An introduction of compression algorithms into SSL/TLS and proposal of compression algorithms specialized for application

摘要

The specification of SSL/TLS defines that data from the upper layer can be compressed in the record layer before they are encrypted. Since only the no-compression is provided for the compression algorithm in the specification, nobody can compress transmission data at the SSL/TLS protocols unless communication peers have a special agreement to use a compression algorithm. However, the compression mechanism should be useful for the users of narrower bandwidth communication lines such as ordinary analog telephone lines and N-ISDN. In order to solve this problem, the paper first introduces general-purpose compression algorithms into SSL/TLS, and shows that the average transfer times for several Japanese text files via HTTP are much improved, especially for narrow bandwidth communication lines. We also compare it with the compression mechanism on HTTP, and the resulting difference between the results of the SSL/TLS compression and HTTP compression is rather small. For improving the compression ratio, we next propose compression algorithms specialized for application protocols. As examples, we focus to HTTP and HTML, and construct the tree structures of the field names and field values. From the tree, the static dictionaries for the compression algorithms are defined. Finally, we implement the compression algorithms and show the compression ratios when several HTML files are transferred.