OpenSSH 6.5 and later support a new, more secure format to encode your private key

ssh-keygen -p -m PEM -f ~/.ssh/id_rsa

Generate PEM format private key with ssh-keygen:

ssh-keygen -m PEM -t rsa -b 4096 -C "email@example.com"

Generate public key from private key:

ssh-keygen -l -f ~/.ssh/id_rsa

Reference:

• https://serverfault.com/questions/939909/ssh-keygen-does-not-create-rsa-private-key
• https://wiki.archlinux.org/index.php/SSH_keys
• https://superuser.com/questions/1515261/how-to-quickly-identify-ssh-private-key-file-formats
• https://serverfault.com/questions/9708/what-is-a-pem-file-and-how-does-it-differ-from-other-openssl-generated-key-file
• https://unix.stackexchange.com/questions/26924/how-do-i-convert-a-ssh-keygen-public-key-into-a-format-that-openssl-pem-read-bio