How to Convert OpenSSH to SSH2 and vise versa

The program SSH (Secure Shell) provides an encrypted channel for logging into another computer over a network, executing commands on a remote computer, and moving files from one computer to another. SSH provides strong host-to-host and user authentication as well as secure encrypted communications over the Internet.

SSH2 is a more secure, efficient, and portable version of SSH .

Connecting two servers running different type of SSH can be a danting task if you does not know how to convert the key. In this article ,we are going to learn about how to convert  keys   SSH( OpenSSH) to SSH2.

How to Generate OpenSSH(SSH v1) key :

umadm@umixserv1 [/home/umadm/.ssh]$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/umadm/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/umadm/.ssh/id_rsa.
Your public key has been saved in /home/umadm/.ssh/id_rsa.pub.
The key fingerprint is:
5b:ac:ea:c3:25:cf:2d:31:a2:aa:83:76:4b:a2:c9:eb umadm@umixserv1
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|                 |
|                 |
|         .       |
|        S o      |
|. o   . .+       |
|+o o + oo        |
|Bo.   =.         |
|#Eo..oo.         |
+-----------------+
umadm@umixserv1 [/home/umadm/.ssh]$

Here we get two encrypted keys  callled   private key( called id_rsa) and public key id_rsa.pub  undr ~$HOME/.ssh directory.
  
You can generate dsa key by using below command.

#ssh-keygen -t dsa

Convert SSH2 to  OpenSSH(SSH):

The command below can be used to convert an SSH2 private key into the OpenSSH format:

ssh-keygen -i -f path/to/private.key > path/to/new/opensshprivate.key

The command below can be used to convert an SSH2 public key into the OpenSSH format:

ssh-keygen -i -f path/to/publicsshkey.pub > path/to/publickey.pub

Here  -i ==> SSH to read an SSH2 key and convert it into the OpenSSH format

Convert OpenSSH(SSH) to SSH2:

The  reverse  process to convert an OpenSSH key into the SSH2 format in the event that a client application requires the other format. This can be done using the following command:

OpenSSH to SSH2 Private key conversion:

ssh-keygen -e -f path/to/opensshprivate.key > path/to/ssh2privatekey/ssh2privatekey

OpenSSH to SSH2 Public key conversion:

ssh-keygen -e -f path/to/publickey.pub > path/to/ssh2privatekey/ssh2publickey.pub

Here  -e ==> SSH to read an OpenSSH key file and convert it to SSH2 format

Note:If you need passwordless authentication  b/w two different hosts , you need to convert the publickey as per the destination server SSH version and  append the public key to   ~/.ssh/authorized_keys or  ~/.ssh2/authorized_keys at destination server.