Convert Putty Key to Openssh Format
If you only have putty key and you want to get openssh format from it, try this one:
puttygen your_input_putty_key_file -O private-openssh -o your_output_key_file
If you only have putty key and you want to get openssh format from it, try this one:
puttygen your_input_putty_key_file -O private-openssh -o your_output_key_file