1 ======== 1 ========
2 dm-crypt 2 dm-crypt
3 ======== 3 ========
4 4
5 Device-Mapper's "crypt" target provides transp 5 Device-Mapper's "crypt" target provides transparent encryption of block devices
6 using the kernel crypto API. 6 using the kernel crypto API.
7 7
8 For a more detailed description of supported p 8 For a more detailed description of supported parameters see:
9 https://gitlab.com/cryptsetup/cryptsetup/wikis 9 https://gitlab.com/cryptsetup/cryptsetup/wikis/DMCrypt
10 10
11 Parameters:: 11 Parameters::
12 12
13 <cipher> <key> <iv_offset> <devi 13 <cipher> <key> <iv_offset> <device path> \
14 <offset> [<#opt_params> <opt_par 14 <offset> [<#opt_params> <opt_params>]
15 15
16 <cipher> 16 <cipher>
17 Encryption cipher, encryption mode and Ini 17 Encryption cipher, encryption mode and Initial Vector (IV) generator.
18 18
19 The cipher specifications format is:: 19 The cipher specifications format is::
20 20
21 cipher[:keycount]-chainmode-ivmode[:ivo 21 cipher[:keycount]-chainmode-ivmode[:ivopts]
22 22
23 Examples:: 23 Examples::
24 24
25 aes-cbc-essiv:sha256 25 aes-cbc-essiv:sha256
26 aes-xts-plain64 26 aes-xts-plain64
27 serpent-xts-plain64 27 serpent-xts-plain64
28 28
29 Cipher format also supports direct specifi 29 Cipher format also supports direct specification with kernel crypt API
30 format (selected by capi: prefix). The IV 30 format (selected by capi: prefix). The IV specification is the same
31 as for the first format type. 31 as for the first format type.
32 This format is mainly used for specificati 32 This format is mainly used for specification of authenticated modes.
33 33
34 The crypto API cipher specifications forma 34 The crypto API cipher specifications format is::
35 35
36 capi:cipher_api_spec-ivmode[:ivopts] 36 capi:cipher_api_spec-ivmode[:ivopts]
37 37
38 Examples:: 38 Examples::
39 39
40 capi:cbc(aes)-essiv:sha256 40 capi:cbc(aes)-essiv:sha256
41 capi:xts(aes)-plain64 41 capi:xts(aes)-plain64
42 42
43 Examples of authenticated modes:: 43 Examples of authenticated modes::
44 44
45 capi:gcm(aes)-random 45 capi:gcm(aes)-random
46 capi:authenc(hmac(sha256),xts(aes))-ra 46 capi:authenc(hmac(sha256),xts(aes))-random
47 capi:rfc7539(chacha20,poly1305)-random 47 capi:rfc7539(chacha20,poly1305)-random
48 48
49 The /proc/crypto contains a list of curren !! 49 The /proc/crypto contains a list of curently loaded crypto modes.
50 50
51 <key> 51 <key>
52 Key used for encryption. It is encoded eit 52 Key used for encryption. It is encoded either as a hexadecimal number
53 or it can be passed as <key_string> prefix 53 or it can be passed as <key_string> prefixed with single colon
54 character (':') for keys residing in kerne 54 character (':') for keys residing in kernel keyring service.
55 You can only use key sizes that are valid 55 You can only use key sizes that are valid for the selected cipher
56 in combination with the selected iv mode. 56 in combination with the selected iv mode.
57 Note that for some iv modes the key string 57 Note that for some iv modes the key string can contain additional
58 keys (for example IV seed) so the key cont 58 keys (for example IV seed) so the key contains more parts concatenated
59 into a single string. 59 into a single string.
60 60
61 <key_string> 61 <key_string>
62 The kernel keyring key is identified by st 62 The kernel keyring key is identified by string in following format:
63 <key_size>:<key_type>:<key_description>. 63 <key_size>:<key_type>:<key_description>.
64 64
65 <key_size> 65 <key_size>
66 The encryption key size in bytes. The kern 66 The encryption key size in bytes. The kernel key payload size must match
67 the value passed in <key_size>. 67 the value passed in <key_size>.
68 68
69 <key_type> 69 <key_type>
70 Either 'logon', 'user', 'encrypted' or 'tr !! 70 Either 'logon' or 'user' kernel key type.
71 71
72 <key_description> 72 <key_description>
73 The kernel keyring key description crypt t 73 The kernel keyring key description crypt target should look for
74 when loading key of <key_type>. 74 when loading key of <key_type>.
75 75
76 <keycount> 76 <keycount>
77 Multi-key compatibility mode. You can defi 77 Multi-key compatibility mode. You can define <keycount> keys and
78 then sectors are encrypted according to th 78 then sectors are encrypted according to their offsets (sector 0 uses key0;
79 sector 1 uses key1 etc.). <keycount> must 79 sector 1 uses key1 etc.). <keycount> must be a power of two.
80 80
81 <iv_offset> 81 <iv_offset>
82 The IV offset is a sector count that is ad 82 The IV offset is a sector count that is added to the sector number
83 before creating the IV. 83 before creating the IV.
84 84
85 <device path> 85 <device path>
86 This is the device that is going to be use 86 This is the device that is going to be used as backend and contains the
87 encrypted data. You can specify it as a p 87 encrypted data. You can specify it as a path like /dev/xxx or a device
88 number <major>:<minor>. 88 number <major>:<minor>.
89 89
90 <offset> 90 <offset>
91 Starting sector within the device where th 91 Starting sector within the device where the encrypted data begins.
92 92
93 <#opt_params> 93 <#opt_params>
94 Number of optional parameters. If there ar 94 Number of optional parameters. If there are no optional parameters,
95 the optional parameters section can be ski !! 95 the optional paramaters section can be skipped or #opt_params can be zero.
96 Otherwise #opt_params is the number of fol 96 Otherwise #opt_params is the number of following arguments.
97 97
98 Example of optional parameters section: 98 Example of optional parameters section:
99 3 allow_discards same_cpu_crypt submit 99 3 allow_discards same_cpu_crypt submit_from_crypt_cpus
100 100
101 allow_discards 101 allow_discards
102 Block discard requests (a.k.a. TRIM) are p 102 Block discard requests (a.k.a. TRIM) are passed through the crypt device.
103 The default is to ignore discard requests. 103 The default is to ignore discard requests.
104 104
105 WARNING: Assess the specific security risk 105 WARNING: Assess the specific security risks carefully before enabling this
106 option. For example, allowing discards on 106 option. For example, allowing discards on encrypted devices may lead to
107 the leak of information about the cipherte 107 the leak of information about the ciphertext device (filesystem type,
108 used space etc.) if the discarded blocks c 108 used space etc.) if the discarded blocks can be located easily on the
109 device later. 109 device later.
110 110
111 same_cpu_crypt 111 same_cpu_crypt
112 Perform encryption using the same cpu that 112 Perform encryption using the same cpu that IO was submitted on.
113 The default is to use an unbound workqueue 113 The default is to use an unbound workqueue so that encryption work
114 is automatically balanced between availabl 114 is automatically balanced between available CPUs.
115 115
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 116 submit_from_crypt_cpus
122 Disable offloading writes to a separate th 117 Disable offloading writes to a separate thread after encryption.
123 There are some situations where offloading 118 There are some situations where offloading write bios from the
124 encryption threads to a single thread degr 119 encryption threads to a single thread degrades performance
125 significantly. The default is to offload 120 significantly. The default is to offload write bios to the same
126 thread because it benefits CFQ to have wri 121 thread because it benefits CFQ to have writes submitted using the
127 same context. 122 same context.
128 123
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> 124 integrity:<bytes>:<type>
138 The device requires additional <bytes> met 125 The device requires additional <bytes> metadata per-sector stored
139 in per-bio integrity structure. This metad 126 in per-bio integrity structure. This metadata must by provided
140 by underlying dm-integrity target. 127 by underlying dm-integrity target.
141 128
142 The <type> can be "none" if metadata is us 129 The <type> can be "none" if metadata is used only for persistent IV.
143 130
144 For Authenticated Encryption with Addition 131 For Authenticated Encryption with Additional Data (AEAD)
145 the <type> is "aead". An AEAD mode additio 132 the <type> is "aead". An AEAD mode additionally calculates and verifies
146 integrity for the encrypted device. The ad 133 integrity for the encrypted device. The additional space is then
147 used for storing authentication tag (and p 134 used for storing authentication tag (and persistent IV if needed).
148 135
149 sector_size:<bytes> 136 sector_size:<bytes>
150 Use <bytes> as the encryption unit instead 137 Use <bytes> as the encryption unit instead of 512 bytes sectors.
151 This option can be in range 512 - 4096 byt 138 This option can be in range 512 - 4096 bytes and must be power of two.
152 Virtual device will announce this size as 139 Virtual device will announce this size as a minimal IO and logical sector.
153 140
154 iv_large_sectors 141 iv_large_sectors
155 IV generators will use sector number counte 142 IV generators will use sector number counted in <sector_size> units
156 instead of default 512 bytes sectors. 143 instead of default 512 bytes sectors.
157 144
158 For example, if <sector_size> is 4096 bytes 145 For example, if <sector_size> is 4096 bytes, plain64 IV for the second
159 sector will be 8 (without flag) and 1 if iv 146 sector will be 8 (without flag) and 1 if iv_large_sectors is present.
160 The <iv_offset> must be multiple of <sector 147 The <iv_offset> must be multiple of <sector_size> (in 512 bytes units)
161 if this flag is specified. 148 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 <<
183 149
184 Example scripts 150 Example scripts
185 =============== 151 ===============
186 LUKS (Linux Unified Key Setup) is now the pref 152 LUKS (Linux Unified Key Setup) is now the preferred way to set up disk
187 encryption with dm-crypt using the 'cryptsetup 153 encryption with dm-crypt using the 'cryptsetup' utility, see
188 https://gitlab.com/cryptsetup/cryptsetup 154 https://gitlab.com/cryptsetup/cryptsetup
189 155
190 :: 156 ::
191 157
192 #!/bin/sh 158 #!/bin/sh
193 # Create a crypt device using dmsetup 159 # Create a crypt device using dmsetup
194 dmsetup create crypt1 --table "0 `bloc 160 dmsetup create crypt1 --table "0 `blockdev --getsz $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0"
195 161
196 :: 162 ::
197 163
198 #!/bin/sh 164 #!/bin/sh
199 # Create a crypt device using dmsetup 165 # Create a crypt device using dmsetup when encryption key is stored in keyring service
200 dmsetup create crypt2 --table "0 `bloc 166 dmsetup create crypt2 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 :32:logon:my_prefix:my_key 0 $1 0"
201 167
202 :: 168 ::
203 169
204 #!/bin/sh 170 #!/bin/sh
205 # Create a crypt device using cryptset 171 # Create a crypt device using cryptsetup and LUKS header with default cipher
206 cryptsetup luksFormat $1 172 cryptsetup luksFormat $1
207 cryptsetup luksOpen $1 crypt1 173 cryptsetup luksOpen $1 crypt1
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.