The number of IoT devices in use is increasing rapidly and so is the number of IoT applications. As in any new technology, the rapid development means rapid increase in security threats and attack surfaces. IoT security has proven to be challenging throughout the past few years. However, another challenging task is to prevent IoT devices from becoming a tool used by malicious attackers to break into other systems. In this paper, we present a conceptual design in which IoT devices are used as tools in brute-force attacks to break encryption keys of block ciphers. The proposed design shows that with adequate number of IoT devices employed in the attack, the attack can succeed in breaking large-key block ciphers.