manual

connected to a computer, and then encrypting them before the user is allowed to
disconnect the drive. This encryption method is less risky than the manual type of
encryption since it is automatic; the user does not have to remember to encrypt
their data
[4]
.
Transparent Encryption
Completely automatic, transparent encryption is the most robust encryption
scheme. Data is encrypted as it is written and, as a result, requires no interaction
from the user. The theft or loss of a USB drive which uses transparent encryption
does not mean that there is a loss of data, because the drive's data is always
encrypted. Although this is the best type of encryption, it is also the most difficult
type to implement in a USB drive because it is difficult to engineer into the drive
architecture
[4]
.
Transparent Encryption in USB Drives
To fill the need for secure portable storage, some USB Flash drive makers
include transparent encryption in their products. Drive engineers can choose
either software-based encryption or hardware-based encryption.
Software-based Encryption
In software-based encryption, the files that perform encryption are stored in a
USB drive's Flash memory. As with typical unsecured USB drives, when the drive
is plugged into a computer’s USB port, it is immediately connected to the system.
Because the encryption program is stored in a fully accessible part of the drive,
hackers can locate the program in the USB drive’s memory and compromise it.
The encryption software itself cannot be protected any more than any other
Windows program, or the operating system wouldn't be able to run it.
Another disadvantage of software-based encryption is that the password has the
ability to be rewound, or “returned to a backed up state so that any password you
may have created recently or after you had stored the files can be removed as if
it had never been installed
[5]
.”
An additional drawback of software-based encryption is that it uses the computer
system’s microprocessor to perform encryption and decryption.