I created a key pair using PGP (GnuPG) for the purpose of encrypting and signing data (documents, emails, and so on). That key was created with the RSA algorithm, and naturally starts with:
-----BEGIN PGP PUBLIC KEY BLOCK----- Version: GnuPG v2
I would like to know, if it is possible, to "convert" that very same key pair for the purpose of authentication using SSH (example: AWS instance or some other remote SSH server). I realize that the result would probably yet another key pair in a different format (.pem for example.)
The idea would be to use the same original RSA key pair (and therefore the same secret passphrase) for all the following purposes: encrypting, signing and SSH authentication.
How would I exactly do that and what are the limitations involved (for example, with private key passphrases, etc)?