77 lines
2.5 KiB
Plaintext
77 lines
2.5 KiB
Plaintext
dm-crypt
|
|
=========
|
|
|
|
Device-Mapper's "crypt" target provides transparent encryption of block devices
|
|
using the kernel crypto API.
|
|
|
|
Parameters: <cipher> <key> <iv_offset> <device path> \
|
|
<offset> [<#opt_params> <opt_params>]
|
|
|
|
<cipher>
|
|
Encryption cipher and an optional IV generation mode.
|
|
(In format cipher[:keycount]-chainmode-ivopts:ivmode).
|
|
Examples:
|
|
des
|
|
aes-cbc-essiv:sha256
|
|
twofish-ecb
|
|
|
|
/proc/crypto contains supported crypto modes
|
|
|
|
<key>
|
|
Key used for encryption. It is encoded as a hexadecimal number.
|
|
You can only use key sizes that are valid for the selected cipher.
|
|
|
|
<keycount>
|
|
Multi-key compatibility mode. You can define <keycount> keys and
|
|
then sectors are encrypted according to their offsets (sector 0 uses key0;
|
|
sector 1 uses key1 etc.). <keycount> must be a power of two.
|
|
|
|
<iv_offset>
|
|
The IV offset is a sector count that is added to the sector number
|
|
before creating the IV.
|
|
|
|
<device path>
|
|
This is the device that is going to be used as backend and contains the
|
|
encrypted data. You can specify it as a path like /dev/xxx or a device
|
|
number <major>:<minor>.
|
|
|
|
<offset>
|
|
Starting sector within the device where the encrypted data begins.
|
|
|
|
<#opt_params>
|
|
Number of optional parameters. If there are no optional parameters,
|
|
the optional paramaters section can be skipped or #opt_params can be zero.
|
|
Otherwise #opt_params is the number of following arguments.
|
|
|
|
Example of optional parameters section:
|
|
1 allow_discards
|
|
|
|
allow_discards
|
|
Block discard requests (a.k.a. TRIM) are passed through the crypt device.
|
|
The default is to ignore discard requests.
|
|
|
|
WARNING: Assess the specific security risks carefully before enabling this
|
|
option. For example, allowing discards on encrypted devices may lead to
|
|
the leak of information about the ciphertext device (filesystem type,
|
|
used space etc.) if the discarded blocks can be located easily on the
|
|
device later.
|
|
|
|
Example scripts
|
|
===============
|
|
LUKS (Linux Unified Key Setup) is now the preferred way to set up disk
|
|
encryption with dm-crypt using the 'cryptsetup' utility, see
|
|
http://code.google.com/p/cryptsetup/
|
|
|
|
[[
|
|
#!/bin/sh
|
|
# Create a crypt device using dmsetup
|
|
dmsetup create crypt1 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0"
|
|
]]
|
|
|
|
[[
|
|
#!/bin/sh
|
|
# Create a crypt device using cryptsetup and LUKS header with default cipher
|
|
cryptsetup luksFormat $1
|
|
cryptsetup luksOpen $1 crypt1
|
|
]]
|