Transform a PGP private key to an OpenSSH private key

pgp2ssh.py

#!/usr/bin/python3

"""
Transform a PGP private key to an OpenSSH private key

Requirements:
    pgpy>=0.6.0

Usage:
    Install dependencies with `pip install pgpy`
    Find GPG Key ID with `gpg --list-secret-keys --with-keygrip`
    Export key with `gpg --armor --export-secret-keys <key-id>`
    python3 pgp2ssh.py <path-to-private-key> > output.pem

Note:
    The output key of this script is NOT encrypted
    You should encrypt it with `ssh-keygen -p -f <path-to-ssh-key>`

References / script inspired by:
    https://0xacab.org/monkeysphere/monkeypy/-/blob/master/monkeysphere/openpgp2ssh.py
"""

import sys
from getpass import getpass

from cryptography.hazmat.primitives import serialization
from pgpy import PGPKey


def key2ssh_private(key: PGPKey):
    material = key._key.keymaterial.__privkey__()
    return material.private_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PrivateFormat.OpenSSH,
        encryption_algorithm=serialization.NoEncryption(),
    ).decode("utf-8")


if __name__ == "__main__":
    with open(sys.argv[-1], encoding="utf-8") as f:
        key, _ = PGPKey.from_blob(f.read())

    key_passphrase = None
    if not key.is_unlocked:
        print("Key is password protected.", file=sys.stderr)
        key_passphrase = getpass(stream=sys.stderr)
    with key.unlock(key_passphrase):
        print(key2ssh_private(key))