Algorithm 1: Encryption steps of GNSS data transmission

Input: GNSS data, a digital certificate from a GNSS data center      Output: the encrypted GNSS RTCM data, the encryption key, the digest value, and the signed inspection certificate

if identical authentication pass then      An SSL VPN to be established between GNSS stations and the GNSS data center        if SSL VPN established then generating a truly random number by cryptographic module embedded in the GNSS development board as an encryption key encrypting the GNSS data with the encryption key of an SM4 algorithm by cryptographic module extracting the public key from a digital certificate encrypting the encryption key with the public key calculating the digest value of GNSS encryption data with an SM3 algorithm by the cryptographic module signing the digest value with an SM2 algorithm by the cryptographic module to obtain a signed inspection certification and identify the certification of GNSS stations outputting all data including the encrypted GNSS RTCM data, the encryption key, the digest value, and the signed inspection certification transmitting all data to the GNSS data center by the communication module embedded in the development board.         end if     end if