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FreeOTFE' is an "on-the-fly" disk encryption (OTFEOn the Fly Encryption) program for PCs running MS Windows and Windows Mobile PDAs (FreeOTFE4PDA). It creates "virtual disks" - anything written to which is automatically encrypted before being stored on the computer's hard drive or USB drive. It is similar in functionality to other disk encryption programs including Microsoft's BitLocker.[1]



FreeOTFE was initially released by Sarah Dean in 2004, and was the first open source disk encryption system that provided a modular architecture allowing 3rd parties to implement additional algorithms if required.

This software is compatible with Linux encrypted volumes (e.g. LUKS, cryptoloop, dm-crypt), allowing data encrypted under Linux to be read (and written) freely. It was the first open source transparent disk encryption system to support Windows Vista and PDAs [2][3][4][5]

Optional two-factor authentication using smart cards and/or hardware security modules (HSMs - also known as security tokens)[6] was introduced in v4.0, using the PKCS#11 (Cryptoki) standard developed by RSA Laboratories.

FreeOTFE also allows any number of "hidden volumes" to be created, giving plausible deniability and deniable encryption, and also has the option of encrypting entire partitions or disks[7]

Portable Use

FreeOTFE Explorer allows access to encrypted disks, without installing any drivers.
FreeOTFE Explorer allows access to encrypted disks, without installing any drivers.

Unlike most disk encryption systems, FreeOTFE can be used in "portable mode", which allows it to be kept on a USB drive or other portable media, together with its encrypted data, and carried around. This allows it to be used under Microsoft Windows without installation of the complete program to "mount" and access the encrypted data through a virtual disk.

In common with other disk encryption systems which offer a "portable" (or "traveller") mode, the use of this mode requires installing device drivers (at least temporarily) to create virtual disks, and as a consequence administrator rights are needed to start this traveller mode.

Driverless Operation

The author of FreeOTFE also offers another program called "FreeOTFE Explorer"[8] which provides a driverless system that allows encrypted disks to be used without administrator rights.

This allows FreeOTFE encrypted data to be used on (for example), library computers or computer kiosks (interactive kiosks) where administrator rights are not available.

Unlike FreeOTFE, FreeOTFE Explorer does not provide on-the-fly encryption through a virtual drive[8]. Instead it works in a similar manner as some archiving software in that it allows files to be stored and extracted from encrypted disk images, in a similar manner as ZIP and RAR archives - though using a Windows Explorer interface.

Algorithms implemented

Due to its architecture, FreeOTFE provides great flexibility to the user with its encryption options.


There are a number of ciphers implemented in FreeOTFE, including:

All of the NIST AES finalists are included in FreeOTFE, and all of the ciphers can be used with multiple different keylengths

Cipher modes

Originally FreeOTFE offered encryption using CBC with ESSIV, though from v3.00 introduced LRW and also the more secure XTS mode, which supersedes LRW in the IEEE P1619 standard for disk encryption.


As with its cipher options, FreeOTFE offers many different hash algorithms:

See also

External links

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