Convert a PuTTY private key to openssh

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Mattias Geniar, February 22, 2020

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I recently got a PuTTY private key sent to me that I wanted to use to log into a remote server. But, I run OpenSSH, not PuTTY.

Here are the steps to convert the PuTTY private key to an OpenSSH private & public key.

Install puttygen

There’s a CLI tool to help with the conversion, it’s available on most Linux distro’s and Mac.

For Linux:

$ apt-get install putty-tools
$ yum install putty

On Mac:

$ brew install putty

On Mac, I ran into the error that PuTTY isn’t compatible with pssh, so I had to run brew unlink pssh first.

Now you have a utility puttygen available.

Converting the private key from PuTTY to OpenSSH

With your private key at hand, now run the following commands.

$ puttygen putty.ppk -O private-openssh -o ~/.ssh/id_putty
$ puttygen putty.ppk -O public-openssh  -o ~/.ssh/
$ chmod 0600 ~/.ssh/id_putty
$ chmod 0666 ~/.ssh/

You can put these files in your ~/.ssh folder to easily refer to them when you SSH into a machine.

$ ssh user@ip -i ~/.ssh/id_putty

With the -i flag you pass along the identity you want to use to authenticate, in this case we refer to the newly created private key.

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