Creation and usage of SSH Identity Files for OpenSSH or SFTP

Here is a quick step by step list how to setup an use an identity file with SSH or SFTP

1. Create a private and a public key with 

    ssh-keygen -t dsa

2. Now you should have something like 

   id_dsa and id_dsa.pub

3. Add the content of the public key file id_dsa.pub to the users .ssh/authorized_keys file folder on the host you want to connect with 

   cat id_dsa.pub >> .ssh/authorized_keys

4. Now you should be ready to connect to the host with i.e.
             sftp -o IdentityFile=id_dsa user@host

     ssh  -i id_dsa user@host