[ADD] accounting: data inalterability check report

Task ID: 2977343

closes odoo/documentation#2703

Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>

content/applications/finance/accounting/reporting/overview.rst

@@ -8,4 +8,5 @@ Overview
    :titlesonly:
 
    overview/main_reports
-   overview/customize
+   overview/customize
+   overview/data_inalterability

content/applications/finance/accounting/reporting/overview/data_inalterability.rst

@@ -0,0 +1,63 @@
+================================
+Data inalterability check report
+================================
+
+Tax authorities in some countries require companies to **prove their posted accounting entries are
+inalterable**, meaning that once an entry has been posted, it can no longer be changed.
+
+To do so, Odoo can use the **SHA-256 algorithm** to create a unique fingerprint for each posted
+entry. This fingerprint is called a hash. The hash is generated by taking an entry's essential data
+(the values of the `date`, `journal_id`, `company_id`, `debit`, `credit`, `account_id`, and
+`partner_id` fields), concatenating it, and inputting it to the SHA-256 hash function, which then
+outputs a fixed size (256-bit) string of characters. The hash function is deterministic (:dfn:`the
+same input always creates the same output`): any minor modification to the original data would
+completely change the resulting hash. Consequently, the SHA-256 algorithm is often used, among
+others, for data integrity verification purposes.
+
+In addition, the previous entry's hash is always added to the next entry to form a **hash chain**.
+This is used to ensure a new entry is not added afterward between two posted entries, as doing so
+would break the hash chain.
+
+.. note::
+   Hashes generated by the SHA-256 algorithm are theoretically not unique, as there is a finite
+   number of possible values. However, this number is exceptionally high: 2²⁵⁶, which is a lot
+   bigger than the number of atoms in the known universe. This is why hashes are considered unique
+   in practice.
+
+.. _data-inalterability/lock:
+
+Lock posted entries with hash
+=============================
+
+To start using the hashing function, go to :menuselection:`Accounting --> Configuration > Journals`.
+Open the journal for which you want to activate the feature, go to the :guilabel:`Advanced Settings`
+tab, and enable :guilabel:`Lock Posted Entries with Hash`.
+
+.. warning::
+   Once you post an entry on a locked journal, you cannot disable the feature anymore, nor edit any
+   posted entry.
+
+.. _data-inalterability/report:
+
+Report download
+===============
+
+To download the data inalterability check report, go to :menuselection:`Accounting --> Configuration
+--> Settings --> Reporting` and click on :guilabel:`Download the Data Inalterability Check Report`.
+
+The report's first section is an overview of all your journals and their configuration. Under the
+inalterability check column, you can see whether or not a journal's posted entries are locked with
+a hash (V) or not (X). The coverage column tells you when a journal's posted entries started being
+locked.
+
+.. image:: data_inalterability/journal-overview.png
+   :align: center
+   :alt: Configuration report for two journals
+
+The second section gives you the result of the data consistency check for each hashed journal. You
+can view the first hashed entry and its corresponding hash and the last hashed entry and its
+corresponding hash.
+
+.. image:: data_inalterability/data-consistency-check.png
+   :align: center
+   :alt: Data consistency check report for a journal