Cloud Computing is a term which allows user to access the set applications to perform a group of functions or tasks on the internet enabled devices. The cloud has been divided into three types: private, public and hybrid which are briefly described in this paper. SaaS, IaaS and PaaS are the services of the cloud. Cloud is generally provided by the third party, thus it faces few security challenges which are required to be resolved. In this paper we have discussed those issues and also the security architecture needed for the same.