# A Low-Complexity Security Scheme for Drone Communication Based on PUF and LDPC
## 1 Introduction  
Ad hoc network drones are increasingly used in various fields, for example, to locate people, drop supplies, and relay communications after natural disasters, but also to monitor some high-risk environments, crop growth, and traffic conditions. However, generic ad hoc network protocols allow devices with the same interface to connect freely. Therefore, some unethical manufacturers have illegally obtained program source code through invasive attacks, creating illegal devices that can join real drone networks. These counterfeit devices can easily access the private local area network (LAN) of drone groups, posing a significant threat to the information security of some sensitive data. Due to limited drone resources, it is difficult to apply complex security protocols in networked drones.  
The physical unclonable function (PUF) is an emerging hardware security primitive that utilizes intrinsic device variations introduced by uncontrollable manufacturing processes as a unique digital identifier; it is used for the authentication and identification of Internet of Things (IoT) devices [1]. As PUFs do not support open-access protocols, the existing attacks against PUFs mainly rely on invasive or semi-invasive techniques [2].  
Physical access to the target device is expensive; so, in some common drone groups, a lightweight PUF-based authentication protocol is used, such as that in [3; 4; 5; 6; 7]. Extracting the PUF as a device fingerprint using the MCU's on-chip SRAM is an efficient and cost-effective method for manufacturers.  
However, SRAM flips some of its bits every time it is powered up; so, it needs to use error coding to generate a stable PUF. Error correction code (ECC) modules used in NADN flash are based on Hamming or BCH codes [8; 9; 10; 11], as flash chips are subject to a small number of bursty errors. However, with the increase in chip integration, its stability gradually decreases, and more powerful error correction codes with higher performance are needed, for example, by using multiple coding cascades. However, RAM-based PUFs are more than 10% unstable, and the cascading code scheme is a huge cost for resource-constrained drones. With the development of 4 G/5 G communication in the past decade, the research on LDPC codes has significantly matured, and they are also applied in error control for flash chips or solid-state drives, such as in [12; 13; 14]. Compared to BCH codes, low-density parity check (LDPC) codes have better performance and faster, simpler encoding/decoding methods, and can be adapted to different code lengths.  
Table 14 lists the abbreviations used in this paper, and the contributions of this study mainly include the following:  
1. A secure communication scheme using on-chip RAM as PUF is proposed to extract the PUF and authorize it to the drone under the guidance of the ground station, which greatly enhances the drone's ability to resist physical capture.
2. A scheme to recover the original PUF using QC-LDPC with lower storage requirements is proposed, and the structural requirements of the coding matrix and special decoding algorithm are given to improve the security of the authentication process.
3. The challenge of offering half of the authentication parties and utilizing the response as a medium for negotiating the secret key is proposed, which greatly enhances the ability of the PUF to resist machine learning.