Usbcrypt
USBCrypt is a commercial (closed source) software intended primarily to encrypt external USB drives. (However, the encryption is not limited to the external drives or to the USB connection: any drive that is recognized by Windows as a valid drive with read-write access can be encrypted with USBCrypt.) USBCrypt software is Windows 7, Vista, XP, 2000-only. It supports AES, and Twofish encryption with the 128- and 256-bit keys, in the XTS and CBC encryption modes.
Recognizing drives encrypted with USBCrypt
USBCrypt encrypts drives by creating the file-based Virtual Encrypted Disks on them. In addition to one or more files that contain the encrypted data, USBCrypt also puts a portable software on the drive, to enable its use on other computers. While the encrypted data files contain no identifying information (and thus support plausible deniability, the presence of other supporting files makes it easy to identify the drives encrypted with USBCrypt: the root folder of the encrypted drive contains the file USBCrypt.exe as well as a folder named USBCrypt-system. The latter contains the encrypted data files as well as USBCrypt software files (DLL and SYS). The file USBCrypt.ini is a text-only file that contains settings as well as license information (including the name of the person or business who has purchased the software).
Spare-key file
When the user is encrypting a drive with USBCrypt software, s/he has the option to create a "spare key" file on the user's computer. This file contains a copy of the encryption key that can be used by the user if s/he forgets the main encryption password. Or, it can be used by a system administrator to get access to the encrypted data in case the employees leave the company and take the passwords with them. Each spare key file contains a copy of just one encryption key for the specific encrypted drive it was created for. It cannot be used to decrypt any other drive, even if the user has used the same password and encryption algorithm. USBCrypt can automatically detect whether it can decrypt a specific drive with a spare key.
Forensic Acquisition
If you encounter a system that has a live USBCrypt drive, it is imperative that you capture the contents of the encrypted drive before disconnecting the drive or shutting down the system. Once the system is shutdown, the contents becomes inaccessible unless you have the proper encryption key generated by a user's password. If the encrypted drive in not live, it is imperative to secure access to the user's computer that was used to encrypt the drive: there is a possibility that the computer still has the "spare key" file stored on its hard drive, assuming the user has the selected the option to create such a file when encrypting the drive.
Attacks
If the "spare key" file for the encrypted drive has not been obtained, then the only option for acquiring the content of a dismounted USBCrypt drive is to do a brute-force password guessing attack. USBCrypt software itself contains a built-in command to perform the brute-force attack on the drives it encrypts.