208 lines · plain
1========2dm-crypt3========4 5Device-Mapper's "crypt" target provides transparent encryption of block devices6using the kernel crypto API.7 8For a more detailed description of supported parameters see:9https://gitlab.com/cryptsetup/cryptsetup/wikis/DMCrypt10 11Parameters::12 13 <cipher> <key> <iv_offset> <device path> \14 <offset> [<#opt_params> <opt_params>]15 16<cipher>17 Encryption cipher, encryption mode and Initial Vector (IV) generator.18 19 The cipher specifications format is::20 21 cipher[:keycount]-chainmode-ivmode[:ivopts]22 23 Examples::24 25 aes-cbc-essiv:sha25626 aes-xts-plain6427 serpent-xts-plain6428 29 Cipher format also supports direct specification with kernel crypt API30 format (selected by capi: prefix). The IV specification is the same31 as for the first format type.32 This format is mainly used for specification of authenticated modes.33 34 The crypto API cipher specifications format is::35 36 capi:cipher_api_spec-ivmode[:ivopts]37 38 Examples::39 40 capi:cbc(aes)-essiv:sha25641 capi:xts(aes)-plain6442 43 Examples of authenticated modes::44 45 capi:gcm(aes)-random46 capi:authenc(hmac(sha256),xts(aes))-random47 capi:rfc7539(chacha20,poly1305)-random48 49 The /proc/crypto contains a list of currently loaded crypto modes.50 51<key>52 Key used for encryption. It is encoded either as a hexadecimal number53 or it can be passed as <key_string> prefixed with single colon54 character (':') for keys residing in kernel keyring service.55 You can only use key sizes that are valid for the selected cipher56 in combination with the selected iv mode.57 Note that for some iv modes the key string can contain additional58 keys (for example IV seed) so the key contains more parts concatenated59 into a single string.60 61<key_string>62 The kernel keyring key is identified by string in following format:63 <key_size>:<key_type>:<key_description>.64 65<key_size>66 The encryption key size in bytes. The kernel key payload size must match67 the value passed in <key_size>.68 69<key_type>70 Either 'logon', 'user', 'encrypted' or 'trusted' kernel key type.71 72<key_description>73 The kernel keyring key description crypt target should look for74 when loading key of <key_type>.75 76<keycount>77 Multi-key compatibility mode. You can define <keycount> keys and78 then sectors are encrypted according to their offsets (sector 0 uses key0;79 sector 1 uses key1 etc.). <keycount> must be a power of two.80 81<iv_offset>82 The IV offset is a sector count that is added to the sector number83 before creating the IV.84 85<device path>86 This is the device that is going to be used as backend and contains the87 encrypted data. You can specify it as a path like /dev/xxx or a device88 number <major>:<minor>.89 90<offset>91 Starting sector within the device where the encrypted data begins.92 93<#opt_params>94 Number of optional parameters. If there are no optional parameters,95 the optional parameters section can be skipped or #opt_params can be zero.96 Otherwise #opt_params is the number of following arguments.97 98 Example of optional parameters section:99 3 allow_discards same_cpu_crypt submit_from_crypt_cpus100 101allow_discards102 Block discard requests (a.k.a. TRIM) are passed through the crypt device.103 The default is to ignore discard requests.104 105 WARNING: Assess the specific security risks carefully before enabling this106 option. For example, allowing discards on encrypted devices may lead to107 the leak of information about the ciphertext device (filesystem type,108 used space etc.) if the discarded blocks can be located easily on the109 device later.110 111same_cpu_crypt112 Perform encryption using the same cpu that IO was submitted on.113 The default is to use an unbound workqueue so that encryption work114 is automatically balanced between available CPUs.115 116high_priority117 Set dm-crypt workqueues and the writer thread to high priority. This118 improves throughput and latency of dm-crypt while degrading general119 responsiveness of the system.120 121submit_from_crypt_cpus122 Disable offloading writes to a separate thread after encryption.123 There are some situations where offloading write bios from the124 encryption threads to a single thread degrades performance125 significantly. The default is to offload write bios to the same126 thread because it benefits CFQ to have writes submitted using the127 same context.128 129no_read_workqueue130 Bypass dm-crypt internal workqueue and process read requests synchronously.131 132no_write_workqueue133 Bypass dm-crypt internal workqueue and process write requests synchronously.134 This option is automatically enabled for host-managed zoned block devices135 (e.g. host-managed SMR hard-disks).136 137integrity:<bytes>:<type>138 The device requires additional <bytes> metadata per-sector stored139 in per-bio integrity structure. This metadata must by provided140 by underlying dm-integrity target.141 142 The <type> can be "none" if metadata is used only for persistent IV.143 144 For Authenticated Encryption with Additional Data (AEAD)145 the <type> is "aead". An AEAD mode additionally calculates and verifies146 integrity for the encrypted device. The additional space is then147 used for storing authentication tag (and persistent IV if needed).148 149sector_size:<bytes>150 Use <bytes> as the encryption unit instead of 512 bytes sectors.151 This option can be in range 512 - 4096 bytes and must be power of two.152 Virtual device will announce this size as a minimal IO and logical sector.153 154iv_large_sectors155 IV generators will use sector number counted in <sector_size> units156 instead of default 512 bytes sectors.157 158 For example, if <sector_size> is 4096 bytes, plain64 IV for the second159 sector will be 8 (without flag) and 1 if iv_large_sectors is present.160 The <iv_offset> must be multiple of <sector_size> (in 512 bytes units)161 if this flag is specified.162 163integrity_key_size:<bytes>164 Use an integrity key of <bytes> size instead of using an integrity key size165 of the digest size of the used HMAC algorithm.166 167 168Module parameters::169 max_read_size170 Maximum size of read requests. When a request larger than this size171 is received, dm-crypt will split the request. The splitting improves172 concurrency (the split requests could be encrypted in parallel by multiple173 cores), but it also causes overhead. The user should tune this parameters to174 fit the actual workload.175 176 max_write_size177 Maximum size of write requests. When a request larger than this size178 is received, dm-crypt will split the request. The splitting improves179 concurrency (the split requests could be encrypted in parallel by multiple180 cores), but it also causes overhead. The user should tune this parameters to181 fit the actual workload.182 183 184Example scripts185===============186LUKS (Linux Unified Key Setup) is now the preferred way to set up disk187encryption with dm-crypt using the 'cryptsetup' utility, see188https://gitlab.com/cryptsetup/cryptsetup189 190::191 192 #!/bin/sh193 # Create a crypt device using dmsetup194 dmsetup create crypt1 --table "0 `blockdev --getsz $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0"195 196::197 198 #!/bin/sh199 # Create a crypt device using dmsetup when encryption key is stored in keyring service200 dmsetup create crypt2 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 :32:logon:my_prefix:my_key 0 $1 0"201 202::203 204 #!/bin/sh205 # Create a crypt device using cryptsetup and LUKS header with default cipher206 cryptsetup luksFormat $1207 cryptsetup luksOpen $1 crypt1208