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: http://code.google.com/p/cryptsetup/wiki/DMCrypt Parameters: \ [<#opt_params> ] Encryption cipher and an optional IV generation mode. (In format cipher[:keycount]-chainmode-ivmode[:ivopts]). Examples: des aes-cbc-essiv:sha256 twofish-ecb /proc/crypto contains supported crypto modes Key used for encryption. It is encoded as a hexadecimal number. 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. Multi-key compatibility mode. You can define keys and then sectors are encrypted according to their offsets (sector 0 uses key0; sector 1 uses key1 etc.). must be a power of two. The IV offset is a sector count that is added to the sector number before creating the IV. 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 :. 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. 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://code.google.com/p/cryptsetup/ [[ #!/bin/sh # Create a crypt device using dmsetup dmsetup create crypt1 --table "0 `blockdev --getsize $1` crypt aes-cbc-essiv:sha256 babebabebabebabebabebabebabebabe 0 $1 0" ]] [[ #!/bin/sh # Create a crypt device using cryptsetup and LUKS header with default cipher cryptsetup luksFormat $1 cryptsetup luksOpen $1 crypt1 ]]