Warning
=======
Mat only removes standard metadata from your files, it does _not_:
  - anonymise their content
  - handle watermarking
  - handle steganography
  - handle any non-standard metadata field/system

If you really want to be anonymous format that does not contain any
metadata, or better : use plain-text.


Implementation notes
====================
Symlink attacks
---------------
MAT output predictable filenames (like yourfile.jpg.bak).
This may lead to symlink attack. Please check if you OS prevent
against them

Test suite
----------
Formats that are not in the test suite are not well-tested,
please do not trust the MAT about them!

Archives handling
-----------------
MAT's GUI handle nested archives like unsupported format:
 - The user can select which unsupported files s·he wants to
    include in the _first level archive_.
 - The user can only select by the mean of the
    "Add unsupported file to archives" option which unsupported
    files s·he wants to include in _deeper levels archives_.


Threat Model
============
The Metadata Anonymisation Toolkit adversary has a number
of goals, capabilities, and counter-attack types that can be
used to guide us towards a set of requirements for the MAT.

Adversary
------------

* Goals:

    - Identifying the source of the document, since a document
    always has one. Who/where/when/how was a picture
    taken, where was the document leaked from and by
    whom, ...

    - Identify the author; in some cases documents may be
    anonymously authored or created. In these cases,
    identifying the author is the goal.

    - Identify the equipment/software used. If the attacker fails
    to directly identify the author and/or source, his next
    goal is to determine the source of the equipment used
    to produce, copy, and transmit the document. This can
    include the model of camera used to take a photo, or
    which software was used to produce an office document.


* Adversary Capabilities - Positioning
    - The adversary created the document specifically for this
    user. This is the strongest position for the adversary to
    have. In this case, the adversary is capable of inserting
    arbitrary, custom watermarks specifically for tracking
    the user. In general, MAT cannot defend against this
    adversary, but we list it for completeness.

    - The adversary created the document for a group of users.
    In this case, the adversary knows that they attempted to
    limit distribution to a specific group of users. They may
    or may not have watermarked the document for these
    users, but they certainly know the format used.

    - The adversary did not create the document, the weakest
    position for the adversary to have. The file format is (most of the time)
     standard, nothing custom is added: MAT
    should be able to remove all meta-information from the
    file.

Requirements
---------------

* Processing
    - The MAT *should* avoid interactions with information.
    Its goal is to remove metadata, and the user is solely
    responsible for the information of the file.

    - The MAT *must* warn when encountering an unknown
    format. For example, in a zipfile, if MAT encounters an
    unknown format, it should warn the user, and ask if the
    file should be added to the anonymised archive that is
    produced.

    - The MAT *must* not add metadata, since its purpose is to
    anonymise files: every added items of metadata decreases
    anonymity.

    - The MAT *should* handle unknown/hidden metadata fields,
    like proprietary extensions of open formats.