Putty saves ssh key in file with .ppk extension. To use the key on Linux systems, you need to convert it to openssh format. When converting ppk file to openssh format, i got error “PuTTY key format too new”.
boby@sok:~$ puttygen key.ppk -O private-openssh -o 2.pem puttygen: error loading `key.ppk': PuTTY key format too new boby@sok:~$
This error is because the puttygen command is older version. Ubuntu 20.04 comes with older version of puttygen command provided by putty-tools.
The solution is to remove putty-tools package, then install latest version of puttygen from source code.
Remove putty-tools with
sudo apt remove putty-tools
Download and install latest puttygen from
https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
As of writing this, latest version of putty is version 0.76
mkdir ~/src cd ~/src wget https://the.earth.li/~sgtatham/putty/latest/putty-0.76.tar.gz tar -xvf putty-0.76.tar.gz cd putty-0.76/ ./configure make sudo cp puttygen /usr/bin/
Once installed, you can check version with
boby@sok:~/src/putty-0.76$ puttygen --version puttygen: Release 0.76 Build platform: 64-bit Unix Compiler: gcc 9.3.0 Source commit: 1fd7baa7344bb38d62a024e5dba3a720c67d05cf boby@sok:~/src/putty-0.76$
You will be able to convert newer version of ppk files to openssh format now.