dm-crypt is a transparent block device encryption subsystem in Linux
kernel versions 2.6 and later and in DragonFly BSD. It is part of the device
mapper (dm) infrastructure, and uses cryptographic routines from the kernel’s
Crypto API. Unlike its predecessor cryptoloop, dm-crypt was designed to
support advanced modes of operation, such as XTS, LRW and ESSIV (see disk
encryption theory for further information), in order to avoid watermarking
attacks. In addition to that, dm-crypt addresses some reliability problems of
cryptoloop.
— Wikipedia