dm-crypt filesystem encryption

Dependencies needed:
Kernel Setup:
Device Drivers > Multi-device support (RAID and LVM) > Device Mapper Support (dm-mod)
Device Drivers > Multi-device support (RAID and LVM) > Crypt Target Support (dm-crypt)
Cryptographic Options > (Select cyphers .. ex. aes, twofish)

Userspace tools needed:
cryptsetup.sh
libdevmapper

cryptsetup.sh Syntax:

Syntax: cryptsetup [<OPTIONS>] <action> <name> [<device>]
  <OPTIONS>:
   -c <cipher> (see /proc/crypto)
   -h {plain/<hash>} (see hashalot)
   -y (verifies the passphrase by asking for it twice)
   -d <file> (read key from file
       e.g. /dev/urandom; useful for swap devices.
       If set, the parameters -h and -y will be ignored)
   -s <keysize> (in bits) (WARNING: in bytes for cryptsetup.sh)
   -b <size> (in sectors)
   -o <offset> (in sectors)
   -p <skipped> (in sectors)
   <action> is one of:
         create - create device
         remove - remove device
         reload - modify active device
         resize - resize active device
         status - show device status
   <name> is the device to create under /dev/mapper/
   <device> is the encrypted device

Create crypto physical device (sized by existing partition):
cryptsetup.sh -c aes -h plain -y -b `blockdev --getsize \
/dev/hdb2` create cryptvol1 /dev/hdb2

Copy over data:
dd if=/dev/hdb2 of=/dev/mapper/cryptvol1 bs=4k

http://www.linux.com/article.pl?sid=04/06/07/2036205
http://www.saout.de/misc/dm-crypt/