bool silc_pkcs_save_private_key(const char *filename,
                                    SilcPrivateKey private_key,
                                    unsigned char *passphrase,
                                    SilcUInt32 passphrase_len,
                                    SilcUInt32 encoding);

    Saves private key into file.  The private key is encrypted into
    the file with the `passphrase' as a key.  The encryption algorithm
    is AES with 256 bit key in CBC mode.  Returns FALSE on error.