In today's mobile world, wireless technology is used in many places. We use it to access online while on the go, connect mobile accessories to a PC, listen to music on the phone, and browse e-mail. Because wireless technology is so universally used, we often think it is safe. However, many of us use wireless technology to enter passwords, send personal data, and share confidential information. In reality, if every point in a wireless communication system has potential vulnerabilities and proper security measures are not in place, personal information can be compromised. We are targeting wireless keyboards based on encryption that are widely used in the real world. Our attack was conducted in a black box manner for the target device, with the exception of the public information. As a result of the attack, we can obtain a 128-bit secret key that is used to encrypt the plaintext when a user types the wireless keyboard. We provide a method to analyze specifically the internal behavior of the target device and provide a template generation method for side-channel attacks. It also shows how you can extract the encryption key from other wireless keyboards using the same chip. Therefore, we can decrypt all the input data even if the user encrypts using the encryption-based wireless keyboard and transmits the encrypted data. The most important part of our contribution is that we have identified problems with wireless keyboard devices that have similar product configurations and provide our know-how to analyze similar vulnerabilities. Our results show that the combination of reverse engineering and side-channel attacks has a significant impact on the security of embedded devices.