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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 | Parameters: <cipher> <key> <iv_offset> <device path> \ |
8 | <offset> [<#opt_params> <opt_params>] | |
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9 | |
10 | <cipher> | |
11 | Encryption cipher and an optional IV generation mode. | |
d1f96423 | 12 | (In format cipher[:keycount]-chainmode-ivopts:ivmode). |
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13 | Examples: |
14 | des | |
15 | aes-cbc-essiv:sha256 | |
16 | twofish-ecb | |
17 | ||
18 | /proc/crypto contains supported crypto modes | |
19 | ||
20 | <key> | |
21 | Key used for encryption. It is encoded as a hexadecimal number. | |
22 | You can only use key sizes that are valid for the selected cipher. | |
23 | ||
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24 | <keycount> |
25 | Multi-key compatibility mode. You can define <keycount> keys and | |
26 | then sectors are encrypted according to their offsets (sector 0 uses key0; | |
27 | sector 1 uses key1 etc.). <keycount> must be a power of two. | |
28 | ||
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29 | <iv_offset> |
30 | The IV offset is a sector count that is added to the sector number | |
31 | before creating the IV. | |
32 | ||
33 | <device path> | |
34 | This is the device that is going to be used as backend and contains the | |
35 | encrypted data. You can specify it as a path like /dev/xxx or a device | |
36 | number <major>:<minor>. | |
37 | ||
38 | <offset> | |
39 | Starting sector within the device where the encrypted data begins. | |
40 | ||
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41 | <#opt_params> |
42 | Number of optional parameters. If there are no optional parameters, | |
43 | the optional paramaters section can be skipped or #opt_params can be zero. | |
44 | Otherwise #opt_params is the number of following arguments. | |
45 | ||
46 | Example of optional parameters section: | |
47 | 1 allow_discards | |
48 | ||
49 | allow_discards | |
50 | Block discard requests (a.k.a. TRIM) are passed through the crypt device. | |
51 | The default is to ignore discard requests. | |
52 | ||
53 | WARNING: Assess the specific security risks carefully before enabling this | |
54 | option. For example, allowing discards on encrypted devices may lead to | |
55 | the leak of information about the ciphertext device (filesystem type, | |
56 | used space etc.) if the discarded blocks can be located easily on the | |
57 | device later. | |
58 | ||
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59 | Example scripts |
60 | =============== | |
61 | LUKS (Linux Unified Key Setup) is now the preferred way to set up disk | |
62 | encryption with dm-crypt using the 'cryptsetup' utility, see | |
adc0485b | 63 | http://code.google.com/p/cryptsetup/ |
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64 | |
65 | [[ | |
66 | #!/bin/sh | |
67 | # Create a crypt device using dmsetup | |
68 | dmsetup create crypt1 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0" | |
69 | ]] | |
70 | ||
71 | [[ | |
72 | #!/bin/sh | |
73 | # Create a crypt device using cryptsetup and LUKS header with default cipher | |
74 | cryptsetup luksFormat $1 | |
75 | cryptsetup luksOpen $1 crypt1 | |
76 | ]] |