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Doc: impact of deleting path/to/repo/nonce 

Fixes: https://github.com/borgbackup/borg/issues/5858
This commit is contained in:
Andrey Bienkowski 2022-01-28 15:58:31 +03:00
parent 4931eadd91
commit 62fe1cab30
1 changed files with 25 additions and 0 deletions
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docs/faq.rst
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@ -710,6 +710,31 @@ Send a private email to the :ref:`security contact <security-contact>`
if you think you have discovered a security issue.
Please disclose security issues responsibly.
How important is path/to/repo/nonce?
------------------------------------
Borg uses :ref:`AES-CTR encryption <borg_security_critique>`. An
essential part of AES-CTR is a sequential counter that must **never**
repeat. If the same value of the counter is used twice in the same repository,
an attacker can decrypt the data. The counter is stored in the home directory
of each user as well as in the repository. When creating a new archive borg uses
the highest of the two values. The value of the counter in the repository may be
higher than your local value if another user has created an archive more recently
than you did.
Since the nonce is not necessary to read the data that is already encrypted,
``borg info``, ``borg list``, ``borg extract`` and ``borg mount`` should work
just fine without it.
If the path/to/repo/nonce is lost, but you still have your local copy,
borg will recreate path/to/repo/nonce the next time you run ``borg create``.
This should be safe for repositories that are only used from one user account
on one machine.
For repositories that are used by multiple users and/or from multiple machines
it is safest to avoid running *any* commands that modify the repository after
the nonce is deleted.
Common issues
#############