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Manage SSH Key File With a Passphrase

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Manage SSH Key File With a Passphrase

We take a look at how to protect your SSH keys by passphrase without inducing a lot of headaches. Read on to find out how.

· DevOps Zone ·
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Any serious DevOps will only SSH by the key file, not with a password. Right? And mostly, our powerful key file can unlock many critical ENVs. Have you ever uploaded your private key to other ENVs, like Jumpbox? What if your key is magically stolen by hackers somehow?

Time to protect your sensitive SSH key with a passphrase, and live with it, headache-free.

Here's a cheat sheet for impatient users, though I recommend reading this post through, even for experienced users.
Name Summary
Load key file ssh-add ~/.ssh/id_rsa
Remove all loaded keys ssh-add -D
Whether it’s encrypted grep “ENCRYPTED” id_rsa
Add/Change passphrase ssh-keygen -p -f id_dsa
Remove passphrase ssh-keygen -p -P $passwd -N “” -f id_rsa
Load key without prompt Check link: here

Add Passphrase to Existing SSH Key

We can easily use ssh-keygen to add a passphrase. This certainly gives us extra security benefit. What’s the impact of this change?

  • You never use your private key other than your computer, right? If yes, there's nothing you need to worry about. One tiny difference: you might be asked to input the passphrase once. Check all loaded keys by ssh-add -l.
  • In some cases, we might use key files to do a passwordless login with remote servers. For example, the SSH tunnel for port forwarding, the SSH from Jumpbox to other machines, etc. Then, we have to make sure that the key file is correctly loaded and recognized. Run ssh-add ./id_rsa, then input passphrase manually. This also can be done automatically, which I will explain it shortly.
# Change file mode to allow overwrite
chmod 700 id_rsa

# Add passphrase to key file
ssh-keygen -p -f id_rsa

# Denny-mac:.ssh mac$ ssh-keygen -p -f id_rsa
# Key has comment 'id_rsa'
# Enter new passphrase (empty for no passp...
# Enter same passphrase again: 
# Your identification has been saved with ...

Load Protected SSH Key Without Prompt

It's a pity that ssh-add itself doesn’t have native support for this. Here is a workaround (a bit tricky, I admit).

# Specify your passphrase here

# Load protected key without prompt
echo "echo $YOUR_PASSPHRASE" > /tmp/mypass
chmod 700 /tmp/mypass
cat id_rsa| SSH_ASKPASS=/tmp/mypass ssh-add -

# Verify loaded certificate
ssh-add -l

Change Passphrase for Existing Private Key

Run the below command. You will be asked to input the old passphrase and a new one. If the key is not encrypted, just press enter in the terminal.

ssh-keygen -p -f ~/.ssh/id_dsa

Remove Passphrase

Use openssl to remove the passphrase. You will need to manually input the old passphrase.

openssl rsa -in id_rsa -out id_rsa_new

The same can be done by ssh-keygen. The amazing part is that there is no required human intervention; it's totally automated.

ssh-keygen -p -P "$OLDPASS" -N "" -f id_rsa

More Reading: Reverse SSH Tunnel: Export Your Mac Laptop to the Internet


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ssh ,devops ,security ,envs

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