## 4 Motivations  
In this section, we outline the motivations behind our work and the potential application domains where it can be adopted. We recall that this work aims to obfuscate the communication between two parties so that no external eavesdropper can intercept the communication between two parties or even determine whether communication is happening. There are several potential use cases for our approach. For instance, it can be adopted in IoT environments where devices need to communicate very sensitive information, such as information revealing personal preferences and user behavior. Additionally, companies may protect their proprietary information and internal communications by utilizing our solution. This ensures that even if communication channels are being monitored, the data remain secure and undetectable. Generally speaking, achieving this goal is fundamental in contexts where high privacy levels are required, particularly in environments subject to censorship and surveillance, where secure and undetectable communication is crucial. Indeed, in many regions, governments and authorities impose strict controls on internet use and actively monitor communication channels to suppress dissent and control the flow of information. These regimes often employ surveillance techniques by acting as global adversaries able to observe all traffic through the network. They implement extensive filtering systems, deep packet inspection (DPI), and other monitoring tools [48] to detect and block unwanted communications. Standard encryption-based solutions, while protecting data content, can still be identified by such systems. Indeed, these solutions do not conceal the act of communication itself but just the exchanged context. On the other hand, in several environments, it is crucial not only to protect the content of communication but also to hide the parties that are communicating. Alternative solutions involve the use of anonymous communication protocols [49] that are designed to hide the identities of the communicating parties and the metadata associated with the communication. These protocols are effective in hiding the communication between parties, even against global adversaries capable of observing all network traffic. However, the use of anonymous communication protocols can itself be a red flag. Censors are often capable of detecting the presence of such protocols due to their distinct traffic patterns and signature behaviors. The fact that an anonymous protocol is being used can alert the censor to potentially suspicious activity. As a result, censors can block or restrict the use of these protocols, thereby preventing parties from utilizing them for secure communication. This highlights the need for communication methods that blend seamlessly with regular, non-sensitive traffic. Our proposal is to leverage the MQTT protocol since it is commonly used in IoT applications. Specifically, our solution allows parties to exchange information through covert channels blended into MQTT packets. The MQTT protocol is commonly used in IoT applications due to its lightweight nature and efficiency in handling devices with limited resources. This ubiquity acts as a cloak for secret communications, as MQTT traffic is generally considered benign and routine. Therefore, by inserting hidden messages in MQTT traffic, we can effectively hide the existence of communication between two parties, i.e., a publisher and a subscriber. This method also benefits from the architecture of MQTT, where publishers and subscribers never communicate directly, but the communication is always mediated by a broker. Additionally, in MQTT, communication on a topic can occur between multiple parties.Indeed, when a client publishes on a given topic, the broker broadcasts the messages to all the subscribers interested in that topic. Additionally, on each topic, there can be multiple publishers. This mechanism is crucial to obscure the direct connection between two parties [50; 51].