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cryptmount Filesystem Manager

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cryptmount is a utility for GNU/Linux operating systems which allows an ordinary user to mount an encrypted filing system without requiring superuser privileges. It is aimed at recent Linux systems using the 2.6 kernel series.

There are currently two main approaches to using encrypted filesystems within the linux kernel:

  • the cryptoloop device driver;
  • the device-mapper system, using the dm-crypt target.

The (older) cryptoloop system has grown in parallel with the loopback device-driver of 2.4 kernel series, but has now been superseded by the device-mapper capabilities of the 2.6 kernel series. The newer devmapper system offers a cleaner organization of encryption and device-access, and superior performance has been noted. Alternative user-space tools which allow individual files to be encrypted are also widely available, but allow some information about file sizes & organization to be exposed.

With the older cryptoloop system, it was possible to describe all the details of an encrypted filesystem within /etc/fstab so that it could be configured completely by 'mount'. This meant that it was particularly easy to give any user permission to mount those encrypted filesystems simply by providing the 'user' option within /etc/fstab.

With the newer device-mapper infrastructure, there are more stages involved in mounting an encrypted filing system, and neither does 'mount' currently allow this nor does the syntax of /etc/fstab lend itself to describing all the necessary filesystem parameters. This is especially so if the filesystem is stored in an ordinary file, which would require separate configuration of a loopback device and a devmapper target before the filesystem could be accessed.

cryptmount was written to make it as easy for ordinary users to access encrypted filesystems on-demand using the newer devmapper mechansism as it was to use the older, now deprecated, cryptoloop methods. This offers the following advantages:

  • access to improved functionality in the kernel
  • transparent support for filesystems stored on either raw disk partitions or loopback files
  • separate encryption of filesystem access keys, allowing access passwords to be changed without re-encrypting the entire filesystem
  • storing multiple encrypted filesystems within a single disk partition, using a designated subset of blocks for each
  • rarely used filesystems do not need to be mounted at system startup
  • un-mounting of each filesystem is locked so that this can only be performed by the user that mounted it, or the superuser
  • encrypted filesystems compatible with cryptsetup
  • encrypted access-keys can be chosen to be compatible with openssl, or managed via libgcrypt, or (for 2.0 release-series) built-in SHA1/Blowfish ciphers
  • support for encrypted swap partitions (superuser only)
  • support for setting up encrypted filesystems or crypto-swap at system boot-up

Link: cryptmount.sourceforge.net

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