TrueCrypt is the opensource community's response to disk encryption. This is important because in order for encryption to be completely secure the source must be open, otherwise there could be a backdoor that is only known to the developer (or the developer's company).

TrueCrypt

Free open-source disk encryption software for Windows XP/2000/2003 and Linux

Main Features:

* Creates a virtual encrypted disk within a file and mounts it as a real disk.

* Encrypts an entire hard disk partition or a device, such as USB flash drive.

* Encryption is automatic, real-time (on-the-fly) and transparent.

* Provides two levels of plausible deniability, in case an adversary forces you to reveal the password:

1) Hidden volume (steganography – more information may be found here).

2) No TrueCrypt volume can be identified (volumes cannot be distinguished from random data).

* Encryption algorithms: AES-256, Blowfish (448-bit key), CAST5, Serpent, Triple DES, and Twofish.

Mode of operation: LRW (CBC supported as legacy).

* Conceived in 2003.

Further information regarding features of the software may be found in the documentation.