Windows 2003, Windows Vista, Windows Server 2008, Windows XP
No additional requirements
Publisher's description of TrueCrypt
Protect your sensitive data with this free open-source disk encryption software. Creates a virtual encrypted disk within a file and mount it as a real disk. Encrypt an entire hard disk partition or a device, such as USB flash drive. Automatically and transparently encrypt in real time.
TrueCrypt provides two levels of plausible deniability, in case an adversary forces you to reveal the password: a hidden volume (steganography- more information may be found here); no TrueCrypt volume can be identified (volumes cannot be distinguished from random data). TrueCrypt uses encryption algorithms AES-256, Blowfish (448-bit key), CAST5, Serpent, Triple DES, and Twofish. It is based on Encryption for the Masses (E4M) 2.02a, conceived in 1997.
Version 6.1 includes new features such as parallelized encryption/decryption on multicore processors/systems, the ability to create and run an encrypted hidden operating system whose existence is impossible to prove (Windows Vista/XP/2008/2003), and the ability to encrypt an entire system drive even if it contains extended/logical partitions (Windows Vista and Windows 200.
The ultimate freeware encryption program, TrueCrypt is loaded with powerful features that those concerned with protecting their data from thievery should want--and have.
It offers 11 algorithms for encrypting your private files in a password-protected volume. You can store your encrypted data in files (containers) or partitions (devices). TrueCrypt works hard to offer powerful data protection, recommending complex passwords, explaining the benefits of hidden volumes, and erasing telltale signs of the encryption process, including mouse movements and keystrokes. Though the interface may not be immediately intuitive, its powerful, on-the-fly encryption for no cost still earns the freeware security tool a top rating.
The useful tips in the extensive help manual and volume-creation wizard provide excellent guidance. In fact, they're required reading, as TrueCrypt lacks any considerable in-program help. For instance, the tutorial explains the entire concept beyond "hidden" volumes, but it doesn't quite explain how to mount them. One obvious downside of any strong encryption program is if you happen to forget your lengthy, secure password, you should consider any protected files as good as gone. However, once files are mounted to a local drive with your password or key, they conveniently behave just like any normal files, allowing you to easily open, copy, delete, or other modify them another way. Dismount the volume, and voila--your previously accessible files are now safely secure from prying eyes.
Users can even create a hidden operating system, encrypted away from nosy busybodies, but make no mistake--TrueCrypt is not for the casual encryption explorer. Be sure to thoroughly understand what you're doing with the program before you do something regrettable.