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@@ -59,135 +59,214 @@ borg init
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Description
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~~~~~~~~~~~
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-This command initializes an empty repository. A repository is a filesystem
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-directory containing the deduplicated data from zero or more archives.
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+This command initializes an empty repository. A repository is a
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+filesystem directory containing the deduplicated data from zero or more
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+archives.
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-Encryption mode TLDR
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-++++++++++++++++++++
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+Encryption mode TL;DR
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++++++++++++++++++++++
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-The encryption mode can only be configured when creating a new repository -
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-you can neither configure it on a per-archive basis nor change the
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-encryption mode of an existing repository.
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+The encryption mode can only be configured when creating a new
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+repository. You can neither configure encryption on a per-archive
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+basis, nor change the encryption mode of an existing repository. You
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+should thus take possible future use into account when deciding on an
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+encryption mode.
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-Use ``repokey``::
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+As a general rule of thumb, use ``repokey`` with a strong passphrase:
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borg init --encryption repokey /path/to/repo
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-Or ``repokey-blake2`` depending on which is faster on your client machines (see below)::
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-
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- borg init --encryption repokey-blake2 /path/to/repo
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-
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-Borg will:
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+However, there are many reasons to choose differently. See the section
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+below for details. In any case, Borg will:
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+
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+1. Ask you to enter a unique and strong passphrase.
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+2. Create a random Borg key (which actually consists of three random
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+ secrets, see :ref:`key_files` for details).
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+3. Encrypt the Borg key with your passphrase.
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+4. Store the encrypted Borg key inside the repository directory (with
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+ ``repokey`` and ``repokey-blake2`` modes; with ``keyfile`` and
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+ ``keyfile-blake2`` modes the Borg key is stored in your home
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+ directory instead, see below). Since we usually have to assume that
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+ an attacker could gain access to the repository (that's why we
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+ encrypt the data in the first place), choosing a strong and unique
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+ passphrase is absolutely crucial.
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+5. Encrypt and sign your backups with the Borg key to prevent anyone
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+ from reading or forging them unless they have the Borg key *and*
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+ know the passphrase.
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+6. Use the Borg key to decrypt and thus access the data stored in your
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+ repository, e.g. when extracting files. The contents can also be
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+ verified to detect accidental corruption or malicious tampering.
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+
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+As you can see, you always need *both* the Borg key and passphrase to
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+access your data. Thus it's crucial to keep a backup of your key
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+*outside* both the repository and the system you create backups of.
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+You can easily run into a "leaving your keys inside your car" situation
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+otherwise. See :ref:`borg_key_export` to create a backup of your key
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+(e.g., by printing it on paper).
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+
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+Encryption is done locally - i.e., if you back up to a remote machine,
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+the remote machine neither sees your passphrase, nor your unencrypted
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+Borg key, nor your unencrypted files. Chunking and ID generation are
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+based on your key to improve privacy.
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+
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+**About hardware acceleration:**
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+
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+Borg encrypts data with AES, which is pretty fast thanks to hardware
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+acceleration on basically all modern Intel, AMD, and ARM CPUs since
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+around the early 2010s (very cheap models since the mid-2010s).
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+
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+As the hashing algorithm, Borg can use either SHA256 or BLAKE2b. ARM
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+CPUs support hardware-accelerated SHA256 hashing since ARMv7 with NEON
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+(around 2011), or ARMv8 (around 2013). AMD CPUs support it since Zen 1
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+(around 2017), i.e. all AMD Ryzen CPUs. Intel CPUs support it since Ice
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+Lake on mobile (10th gen, around 2021), and Rocket Lake on desktop
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+(11th gen, around 2021). Very cheap models have received support a few
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+years later. If your CPU doesn't support hardware-accelerated SHA256
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+hashing, you might want to give BLAKE2b hashing a try - it's likely
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+faster then. So, instead of ``repokey`` mode, use ``repokey-blake2``
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+(or any of the other ``-blake2`` modes for that matter).
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-1. Ask you to come up with a passphrase.
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-2. Create a borg key (which contains 3 random secrets. See :ref:`key_files`).
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-3. Encrypt the key with your passphrase.
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-4. Store the encrypted borg key inside the repository directory (in the repo config).
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- This is why it is essential to use a secure passphrase.
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-5. Encrypt and sign your backups to prevent anyone from reading or forging them unless they
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- have the key and know the passphrase. Make sure to keep a backup of
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- your key **outside** the repository - do not lock yourself out by
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- "leaving your keys inside your car" (see :ref:`borg_key_export`).
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- For remote backups the encryption is done locally - the remote machine
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- never sees your passphrase, your unencrypted key or your unencrypted files.
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- Chunking and id generation are also based on your key to improve
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- your privacy.
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-6. Use the key when extracting files to decrypt them and to verify that the contents of
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- the backups have not been accidentally or maliciously altered.
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+Hardware acceleration is always used automatically when available.
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Picking a passphrase
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++++++++++++++++++++
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-Make sure you use a good passphrase. Not too short, not too simple. The real
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-encryption / decryption key is encrypted with / locked by your passphrase.
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-If an attacker gets your key, he can't unlock and use it without knowing the
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-passphrase.
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-
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-Be careful with special or non-ascii characters in your passphrase:
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-
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-- Borg processes the passphrase as unicode (and encodes it as utf-8),
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- so it does not have problems dealing with even the strangest characters.
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-- BUT: that does not necessarily apply to your OS / VM / keyboard configuration.
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+Make sure you use a good passphrase. Not too short, not too simple. The
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+real encryption / decryption key is encrypted with / locked by your
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+passphrase. If an attacker gets your borg key, they can't unlock and use
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+it without knowing the passphrase.
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-So better use a long passphrase made from simple ascii chars than one that
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-includes non-ascii stuff or characters that are hard/impossible to enter on
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-a different keyboard layout.
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+Be careful with special or non-ASCII characters in your passphrase:
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-You can change your passphrase for existing repos at any time, it won't affect
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-the encryption/decryption key or other secrets.
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+- Borg processes the passphrase as Unicode (and encodes it as UTF-8), so
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+ it does not have problems dealing with even the strangest characters.
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+- BUT: that does not necessarily apply to your OS / VM / keyboard
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+ configuration.
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-More encryption modes
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-+++++++++++++++++++++
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+So it is better to use a long passphrase made from simple ASCII
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+characters than one that includes non-ASCII characters or characters
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+that are hard or impossible to enter on a different keyboard layout.
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-Only use ``--encryption none`` if you are OK with anyone who has access to
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-your repository being able to read your backups and tamper with their
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-contents without you noticing.
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+You can change your passphrase for existing repositories at any time; it
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+won't affect the encryption/decryption key or other secrets. See
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+:ref:`borg_key_change-passphrase`.
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-If you want "passphrase and having-the-key" security, use ``--encryption keyfile``.
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-The key will be stored in your home directory (in ``~/.config/borg/keys``).
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+More about encryption modes
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++++++++++++++++++++++++++++
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-If you do **not** want to encrypt the contents of your backups, but still
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-want to detect malicious tampering use ``--encryption authenticated``.
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-To normally work with ``authenticated`` repos, you will need the passphrase, but
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-there is an emergency workaround, see ``BORG_WORKAROUNDS=authenticated_no_key`` docs.
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+Choosing the right encryption mode isn't always easy and many factors
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+can change which mode is best for you. However, note that you can't
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+really do anything *wrong* if you choose ``repokey`` with a strong
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+passphrase. So, if you're not sure, choose ``repokey`` (or
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+``repokey-blake2``, depending on your hardware, see above).
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-If ``BLAKE2b`` is faster than ``SHA-256`` on your hardware, use ``--encryption authenticated-blake2``,
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-``--encryption repokey-blake2`` or ``--encryption keyfile-blake2``. Note: for remote backups
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-the hashing is done on your local machine.
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+Borg supports the following encryption modes:
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.. nanorst: inline-fill
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-
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-+----------+---------------+------------------------+--------------------------+
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-| Hash/MAC | Not encrypted | Not encrypted, | Encrypted (AEAD w/ AES) |
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-| | no auth | but authenticated | and authenticated |
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-+----------+---------------+------------------------+--------------------------+
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-| SHA-256 | none | `authenticated` | repokey |
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-| | | | keyfile |
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-+----------+---------------+------------------------+--------------------------+
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-| BLAKE2b | n/a | `authenticated-blake2` | `repokey-blake2` |
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-| | | | `keyfile-blake2` |
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-+----------+---------------+------------------------+--------------------------+
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+.. class:: borg-encryption-table
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+
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++----------+-------------------+--------------------------+-------------------------+
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+| Hash/MAC | Not Encrypted | Encrypted (AEAD w/ AES) |
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++ +-------------------+--------------------------+-------------------------+
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+| | Not Authenticated | Authenticated |
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++==========+===================+==========================+=========================+
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+| SHA-256 | ``none`` | ``authenticated`` | ``repokey`` |
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+| | | | ``keyfile`` |
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++----------+-------------------+--------------------------+-------------------------+
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+| BLAKE2b | n/a | ``authenticated-blake2`` | ``repokey-blake2`` |
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+| | | | ``keyfile-blake2`` |
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++----------+-------------------+--------------------------+-------------------------+
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.. nanorst: inline-replace
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-Modes `marked like this` in the above table are new in Borg 1.1 and are not
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-backwards-compatible with Borg 1.0.x.
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-
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-On modern Intel/AMD CPUs (except very cheap ones), AES is usually
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-hardware-accelerated.
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-BLAKE2b is faster than SHA256 on Intel/AMD 64-bit CPUs
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-(except AMD Ryzen and future CPUs with SHA extensions),
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-which makes `authenticated-blake2` faster than `none` and `authenticated`.
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-
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-On modern ARM CPUs, NEON provides hardware acceleration for SHA256 making it faster
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-than BLAKE2b-256 there. NEON accelerates AES as well.
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-
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-Hardware acceleration is always used automatically when available.
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-
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-`repokey` and `keyfile` use AES-CTR-256 for encryption and HMAC-SHA256 for
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-authentication in an encrypt-then-MAC (EtM) construction. The chunk ID hash
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-is HMAC-SHA256 as well (with a separate key).
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-These modes are compatible with Borg 1.0.x.
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-
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-`repokey-blake2` and `keyfile-blake2` are also authenticated encryption modes,
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-but use BLAKE2b-256 instead of HMAC-SHA256 for authentication. The chunk ID
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-hash is a keyed BLAKE2b-256 hash.
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-These modes are new and *not* compatible with Borg 1.0.x.
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-
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-`authenticated` mode uses no encryption, but authenticates repository contents
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-through the same HMAC-SHA256 hash as the `repokey` and `keyfile` modes (it uses it
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-as the chunk ID hash). The key is stored like `repokey`.
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-This mode is new and *not* compatible with Borg 1.0.x.
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-
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-`authenticated-blake2` is like `authenticated`, but uses the keyed BLAKE2b-256 hash
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-from the other blake2 modes.
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-This mode is new and *not* compatible with Borg 1.0.x.
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-
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-`none` mode uses no encryption and no authentication. It uses SHA256 as chunk
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-ID hash. This mode is not recommended, you should rather consider using an authenticated
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-or authenticated/encrypted mode. This mode has possible denial-of-service issues
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-when running ``borg create`` on contents controlled by an attacker.
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-Use it only for new repositories where no encryption is wanted **and** when compatibility
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-with 1.0.x is important. If compatibility with 1.0.x is not important, use
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-`authenticated-blake2` or `authenticated` instead.
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-This mode is compatible with Borg 1.0.x.
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+Borg 1.0 and older support ``none``, ``repokey``, and ``keyfile``
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+modes only. If you need such old clients to be able to access your
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+repo, you can't use any of the other modes.
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+
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+**About modes without encryption:**
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+
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+Avoid using ``none`` mode. If you think about using ``none`` mode,
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+please reconsider and be absolutely sure. Using any mode other than
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+``none`` allows Borg to detect accidental corruption or malicious
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+tampering with the repo. It also prevents denial-of-service attacks
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+against clients. Instead of ``none`` mode, you likely want to use
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+``authenticated`` mode, or ``repokey`` or ``keyfile`` modes with an
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+empty passphrase instead (see below).
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+
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+If you don't want to encrypt your data, use ``authenticated`` or
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+``authenticated-blake2`` modes. These modes require a passphrase in
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+normal operation, but in emergency situations you can access the repo
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+without the passphrase with ``BORG_WORKAROUNDS=authenticated_no_key``
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+(see :ref:`environment-variables`).
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+
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+If you just don't want to choose a passphrase, use ``keyfile`` or
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+``keyfile-blake2`` modes with an empty passphrase. These modes are
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+generally safe even without a passphrase, but keeping an offsite
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+backup of the Borg key is also important then. See below for details.
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+
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+If you can assure that an attacker can't gain access to your repo, e.g.
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+when independently encrypting your repository disk or filesystem, you
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+can think about using ``repokey`` or ``repokey-blake2`` modes with an
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+empty passphrase. However, keep in mind that if an attacker still
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+somehow manages to gain access, they have full access to your repo. In
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+such situations choosing ``repokey`` over ``authenticated`` mode has
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+the advantage of allowing you to add a passphrase later using
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+:ref:`borg_key_change-passphrase`.
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+
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+**About modes with encryption:**
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+
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+With ``repokey`` and ``repokey-blake2`` modes the key is stored with
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+the repo and encrypted with your passphrase. If an attacker gains
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+access to your repo and knows the passphrase, he can access and tamper
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+with the repo. The repo's security thus relies on the strength of your
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+passphrase. Creating an offsite backup of your Borg key (e.g., by
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+printing it on paper) is recommended, see :ref:`borg_key_export`.
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+
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+If you're thinking about storing the passphrase on the disk of the
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+system you're backing up, consider using the ``keyfile`` method
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+instead. It generally provides the same or better security then.
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+
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+With ``keyfile`` and ``keyfile-blake2`` modes the key is stored on your
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+local machine (in ``~/.config/borg/keys``) instead. An attacker gaining
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+access to your repo then needs both the Borg key, and your passphrase to
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+access and tamper with the repo. However, if you lose the key, you lose
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+access to the repo, too. You **must** create an offsite backup of your
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+Borg key, e.g. by printing it on paper. Storing a copy of the Borg key
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+on the system you're creating backups of is **NOT** sufficient. Use
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+:ref:`borg_key_export` to create the backup.
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+
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+The ``keyfile`` and ``keyfile-blake2`` modes allow for "passphrase and
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+having-the-key" security when using a strong passphrase, but can also
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+be used with an empty passphrase. Storing a (easily readable)
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+passphrase on the disk of the system you're backing up with
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+``keyfile`` and ``keyfile-blake2`` modes adds no security over using an
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+empty passphrase.
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+
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+**Technical details:**
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+
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+``repokey`` and ``keyfile`` use AES-CTR-256 for encryption and
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+HMAC-SHA256 for authentication in an encrypt-then-MAC (EtM)
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+construction. The chunk ID hash is HMAC-SHA256 (with a separate key).
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+These modes are compatible with all Borg versions.
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+
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+``repokey-blake2`` and ``keyfile-blake2`` are also authenticated
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+encryption modes, but use BLAKE2b-256 instead of HMAC-SHA256 for
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+authentication. The chunk ID hash is a keyed BLAKE2b-256 hash. These
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+modes are only compatible with Borg 1.1 and later.
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+
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+``authenticated`` mode uses no encryption, but authenticates repo
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+contents through the same HMAC-SHA256 hash as the ``repokey`` and
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+``keyfile`` modes (it uses it as the chunk ID hash). The key is stored
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+like ``repokey`` within the repo. This mode is only compatible with
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+Borg 1.1 and later.
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+
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+``authenticated-blake2`` is like ``authenticated``, but uses the keyed
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+BLAKE2b-256 hash from the other BLAKE2b modes. This mode is only
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+compatible with Borg 1.1 and later.
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+
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+``none`` mode uses no encryption and no authentication. It uses SHA256
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+as chunk ID hash. This mode is not recommended. You should instead
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+consider using an authenticated or authenticated/encrypted mode. This
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+mode has possible denial-of-service issues when running ``borg create``
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+on contents controlled by an attacker. See above for alternatives.
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+This mode is compatible with all Borg versions.
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