Abstract: This paper proposed a Secure LZW (SLZW) coding algorithm, where encryption was embedded into the improved LZW coding process, and SLZW can fulfill compression and encryption in a single step. In SLZW algorithm, dynamic Huffman tree was utilized to code the dictionary of LZW, and the initialization and updating of Huffman tree were controlled by a sequence of keystream generated by Coupled Map Lattcie (CML). The code words were further XORed with the keystream to generate the ciphertext. The SLZW was applied to GIF image encryption. The experimental results and their analyses indicate that the proposed SLZW algorithm not only has good security, but can also improves the compression ratio by about 10%. Therefore, SLZW can find its wide applications in practice.

Key words: data compression, image encryption, Huffman coding, Coupled Map Lattcie (CML)

摘要： 提出了一种安全的LZW编码算法——SLZW。该算法在改进的LZW编码过程中嵌入加密，从而能够同时完成压缩和加密。SLZW编码利用动态Huffman树作为LZW的字典，并且通过耦合映像格子(CML)产生的密钥流对字典的构建和更新进行控制，编码输出进一步和密钥流进行异或后产生密文。并且，该算法被应用于GIF图像加密中，实验结果和分析表明，该算法不仅具有较好的安全性，同时也将标准LZW算法的压缩效率提高了10%左右，具有广泛的实用性。

关键词: 数据压缩, 图像加密, Huffman编码, 耦合映像格子