# A Low-Complexity Security Scheme for Drone Communication Based on PUF and LDPC
## 3 Security Architecture
### Error Correction Schemes
#### 3.4.3 Decoding Algorithm Selection
If the attacker uses the \(Corrupt()\) operation after obtaining the secret key and models the fingerprint PUF to obtain the second stage secret key \(h(b)\) the attacker can obtain the extracted information of the identity PUF, but still cannot decrypt \(\hat{ID}\oplus n\) and \(n\oplus m\). Since the protocol in this paper is based on unstable PUFs and the challenge of identity PUFs comes from the power supply, the \(Corrupt()\) operation or power down changes the current response \(\hat{ID}_{i}\) and \(m\) is difficult to compute. In summary, since the attacker cannot know either the power-up response \(\hat{ID}\) of the identity PUF or the parity information \(C_{\delta}\) given by the GS, a fake drone is not possible. In conclusion, it is not possible to fake the drone since the attacker cannot know the power-on response of the identity PUF or the parity information provided by the base station. Without passing the authentication, it is not possible to obtain the GS's broadcast secret key and the P2P secret key set. Therefore, the main research focus of this paper is proven to be finished. \(\square\)

Theorem 4.2: _The proposed protocol is resistant to attacks that prevent authentication._

Proof of Theorem 4.2.: According to Theorem 4.1, it is known that an attacker can obtain key \(key_{i}\) and key \(h(b)\) by operation \(Corrupt()\). These keys are only valid for a compromised drone, but the administrator will not assign a corrupted drone to a mission. It is contradictory for an attacker to disassemble a drone to perform a tamper attack and replay the attack on it. It is also impossible for an attack on the GS, as it is proposed in Section 3.1.1 that the GS authenticates based on the drone specified by the administrator. In short, it is meaningless for an attacker to attempt to attack the authentication process, e.g., replay attacks, tampering attacks, DoS attacks, and so on. \(\square\)

Theorem 4.3: _An attacker cannot break the protocol of this paper even if they invoke operations \(Reveal()\), \(Hash()\), and \(Test()\)._

Proof of Theorem 4.3.: Operation \(Reveal()\) is analyzed in Theorem 4.2. A total of five hash operations are used in this paper: \(h(b)\), \(h(T_{4},b)\), \(h(T_{5},b)\), \(h(C_{\delta})\), and \(h(k)\). The case where parameter \(b\) is cracked is analyzed in Theorems 4.1 and 4.2; operation \(Hash()\) does not work for the protocol of this paper as the sequences \(C_{\delta}\), \(k\) are not available. In addition, the secret keys used in this paper are all 32 bytes, so the probability of success of operation \(Test()\) is extremely small. \(\square\)

### Intrusive Attack

As can be seen from the introductory section, attacks on RAM-based PUFs mainly rely on intrusive or semi-intrusive techniques. Intrusive attacks are mainly used to break crypto-chips through physical disassembly (e.g., lasers, microscopy, etching, etc. ), while RAM-based PUFs can also be viewed as a type of crypto-chip. Since this paper's protocol requires an administrator to assign a drone, these attacks that are destructive to the chip are not effective for this paper's protocol. However, side-channel analysis is an efficient semi-intrusive attack that does not require destroying the chip to obtain the leaked secret key information, such as through power consumption or electromagnetic radiation analysis. Therefore, the purpose of this study is to increase the cost of intrusive attacks as much as possible. Since the fingerprint PUF information needs to be obtained before it is possible to obtain the location of the identity PUF, the attacker needs to read the whole read chip RAM. In this study, the GS introduces additional noise to the response of the identity PUF to make the ECC error correction performance reach a critical value. The addition of noise is based on the predicted unstable set, which is essentially the response characteristics of the PUF so that each accidental bit-flip when copying the entire RAM exponentially increases the probability of ECC decoding failure, which leads to authentication failure.