Cloud computing has been envisioned as next-generation architecture of IT enterprise. Cloud computing is the internet based model which delivers computing services on demand. Cloud storage moves the user's data to large data centers, which are remotely located and on which user does not have any control. Apart having more benefits, this unique feature of the cloud also poses many new security challenges which need to be clearly understood and resolved. The important concerns that need to be addressed in cloud computing is to assure the integrity of data i.e. correctness of the user's data in the cloud.