1 ========
2 dm-crypt
3 ========
4
5 Device-Mapper's "crypt" target provides transp
6 using the kernel crypto API.
7
8 For a more detailed description of supported p
9 https://gitlab.com/cryptsetup/cryptsetup/wikis
10
11 Parameters::
12
13 <cipher> <key> <iv_offset> <devi
14 <offset> [<#opt_params> <opt_par
15
16 <cipher>
17 Encryption cipher, encryption mode and Ini
18
19 The cipher specifications format is::
20
21 cipher[:keycount]-chainmode-ivmode[:ivo
22
23 Examples::
24
25 aes-cbc-essiv:sha256
26 aes-xts-plain64
27 serpent-xts-plain64
28
29 Cipher format also supports direct specifi
30 format (selected by capi: prefix). The IV
31 as for the first format type.
32 This format is mainly used for specificati
33
34 The crypto API cipher specifications forma
35
36 capi:cipher_api_spec-ivmode[:ivopts]
37
38 Examples::
39
40 capi:cbc(aes)-essiv:sha256
41 capi:xts(aes)-plain64
42
43 Examples of authenticated modes::
44
45 capi:gcm(aes)-random
46 capi:authenc(hmac(sha256),xts(aes))-ra
47 capi:rfc7539(chacha20,poly1305)-random
48
49 The /proc/crypto contains a list of curren
50
51 <key>
52 Key used for encryption. It is encoded eit
53 or it can be passed as <key_string> prefix
54 character (':') for keys residing in kerne
55 You can only use key sizes that are valid
56 in combination with the selected iv mode.
57 Note that for some iv modes the key string
58 keys (for example IV seed) so the key cont
59 into a single string.
60
61 <key_string>
62 The kernel keyring key is identified by st
63 <key_size>:<key_type>:<key_description>.
64
65 <key_size>
66 The encryption key size in bytes. The kern
67 the value passed in <key_size>.
68
69 <key_type>
70 Either 'logon', 'user', 'encrypted' or 'tr
71
72 <key_description>
73 The kernel keyring key description crypt t
74 when loading key of <key_type>.
75
76 <keycount>
77 Multi-key compatibility mode. You can defi
78 then sectors are encrypted according to th
79 sector 1 uses key1 etc.). <keycount> must
80
81 <iv_offset>
82 The IV offset is a sector count that is ad
83 before creating the IV.
84
85 <device path>
86 This is the device that is going to be use
87 encrypted data. You can specify it as a p
88 number <major>:<minor>.
89
90 <offset>
91 Starting sector within the device where th
92
93 <#opt_params>
94 Number of optional parameters. If there ar
95 the optional parameters section can be ski
96 Otherwise #opt_params is the number of fol
97
98 Example of optional parameters section:
99 3 allow_discards same_cpu_crypt submit
100
101 allow_discards
102 Block discard requests (a.k.a. TRIM) are p
103 The default is to ignore discard requests.
104
105 WARNING: Assess the specific security risk
106 option. For example, allowing discards on
107 the leak of information about the cipherte
108 used space etc.) if the discarded blocks c
109 device later.
110
111 same_cpu_crypt
112 Perform encryption using the same cpu that
113 The default is to use an unbound workqueue
114 is automatically balanced between availabl
115
116 high_priority
117 Set dm-crypt workqueues and the writer thr
118 improves throughput and latency of dm-cryp
119 responsiveness of the system.
120
121 submit_from_crypt_cpus
122 Disable offloading writes to a separate th
123 There are some situations where offloading
124 encryption threads to a single thread degr
125 significantly. The default is to offload
126 thread because it benefits CFQ to have wri
127 same context.
128
129 no_read_workqueue
130 Bypass dm-crypt internal workqueue and pro
131
132 no_write_workqueue
133 Bypass dm-crypt internal workqueue and pro
134 This option is automatically enabled for h
135 (e.g. host-managed SMR hard-disks).
136
137 integrity:<bytes>:<type>
138 The device requires additional <bytes> met
139 in per-bio integrity structure. This metad
140 by underlying dm-integrity target.
141
142 The <type> can be "none" if metadata is us
143
144 For Authenticated Encryption with Addition
145 the <type> is "aead". An AEAD mode additio
146 integrity for the encrypted device. The ad
147 used for storing authentication tag (and p
148
149 sector_size:<bytes>
150 Use <bytes> as the encryption unit instead
151 This option can be in range 512 - 4096 byt
152 Virtual device will announce this size as
153
154 iv_large_sectors
155 IV generators will use sector number counte
156 instead of default 512 bytes sectors.
157
158 For example, if <sector_size> is 4096 bytes
159 sector will be 8 (without flag) and 1 if iv
160 The <iv_offset> must be multiple of <sector
161 if this flag is specified.
162
163 integrity_key_size:<bytes>
164 Use an integrity key of <bytes> size instea
165 of the digest size of the used HMAC algorit
166
167
168 Module parameters::
169 max_read_size
170 Maximum size of read requests. When a re
171 is received, dm-crypt will split the req
172 concurrency (the split requests could be
173 cores), but it also causes overhead. The
174 fit the actual workload.
175
176 max_write_size
177 Maximum size of write requests. When a r
178 is received, dm-crypt will split the req
179 concurrency (the split requests could be
180 cores), but it also causes overhead. The
181 fit the actual workload.
182
183
184 Example scripts
185 ===============
186 LUKS (Linux Unified Key Setup) is now the pref
187 encryption with dm-crypt using the 'cryptsetup
188 https://gitlab.com/cryptsetup/cryptsetup
189
190 ::
191
192 #!/bin/sh
193 # Create a crypt device using dmsetup
194 dmsetup create crypt1 --table "0 `bloc
195
196 ::
197
198 #!/bin/sh
199 # Create a crypt device using dmsetup
200 dmsetup create crypt2 --table "0 `bloc
201
202 ::
203
204 #!/bin/sh
205 # Create a crypt device using cryptset
206 cryptsetup luksFormat $1
207 cryptsetup luksOpen $1 crypt1
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