Part 4a - Securing SSH (Windows Systems)

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Last updated: Jul 18, 2019 by Nathan Bode (Unlicensed)
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SSH provides an authentication option that utilises an RSA public / private key pair. This allows you to lock your node, to only be accessible via SSH by use of the private key, preventing all password-based access. While this provides an additional level of security when accessing your node remotely, care should be taken to prevent locking yourself out of your node. If you already have an existing SSH RSA public / private key pair, you may choose to use that key pair to access your node. If you are at all unsure, please ask within Discord, or via a zenhelp ticket before proceeding with these steps.

**THIS IS A DELIBERATELY BOLD AND RED WARNING - ENSURE YOU UNDERSTAND WHAT YOU ARE DOING BEFORE PROCEEDING - PLEASE READ THE TEXT BELOW THIS WARNING BEFORE CONTINUING**



**ENSURE you OPEN A SECOND TERMINAL SESSION (FROM STEP 10) on your local machine and are logged into your node with BOTH terminal sessions while following these steps**


NOTE: This page only applies to PuTTY terminals on Windows 7 64-bit and newer, for Mac OS and Linux users see:


DescriptionCommand

Generate an SSH key-pair - steps 4 - 7, 10 - 13 are performed on your local machine, not your node

1

Steps 1 - 13 are a pre-requisite for securing SSH in steps 15 and 16 below, the intention is to generate an RSA key pair in order to turn off password access via SSH.

Ensure you are still logged in with your first session (opened in Part 2)

A second terminal will be used after step 10


On your node

2Create a .ssh directory and inside that directory an authorized_keys file
mkdir -p ~/.ssh; touch ~/.ssh/authorized_keys; chmod 700 ~/.ssh
3

Edit the authorized_keys file using nano


NOTE: Minimize this terminal and proceed with the following steps

nano ~/.ssh/authorized_keys

On Your Local Machine

4

Launch PuTTYgen by navigating to PuTTY (64-Bit) folder under applications in your start menu, or if on Windows 10, click start and type puttygen

5

NOTE: If you already have an existing key used for other nodes, click "Load" and navigate to your ".ppk" file, open it and enter the password to load the public key, then skip to step 7 to continue

NOTE: If you DO NOT have an existing key, continue with the following

Under "Parameters", select RSA and in the field "Number of bits" enter 2048.

  • Click "Generate" and move your cursor around to generate randomness to create your private/public key pair
  • If you do already have a key, it is recommended to back it up ASAP, see links in step 4 below

6

Create a unique "Key comment" and a strong "Key passphrase" and re-enter to "Confirm passphrase".

DO NOT LOSE THIS PASSWORD, IT SHOULD NOT BE THE SAME AS THE USER PASSWORD!

Click "Save private key" and store the ".ppk" file in a secure location, such as an encrypted thumb drive

7

Right click the key text in the box labeled: "Public key for pasting into OpenSSH authorized_keys file"

Click "Select All"

Right click the key text again and select "Copy"


On your node

8

Go back to your PuTTY terminal minimized in step 3

Paste the Public key copied above into PuTTY terminal by right clicking into an open space inside the window

Save and exit by hitting Ctrl+X, type y, then hit enter

9

Update the file's permissions


NOTE: Minimize this terminal and proceed with the following steps

Keep this terminal running in the background for the rest of this page

chmod 600 ~/.ssh/authorized_keys

On Your Local Machine

10

Launch PuTTY for a SECOND TERMINAL WINDOW and enter the <USER>@<FQDN> into the "Host Name" field

  • Substitute <USER> with your node non-root username, remove <brackets>
  • Substitute <FQDN> with the Fully-Qualified Domain Name of your node, remove <brackets>
  • Ensure "Port" is set to 22, "Connection type" is SSH and "Close window on exit" is set to Always
  • Enter a name for the node into the "Saved Sessions" field and click "Save"

11

Load your saved session created in step 10 and load your private key into the session

  • Select the Session under "Saved Sessions" and click "Load"
  • Expand "Connection" and "SSH" and select "Auth" from the left window pane, under "Category"
  • Click "Browse" in the right widow pane and navigate to and open the .ppk file created in step 4


12

Save changes made to your session from step 11

  • Scroll back to the top of the left window pane, under "Category" and select "Session"
  • Ensure that under "Host Name (or IP address)", you have your <USER>@<FQDN>
  • Under the "Saved Sessions" box on the right, select your saved session from the list and click "Save"
  • Once your session has been saved, you can click "Load" and then "Open" to connect to your node

13

Enter your password for the key created in step 4, you will notice it will display the "Key comment" made in step 4

If you do not see the "Key comment", go back and re-check your work

Repeat the login in steps 12 and 13 as many times as necessary to be confident that you are logging in without a USER password, instead using the RSA key password. Failure to complete this step will result in locking yourself out of your node.


On your node

14

NOTE: Proceed with steps 15 and 16 ONLY if you have established key-based login to your node AND TESTED YOU CAN ACCESS WITH THE RSA KEY PASSWORD (NOT THE USER PASSWORD)

15

Edit sshd_config to secure the SSH daemon


NOTE: The RSA Key password is only used to login to your node, all other password prompts will require your non-root user password

Copy and paste the entire block

sudo sed -i '/PermitRootLogin/d' /etc/ssh/sshd_config && \
sudo sed -i '/PasswordAuthentication/d' /etc/ssh/sshd_config && \
sudo sed -i '/ChallengeResponseAuthentication/d' /etc/ssh/sshd_config && \
echo -e "PermitRootLogin no\nPasswordAuthentication no\nChallengeResponseAuthentication no" | sudo tee -a  /etc/ssh/sshd_config
16Restart SSH with the new configuration


sudo systemctl restart sshd

Part 3

Part 4a of 11 - Securing SSH (Windows Systems)

Part 5



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