.. _sussie-hashing-label:

Hashing
-------

.. index::
    single: Hashing

This tools has two main functionalities:

* It creates the hash for the files with the selected extensions.
* It checks that those hashes are still valid after having moved the dataset folder.

The task is to verify that no file corruption occurred during the handling (e.g., copying/moving) of the survey data files.

.. _tab_hashing:
.. figure:: ./_static/tab_hashing.png
    :width: 600px
    :align: center
    :alt: hashing
    :figclass: align-center

    The *Hashing* tab.

Which hashing algorithm should we use?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For the large majority of our needs, it should be sufficient to use the simplest (and quickest) one: `SHA1 <https://en.wikipedia.org/wiki/SHA-1>`_.

The following table provides some indicative computation times after a test performed by hashing 100 FAU files (with a total size of about 20 GB):

=================================================== ===========================
                Hashing Algorithm                        Computation Time
=================================================== ===========================
SHA1                                                1.5 mins
SHA224                                              1.9 mins
SHA256                                              2.8 mins
=================================================== ===========================

Which file extensions should we hash?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

At least, we should hash the FAU raw files.

It is possible to hash all the files by putting “.*” in the “File Extensions“ field, but the computation time will increase.