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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 | ||
ed04d981 | 7 | For a more detailed description of supported parameters see: |
e44f23b3 | 8 | https://gitlab.com/cryptsetup/cryptsetup/wikis/DMCrypt |
ed04d981 | 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> | |
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24 | Key used for encryption. It is encoded either as a hexadecimal number |
25 | or it can be passed as <key_string> prefixed with single colon | |
26 | character (':') for keys residing in kernel keyring service. | |
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27 | You can only use key sizes that are valid for the selected cipher |
28 | in combination with the selected iv mode. | |
29 | Note that for some iv modes the key string can contain additional | |
30 | keys (for example IV seed) so the key contains more parts concatenated | |
31 | into a single string. | |
e3dcc5a3 | 32 | |
c538f6ec OK |
33 | <key_string> |
34 | The kernel keyring key is identified by string in following format: | |
35 | <key_size>:<key_type>:<key_description>. | |
36 | ||
37 | <key_size> | |
38 | The encryption key size in bytes. The kernel key payload size must match | |
39 | the value passed in <key_size>. | |
40 | ||
41 | <key_type> | |
42 | Either 'logon' or 'user' kernel key type. | |
43 | ||
44 | <key_description> | |
45 | The kernel keyring key description crypt target should look for | |
46 | when loading key of <key_type>. | |
47 | ||
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48 | <keycount> |
49 | Multi-key compatibility mode. You can define <keycount> keys and | |
50 | then sectors are encrypted according to their offsets (sector 0 uses key0; | |
51 | sector 1 uses key1 etc.). <keycount> must be a power of two. | |
52 | ||
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53 | <iv_offset> |
54 | The IV offset is a sector count that is added to the sector number | |
55 | before creating the IV. | |
56 | ||
57 | <device path> | |
58 | This is the device that is going to be used as backend and contains the | |
59 | encrypted data. You can specify it as a path like /dev/xxx or a device | |
60 | number <major>:<minor>. | |
61 | ||
62 | <offset> | |
63 | Starting sector within the device where the encrypted data begins. | |
64 | ||
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65 | <#opt_params> |
66 | Number of optional parameters. If there are no optional parameters, | |
67 | the optional paramaters section can be skipped or #opt_params can be zero. | |
68 | Otherwise #opt_params is the number of following arguments. | |
69 | ||
70 | Example of optional parameters section: | |
0f5d8e6e | 71 | 3 allow_discards same_cpu_crypt submit_from_crypt_cpus |
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72 | |
73 | allow_discards | |
74 | Block discard requests (a.k.a. TRIM) are passed through the crypt device. | |
75 | The default is to ignore discard requests. | |
76 | ||
77 | WARNING: Assess the specific security risks carefully before enabling this | |
78 | option. For example, allowing discards on encrypted devices may lead to | |
79 | the leak of information about the ciphertext device (filesystem type, | |
80 | used space etc.) if the discarded blocks can be located easily on the | |
81 | device later. | |
82 | ||
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83 | same_cpu_crypt |
84 | Perform encryption using the same cpu that IO was submitted on. | |
85 | The default is to use an unbound workqueue so that encryption work | |
86 | is automatically balanced between available CPUs. | |
87 | ||
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88 | submit_from_crypt_cpus |
89 | Disable offloading writes to a separate thread after encryption. | |
90 | There are some situations where offloading write bios from the | |
91 | encryption threads to a single thread degrades performance | |
92 | significantly. The default is to offload write bios to the same | |
93 | thread because it benefits CFQ to have writes submitted using the | |
94 | same context. | |
95 | ||
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96 | Example scripts |
97 | =============== | |
98 | LUKS (Linux Unified Key Setup) is now the preferred way to set up disk | |
99 | encryption with dm-crypt using the 'cryptsetup' utility, see | |
e44f23b3 | 100 | https://gitlab.com/cryptsetup/cryptsetup |
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101 | |
102 | [[ | |
103 | #!/bin/sh | |
104 | # Create a crypt device using dmsetup | |
95f21c5c | 105 | dmsetup create crypt1 --table "0 `blockdev --getsz $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0" |
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106 | ]] |
107 | ||
c538f6ec OK |
108 | [[ |
109 | #!/bin/sh | |
110 | # Create a crypt device using dmsetup when encryption key is stored in keyring service | |
111 | dmsetup create crypt2 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 :32:logon:my_prefix:my_key 0 $1 0" | |
112 | ]] | |
113 | ||
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114 | [[ |
115 | #!/bin/sh | |
116 | # Create a crypt device using cryptsetup and LUKS header with default cipher | |
117 | cryptsetup luksFormat $1 | |
118 | cryptsetup luksOpen $1 crypt1 | |
119 | ]] |