The information housed on the cloud is often seen as valuable to individuals with malicious intent. There is a lot of personal information and potentially secure data that people store on their computers, and this information is now being transferred to the cloud. This makes it critical for you to understand the security measures that your cloud provider has in place, and it is equally important to take personal precautions to secure your data. In the world of cloud computing, security is the big issue because of open system architecture. The data transferred through cloud should be secure and there is a possible to attack the data in middle. In this paper, we deal with key exchange between cloud user's using cellular automata. It is hard to trace the key by man-in-the-middle-attack because of Strong encryption algorithm (Triple-DES) with CA (Cellular Automata) Rules. Besides CRC (Cyclic Redundancy Check) is done to ensure data integrity at the user's end.