate) can be used for a total of four host keys.

On Windows, the host keys can be configured with the SSH Tectia Server Configuration tool on the Identity page. See Identity.