def asn1_from_ecdsap256_private_key(priv_key, pub_key):
    """
    Returns the ASN.1 encoding of a ECDSAP256 private ket.

    :priv_key: an ECDSAP256PrivateKey instance
    :returns: the ASN.1 encoding as a byte string
    """
    encoded_len = _lib.xtt_asn1_private_key_length()
    encoded = _ffi.new('unsigned char[]', encoded_len)
    rc = _lib.xtt_asn1_from_ecdsap256_private_key(priv_key.native, pub_key.native, encoded, len(encoded))
    if rc == RC.SUCCESS:
        return _ffi.buffer(encoded)[:]
    else:
        raise error_from_code(rc)
Returns the ASN.1 encoding of a ECDSAP256 private ket.

    :priv_key: an ECDSAP256PrivateKey instance
    :returns: the ASN.1 encoding as a byte string