Smart grid has been spread worldwide, but its data security and privacy have not got enough attention. In this paper, we propose a VoIP steganography method based on AES to achieve a real-time covert communication over smart grids. The covert communication system is implemented by embedding secret message encrypted with symmetric cryptography AES into an audio signal encoded by PCM codec. In order to meet the requirement of real-time, we encrypt the secret message and embed it with different algorithms into audio packets before sending them. So observers cannot detect it by using a simple statistical analysis. At the receiving end, we employ the corresponding method to retrieve the secret message, and then decrypt it to get the original message. For different embedding methods, each packet has a different capacity for embedding the secret message.
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