.. hazmat::

Key Serialization
=================

.. currentmodule:: cryptography.hazmat.primitives.serialization

There are several common schemes for serializing asymmetric private and public
keys to bytes. They generally support encryption of private keys and additional
key metadata.


Traditional OpenSSL Format
~~~~~~~~~~~~~~~~~~~~~~~~~~

The "traditional" PKCS #1 based serialization format used by OpenSSL.
It supports password based symmetric key encryption. Commonly found in
OpenSSL based TLS applications. It is usually found in PEM format with a
header that mentions the type of the serialized key. e.g.
``-----BEGIN RSA PRIVATE KEY-----``.

.. function:: load_pem_traditional_openssl_private_key(data, password, backend)

    .. versionadded:: 0.5

    Deserialize a private key from PEM encoded data to one of the supported
    asymmetric private key types.

    :param bytes data: The PEM encoded key data.

    :param bytes password: The password to use to decrypt the data. Should
        be ``None`` if the private key is not encrypted.
    :param backend: A
        :class:`~cryptography.hazmat.backends.interfaces.TraditionalOpenSSLSerializationBackend`
        provider.

    :returns: A new instance of a private key.

    :raises ValueError: If the PEM data could not be decrypted or if its
        structure could not be decoded successfully.

    :raises TypeError: If a ``password`` was given and the private key was
        not encrypted. Or if the key was encrypted but no
        password was supplied.

    :raises UnsupportedAlgorithm: If the serialized key is of a type that
        is not supported by the backend or if the key is encrypted with a
        symmetric cipher that is not supported by the backend.