http://burnz.wordpress.com/2007/12/14/ssh-convert-openssh-to-ssh2-and-vise-versa/
Convert OpenSSH key to SSH2 key
Run the OpenSSH version of ssh-keygen on your OpenSSH public key to convert
it into the format needed by SSH2 on the remote machine. This must be done on
the system running OpenSSH.
#ssh-keygen -e -f ~/.ssh/id_dsa.pub > ~/.ssh/id_dsa_ssh2.pub
Convert SSH2 key to OpenSSH key
Run the OpenSSH version of ssh-keygen on your ssh2 public key to convert it
into the format needed by OpenSSH. This needs to be done on the system
running OpenSSH.
#ssh-keygen -i -f ~/.ssh/id_dsa_1024_a.pub > ~/.ssh/id_dsa_1024_a_openssh.pub
