TrueCrypt
Free Open-Source on the fly encryption.
Main Features:
- Creates a virtual encrypted disk within a file and mounts it as a real disk.
- Encrypts an entire partition or storage device such as USB flash drive or hard drive.
- Encrypts a partition or drive where Windows is installed (pre-boot authentication).
- Encryption is automatic, real-time (on-the-fly) and transparent.
- Parallelization and pipelining allow data to be read and written as fast as if the drive was not encrypted.
- Provides plausible deniability, in case an adversary forces you to reveal the password:Hidden volume (steganography) and hidden operating system.
- Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS. Further information regarding features of the software may be found in the documentation.