Establishing SSH Hand-Shake

An SSH Key is a credential used in the SSH protocol (also reffered to as Secure Shell) to establish a secure remote login from one computer to another. It provides for strong authentication and it protects communications security and integrity with strong encryption. It s a secure althernative to a non-protected login protocols such as (telnet, rlogin, and insecure file transfer methods (ftp).

The protocol works in a client-server model by establishing connection from an SSH client to an SSH server. The connection is driven by the client and establishes connection by using the public key crytography to verifiy the identity of the SSH Server. The SSH protocol after successful handshake uses the strong encryption hashing algorithms to ensure the privacy and integrity of the data that is exhanged between the client and server.

There are several options when using the ssh-keygen command. As listed below:

Usage: ssh-keygen [options]
Options:
  -b bits     Number of bits in the key to create.
  -c          Change comment in private and public key files.
  -e          Convert OpenSSH to IETF SECSH key file.
  -f filename Filename of the key file.
  -i          Convert IETF SECSH to OpenSSH key file.
  -l          Show fingerprint of key file.
  -p          Change passphrase of private key file.
  -q          Quiet.
  -y          Read private key file and print public key.
  -t type     Specify type of key to create.
  -B          Show bubblebabble digest of key file.
  -C comment  Provide new comment.
  -N phrase   Provide new passphrase.
  -P phrase   Provide old passphrase.

The "ssh-keygen -t rsa" will create the ssh key for user:

Generating public/private rsa key pair.
Enter file in which to save the key (/export/home/userid/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /export/home/userid/.ssh/id_rsa.
Your public key has been saved in /export/home/userid/.ssh/id_rsa.pub.
The key fingerprint is:
0f:85:1d:30:a9:e3:ba:c4:34:80:68:ea:73:c8:82:a4 userid@sshclientserver

/export/home/userid/.ssh>ls -l id*
-rw-------   1 userid   usergrp      887 Apr 11 08:48 id_rsa
-rw-r--r--   1 userid   usergrp      238 Apr 11 08:48 id_rsa.pub
/export/home/userid/.ssh>cat id_rsa.pub
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEAzvOj7VjLfDpHwmbdrdQAsiNeTTg+
M2X2d8+nSM8HZQlNoX5EWZFVCDQP2ORbKS79nrkdrrQzyJhKdeLktabdqNrVQn5J
S4umnHgvoQySa7Fi6SVXyWLSzECC9L0SOxlaHVvhs36oGNJq+fSl+kqWv3qA0aJm
YyTDIzXefRRqqak= userid@clientservername
/export/home/userid/.ssh>cat id_rsa
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
/export/home/userid/.ssh>

Create the directory

ssh userid@sshserver mkdir -p .ssh

You will be prompted for credentials

Upload the id_rsa.pub command

cat .id_rsa.pub|ssh userid@sshserver 'cat >> .ssh/authorized_keys'

Change permissions

ssh userid@sshserver "chmod 700 .ssh; chmod 640 .ssh/authorized_keys"

You can now logon to sshserver without any password

The following script will allow you to generate the SSH key and ftp to destionation SSH server and added it to the authorized_keys file without being prompted.

#!/bin/bash

# -------------------------------------------
# Generate the key
# -------------------------------------------
cd $HOME
mkdir -p $HOME/.ssh
cd $HOME/.ssh
ssh-keygen -q -t rsa -N '' -f $HOME/.ssh/id_rsa

# -------------------------------------------
# FTP/APPEND key to the destination
# -------------------------------------------
FL=id_rsa.pub
DEST=ipaddress
TODIR=/home/userid/.ssh
FLDIR=$HOME/.ssh
USERID=userid
PASSWD=userpasswd

ftp -v -n $DEST <<EOF; 
user $USERID \
$PASSWD
lcd $FLDIR
cd  $TODIR
append $FL authorized_keys
EOF

exit 0