Disk encryption software
Disk encryption generally refers to wholesale encryption that operates on an entire volume mostly transparently to the user, the system, and applications. This is generally distinguished from file-level encryption that operates by user invocation on a single file or group of files, and which requires the user to decide which specific files should be encrypted. Disk encryption usually includes all aspects of the disk, including directories, so that an adversary cannot determine content, name or size of any file. It is well suited to portable devices such as laptop computers and thumb drives which are particularly susceptible to being lost or stolen. If used properly, someone finding a lost device cannot penetrate actual data, or even know what files might be present.
Mcrypt
mcrypt is a replacement for the popular Unix crypt command.
crypt was a file encryption tool that used an algorithm very close to the
World War II Enigma cipher. Mcrypt provides the same functionality but uses several modern algorithms such as AES. Libmcrypt, Mcrypt's companion, is a library of code which contains the actual encryption functions and provides an easy method for use. The last update to libmcrypt was in 2007, despite years of unmerged patches. These facts have led security experts to declare mcrypt abandonware and discourage its use in new development. Prefer ccrypt, libressl, and others.