Numerous cloud service providers are available across the world providing online storage. Most of these providers give us a couple of GBs of storage space in the cloud. Worrying about our privacy is reasonable, because we don't know how these server software exactly work, thus we certainly do not know which users can access all our data beyond people we intentionally gave permission to. In order to protect our files in the cloud, we have to encrypt them right before uploading, also, decrypt them after downloading. It is a great advantage when all these operations are executed transparently and automatically. The purpose of this thesis is to design and implement a file system driver for Windows platform, which is capable of intercepting and manipulating file reading and writing requests. This driver filters all the intercepted requests first, then they are forwarded to an application which is able to modify the requests to preform encryption and decryption tasks. The design and implementation of a Proof of Concept user-space application is also part of the thesis, which has to cooperate with the file system driver to perform data manipulation.