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27 KiB
Markdown
830 lines
27 KiB
Markdown
---
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title: "Crypt"
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description: "Encryption overlay remote"
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versionIntroduced: "v1.33"
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---
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# {{< icon "fa fa-lock" >}} Crypt
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Rclone `crypt` remotes encrypt and decrypt other remotes.
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A remote of type `crypt` does not access a [storage system](https://rclone.org/overview/)
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directly, but instead wraps another remote, which in turn accesses
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the storage system. This is similar to how [alias](https://rclone.org/alias/),
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[union](https://rclone.org/union/), [chunker](https://rclone.org/chunker/)
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and a few others work. It makes the usage very flexible, as you can
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add a layer, in this case an encryption layer, on top of any other
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backend, even in multiple layers. Rclone's functionality
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can be used as with any other remote, for example you can
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[mount](https://rclone.org/commands/rclone_mount/) a crypt remote.
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Accessing a storage system through a crypt remote realizes client-side
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encryption, which makes it safe to keep your data in a location you do
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not trust will not get compromised.
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When working against the `crypt` remote, rclone will automatically
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encrypt (before uploading) and decrypt (after downloading) on your local
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system as needed on the fly, leaving the data encrypted at rest in the
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wrapped remote. If you access the storage system using an application
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other than rclone, or access the wrapped remote directly using rclone,
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there will not be any encryption/decryption: Downloading existing content
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will just give you the encrypted (scrambled) format, and anything you
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upload will *not* become encrypted.
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The encryption is a secret-key encryption (also called symmetric key encryption)
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algorithm, where a password (or pass phrase) is used to generate real encryption key.
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The password can be supplied by user, or you may chose to let rclone
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generate one. It will be stored in the configuration file, in a lightly obscured form.
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If you are in an environment where you are not able to keep your configuration
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secured, you should add
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[configuration encryption](https://rclone.org/docs/#configuration-encryption)
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as protection. As long as you have this configuration file, you will be able to
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decrypt your data. Without the configuration file, as long as you remember
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the password (or keep it in a safe place), you can re-create the configuration
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and gain access to the existing data. You may also configure a corresponding
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remote in a different installation to access the same data.
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See below for guidance to [changing password](#changing-password).
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Encryption uses [cryptographic salt](https://en.wikipedia.org/wiki/Salt_(cryptography)),
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to permute the encryption key so that the same string may be encrypted in
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different ways. When configuring the crypt remote it is optional to enter a salt,
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or to let rclone generate a unique salt. If omitted, rclone uses a built-in unique string.
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Normally in cryptography, the salt is stored together with the encrypted content,
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and do not have to be memorized by the user. This is not the case in rclone,
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because rclone does not store any additional information on the remotes. Use of
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custom salt is effectively a second password that must be memorized.
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[File content](#file-encryption) encryption is performed using
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[NaCl SecretBox](https://godoc.org/golang.org/x/crypto/nacl/secretbox),
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based on XSalsa20 cipher and Poly1305 for integrity.
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[Names](#name-encryption) (file- and directory names) are also encrypted
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by default, but this has some implications and is therefore
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possible to be turned off.
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## Configuration
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Here is an example of how to make a remote called `secret`.
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To use `crypt`, first set up the underlying remote. Follow the
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`rclone config` instructions for the specific backend.
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Before configuring the crypt remote, check the underlying remote is
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working. In this example the underlying remote is called `remote`.
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We will configure a path `path` within this remote to contain the
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encrypted content. Anything inside `remote:path` will be encrypted
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and anything outside will not.
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Configure `crypt` using `rclone config`. In this example the `crypt`
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remote is called `secret`, to differentiate it from the underlying
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`remote`.
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When you are done you can use the crypt remote named `secret` just
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as you would with any other remote, e.g. `rclone copy D:\docs secret:\docs`,
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and rclone will encrypt and decrypt as needed on the fly.
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If you access the wrapped remote `remote:path` directly you will bypass
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the encryption, and anything you read will be in encrypted form, and
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anything you write will be unencrypted. To avoid issues it is best to
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configure a dedicated path for encrypted content, and access it
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exclusively through a crypt remote.
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```
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No remotes found, make a new one?
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n) New remote
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s) Set configuration password
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q) Quit config
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n/s/q> n
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name> secret
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Type of storage to configure.
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Enter a string value. Press Enter for the default ("").
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Choose a number from below, or type in your own value
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[snip]
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XX / Encrypt/Decrypt a remote
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\ "crypt"
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[snip]
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Storage> crypt
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** See help for crypt backend at: https://rclone.org/crypt/ **
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Remote to encrypt/decrypt.
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Normally should contain a ':' and a path, eg "myremote:path/to/dir",
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"myremote:bucket" or maybe "myremote:" (not recommended).
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Enter a string value. Press Enter for the default ("").
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remote> remote:path
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How to encrypt the filenames.
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Enter a string value. Press Enter for the default ("standard").
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Choose a number from below, or type in your own value.
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/ Encrypt the filenames.
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1 | See the docs for the details.
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\ "standard"
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2 / Very simple filename obfuscation.
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\ "obfuscate"
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/ Don't encrypt the file names.
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3 | Adds a ".bin" extension only.
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\ "off"
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filename_encryption>
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Option to either encrypt directory names or leave them intact.
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NB If filename_encryption is "off" then this option will do nothing.
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Enter a boolean value (true or false). Press Enter for the default ("true").
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Choose a number from below, or type in your own value
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1 / Encrypt directory names.
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\ "true"
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2 / Don't encrypt directory names, leave them intact.
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\ "false"
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directory_name_encryption>
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Password or pass phrase for encryption.
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y) Yes type in my own password
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g) Generate random password
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y/g> y
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Enter the password:
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password:
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Confirm the password:
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password:
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Password or pass phrase for salt. Optional but recommended.
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Should be different to the previous password.
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y) Yes type in my own password
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g) Generate random password
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n) No leave this optional password blank (default)
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y/g/n> g
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Password strength in bits.
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64 is just about memorable
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128 is secure
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1024 is the maximum
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Bits> 128
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Your password is: JAsJvRcgR-_veXNfy_sGmQ
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Use this password? Please note that an obscured version of this
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password (and not the password itself) will be stored under your
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configuration file, so keep this generated password in a safe place.
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y) Yes (default)
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n) No
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y/n>
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Edit advanced config? (y/n)
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y) Yes
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n) No (default)
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y/n>
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Remote config
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--------------------
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[secret]
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type = crypt
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remote = remote:path
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password = *** ENCRYPTED ***
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password2 = *** ENCRYPTED ***
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--------------------
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y) Yes this is OK (default)
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e) Edit this remote
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d) Delete this remote
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y/e/d>
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```
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**Important** The crypt password stored in `rclone.conf` is lightly
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obscured. That only protects it from cursory inspection. It is not
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secure unless [configuration encryption](https://rclone.org/docs/#configuration-encryption) of `rclone.conf` is specified.
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A long passphrase is recommended, or `rclone config` can generate a
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random one.
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The obscured password is created using AES-CTR with a static key. The
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IV (nonce) is stored verbatim at the beginning of the obscured password. This
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static key is shared between all versions of rclone.
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If you reconfigure rclone with the same passwords/passphrases
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elsewhere it will be compatible, but the obscured version will be different
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due to the different salt.
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Rclone does not encrypt
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* file length - this can be calculated within 16 bytes
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* modification time - used for syncing
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### Specifying the remote
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When configuring the remote to encrypt/decrypt, you may specify any
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string that rclone accepts as a source/destination of other commands.
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The primary use case is to specify the path into an already configured
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remote (e.g. `remote:path/to/dir` or `remote:bucket`), such that
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data in a remote untrusted location can be stored encrypted.
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You may also specify a local filesystem path, such as
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`/path/to/dir` on Linux, `C:\path\to\dir` on Windows. By creating
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a crypt remote pointing to such a local filesystem path, you can
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use rclone as a utility for pure local file encryption, for example
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to keep encrypted files on a removable USB drive.
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**Note**: A string which do not contain a `:` will by rclone be treated
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as a relative path in the local filesystem. For example, if you enter
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the name `remote` without the trailing `:`, it will be treated as
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a subdirectory of the current directory with name "remote".
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If a path `remote:path/to/dir` is specified, rclone stores encrypted
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files in `path/to/dir` on the remote. With file name encryption, files
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saved to `secret:subdir/subfile` are stored in the unencrypted path
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`path/to/dir` but the `subdir/subpath` element is encrypted.
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The path you specify does not have to exist, rclone will create
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it when needed.
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If you intend to use the wrapped remote both directly for keeping
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unencrypted content, as well as through a crypt remote for encrypted
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content, it is recommended to point the crypt remote to a separate
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directory within the wrapped remote. If you use a bucket-based storage
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system (e.g. Swift, S3, Google Compute Storage, B2) it is generally
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advisable to wrap the crypt remote around a specific bucket (`s3:bucket`).
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If wrapping around the entire root of the storage (`s3:`), and use the
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optional file name encryption, rclone will encrypt the bucket name.
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### Changing password
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Should the password, or the configuration file containing a lightly obscured
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form of the password, be compromised, you need to re-encrypt your data with
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a new password. Since rclone uses secret-key encryption, where the encryption
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key is generated directly from the password kept on the client, it is not
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possible to change the password/key of already encrypted content. Just changing
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the password configured for an existing crypt remote means you will no longer
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able to decrypt any of the previously encrypted content. The only possibility
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is to re-upload everything via a crypt remote configured with your new password.
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Depending on the size of your data, your bandwidth, storage quota etc, there are
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different approaches you can take:
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- If you have everything in a different location, for example on your local system,
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you could remove all of the prior encrypted files, change the password for your
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configured crypt remote (or delete and re-create the crypt configuration),
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and then re-upload everything from the alternative location.
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- If you have enough space on the storage system you can create a new crypt
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remote pointing to a separate directory on the same backend, and then use
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rclone to copy everything from the original crypt remote to the new,
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effectively decrypting everything on the fly using the old password and
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re-encrypting using the new password. When done, delete the original crypt
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remote directory and finally the rclone crypt configuration with the old password.
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All data will be streamed from the storage system and back, so you will
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get half the bandwidth and be charged twice if you have upload and download quota
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on the storage system.
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**Note**: A security problem related to the random password generator
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was fixed in rclone version 1.53.3 (released 2020-11-19). Passwords generated
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by rclone config in version 1.49.0 (released 2019-08-26) to 1.53.2
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(released 2020-10-26) are not considered secure and should be changed.
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If you made up your own password, or used rclone version older than 1.49.0 or
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newer than 1.53.2 to generate it, you are *not* affected by this issue.
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See [issue #4783](https://github.com/rclone/rclone/issues/4783) for more
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details, and a tool you can use to check if you are affected.
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### Example
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Create the following file structure using "standard" file name
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encryption.
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```
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plaintext/
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├── file0.txt
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├── file1.txt
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└── subdir
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├── file2.txt
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├── file3.txt
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└── subsubdir
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└── file4.txt
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```
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Copy these to the remote, and list them
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```
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$ rclone -q copy plaintext secret:
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$ rclone -q ls secret:
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7 file1.txt
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6 file0.txt
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8 subdir/file2.txt
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10 subdir/subsubdir/file4.txt
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9 subdir/file3.txt
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```
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The crypt remote looks like
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```
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$ rclone -q ls remote:path
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55 hagjclgavj2mbiqm6u6cnjjqcg
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54 v05749mltvv1tf4onltun46gls
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57 86vhrsv86mpbtd3a0akjuqslj8/dlj7fkq4kdq72emafg7a7s41uo
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58 86vhrsv86mpbtd3a0akjuqslj8/7uu829995du6o42n32otfhjqp4/b9pausrfansjth5ob3jkdqd4lc
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56 86vhrsv86mpbtd3a0akjuqslj8/8njh1sk437gttmep3p70g81aps
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```
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The directory structure is preserved
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```
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$ rclone -q ls secret:subdir
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8 file2.txt
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9 file3.txt
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10 subsubdir/file4.txt
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```
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Without file name encryption `.bin` extensions are added to underlying
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names. This prevents the cloud provider attempting to interpret file
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content.
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```
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$ rclone -q ls remote:path
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54 file0.txt.bin
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57 subdir/file3.txt.bin
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56 subdir/file2.txt.bin
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58 subdir/subsubdir/file4.txt.bin
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55 file1.txt.bin
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```
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### File name encryption modes
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Off
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* doesn't hide file names or directory structure
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* allows for longer file names (~246 characters)
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* can use sub paths and copy single files
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Standard
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* file names encrypted
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* file names can't be as long (~143 characters)
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* can use sub paths and copy single files
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* directory structure visible
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* identical files names will have identical uploaded names
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* can use shortcuts to shorten the directory recursion
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Obfuscation
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This is a simple "rotate" of the filename, with each file having a rot
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distance based on the filename. Rclone stores the distance at the
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beginning of the filename. A file called "hello" may become "53.jgnnq".
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Obfuscation is not a strong encryption of filenames, but hinders
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automated scanning tools picking up on filename patterns. It is an
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intermediate between "off" and "standard" which allows for longer path
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segment names.
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There is a possibility with some unicode based filenames that the
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obfuscation is weak and may map lower case characters to upper case
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equivalents.
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Obfuscation cannot be relied upon for strong protection.
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* file names very lightly obfuscated
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* file names can be longer than standard encryption
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* can use sub paths and copy single files
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* directory structure visible
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* identical files names will have identical uploaded names
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Cloud storage systems have limits on file name length and
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total path length which rclone is more likely to breach using
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"Standard" file name encryption. Where file names are 143 or fewer
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characters in length issues should not be encountered, irrespective of
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cloud storage provider.
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An experimental advanced option `filename_encoding` is now provided to
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address this problem to a certain degree.
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For cloud storage systems with case sensitive file names (e.g. Google Drive),
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`base64` can be used to reduce file name length.
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For cloud storage systems using UTF-16 to store file names internally
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(e.g. OneDrive, Dropbox, Box), `base32768` can be used to drastically reduce
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file name length.
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An alternative, future rclone file name encryption mode may tolerate
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backend provider path length limits.
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### Directory name encryption
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Crypt offers the option of encrypting dir names or leaving them intact.
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There are two options:
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True
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Encrypts the whole file path including directory names
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Example:
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`1/12/123.txt` is encrypted to
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`p0e52nreeaj0a5ea7s64m4j72s/l42g6771hnv3an9cgc8cr2n1ng/qgm4avr35m5loi1th53ato71v0`
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False
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Only encrypts file names, skips directory names
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Example:
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`1/12/123.txt` is encrypted to
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`1/12/qgm4avr35m5loi1th53ato71v0`
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### Modification times and hashes
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Crypt stores modification times using the underlying remote so support
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depends on that.
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Hashes are not stored for crypt. However the data integrity is
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protected by an extremely strong crypto authenticator.
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Use the `rclone cryptcheck` command to check the
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integrity of an encrypted remote instead of `rclone check` which can't
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check the checksums properly.
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{{< rem autogenerated options start" - DO NOT EDIT - instead edit fs.RegInfo in backend/crypt/crypt.go then run make backenddocs" >}}
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### Standard options
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Here are the Standard options specific to crypt (Encrypt/Decrypt a remote).
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#### --crypt-remote
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Remote to encrypt/decrypt.
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Normally should contain a ':' and a path, e.g. "myremote:path/to/dir",
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"myremote:bucket" or maybe "myremote:" (not recommended).
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Properties:
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- Config: remote
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- Env Var: RCLONE_CRYPT_REMOTE
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- Type: string
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- Required: true
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#### --crypt-filename-encryption
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How to encrypt the filenames.
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Properties:
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- Config: filename_encryption
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- Env Var: RCLONE_CRYPT_FILENAME_ENCRYPTION
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- Type: string
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- Default: "standard"
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- Examples:
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- "standard"
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- Encrypt the filenames.
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- See the docs for the details.
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- "obfuscate"
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- Very simple filename obfuscation.
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- "off"
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- Don't encrypt the file names.
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- Adds a ".bin", or "suffix" extension only.
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#### --crypt-directory-name-encryption
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Option to either encrypt directory names or leave them intact.
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NB If filename_encryption is "off" then this option will do nothing.
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Properties:
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- Config: directory_name_encryption
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- Env Var: RCLONE_CRYPT_DIRECTORY_NAME_ENCRYPTION
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- Type: bool
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- Default: true
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- Examples:
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- "true"
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- Encrypt directory names.
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- "false"
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- Don't encrypt directory names, leave them intact.
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#### --crypt-password
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Password or pass phrase for encryption.
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**NB** Input to this must be obscured - see [rclone obscure](/commands/rclone_obscure/).
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Properties:
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- Config: password
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- Env Var: RCLONE_CRYPT_PASSWORD
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- Type: string
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- Required: true
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#### --crypt-password2
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Password or pass phrase for salt.
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Optional but recommended.
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Should be different to the previous password.
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**NB** Input to this must be obscured - see [rclone obscure](/commands/rclone_obscure/).
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||
|
||
Properties:
|
||
|
||
- Config: password2
|
||
- Env Var: RCLONE_CRYPT_PASSWORD2
|
||
- Type: string
|
||
- Required: false
|
||
|
||
### Advanced options
|
||
|
||
Here are the Advanced options specific to crypt (Encrypt/Decrypt a remote).
|
||
|
||
#### --crypt-server-side-across-configs
|
||
|
||
Deprecated: use --server-side-across-configs instead.
|
||
|
||
Allow server-side operations (e.g. copy) to work across different crypt configs.
|
||
|
||
Normally this option is not what you want, but if you have two crypts
|
||
pointing to the same backend you can use it.
|
||
|
||
This can be used, for example, to change file name encryption type
|
||
without re-uploading all the data. Just make two crypt backends
|
||
pointing to two different directories with the single changed
|
||
parameter and use rclone move to move the files between the crypt
|
||
remotes.
|
||
|
||
Properties:
|
||
|
||
- Config: server_side_across_configs
|
||
- Env Var: RCLONE_CRYPT_SERVER_SIDE_ACROSS_CONFIGS
|
||
- Type: bool
|
||
- Default: false
|
||
|
||
#### --crypt-show-mapping
|
||
|
||
For all files listed show how the names encrypt.
|
||
|
||
If this flag is set then for each file that the remote is asked to
|
||
list, it will log (at level INFO) a line stating the decrypted file
|
||
name and the encrypted file name.
|
||
|
||
This is so you can work out which encrypted names are which decrypted
|
||
names just in case you need to do something with the encrypted file
|
||
names, or for debugging purposes.
|
||
|
||
Properties:
|
||
|
||
- Config: show_mapping
|
||
- Env Var: RCLONE_CRYPT_SHOW_MAPPING
|
||
- Type: bool
|
||
- Default: false
|
||
|
||
#### --crypt-no-data-encryption
|
||
|
||
Option to either encrypt file data or leave it unencrypted.
|
||
|
||
Properties:
|
||
|
||
- Config: no_data_encryption
|
||
- Env Var: RCLONE_CRYPT_NO_DATA_ENCRYPTION
|
||
- Type: bool
|
||
- Default: false
|
||
- Examples:
|
||
- "true"
|
||
- Don't encrypt file data, leave it unencrypted.
|
||
- "false"
|
||
- Encrypt file data.
|
||
|
||
#### --crypt-pass-bad-blocks
|
||
|
||
If set this will pass bad blocks through as all 0.
|
||
|
||
This should not be set in normal operation, it should only be set if
|
||
trying to recover an encrypted file with errors and it is desired to
|
||
recover as much of the file as possible.
|
||
|
||
Properties:
|
||
|
||
- Config: pass_bad_blocks
|
||
- Env Var: RCLONE_CRYPT_PASS_BAD_BLOCKS
|
||
- Type: bool
|
||
- Default: false
|
||
|
||
#### --crypt-strict-names
|
||
|
||
If set, this will raise an error when crypt comes across a filename that can't be decrypted.
|
||
|
||
(By default, rclone will just log a NOTICE and continue as normal.)
|
||
This can happen if encrypted and unencrypted files are stored in the same
|
||
directory (which is not recommended.) It may also indicate a more serious
|
||
problem that should be investigated.
|
||
|
||
Properties:
|
||
|
||
- Config: strict_names
|
||
- Env Var: RCLONE_CRYPT_STRICT_NAMES
|
||
- Type: bool
|
||
- Default: false
|
||
|
||
#### --crypt-filename-encoding
|
||
|
||
How to encode the encrypted filename to text string.
|
||
|
||
This option could help with shortening the encrypted filename. The
|
||
suitable option would depend on the way your remote count the filename
|
||
length and if it's case sensitive.
|
||
|
||
Properties:
|
||
|
||
- Config: filename_encoding
|
||
- Env Var: RCLONE_CRYPT_FILENAME_ENCODING
|
||
- Type: string
|
||
- Default: "base32"
|
||
- Examples:
|
||
- "base32"
|
||
- Encode using base32. Suitable for all remote.
|
||
- "base64"
|
||
- Encode using base64. Suitable for case sensitive remote.
|
||
- "base32768"
|
||
- Encode using base32768. Suitable if your remote counts UTF-16 or
|
||
- Unicode codepoint instead of UTF-8 byte length. (Eg. Onedrive, Dropbox)
|
||
|
||
#### --crypt-suffix
|
||
|
||
If this is set it will override the default suffix of ".bin".
|
||
|
||
Setting suffix to "none" will result in an empty suffix. This may be useful
|
||
when the path length is critical.
|
||
|
||
Properties:
|
||
|
||
- Config: suffix
|
||
- Env Var: RCLONE_CRYPT_SUFFIX
|
||
- Type: string
|
||
- Default: ".bin"
|
||
|
||
#### --crypt-description
|
||
|
||
Description of the remote.
|
||
|
||
Properties:
|
||
|
||
- Config: description
|
||
- Env Var: RCLONE_CRYPT_DESCRIPTION
|
||
- Type: string
|
||
- Required: false
|
||
|
||
### Metadata
|
||
|
||
Any metadata supported by the underlying remote is read and written.
|
||
|
||
See the [metadata](/docs/#metadata) docs for more info.
|
||
|
||
## Backend commands
|
||
|
||
Here are the commands specific to the crypt backend.
|
||
|
||
Run them with
|
||
|
||
rclone backend COMMAND remote:
|
||
|
||
The help below will explain what arguments each command takes.
|
||
|
||
See the [backend](/commands/rclone_backend/) command for more
|
||
info on how to pass options and arguments.
|
||
|
||
These can be run on a running backend using the rc command
|
||
[backend/command](/rc/#backend-command).
|
||
|
||
### encode
|
||
|
||
Encode the given filename(s)
|
||
|
||
rclone backend encode remote: [options] [<arguments>+]
|
||
|
||
This encodes the filenames given as arguments returning a list of
|
||
strings of the encoded results.
|
||
|
||
Usage Example:
|
||
|
||
rclone backend encode crypt: file1 [file2...]
|
||
rclone rc backend/command command=encode fs=crypt: file1 [file2...]
|
||
|
||
|
||
### decode
|
||
|
||
Decode the given filename(s)
|
||
|
||
rclone backend decode remote: [options] [<arguments>+]
|
||
|
||
This decodes the filenames given as arguments returning a list of
|
||
strings of the decoded results. It will return an error if any of the
|
||
inputs are invalid.
|
||
|
||
Usage Example:
|
||
|
||
rclone backend decode crypt: encryptedfile1 [encryptedfile2...]
|
||
rclone rc backend/command command=decode fs=crypt: encryptedfile1 [encryptedfile2...]
|
||
|
||
|
||
{{< rem autogenerated options stop >}}
|
||
|
||
## Backing up an encrypted remote
|
||
|
||
If you wish to backup an encrypted remote, it is recommended that you use
|
||
`rclone sync` on the encrypted files, and make sure the passwords are
|
||
the same in the new encrypted remote.
|
||
|
||
This will have the following advantages
|
||
|
||
* `rclone sync` will check the checksums while copying
|
||
* you can use `rclone check` between the encrypted remotes
|
||
* you don't decrypt and encrypt unnecessarily
|
||
|
||
For example, let's say you have your original remote at `remote:` with
|
||
the encrypted version at `eremote:` with path `remote:crypt`. You
|
||
would then set up the new remote `remote2:` and then the encrypted
|
||
version `eremote2:` with path `remote2:crypt` using the same passwords
|
||
as `eremote:`.
|
||
|
||
To sync the two remotes you would do
|
||
|
||
rclone sync --interactive remote:crypt remote2:crypt
|
||
|
||
And to check the integrity you would do
|
||
|
||
rclone check remote:crypt remote2:crypt
|
||
|
||
## File formats
|
||
|
||
### File encryption
|
||
|
||
Files are encrypted 1:1 source file to destination object. The file
|
||
has a header and is divided into chunks.
|
||
|
||
#### Header
|
||
|
||
* 8 bytes magic string `RCLONE\x00\x00`
|
||
* 24 bytes Nonce (IV)
|
||
|
||
The initial nonce is generated from the operating systems crypto
|
||
strong random number generator. The nonce is incremented for each
|
||
chunk read making sure each nonce is unique for each block written.
|
||
The chance of a nonce being reused is minuscule. If you wrote an
|
||
exabyte of data (10¹⁸ bytes) you would have a probability of
|
||
approximately 2×10⁻³² of re-using a nonce.
|
||
|
||
#### Chunk
|
||
|
||
Each chunk will contain 64 KiB of data, except for the last one which
|
||
may have less data. The data chunk is in standard NaCl SecretBox
|
||
format. SecretBox uses XSalsa20 and Poly1305 to encrypt and
|
||
authenticate messages.
|
||
|
||
Each chunk contains:
|
||
|
||
* 16 Bytes of Poly1305 authenticator
|
||
* 1 - 65536 bytes XSalsa20 encrypted data
|
||
|
||
64k chunk size was chosen as the best performing chunk size (the
|
||
authenticator takes too much time below this and the performance drops
|
||
off due to cache effects above this). Note that these chunks are
|
||
buffered in memory so they can't be too big.
|
||
|
||
This uses a 32 byte (256 bit key) key derived from the user password.
|
||
|
||
#### Examples
|
||
|
||
1 byte file will encrypt to
|
||
|
||
* 32 bytes header
|
||
* 17 bytes data chunk
|
||
|
||
49 bytes total
|
||
|
||
1 MiB (1048576 bytes) file will encrypt to
|
||
|
||
* 32 bytes header
|
||
* 16 chunks of 65568 bytes
|
||
|
||
1049120 bytes total (a 0.05% overhead). This is the overhead for big
|
||
files.
|
||
|
||
### Name encryption
|
||
|
||
File names are encrypted segment by segment - the path is broken up
|
||
into `/` separated strings and these are encrypted individually.
|
||
|
||
File segments are padded using PKCS#7 to a multiple of 16 bytes
|
||
before encryption.
|
||
|
||
They are then encrypted with EME using AES with 256 bit key. EME
|
||
(ECB-Mix-ECB) is a wide-block encryption mode presented in the 2003
|
||
paper "A Parallelizable Enciphering Mode" by Halevi and Rogaway.
|
||
|
||
This makes for deterministic encryption which is what we want - the
|
||
same filename must encrypt to the same thing otherwise we can't find
|
||
it on the cloud storage system.
|
||
|
||
This means that
|
||
|
||
* filenames with the same name will encrypt the same
|
||
* filenames which start the same won't have a common prefix
|
||
|
||
This uses a 32 byte key (256 bits) and a 16 byte (128 bits) IV both of
|
||
which are derived from the user password.
|
||
|
||
After encryption they are written out using a modified version of
|
||
standard `base32` encoding as described in RFC4648. The standard
|
||
encoding is modified in two ways:
|
||
|
||
* it becomes lower case (no-one likes upper case filenames!)
|
||
* we strip the padding character `=`
|
||
|
||
`base32` is used rather than the more efficient `base64` so rclone can be
|
||
used on case insensitive remotes (e.g. Windows, Box, Dropbox, Onedrive etc).
|
||
|
||
### Key derivation
|
||
|
||
Rclone uses `scrypt` with parameters `N=16384, r=8, p=1` with an
|
||
optional user supplied salt (password2) to derive the 32+32+16 = 80
|
||
bytes of key material required. If the user doesn't supply a salt
|
||
then rclone uses an internal one.
|
||
|
||
`scrypt` makes it impractical to mount a dictionary attack on rclone
|
||
encrypted data. For full protection against this you should always use
|
||
a salt.
|
||
|
||
## SEE ALSO
|
||
|
||
* [rclone cryptdecode](/commands/rclone_cryptdecode/) - Show forward/reverse mapping of encrypted filenames
|