The built-in SSH client of your Macintosh, started by typing ssh user@server in a terminal, and also used by Transmit.app, is the open-source implementation OpenSSH.

For public-key authentication, you have to do one more step to get your public SSH key to work with the commercial Tectia SSH implementation (by SSH Communications Security), which is used on some servers. Here is what you have to do using SSH protocol version 2:

If you don’t already have one, create a DSA key:

ssh-keygen -t dsa -N ’’ -f $HOME/.ssh/id_dsa

Convert the DSA key into a format compatible with an SSH Tectia server:

ssh-keygen -e -f $HOME/.ssh/id_dsa > id_dsa_tectia.pub

Copy the id_dsa_tectia.pub file to the Tectia SSH server:

sftp user@ssh_tectia_host
put id_dsa_tectia.pub .ssh2

Add the appropriate ~/.ssh2/authorization file entry in the Tectia SSH server:

ssh user@ssh_tectia_host ’echo "key id_dsa_tectia.pub">> .ssh2/authorization’

Login to the Tectia SSH server, this time without supplying a password.

Note that you can determine which versions of the ssh protocol an ssh server supports by examining the service banner. The service banner includes both the remote protocol version and the remote software version. If you don’t see OpenSSH in the version string, you most probably are connecting to a Tectia SSH server.