Introduction

If your system is available through ssh on the Internet key based authentication should must be used.

Even with preventative software such as fail2ban we have observed honeypot system being compromised within 3 days of being set up.

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As long as the major number (the first digit) is close you should have no issues.

Installing SSH

This installs the SSH server and client,

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Note if you find that connecting via SSH is slow you might want to disable DNS lookup.

Generate Public and Private Keys on Client Machine

In principle, the generation of the Public and Private keys are done by user themselves on their own machine. This is because even the Unix Administrator should not have the user's private key.

With a Unix based system, this can be accomplished with the command line as follows(below). Windows does not have a native way of doing this, but most Windows ssh client programs will provide a means of key generation.

Windows Client

If you are on a Windows machine, make sure to store your private key on a protected location. Usually this would be your Windows desktop or home directory.

Putty is one of the most popular Windows SSH Clients and your keys can be setup using puttyGen. However, Putty also has not been updated in years and I've found the generated keys to be problematic (for example will not work on my Mac). Instead, I recommend BitVise SSH Client Tunnelier for the key generation.

For console work, I still use Putty (actually Kitty) for normal console work, but still keep BitVise for its superior interface for file uploads and port tunnelling.

Unix Client

On Ubuntu it's super easy and your generated private key also work with Windows SSH clients.

ssh-keygen without parameters generates 2048 RSA public and private keys,

• Private key kept on the client machine = id_rsa
• Public key put on the target server machine = id_rsa.pub which will then be added into ~/.ssh/authorized_keys

ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/tinpham/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /Users/tinpham/.ssh/id_rsa.
Your public key has been saved in /Users/tinpham/.ssh/id_rsa.pub.
The key fingerprint is:
c7:6c:3e:87:4a:09:90:ef:6d:a9:88:f8:f0:89:d2:13 tinpham@Tin-Phams-iMac.local
The key's randomart image is:
+--[ RSA 2048]----+
|        . oo.    |
|         s ..  . |
|          ...++ .|
|       T . +.=...|
|        F o + *. |
|         + o + . |
|          C .    |
|         . +     |
|                 |
+-----------------+

On a Unix system file permissions should automatically be set to protect your key files from other accounts.

Windows Client

If you are on a Windows machine, make sure to store your private key on a protected location. Usually this would be your Windows desktop or home directory.

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Test Key Based Authentication

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http://www.freetutorialssubmit.com/convert-ssh-private-key-with-putty-keygen/1400 - sometimes you need to use different formats of keys.