Ubuntu Manpage: cryfs - cryptographic filesystem for the cloud

NAME

       cryfs - cryptographic filesystem for the cloud

SYNOPSIS

       cryfs [-c file] [-f] [options] basedir mountpoint
       cryfs --help|--version|--show-ciphers

DESCRIPTION

       CryFS encrypts your files, so you can safely store them anywhere.

       The  goal  of  CryFS  is  not  only  to  keep  file contents, but also file sizes, metadata and directory
       structure confidential.  CryFS uses encrypted same-size blocks to store both the files themselves and the
       block's relations to another.  These blocks are stored as individual files in the base  directory,  which
       can then be synchronized with cloud services such as Dropbox.

       The  blocks  are  encrypted  using a random key, which is stored in a configuration file encrypted by the
       user's passphrase.  By default, it will be stored together with the data in the base directory,  but  you
       can choose a different location if you do not want it in your cloud or when using a weak passphrase.

USING CRYFS

   Selecting base and mount directories
       While  you  can  access  your files through your mount directory, CryFS actually places them in your base
       directory after encrypting.  CryFS will encrypt and decrypt your files 'on the fly' as they are accessed,
       so files will never be stored on the disk in unencrypted form.

       You can choose any empty directory as your base, but your mount directory should be outside of any  cloud
       storage, as your cloud may try to sync your (temporarily mounted) unencrypted files as well.

   Setup and usage of your encrypted directory
       Creating and mounting your encrypted storage use the same command-line syntax:
              cryfs basedir mountpoint

       If  CryFS  detects an encrypted storage in the given base directory, you will be asked for the passphrase
       to unlock and mount it. Otherwise, CryFS will help you with  creating  one,  just  follow  the  on-screen
       instructions.

       After you are done working with your encrypted files, unmount your storage with the command
              cryfs-unmount mountpoint

   Changing your passphrase
       As the encryption key to your CryFS storage is stored in your configuration file, it would be possible to
       re-encrypt it using a different passphrase (although this feature has not been implemented yet).

       However,  this  does  not change the actual encryption key of your storage, so someone with access to the
       old passphrase and configuration file (for example through the file history of your cloud  or  your  file
       system) could still access your files, even those created after the password change.

       For  this reason, the recommended way to change your passphrase is to create a new CryFS storage with the
       new passphrase and move your files from the old to the new one.

OPTIONS

Getting help
-h, --help
Show a help message containing short descriptions for all options.

--show-ciphers
Show a list of all supported encryption ciphers.

--version
Show the CryFS version number.

Encryption parameters
--blocksize arg
Set the block size to arg bytes. Defaults to 32768.

A higher block size may help reducing the file count in your base directory (especially when
storing large files), but will also waste more space when storing smaller files.

--cipher arg
Use arg as the cipher for the encryption. Defaults to aes-256-gcm.

-c file, --config file
Use file as configuration file for this CryFS storage instead of basedir/cryfs.config

General options
-f, --foreground
Run CryFS in the foreground. Stop using CTRL-C.

--allow-filesystem-upgrade
Allow upgrading the file system if it was created with an old CryFS version. After the upgrade,
older CryFS versions might not be able to use the file system anymore.

--allow-integrity-violations
By default, CryFS checks for integrity violations, i.e. will notice if an adversary modified or
rolled back the file system. Using this flag, you can disable the integrity checks. This can for
example be helpful for loading an old snapshot of your file system without CryFS thinking an
adversary rolled it back.

--allow-replaced-filesystem
By default, CryFS remembers file systems it has seen in this base directory and checks that it
didn't get replaced by an attacker with an entirely different file system since the last time it
was loaded. However, if you do want to replace the file system with an entirely new one, you can
pass in this option to disable the check.

--create-missing-basedir
Creates the base directory even if there is no directory currently there, skipping the normal
confirmation message to create it later.

--create-missing-mountpoint
Creates the mountpoint even if there is no directory currently there, skipping the normal
confirmation message to create it later.

--missing-block-is-integrity-violation=true
When CryFS encounters a missing ciphertext block, it cannot cannot (yet) know if it was deleted by
an unauthorized adversary or by a second authorized client. This is one of the restrictions of the
integrity checks currently in place. You can enable this flag to treat missing ciphertext blocks
as integrity violations, but then your file system will not be usable by multiple clients anymore.
By default, this flag is disabled.

--logfile file
Write status information to file. If no logfile is given, CryFS will write them to syslog in
background mode, or to stdout in foreground mode.

--unmount-idle arg
Unmount automatically after arg minutes of inactivity.

FUSE Options

       -o option, --fuse-option option
              Pass through options to the FUSE filesystem driver.

       For example:

       -o allow_other
              This option overrides the security measure restricting file access to  the  filesystem  owner,  so
              that all users (including root) can access the files.

       -o allow_root
              This option is similar to allow_other but file access is limited to the filesystem owner and root.
              This option and allow_other are mutually exclusive.

ENVIRONMENT

       CRYFS_FRONTEND=noninteractive
              With  this  option set, CryFS will only ask for the encryption passphrase once.  Instead of asking
              the user for parameters not specified on the command line, it will just use  the  default  values.
              CryFS will also not ask you to confirm your passphrase when creating a new CryFS storage.

              Set this environment variable when automating CryFS using external tools or shell scripts.

       CRYFS_NO_UPDATE_CHECK=true
              By  default,  CryFS  connects  to the internet to check for known security vulnerabilities and new
              versions. This option disables this.

       CRYFS_LOCAL_STATE_DIR=[path]
              Sets the directory cryfs uses to store local state. This local state is used  to  recognize  known
              file  systems and run integrity checks (i.e. check that they haven't been modified by an attacker.
              Default value: ${HOME}/.cryfs

AUTHORS

       CryFS was created by Sebastian Messmer and contributors.  This man page was written by Maximilian Wende.

                                                                                                        cryfs(1)