Much of the information on a device is stored in files. To protect information on a device, we need to have mechanisms that secure files. There are two main reasons to deploy cryptography to protect a file:

  1. Storage protection: Most computing devices, including desktops, laptops, and smartphones, have security controls that provide some protection against unauthorized parties accessing the files stored on them. The most common control is to provide entity authentication to the device itself using a password-based mechanism. However, controls alone don’t provide strong protection since they can be relatively easy to overcome. Further, many dedicated storage devices such as DVDs, memory cards, and USB tokens have no default file storage protection mechanism, and the contents can be recovered by anyone who obtains the device itself.

  2. Transfer protection: A user may want to transfer a file from one device to another. Even if the devices at either end of the communication channel have strong protection, the channel itself might be insecure. Anyone monitoring it could potentially access the file in transit.

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