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Milan Broze3dcc5a2008-04-24 22:11:03 +01001dm-crypt
2=========
3
4Device-Mapper's "crypt" target provides transparent encryption of block devices
5using the kernel crypto API.
6
Milan Brozed04d982013-10-28 23:21:04 +01007For a more detailed description of supported parameters see:
Milan Broze44f23b2015-04-05 18:03:10 +02008https://gitlab.com/cryptsetup/cryptsetup/wikis/DMCrypt
Milan Brozed04d982013-10-28 23:21:04 +01009
Milan Broz772ae5f2011-08-02 12:32:08 +010010Parameters: <cipher> <key> <iv_offset> <device path> \
11 <offset> [<#opt_params> <opt_params>]
Milan Broze3dcc5a2008-04-24 22:11:03 +010012
13<cipher>
14 Encryption cipher and an optional IV generation mode.
Milan Brozed04d982013-10-28 23:21:04 +010015 (In format cipher[:keycount]-chainmode-ivmode[:ivopts]).
Milan Broze3dcc5a2008-04-24 22:11:03 +010016 Examples:
17 des
18 aes-cbc-essiv:sha256
19 twofish-ecb
20
21 /proc/crypto contains supported crypto modes
22
23<key>
24 Key used for encryption. It is encoded as a hexadecimal number.
Milan Brozed04d982013-10-28 23:21:04 +010025 You can only use key sizes that are valid for the selected cipher
26 in combination with the selected iv mode.
27 Note that for some iv modes the key string can contain additional
28 keys (for example IV seed) so the key contains more parts concatenated
29 into a single string.
Milan Broze3dcc5a2008-04-24 22:11:03 +010030
Milan Brozd1f96422011-01-13 19:59:54 +000031<keycount>
32 Multi-key compatibility mode. You can define <keycount> keys and
33 then sectors are encrypted according to their offsets (sector 0 uses key0;
34 sector 1 uses key1 etc.). <keycount> must be a power of two.
35
Milan Broze3dcc5a2008-04-24 22:11:03 +010036<iv_offset>
37 The IV offset is a sector count that is added to the sector number
38 before creating the IV.
39
40<device path>
41 This is the device that is going to be used as backend and contains the
42 encrypted data. You can specify it as a path like /dev/xxx or a device
43 number <major>:<minor>.
44
45<offset>
46 Starting sector within the device where the encrypted data begins.
47
Milan Broz772ae5f2011-08-02 12:32:08 +010048<#opt_params>
49 Number of optional parameters. If there are no optional parameters,
50 the optional paramaters section can be skipped or #opt_params can be zero.
51 Otherwise #opt_params is the number of following arguments.
52
53 Example of optional parameters section:
Mikulas Patocka0f5d8e62015-02-13 08:27:08 -050054 3 allow_discards same_cpu_crypt submit_from_crypt_cpus
Milan Broz772ae5f2011-08-02 12:32:08 +010055
56allow_discards
57 Block discard requests (a.k.a. TRIM) are passed through the crypt device.
58 The default is to ignore discard requests.
59
60 WARNING: Assess the specific security risks carefully before enabling this
61 option. For example, allowing discards on encrypted devices may lead to
62 the leak of information about the ciphertext device (filesystem type,
63 used space etc.) if the discarded blocks can be located easily on the
64 device later.
65
Mikulas Patockaf3396c582015-02-13 08:23:09 -050066same_cpu_crypt
67 Perform encryption using the same cpu that IO was submitted on.
68 The default is to use an unbound workqueue so that encryption work
69 is automatically balanced between available CPUs.
70
Mikulas Patocka0f5d8e62015-02-13 08:27:08 -050071submit_from_crypt_cpus
72 Disable offloading writes to a separate thread after encryption.
73 There are some situations where offloading write bios from the
74 encryption threads to a single thread degrades performance
75 significantly. The default is to offload write bios to the same
76 thread because it benefits CFQ to have writes submitted using the
77 same context.
78
Milan Broze3dcc5a2008-04-24 22:11:03 +010079Example scripts
80===============
81LUKS (Linux Unified Key Setup) is now the preferred way to set up disk
82encryption with dm-crypt using the 'cryptsetup' utility, see
Milan Broze44f23b2015-04-05 18:03:10 +020083https://gitlab.com/cryptsetup/cryptsetup
Milan Broze3dcc5a2008-04-24 22:11:03 +010084
85[[
86#!/bin/sh
87# Create a crypt device using dmsetup
88dmsetup create crypt1 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0"
89]]
90
91[[
92#!/bin/sh
93# Create a crypt device using cryptsetup and LUKS header with default cipher
94cryptsetup luksFormat $1
95cryptsetup luksOpen $1 crypt1
96]]