A public key is always created for Tectia Server during the installation phase. In addition, the Server administrator can generate more public-key pairs for the host, according to need.

The server is authenticated with a digital signature based on an RSA, DSA, ECDSA or Ed25519 public-key algorithm. At the beginning of each connection, the server sends its public key to the client for validation.

The key pair that the server uses in server authentication is defined in the server configuration file, ssh-server-config.xml, 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 "<INSTALLDIR>\SSH Tectia Server" directory on Windows. By default, this key pair is used for server authentication.

Each 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_rsa" />
    <public file="/etc/ssh2/hostkey_rsa.pub" />
  </hostkey>

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

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

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

We recommend that you use a maximum of one key pair of each type (RSA, DSA, ECDSA, Ed25519). If also certificates are used in server authentication, an additional three host key pairs (RSA/ DSA/ECDSA with certificate) can be used for a total of seven host keys.

The host keys can be configured with the Tectia Server Configuration tool on the Identity page. See Identity.