Documentation/device-mapper/dm-crypt.txt

   1 dm-crypt
   2 =========
   3
   4 Device-Mapper's "crypt" target provides transparent encryption of block devices
   5 using the kernel crypto API.
   6
   7 Parameters: <cipher> <key> <iv_offset> <device path> <offset>
   8
   9 <cipher>
  10     Encryption cipher and an optional IV generation mode.
  11     (In format cipher[:keycount]-chainmode-ivopts:ivmode).
  12     Examples:
  13        des
  14        aes-cbc-essiv:sha256
  15        twofish-ecb
  16
  17     /proc/crypto contains supported crypto modes
  18
  19 <key>
  20     Key used for encryption. It is encoded as a hexadecimal number.
  21     You can only use key sizes that are valid for the selected cipher.
  22
  23 <keycount>
  24     Multi-key compatibility mode. You can define <keycount> keys and
  25     then sectors are encrypted according to their offsets (sector 0 uses key0;
  26     sector 1 uses key1 etc.).  <keycount> must be a power of two.
  27
  28 <iv_offset>
  29     The IV offset is a sector count that is added to the sector number
  30     before creating the IV.
  31
  32 <device path>
  33     This is the device that is going to be used as backend and contains the
  34     encrypted data.  You can specify it as a path like /dev/xxx or a device
  35     number <major>:<minor>.
  36
  37 <offset>
  38     Starting sector within the device where the encrypted data begins.
  39
  40 Example scripts
  41 ===============
  42 LUKS (Linux Unified Key Setup) is now the preferred way to set up disk
  43 encryption with dm-crypt using the 'cryptsetup' utility, see
  44 http://code.google.com/p/cryptsetup/
  45
  46 [[
  47 #!/bin/sh
  48 # Create a crypt device using dmsetup
  49 dmsetup create crypt1 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0"
  50 ]]
  51
  52 [[
  53 #!/bin/sh
  54 # Create a crypt device using cryptsetup and LUKS header with default cipher
  55 cryptsetup luksFormat $1
  56 cryptsetup luksOpen $1 crypt1
  57 ]]