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83 lines
2.8 KiB
83 lines
2.8 KiB
dm-crypt |
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========= |
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Device-Mapper's "crypt" target provides transparent encryption of block devices |
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using the kernel crypto API. |
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For a more detailed description of supported parameters see: |
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http://code.google.com/p/cryptsetup/wiki/DMCrypt |
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Parameters: <cipher> <key> <iv_offset> <device path> \ |
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<offset> [<#opt_params> <opt_params>] |
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<cipher> |
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Encryption cipher and an optional IV generation mode. |
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(In format cipher[:keycount]-chainmode-ivmode[:ivopts]). |
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Examples: |
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des |
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aes-cbc-essiv:sha256 |
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twofish-ecb |
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/proc/crypto contains supported crypto modes |
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<key> |
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Key used for encryption. It is encoded as a hexadecimal number. |
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You can only use key sizes that are valid for the selected cipher |
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in combination with the selected iv mode. |
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Note that for some iv modes the key string can contain additional |
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keys (for example IV seed) so the key contains more parts concatenated |
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into a single string. |
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<keycount> |
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Multi-key compatibility mode. You can define <keycount> keys and |
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then sectors are encrypted according to their offsets (sector 0 uses key0; |
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sector 1 uses key1 etc.). <keycount> must be a power of two. |
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<iv_offset> |
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The IV offset is a sector count that is added to the sector number |
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before creating the IV. |
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<device path> |
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This is the device that is going to be used as backend and contains the |
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encrypted data. You can specify it as a path like /dev/xxx or a device |
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number <major>:<minor>. |
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<offset> |
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Starting sector within the device where the encrypted data begins. |
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<#opt_params> |
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Number of optional parameters. If there are no optional parameters, |
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the optional paramaters section can be skipped or #opt_params can be zero. |
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Otherwise #opt_params is the number of following arguments. |
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Example of optional parameters section: |
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1 allow_discards |
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allow_discards |
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Block discard requests (a.k.a. TRIM) are passed through the crypt device. |
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The default is to ignore discard requests. |
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WARNING: Assess the specific security risks carefully before enabling this |
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option. For example, allowing discards on encrypted devices may lead to |
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the leak of information about the ciphertext device (filesystem type, |
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used space etc.) if the discarded blocks can be located easily on the |
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device later. |
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Example scripts |
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=============== |
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LUKS (Linux Unified Key Setup) is now the preferred way to set up disk |
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encryption with dm-crypt using the 'cryptsetup' utility, see |
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http://code.google.com/p/cryptsetup/ |
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[[ |
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#!/bin/sh |
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# Create a crypt device using dmsetup |
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dmsetup create crypt1 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0" |
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]] |
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[[ |
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#!/bin/sh |
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# Create a crypt device using cryptsetup and LUKS header with default cipher |
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cryptsetup luksFormat $1 |
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cryptsetup luksOpen $1 crypt1 |
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]]
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