The concept of Cloud Computing has been distinguished as one of the major computing models in recent years. This distinguish comes as a reflection of a rapid and intense interest from academic and industrial organisations which present it as an active area of research. Security has been always raised as one of the most critical issues of cloud computing where resolving such an issue would result in a constant growth in the use and popularity of cloud. Furthermore, issues related to service availability and interoperability has gained a substantial interest. Failing to address such issues would jeopardise consumers’ satisfactions. This article mainly discusses the causes of obstacles and challenges related to security, reliability, privacy and service availability. In this work, we analyse and compare the performance of selected algorithms over “Google App Engine” which is a web framework and could computing platform. A comparative analysis of the efficiency of Advanced Encryption Standard “AES” (Rigndael), Rivest-Shamir-Adleman “RSA” and Triple Data Encryption “DES” have been performed locally and over the cloud as well. The efficiency analyses covered encryption and decryption procedures separately. Experiments results are given to analyses the effectiveness of each algorithm. The results show that Triple DES manifested a higher time efficiency ratio over cloud when subjected to different data loads compares to AES and RSA.