Ubuntu SSH How-to

Scenario: generate SSH key pairs and use PuTTY to logon to Ubuntu without inputing user & password each time.
Steps:

• Create the Cryptographic Keys:

  $ ssh-keygen -t rsa

  Assign the pass phrase (press [enter] key twice if you don't want a passphrase). It will create 2 files in ~/.ssh directory as follows:
  ~/.ssh/id_rsa : identification (private) key
  ~/.ssh/id_rsa.pub : public key

• Use WinSCP to copy the id_rsa (private key) to desktop, use PuTTYgen.exe to load this key and save private key to PuTTY's format.

• Add id_rsa.pub in ~/.ssh/authorized_keys (or authorized_keys2), just in 1 line. Or simply

  mv id_rsa.pub authorized_keys

• Be sure both the home directory and the .ssh directory be owned and writable only by the owner (700 recommended for .ssh)

• Any error see /var/log/auth.log

• sshd protocol 1 is insecure, so vi /etc/ssh/sshd_config:
  [...]
  Protocol 2
  PasswordAuthentication no # if want to disable interactive logon

• Restart sshd:

  $ sudo /etc/init.d/ssh restart

• Use the saved private key in PuTTY:
  PuTTY Configuration -> Connection -> SSH -> Auth -> Private key file for authentication,
  then load the private key. Or use PAGEANT to load this automatically.

• Change passphrase:
  If it's already converted to PuTTY format, use PuTTYgen.exe to convert it back to OpenSSH format, then
  

  $ ssh-keygen -p

  Enter file in which the key is (id_rsa):...

Reference:

• http://www.howtoforge.com/ssh_key_based_logins_PuTTY

• http://www.cyberciti.biz/tips/ssh-public-key-based-authentication-how-to.html

• http://kimmo.suominen.com/docs/ssh/

• http://alexandria.wiki.sourceforge.net/SSH+Key+Generation