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Diffstat (limited to 'Documentation/device-mapper/dm-crypt.txt')
| -rw-r--r-- | Documentation/device-mapper/dm-crypt.txt | 39 |
1 files changed, 35 insertions, 4 deletions
diff --git a/Documentation/device-mapper/dm-crypt.txt b/Documentation/device-mapper/dm-crypt.txt index 6680cab2c70..c81839b52c4 100644 --- a/Documentation/device-mapper/dm-crypt.txt +++ b/Documentation/device-mapper/dm-crypt.txt @@ -4,11 +4,15 @@ dm-crypt Device-Mapper's "crypt" target provides transparent encryption of block devices using the kernel crypto API. -Parameters: <cipher> <key> <iv_offset> <device path> <offset> +For a more detailed description of supported parameters see: +http://code.google.com/p/cryptsetup/wiki/DMCrypt + +Parameters: <cipher> <key> <iv_offset> <device path> \ + <offset> [<#opt_params> <opt_params>] <cipher> Encryption cipher and an optional IV generation mode. - (In format cipher-chainmode-ivopts:ivmode). + (In format cipher[:keycount]-chainmode-ivmode[:ivopts]). Examples: des aes-cbc-essiv:sha256 @@ -18,7 +22,16 @@ Parameters: <cipher> <key> <iv_offset> <device path> <offset> <key> Key used for encryption. It is encoded as a hexadecimal number. - You can only use key sizes that are valid for the selected cipher. + 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. + +<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 @@ -32,11 +45,29 @@ Parameters: <cipher> <key> <iv_offset> <device path> <offset> <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: + 1 allow_discards + +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. + 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 -http://luks.endorphin.org/ +http://code.google.com/p/cryptsetup/ [[ #!/bin/sh |