## 1 Introduction
The device can detect that this prohibition is quite different from what should be injected from the device (dotted blue line) and the anomaly detection algorithm will likely disregard this command. * _Jamming_: Jamming attacks can be used to block any incoming packets to the IMD and block its regular work [7]. Moreover, this technique can be used to prevent other types of attacks on the device, mainly resource depletion and denial of service attacks. Attackers can blast the device with incoming messages, that can lead to a drastic drop in the battery level and overflows of  
Figure 1: Daily Dosage Monitoring of an Infusion Device of a Patient. memory and storage. In such scenarios, jamming techniques can be launched from the device itself or from an annexed Wearable External Device. If the device senses the existence of these messages, jamming techniques prevent the device from receiving and treating these packets. In this work, we intend to protect the IMD wireless communications through developing an efficient encryption scheme. We will design a novel technique to generate pseudo-random keys to be used as cryptographic symmetric keys similar to the work in [8]. This key will be employed to cipher the exchanged packets between the devices used by patients and their doctors. This work does not aim specifically at a specific IMD but tackles any implantable systems that use wireless communications between its devices, e.g., an implanted pacemaker and its external monitoring device [9]. In addition, we also present a new encryption system to protect the wireless communication between the IMDs. In the sender's device, a key generator will generate an encryption key using a Pseudo-Random Number Generator (PRNG) based on a chaotic system [10]. This key will be applied to cipher the message to be sent by the device. In order for the receiving device to be able to decipher the sent message, it has to generate internally the same encryption key used in the first place. The sender will not communicate the key directly on the wireless channel. The sender needs only to communicate publicly the seed used for its encryption key generation as shown in Figure 2. Even though the seed is thought to be enough to generate the same key, the case of the chaotic system differs: the two devices use the same chaotic generator to deliver the encryption key. However, this pseudo-random generator has two inputs instead of one: the _seed_ and the _initial conditions_. The initial conditions are already shared between the two devices through a given physical synchronization method. Therefore, when the receiver receives this seed, its internal key generator will be able to generate the right key to be used for deciphering the message it has received. Thus, the wireless communication can take place securely. [PERSON] et al. [11] explained how it is possible to realize a chaotic system to map a random sequence of numbers. They also detailed how this sequence can encrypt colored images using an XOR operation with the matrix values defining the image. This encryption was applied to digital color images in the context of internet communications, and achieved a high level of security. [PERSON] et al. [12] also showed how to achieve a high performance data encryption using chaotic systems for image ciphering. The chaotic carrier signal they achieved has a strong randomness, a broadband spectrum and was likely unpredictable. [PERSON] et al. [13] presented in their work a very large scale integration (VLSI) implementation of a precise case of the chaotic encryption schemes. They described a system employing a Lorenz oscillator. This scheme is known for its complexity in hardware implementation, but they  
Figure 2: Block Diagram of the Communication between the Devices with the Cryptographic System. overcome it by developing a new Generalized Lorenz System suitable for their case. For the case of [PERSON] et al.