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1 | dm-crypt |
2 | ========= | |
3 | ||
4 | Device-Mapper's "crypt" target provides transparent encryption of block devices | |
5 | using the kernel crypto API. | |
6 | ||
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7 | For a more detailed description of supported parameters see: |
8 | http://code.google.com/p/cryptsetup/wiki/DMCrypt | |
9 | ||
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10 | Parameters: <cipher> <key> <iv_offset> <device path> \ |
11 | <offset> [<#opt_params> <opt_params>] | |
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12 | |
13 | <cipher> | |
14 | Encryption cipher and an optional IV generation mode. | |
ed04d981 | 15 | (In format cipher[:keycount]-chainmode-ivmode[:ivopts]). |
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16 | 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. | |
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25 | 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. | |
e3dcc5a3 | 30 | |
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31 | <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 | ||
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36 | <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 | ||
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48 | <#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: | |
54 | 1 allow_discards | |
55 | ||
56 | allow_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 | ||
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66 | Example scripts |
67 | =============== | |
68 | LUKS (Linux Unified Key Setup) is now the preferred way to set up disk | |
69 | encryption with dm-crypt using the 'cryptsetup' utility, see | |
adc0485b | 70 | http://code.google.com/p/cryptsetup/ |
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71 | |
72 | [[ | |
73 | #!/bin/sh | |
74 | # Create a crypt device using dmsetup | |
75 | dmsetup create crypt1 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0" | |
76 | ]] | |
77 | ||
78 | [[ | |
79 | #!/bin/sh | |
80 | # Create a crypt device using cryptsetup and LUKS header with default cipher | |
81 | cryptsetup luksFormat $1 | |
82 | cryptsetup luksOpen $1 crypt1 | |
83 | ]] |