borg init

borg [common options] init [options] [REPOSITORY]
positional arguments
  REPOSITORY repository to create
optional arguments
  -e MODE, --encryption MODE select encryption key mode (required)
  --append-only create an append-only mode repository. Note that this only affects the low level structure of the repository, and running delete or prune will still be allowed. See Append-only mode (forbid compaction) in Additional Notes for more details.
  --storage-quota QUOTA Set storage quota of the new repository (e.g. 5G, 1.5T). Default: no quota.
  --make-parent-dirs create the parent directories of the repository directory, if they are missing.
  --key-algorithm the algorithm we use to derive a key encryption key from your passphrase. Default: argon2

Common options

Description

This command initializes an empty repository. A repository is a filesystem directory containing the deduplicated data from zero or more archives.

Encryption mode TLDR

The encryption mode can only be configured when creating a new repository - you can neither configure it on a per-archive basis nor change the mode of an existing repository. This example will likely NOT give optimum performance on your machine (performance tips will come below):

borg init --encryption repokey /path/to/repo

Borg will:

  1. Ask you to come up with a passphrase.
  2. Create a borg key (which contains some random secrets. See Key files).
  3. Derive a “key encryption key” from your passphrase
  4. Encrypt and sign the key with the key encryption key
  5. Store the encrypted borg key inside the repository directory (in the repo config). This is why it is essential to use a secure passphrase.
  6. Encrypt and sign your backups to prevent anyone from reading or forging them unless they have the key and know the passphrase. Make sure to keep a backup of your key outside the repository - do not lock yourself out by “leaving your keys inside your car” (see borg key export). For remote backups the encryption is done locally - the remote machine never sees your passphrase, your unencrypted key or your unencrypted files. Chunking and id generation are also based on your key to improve your privacy.
  7. Use the key when extracting files to decrypt them and to verify that the contents of the backups have not been accidentally or maliciously altered.

Picking a passphrase

Make sure you use a good passphrase. Not too short, not too simple. The real encryption / decryption key is encrypted with / locked by your passphrase. If an attacker gets your key, he can’t unlock and use it without knowing the passphrase.

Be careful with special or non-ascii characters in your passphrase:

  • Borg processes the passphrase as unicode (and encodes it as utf-8), so it does not have problems dealing with even the strangest characters.
  • BUT: that does not necessarily apply to your OS / VM / keyboard configuration.

So better use a long passphrase made from simple ascii chars than one that includes non-ascii stuff or characters that are hard/impossible to enter on a different keyboard layout.

You can change your passphrase for existing repos at any time, it won’t affect the encryption/decryption key or other secrets.

Choosing an encryption mode

Depending on your hardware, hashing and crypto performance may vary widely. The easiest way to find out about what’s fastest is to run borg benchmark cpu.

repokey modes: if you want ease-of-use and “passphrase” security is good enough - the key will be stored in the repository (in repo_dir/config).

keyfile modes: if you rather want “passphrase and having-the-key” security - the key will be stored in your home directory (in ~/.config/borg/keys).

The following table is roughly sorted in order of preference, the better ones are in the upper part of the table, in the lower part is the old and/or unsafe(r) stuff:

Mode (K = keyfile or repokey) ID-Hash Encryption Authentication V >=
K-blake2-chacha20-poly1305 BLAKE2b CHACHA20 POLY1305 1.3
K-chacha20-poly1305 HMAC-SHA-256 CHACHA20 POLY1305 1.3
K-blake2-aes-ocb BLAKE2b AES256-OCB AES256-OCB 1.3
K-aes-ocb HMAC-SHA-256 AES256-OCB AES256-OCB 1.3
K-blake2 BLAKE2b AES256-CTR BLAKE2b 1.1
K HMAC-SHA-256 AES256-CTR HMAC-SHA256 any
authenticated-blake2 BLAKE2b none BLAKE2b 1.1
authenticated HMAC-SHA-256 none HMAC-SHA256 1.1
none SHA-256 none none any

none mode uses no encryption and no authentication. You’re advised to NOT use this mode as it would expose you to all sorts of issues (DoS, confidentiality, tampering, …) in case of malicious activity in the repository.

If you do not want to encrypt the contents of your backups, but still want to detect malicious tampering use an authenticated mode. It’s like repokey minus encryption.

Key derivation functions

  • --key-algorithm argon2 is the default and is recommended. The key encryption key is derived from your passphrase via argon2-id. Argon2 is considered more modern and secure than pbkdf2.
  • You can use --key-algorithm pbkdf2 if you want to access your repo via old versions of borg.

Our implementation of argon2-based key algorithm follows the cryptographic best practices:

  • It derives two separate keys from your passphrase: one to encrypt your key and another one to sign it. --key-algorithm pbkdf2 uses the same key for both.
  • It uses encrypt-then-mac instead of encrypt-and-mac used by --key-algorithm pbkdf2

Neither is inherently linked to the key derivation function, but since we were going to break backwards compatibility anyway we took the opportunity to fix all 3 issues at once.

Examples

# Local repository, recommended repokey AEAD crypto modes
$ borg init --encryption=repokey-aes-ocb /path/to/repo
$ borg init --encryption=repokey-chacha20-poly1305 /path/to/repo
$ borg init --encryption=repokey-blake2-aes-ocb /path/to/repo
$ borg init --encryption=repokey-blake2-chacha20-poly1305 /path/to/repo

# Local repository (no encryption), not recommended
$ borg init --encryption=none /path/to/repo

# Remote repository (accesses a remote borg via ssh)
# repokey: stores the (encrypted) key into <REPO_DIR>/config
$ borg init --encryption=repokey-aes-ocb user@hostname:backup

# Remote repository (accesses a remote borg via ssh)
# keyfile: stores the (encrypted) key into ~/.config/borg/keys/
$ borg init --encryption=keyfile-aes-ocb user@hostname:backup