关键词: NMEA 0183 协议, 安全编码, 无损编码, 卫星报文, 哈夫曼编码

Abstract: The Global Navigation Satellite System (GNSS) has become a vital infrastructure for daily life, social resource management, and national strategic guidance. The NMEA 0183 standard protocol is widely used to transmit relevant information. To mitigate the various security risks associated with the transmission of plaintext geographic location information via NMEA messages, a lossless security encoding scheme leveraging the NMEA message format characteristics was proposed. Firstly, the readable message content was converted into an unreadable character string through common cryptographic techniques such as XOR and permutation, obscuring some obvious NMEA message format identifiers. Secondly, the data was completely obfuscated and de-characterized through bit-level merging and splitting operations, reducing the number of data character types to a smaller number. Finally, the binaryHuffman tree encoding principle was used to compress the large data volume generated by the first two steps, ensuring that no excessive transceiver load was introduced. Experimental results demonstrate that the standardized original NMEA messages are successfully converted into meaningless data streams with constrained character types, effectively resisting intermediate tampering and replay attacks. Furthermore, the data compression scheme ensures that the encoded data volume remains within an acceptable range.

Key words: NMEA 0183 protocol, Security coding, Lossless coding, Satellite message, Huffman coding