Hi sir
the procedure to connect from RouterOS as client to another ssh server is slightly different:
1) you need to import both public and private key under
/user ssh-keys private
/user ssh-keys private import private-key-file=sshkey public-key-file=sshkey.pub user=connect
2) make sure that you copied on the Linux server side, the generated key to the authorized_keys file under the correct linux user home dir (in my case the user is called connect) :
cat sshkey.pub >> /home/connect/.ssh/authorized_keys
3) make sure that inside /etc/ssh/sshd config file (or equivalent other distro file) , you have added the source ip of mikrotik client to the AllowUsers row.
4) following the previous steps, you will succeed to enter ssh server from mikrotik ssh client without any password (100% guarantee at least on my current installed RoS 5.16):
[connect@ROUTER-GREENCOMPUTING] > /system ssh 172.23.1.2 user=connect
Linux connectiviaPBX 2.6.32-24-generic-pae #39-Ubuntu SMP Wed Jul 28 07:39:26 UTC 2010 i686 GNU/Linux
Ubuntu 10.04.1 LTS
Welcome to Ubuntu!
* Documentation: https://help.ubuntu.com/
Last login: Mon Aug 13 01:05:25 2012 from 172.21.1.1
connect@greenComputing:~$
I hope this will help you tor each your goal.