Security has become one of the major issues for data communication over wired and wireless networks. In Wireless Sensor Networks (WSNs), the hackers can inject false data via compromised nodes and can able to alter the original files. There are many chances to perform a Denial of Service (DoS) attack in WSNs. Initially send the dynamic key to all the cluster nodes followed by neighboring nodes. Then send the file which will be hidden and is secured by encrypting using Advanced Encryption Standard (AES) algorithm thereby mitigating from the DoS attack and Sybil attack. AES is secure enough to protect classified information up to the top secret level, which is highest security.