Add helper for writing private keys to disk

src/sshecret/crypto.py

@@ -104,6 +104,20 @@ def generate_pem(private_key: rsa.RSAPrivateKey) -> str:
     return pem.decode()
 
 
+def write_private_key(private_key: rsa.RSAPrivateKey, filename: Path) -> None:
+    """Write private key to disk."""
+    encryption_algorithm = serialization.NoEncryption()
+    with open(filename, "wb") as f:
+        pem = private_key.private_bytes(
+            encoding=serialization.Encoding.PEM,
+            format=serialization.PrivateFormat.OpenSSH,
+            encryption_algorithm=encryption_algorithm,
+        )
+        lines = f.write(pem)
+        LOG.debug("Wrote %s lines", lines)
+        f.flush()
+
+
 def create_private_rsa_key(filename: Path, password: str | None = None) -> None:
     """Create an RSA Private key at the given path.