Updates to Truecrypt were officially discontinued in 2014-05
TrueCrypt is a software system for establishing and maintaining an on-the-fly-encrypted volume (data storage device). On-the-fly encryption means that data is automatically encrypted right before it is saved and decrypted right after it is loaded, without any user intervention. No data stored on an encrypted volume can be read (decrypted) without using the correct password/keyfile(s). The entire file system is encrypted e.g., file names, folder names, contents of every file, free space, meta data, etc.
Truecrypt uses a well-known block device mapper (DM) encryption layer. The block device can be a loop back file, partition or the entire drive
The volume header is encrypted using a header encryption key derived from a password/keyfile(s). Note that the volume header contains the master encryption key with which the volume is encrypted. Therefore password changes are quick
The Keyfile is a file whose content can be combined with a password/passphrase
fuse : file system in user space
Paul Le Roux for making his Encryption for the Masses (E4M) source code available. TrueCrypt 1.0 was derived from E4M and some parts of the E4M source code are still incorporated in the latest version of the TrueCrypt source code. E4M Encryption for the Masses. Copyright (C) 1998-2000 Paul Le Roux
Brian Gladman, who wrote the AES, Twofish, and SHA-512 routines. Copyright (c) 1998-2008, Brian Gladman, Worcester, UK.
Peter Gutmann for his paper on random numbers and for creating his cryptlib, which was the source of parts of the random number generator source code
Mark Adler et al., who wrote the Inflate routine. Copyright (C) 2002-2004 Mark Adler, version 1.8, 9 Jan 2004
Wei Dai, who wrote the Serpent and RIPEMD-160 routines
The designers of the encryption algorithms, hash algorithms, and the mode of operation: Horst Feistel, Don Coppersmith, Walt Tuchmann, Lars Knudsen, Ross Anderson, Eli Biham, Bruce Schneier, David Wagner, John Kelsey, Niels Ferguson, Doug Whiting, Chris Hall, Joan Daemen, Vincent Rijmen, Carlisle Adams, Stafford Tavares, Phillip Rogaway, Hans Dobbertin, Antoon Bosselaers, Bart Preneel, Paulo S. L. M. Barreto