mirror of https://gitee.com/openkylin/linux.git
174 lines
6.0 KiB
ReStructuredText
174 lines
6.0 KiB
ReStructuredText
========
|
|
dm-crypt
|
|
========
|
|
|
|
Device-Mapper's "crypt" target provides transparent encryption of block devices
|
|
using the kernel crypto API.
|
|
|
|
For a more detailed description of supported parameters see:
|
|
https://gitlab.com/cryptsetup/cryptsetup/wikis/DMCrypt
|
|
|
|
Parameters::
|
|
|
|
<cipher> <key> <iv_offset> <device path> \
|
|
<offset> [<#opt_params> <opt_params>]
|
|
|
|
<cipher>
|
|
Encryption cipher, encryption mode and Initial Vector (IV) generator.
|
|
|
|
The cipher specifications format is::
|
|
|
|
cipher[:keycount]-chainmode-ivmode[:ivopts]
|
|
|
|
Examples::
|
|
|
|
aes-cbc-essiv:sha256
|
|
aes-xts-plain64
|
|
serpent-xts-plain64
|
|
|
|
Cipher format also supports direct specification with kernel crypt API
|
|
format (selected by capi: prefix). The IV specification is the same
|
|
as for the first format type.
|
|
This format is mainly used for specification of authenticated modes.
|
|
|
|
The crypto API cipher specifications format is::
|
|
|
|
capi:cipher_api_spec-ivmode[:ivopts]
|
|
|
|
Examples::
|
|
|
|
capi:cbc(aes)-essiv:sha256
|
|
capi:xts(aes)-plain64
|
|
|
|
Examples of authenticated modes::
|
|
|
|
capi:gcm(aes)-random
|
|
capi:authenc(hmac(sha256),xts(aes))-random
|
|
capi:rfc7539(chacha20,poly1305)-random
|
|
|
|
The /proc/crypto contains a list of curently loaded crypto modes.
|
|
|
|
<key>
|
|
Key used for encryption. It is encoded either as a hexadecimal number
|
|
or it can be passed as <key_string> prefixed with single colon
|
|
character (':') for keys residing in kernel keyring service.
|
|
You can only use key sizes that are valid for the selected cipher
|
|
in combination with the selected iv mode.
|
|
Note that for some iv modes the key string can contain additional
|
|
keys (for example IV seed) so the key contains more parts concatenated
|
|
into a single string.
|
|
|
|
<key_string>
|
|
The kernel keyring key is identified by string in following format:
|
|
<key_size>:<key_type>:<key_description>.
|
|
|
|
<key_size>
|
|
The encryption key size in bytes. The kernel key payload size must match
|
|
the value passed in <key_size>.
|
|
|
|
<key_type>
|
|
Either 'logon' or 'user' kernel key type.
|
|
|
|
<key_description>
|
|
The kernel keyring key description crypt target should look for
|
|
when loading key of <key_type>.
|
|
|
|
<keycount>
|
|
Multi-key compatibility mode. You can define <keycount> keys and
|
|
then sectors are encrypted according to their offsets (sector 0 uses key0;
|
|
sector 1 uses key1 etc.). <keycount> must be a power of two.
|
|
|
|
<iv_offset>
|
|
The IV offset is a sector count that is added to the sector number
|
|
before creating the IV.
|
|
|
|
<device path>
|
|
This is the device that is going to be used as backend and contains the
|
|
encrypted data. You can specify it as a path like /dev/xxx or a device
|
|
number <major>:<minor>.
|
|
|
|
<offset>
|
|
Starting sector within the device where the encrypted data begins.
|
|
|
|
<#opt_params>
|
|
Number of optional parameters. If there are no optional parameters,
|
|
the optional paramaters section can be skipped or #opt_params can be zero.
|
|
Otherwise #opt_params is the number of following arguments.
|
|
|
|
Example of optional parameters section:
|
|
3 allow_discards same_cpu_crypt submit_from_crypt_cpus
|
|
|
|
allow_discards
|
|
Block discard requests (a.k.a. TRIM) are passed through the crypt device.
|
|
The default is to ignore discard requests.
|
|
|
|
WARNING: Assess the specific security risks carefully before enabling this
|
|
option. For example, allowing discards on encrypted devices may lead to
|
|
the leak of information about the ciphertext device (filesystem type,
|
|
used space etc.) if the discarded blocks can be located easily on the
|
|
device later.
|
|
|
|
same_cpu_crypt
|
|
Perform encryption using the same cpu that IO was submitted on.
|
|
The default is to use an unbound workqueue so that encryption work
|
|
is automatically balanced between available CPUs.
|
|
|
|
submit_from_crypt_cpus
|
|
Disable offloading writes to a separate thread after encryption.
|
|
There are some situations where offloading write bios from the
|
|
encryption threads to a single thread degrades performance
|
|
significantly. The default is to offload write bios to the same
|
|
thread because it benefits CFQ to have writes submitted using the
|
|
same context.
|
|
|
|
integrity:<bytes>:<type>
|
|
The device requires additional <bytes> metadata per-sector stored
|
|
in per-bio integrity structure. This metadata must by provided
|
|
by underlying dm-integrity target.
|
|
|
|
The <type> can be "none" if metadata is used only for persistent IV.
|
|
|
|
For Authenticated Encryption with Additional Data (AEAD)
|
|
the <type> is "aead". An AEAD mode additionally calculates and verifies
|
|
integrity for the encrypted device. The additional space is then
|
|
used for storing authentication tag (and persistent IV if needed).
|
|
|
|
sector_size:<bytes>
|
|
Use <bytes> as the encryption unit instead of 512 bytes sectors.
|
|
This option can be in range 512 - 4096 bytes and must be power of two.
|
|
Virtual device will announce this size as a minimal IO and logical sector.
|
|
|
|
iv_large_sectors
|
|
IV generators will use sector number counted in <sector_size> units
|
|
instead of default 512 bytes sectors.
|
|
|
|
For example, if <sector_size> is 4096 bytes, plain64 IV for the second
|
|
sector will be 8 (without flag) and 1 if iv_large_sectors is present.
|
|
The <iv_offset> must be multiple of <sector_size> (in 512 bytes units)
|
|
if this flag is specified.
|
|
|
|
Example scripts
|
|
===============
|
|
LUKS (Linux Unified Key Setup) is now the preferred way to set up disk
|
|
encryption with dm-crypt using the 'cryptsetup' utility, see
|
|
https://gitlab.com/cryptsetup/cryptsetup
|
|
|
|
::
|
|
|
|
#!/bin/sh
|
|
# Create a crypt device using dmsetup
|
|
dmsetup create crypt1 --table "0 `blockdev --getsz $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0"
|
|
|
|
::
|
|
|
|
#!/bin/sh
|
|
# Create a crypt device using dmsetup when encryption key is stored in keyring service
|
|
dmsetup create crypt2 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 :32:logon:my_prefix:my_key 0 $1 0"
|
|
|
|
::
|
|
|
|
#!/bin/sh
|
|
# Create a crypt device using cryptsetup and LUKS header with default cipher
|
|
cryptsetup luksFormat $1
|
|
cryptsetup luksOpen $1 crypt1
|