SecItem.type SecItem.len, SecItem.data PK11SymKey.key_data,
        PK11SymKey.key_length, PK11SymKey.slot create_context_by_sym_key
        param_from_iv generate_new_param get_iv_length get_block_size
        get_pad_mechanism
    SecItem's now support indexing and slicing on their data
    Clean up parsing and parameter validation of variable arg functions