## 3 Development History of Navigation Signal Authentication Technology
### Security  
The security of its authentication service is the prerequisite of satellite navigation signal authentication. The security refers to the ability to deal with spoofing attacks, which can be divided into two types according to the attack methods: one is to directly crack the cryptographic algorithm, which involves the security of the cryptographic algorithm itself; the other is to predict or estimate the authentication security code (authentication message or authentication spreading code), which involves the security of the authentication protocol. (1) Cryptographic Algorithm Security  
A cryptographic algorithm is a specific rule that uses a key to transform information into plaintext and ciphertext. Navigation signal authentication involves cryptographic algorithms, including digital signature algorithms, hash algorithms, and encryption algorithms. The security of cryptographic algorithms is determined by the length of the cryptographic algorithm key. For example, these include the ECDSA-P256, SHA256, AES128, and other cryptographic algorithms promulgated by the National Institute of Standards and Technology (NIST) [65; 66]; and the SM2 public key cryptography algorithm, the SM3 cryptographic hash algorithm, and SM4 block cipher algorithm of the Chinese commercial cryptography standard [67; 68; 69; 70]. The existing navigation signal authentication adopts the authentication protocol based on the cryptographic algorithm. For example, the navigation message authentication protocol includes the digital signature and the TESLA. The security of the digital signature algorithm is guaranteed by standard algorithms, such as ECDSA, SM2, etc. The security of the TESLA protocol involves a digital signature algorithm, message authentication code algorithm, and hash algorithm. The existing cryptographic algorithm standards all meet the security requirements. With the continuous progress of quantum computing technology and quantum algorithms, more powerful attack methods are provided for key breaking. The well-known Shor quantum algorithm and Grover quantum algorithm pose a threat to the security of classical cryptosystems, especially for public key cryptosystems based on mathematical problems such as the factorization of large numbers and discrete logarithms, which have brought about unprecedented challenges. Table 6 shows the impact of quantum computers on classical cryptography. Therefore, considering the security of the BDS signal authentication cryptographic algorithm, how to choose the appropriate cryptographic algorithm, cryptographic security level and key update cycle while taking into account new future cryptographic algorithms, such as post-quantum cryptography to resist future quantum computing attacks will become an important direction of future research. (2) Authentication Protocol Security  
The satellite navigation signal adopts a one-way broadcast signal system, and its authentication protocol includes an asymmetric cryptosystem and TESLA [71]. The authentication protocol based on an asymmetric cryptographic system uses CA (Certification Authority) digital certificate to achieve identity authentication, and asymmetric cryptographic algorithm to realize message authentication. Authentication protocols \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Cryptographic Algorithm** & **Type** & **Functional** & **Quantum Computing Impact** \\ \hline AES, SM4 [66; 70] & Symmetric cipher & Encryption and decryption & Need to increase key length \\ \hline SHA-2, SHA-3, SM3 [27; 69] & Hash & Hash Function & Need to increase \\  & & & output length \\ \hline RSA, ECDSA, DSA, SM2 [27; 65; 67; 68] & Public key cryptography & Digital signature, key distribution & No longer safe \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The impact of quantum computers on classical cryptography. are determined by asymmetric cryptographic algorithms, such as the ECDSA algorithm and the EC Schnorr algorithm, which is determined by cryptographic algorithm and key management security.